Program Administration and Installation Design of the Nuclear Reactor Project at North Carolina State College

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Nuclear Reactor

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CONFIDENTIAL PROGRAM ADMINISTRATION AND INSTALLATION DESIGN<lb/> OF THE<lb/> NUCLEAR REACTOR PROJECT<lb/> AT<lb/> NORTH CAROLINA STATE COLLEGE

July 5, 1950

Clifford K. Beck and Arthur C. Menius (on Theoretical Calculations) George N. Webb Arthur W. Waltner (on Instrumentation) P. B. Leonard F. H. Stinson J. D. Paulson (on Drafting)

RESTRICTED DATA This document contains restricted data as defined in the Atomic Energy Act of 1946.

CAUTION This document contains information affecting the National Defense of the United States. Its transmission or the disclosure of its contents in any manner to an unauthorized person is prohibited and may result in severe criminal penalties under applicable Federal laws.

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CONFIDENTIAL PROGRAM ADMINISTRATION AND INSTALLATION DESIGN<lb/> OF THE<lb/> NUCLEAR REACTOR PROJECT<lb/> AT<lb/> NORTH CAROLINA STATE COLLEGE

DISTRIBUTION OF REPORT Series A - 25 Copies 68 Pages: i to vi and 1-62; 13 Figures

Copy No. U.S.A.E.C. Joseph Platt1 - 6 U.S.A.E.C. Herman Roth7 - 10 U.S.A.E.C. Declassification office11 - 16 Dean J. H. Lampe17 - 18 O.R.N.L. Richard Stevenson19 - 20 Clifford K. Beck20 - 25

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CONFIDENTIAL PROGRAM ADMINISTRATION AND INSTALLATION DESIGN OF THE NUCLEAR REACTOR PROJECT AT NORTH CAROLINA STATE COLLEGE TABLE OF CONTENTS Abstract v I. The Nuclear Reactor Project 1 A. General Background 1 B. Administrative Arrangement 2 C. Classification 4 D. Safety and Security of Fissionable Fuel 5 II. The Nuclear Reactor 7 A. General Regional Conditions 7 B. Building 12 C. Ventilation, Sewage, Waste Disposal 14 D. Reactor Design 16 1. General 16 2. Shielding Arrangement 17 3. Fuel Container 18 4. The Cooling System 20 5. The Nuclear Fuel 22 6. Reactor Envelope 24 7. The Reflector 26 8. Second Liquid Catch Basin 27 9. The Lead Shield 28 10. Safety and Control Rods 28 11. Instrumentation and Control 29 12. Operating Level; Radiation Fluxes; Reactivity of Solution 36 13. Thermal Column 39 14. Sample Exposure Ports 39 15. Sampling Replenishing Lines 41 16. Solution Level Indicator 42 17. Gas Disposal 43 III. Reactor Hazards 48 A. Normal Hazards 48 1. Radiation 48 2. Radiochemical and Radiophysical Hazards 50 B. Emergency Hazards 51 1. Leak or Rupture in the Reactor 51 2. H2 - 02 Explosion 52 3. Inadvertent Removal of Control and Safety Rods 52 4. Failure of Water Supply 56 5. Escape of Radioactive Gases from the Stack 57 6. Effect of Water Removal for the Cooling Coils 59 7. Addition of Water or U235 Solution to the Free Volumes in the Reactor 59 C. Catastrophic Hazards 60

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TABLE OF CONTENTS (Continued)

Figure1. Topographic map of Raleigh 2. N. C. State College Campus 3. Schematic Floor Plan of Reactor Building 4. Reactor Shielding Skeleton 5. Complete Reactor Shielding Assembly 6. Fuel Container 7. Reactor Envelope and Sampling Tube 8. Horizontal Cross Section through Thermal Column 9. Exposure Ports 10. Liquid Level Indicator 11. Decay of Reactor Product Gases 12. Gas Disposal System - Schematic Diagram 13. Five Second Rod Removal Emergency

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CONFIDENTIAL PROGRAM ADMINISTRATION AND INSTALLATION DESIGN OF THE NUCLEAR REACTOR PROJECT AT NORTH CAROLINA STATE COLLEGE

ABSTRACT

North Carolina State College of The University of North Carolina has pro- posed that a "water-boiler" nuclear reactor be built and operated on the college campus as an unclassified tool of instruction and research. A brief statement of the reactor project objectives and administrative procedure is made in this report.

The main body of the report concerns the general design and arrangement of the reactor. Most of the design has been based on ideas and extension of ideas and emperical data from Los Alamos and Oak Ridge reactors. The Los Alamos "water- boiler" has operated entirely satisfactorily for several years, and the Oak Ridge "Homogeneous Reactor", though not yet built, has received intensive study. The ideas and experience with these units have been incorporated into the design of the State College reactor, with minor changes as necessary and with the addition of extra features wherever the inherent safety of the machine or its resistance to sabotage could be improved.

A tabulation has been included of hazards which could result from operation or misoperation of the proposed unit. Many safeguards have been included to prevent injury through such obvious and inherent hazards as exposure to radiation from the reactor and carelessness in handling radioactive materials in routine operations.

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It is demonstrated that pressure rupture or explosion of the reactor by nuclear reaction is impossible. The "bubble effect" and a large negative tempera- ture coefficient prevent any runaway whatever, and insure automatic upper limits to the level of operation, even if all normal and emergency safety devices fail.

The only important danger inherent in the reactor installation lies in sabotage through non-nuclear explosion, aimed at wrecking the reactor and blasting the radioactive solution and attendant vapors and gases over the surrounding area. Even a catastrophe of this sort would cause little damage beyond that involved in the catastrophic event itself. A number of precautions against sabotage are in- cluded in the design.

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CONFIDENTIAL I. THE NUCLEAR REACTOR PROJECT A. GENERAL BACKGROUND

In recognition of the vital role that nuclear phenomena and processes flow have and increasingly will have in our society, and in discharging her responsibility to the students of the State and Nation in providing training opportunities in essential vocational fields, The North Carolina State College of the University of North Carolina has initiated a training program in Nuclear Engineering for qualified students. This curriculum, which provides training opportunities at both the undergraduate and graduate level, consists of (1) classroom instruction in theory and basic information, (2) extensive laboratory practice of nuclear technology, and (3) research facilities and opportunities for advanced students.

One of the basic units intended for use as the heart of the advanced instructional and research programs is a low-power nuclear reactor, of the uranium "water-boiler" type. It has been proposed that this reactor be built and operated on the State College campus, by State College, as an unclassified tool for research and instruction.

In June, 1950, a contract was given by the Atomic Energy Commission to N. C. State College, directing that the design of a reactor be drawn up, together with a description of the proposed method of operation and analysis

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of the potential hazards associated with the machine. The report below contains the items and information stipulated in the contract.

B. ADMINISTRATIVE ARRANGENT 1. Design and Construction Period

It is intended that the Nuclear Reactor be designed, constructed, and operated by North Carolina State College with the consent, advice and assistance of the Atomic Energy Commission, the necessary finances being supplied by State College. The Commission will furnish information and assistance in the design stage; it may furnish certain instruments, materials and purchasing facilities during the construction period; and will supply the fissionable fuel necessary for operation.

At State College, the nuclear engineering training program and the Reactor Project will be a part of and under the direction of the Physics Department. During the design and construction phases of the project, the money necessary for these activities from whatever sources obtained, will be placed in the State Treasurer's office, along with other college funds, in a separate account earmarked for the Reactor Project, and made available to the Physics Department for use in obtaining personnel services, supplies, travel, etc.

2. Operation

Responsibility for operation of the Nuclear Reactor will also be assigned the Physics Department. It is intended however that the machine serve as a tool for instruction and research not for the Physics Department only, but also for a large group of other departments, organizations and institutions, many perhaps not even connected with State College. It will be necessary

therefore to arrange schedules of operation, assign priorities to projects, access costs, etc. No definite rules and regulations for handling these matters can be made at this time. A few general guiding principles may be stated, however;

1. The general responsibility for the entire operation of the Reactor will be allocated to a Scientific Director (named in the A.E.C. contract as Dr. Clifford Beck, Chairman of the Physics Department). The designation of subsequent directors, in general, will be agreed upon by both State College and the A.E.C. 2. An advisory Committee, selected by the Scientific Director, will assist in the establishment of policies, rules and regulations governing operations. 3. The widest and most extensive use of the Reactor will be en- couraged, and its availability for use on acceptable projects will be maintained at the maximum consistant with safety, efficiency of operation and finances. 4. Finances for operation will be available for a specially earmarked fund in the State Treasury. Income from sponsored projects involving use of the reactor, from charges for reactor usage, and from all other sources will be placed in the Reactor Account in the State Treasury for subsequent use in the Project. 5. Individuals or groups desiring irradiation of samples or other use of the reactor, not involving experimentation on human beings, must produce evidence to the satisfaction of the Scientific Director or his designated representatives that they are competent to handle radioactive materials and that their facilities are adequate. 6. When projects involve experimentation on humans, prior approval of the project must be obtained from the Atomic Energy Commission's Isotope Branch, in addition to the stipulation above.

7. Careful and complete records will be kept of all reactor operations, sample irradiation, etc., and of all individuals participating in experimentation involving the reactor. C. CLASSIFICATION

It is the basic intent that the Nuclear Reactor be operated as a completely unclassified project, on research problems which also are unclassified. Provisions will be made within safe limits for public observation of the reactor and its operation. It will be the intent that students and research participants having access to the reactor and its radiations, but not to classified operation or construction details of the installations (if any), may participate freely in the project upon satisfactory evidence to the Scientific Director and the College Administration of their American loyalty.

Those persons who, because of their intimate connection with the design and behavior of the reactor must have knowledge of classified information, will be investigated by the F. B. I. and be given security clearance by normal procedures followed by the Atomic Energy Commission.

Despite the desire to operate the Reactor as completely unclassified as possible, it will be the strong intent of State College to guard vigilantly against the release of classified information to any unauthorized individuals. The Scientific Director and several of the college staff members associated with the project will maintain "Q-clearance" status with the Atomic Energy Commission and will keep up-to-date on declassificable information. In the course of any investigation, whether considered unclassified or not, should any classified information be encountered, this will be declared classified and further disclosure to unauthorized individuals will not be permitted except through regular Commission channels. Any information of doubtful classification will also be handled as classified and submitted for clarification of classification status.

D. SAFETY AND SECURITY OF FISSIONABLE FUEL

The enriched U235, in either solid or liquid (sulfate) solution form, will be delivered to State College at the appropriate time for use in the reactor. At least three separate containers, of less than 350 g (U235) each, will be used in transporting the material. The containers will be stored in fire-proof, combination-lock, storage receptacles, with at least 24" between each container. In all operations involving fissionable material, no more than 350 grams will be handled at one time or allowed to come nearer than 24" to other fissionable material. These same rules for handling and storage will be followed at all subsequent times.

The sulfate solution will be placed into the reactor cylinder through the sampling tube extending to the top of the concrete shield. (Described later.) When all the solution has been added, the safe-door covering the end of the sampling tube will be closed and locked. All beam ports and other openings through the concrete shielding will be closed by combination-lock, wall-type safe-doors built into the concrete shielding. Every external opening through which access to the inside of the concrete shield could be gained will be closed and locked. Thus, the fissionable fuel will be contained in a closed (stainless steel) system located completely inside massive concrete shielding in which all external openings are securely closed.

When the reactor is in operation, or when apparatus is mounted permanently into one of the beam ports, the safe door on one or more ports will be unlocked and open. At other times, all openings into the shielding will be securely closed.

In addition, when members of the research staff are not present, the electrical gear at the control console, to all parts of the reactor, to the crane, and to other equipment relating to the reactor, will be de-energized and the switches will be locked.

The reactor building, especially the Reactor Room, and the gates in the external area fence will be locked, and the area around the building will be well lighted at night. The college watchmen will direct particular attention to this building on their rounds of the campus.

The design of the assembly, the precautions listed above and the ex- tremely radioactive nature of the material after initial operation, are believed entirely adequate to insure the physical security from theft of the fissionable material. No nuclear fuel, other than that in the reactor itself, will be located at this site. The danger to be guarded against, if any, is in sabotage aimed at wrecking the reactor or spreading the radioactive fuel around the neighborhood by non-nuclear (e.g., T.N.T.) explosive blast. This cannot be accomplished unless the explosive is gotten inside the concrete shield. It is proposed that the precautions listed above and the design of the reactor will be adequate to prevent this. The Atomic Energy Commission may, however, prefer to place on duty at the site a full-time guard or perhaps a guard on duty when members of the research staff are not present, in addition to the above pre- cautions.

CONFIDENTIAL II. THE NUCLEAR REACTOR A. GENERAL REGIONAL CONDITIONS 1. Location of State College

Raleigh, North Carolina, lies in Wake County, at latitude 35°-47'-20" north and longitude 78°-40'-40" west. The population is about 65,000. Raleigh is the capitol of the State, and governmental business engages a goodly portion of the inhabitants. Meredith College (for women), Peace Junior College (for women), St. Mary's Junior College (for women), the State School for the Blind, and N. C. State College of the University of North Carolina are located in the city. Convergence of highways and railroads places Raleigh in good strategic location for a thriving goods outlet and commodity distribution center of the State. There are few manufacturing and heavy industries in the the city.

The campus of North Carolina State College lies toward the western edge of Raleigh (Figure 1). Hillsboro Street extends westerly from the Capitol Building at the center of Raleigh, and, at distances between 1 1/2 to 2 5/8 miles from the Capitol, forms the northern boundary of the college campus. The campus thus extends east and west 1 1/8 miles along the south side of Hillsboro. The north-south dimension of the campus proper is about 1/2 mile. The tracks of the Seaboard and Southern railroad run through the middle of the campus, roughly parallel to Hillsboro Street. Between Hillsboro Street and the railroad, therefore, is an area of 1000 to 1500 feet in width and 1 1/8 miles in length. Most of the college buildings, except new dormitories and athletic buildings, lie in this tract. The new dormitories and gymnasia lie south of the railroad.

There are four general functional groupings of buildings on the campus. At the eastern end, toward Raleigh, are the College administrative buildings

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and the classroom buildings of the Basic Division. Next westward lie the classroom buildings and laboratories of the Engineering Division, followed by the buildings of the Agricultural Division. Finally, on the western end of the campus, are located the structures belonging to the Textile Division.

2. Topography, Soil Conditions

The land comprising the campus of State College is gently rolling, and varies between 350 and 420 feet above sea level (Figure 1). "The undisturbed soil in this area consists primarily of a residual soil developed from metamorphic rock classified by geologists as Mica Gneiss. This soil is classified under the Agricultural Soil Survey System as a "Cecil Clay Loam." It is very plastic, highly impervious, inorganic, red clay-tough near the plastic limit. In the proximity of Rocky Branch and its tributaries there occurs alluvial soil of variable nature. The occurrence of natural drainage ways is limited to Rocky Branch and its tributaries. This stream discharges into an artificial lake, known as Pullen Lake. The highly impervious nature of the soil, underlaid with bedrock, precludes the frequent occurrence of underground drainage ways."

3. Meteorological data

Certain meteorological data have been recorded at Raleigh for about 60 years. Certain of these data of interest in the operation schedules of the reactor are tabulated below:

(a) Wind velocities and directions: 1. Calm 11%

2. 4 - 15 mph. . . . . . . 83% Southwest 14% Northeast 10 South 8 North 7 SSW 7 West 6 Northwest 6 All other 25 3. 16 - 31 mph. . . . . . . 7% SW 1.3% NW 1.2 All other 4.5 (b) Precipitation 1. Average yearly rainfall 46.5 inches. 2. Average yearly snowfall 7.6 inches. 3. Average wettest month: July 5.8 inches. 4. Average dryest month: November 2.3 inches. 5. Greatest rainfall in 24 hours: September 1929 6.66 inches. 6. Lowest average humidity: Feb., Mar., April - about 48% at 1 PM. 7. Highest average humidity: July, August - about 58% at 1 PM. (c) Temperature 1. Yearly average daily maximum 70°F. 2. Yearly average daily minimum 50.7°F. 3. Highest monthly average: Maximum 87.9 July. Minimum 69.2 July. 4. Lowest monthly average: Maximum 50.9 Jan. Minimum 33.3 Jan. 5. Record highest, July 1940 104°F. 6. Record lowest, February 1899 -2°F.

(d) Weather conditions (over 60 years), average number of days per year 1. Clear 133 days/year. 2. Cloudy 118 " 3. Partly cloudy 114 " 4. Rain 0.01 inches or more 120 " 5. Snow 0.01 inches or more 4 " 6. Thunderstorms 41 " 7. Heavy fog 12 " 8. Maximum temp. 90°F or above 37 " 9. Minimum temp. 32°F or below 50 "

Inversion layers and other unusual meteorological effects occur, but data on the frequency and extent of these conditions are not readily available. Additional data are being obtained.

4. Specific Location or the Reactor

The Nuclear Reactor will be located in one or the other of two proposed positions on the State College campus. The two locations are shown in Figure 2.

Position A: South of old Zoology Building. It is planned that the old Zoology Building shall be removed, but this is not likely to occur in less than three or five years. With the building removed, this site would constitute the optimum choice for the location of the Reactor Building. It is intended that the Reactor facility be located in the space south of the old Zoology Building and north of the railroad, between the Diesel Building and the Riddick Laboratories. The facility will be so designed that (a) suitable interim operation until removal of old Zoology can be achieved and (b) ultimate expansion, after removal of the Zoology Building, into an optimum facility can be undertaken.

Should it turn out that the space behind old Zoology is insufficient for an interim Reactor facility, or should further study reveal a strong un- desirability from the safety standpoint of crowding the Reactor facility for interim operation into cramped space immediately adjacent to a classroom building, then the Reactor facility will be located in Position B.

Position B: North of Old Zoology Building. The Reactor will be located between Daniels and Polk Halls, north of University Drive, if the space south of old Zoology proves unsuitable. If the Reactor is placed in this location, a three or four story new physics laboratory building will also be placed in this area in order to reestablish an architecturally acceptable landscape plan for this portion of the campus. The new building, as shown on Figure 2, would extend in an east-west position between Polk and Daniels Halls, in line with the north ends of these two buildings. Part of the Reactor laboratories would be located in this new building.

In either of these two locations the environmental conditions are essentially the same. Six large buildings are nearby: Withers, Daniels, Riddick, Diesel-Mechanical, Polk, and, of course, Old Zoology. Patterson Hall is directly north, 1020 feet from Position A and 980 feet from Position B. The elevation is 410 to 415 feet above sea level: one of the highest elevations in the entire neighborhood. The general slope is south, east and west from these locations, 2000 feet to the east and 1500 feet to the west respectively are located the troughs of north-south surface drainage ways. In the west trough there is also a small underground water channel. There are no other known surface or underground flow channels in the vicinity. The drainage ways from this area lead eventually to Rocky Branch.

The non-college activity nearest the proposed reactor location is a small shopping center on Hillsboro Street, 2200 feet north. East, south and west the college property extends 3000, 6000, and 3000 feet respectively from

the reactor site. The nearest college dormitories are 2300 feet southwest; these are at 40 feet lower elevation than the reactor site. The Seaboard and Southern Railroad runs east and west at 500 and 1200 feet south re- spectively of the two proposed reactor sites. The railroad elevation is 30 feet lower than that of the reactor site.

B. BUILDING

A building is being designed to house the Reactor and the activities associated therewith. Figure 3 shows sketches of the functional components of the proposed building. The finished design may have somewhat different floor plan from that shown, but it is intended that it contain the four essential components shown:

1. The Reactor Room. The octagonally shaped reactor will be located in the center of an octagonally shaped room, with 25 feet of clear space between any side of the reactor and the nearest wall of the building. The floor level in the reactor room (and the bottom of the reactor assembly) will be 8 feet below ground level. Horizontal radiation beams from the reactor will pass through narrow openings in the building walls to underground radiation traps buried outside the building. Overhead space in the unceiled room, extending to the roof 40 feet above floor level will provide ample space for a 10 to 20 ton crane, blowers, filters, and ventilation equipment, and supports for the gas-stack which extends above the roof of the building. The wall of the reactor room will be of 16" masonry and steel (for the crane supports) except on one side adjacent to the Control Observation Room where a large 16-inch water observation window will be located. Numerous crash-doors will provide emergency exits from the reactor room. Blowers will draw in air through ventilators in the walls, filter it, and discharge it to the stack above the roof. The ventilators will be arranged for outside closure, if

necessary, so that the entire Reactor Room can be sealed up from the outside to prevent other than minor escape of gases from inside in case excessive gas contamination should occur in the room. 2. The Research Wing. Adjacent to one aide of the Reactor Room a laboratory wing devoted to pre- and post-handling of exposure samples involved in research projects is proposed. The laboratories in this wing will have facilities for radio-chemical work and radioactivity measurements, in addition to the usual research facilities. The electronic instrument rooms will be air-conditioned. Exhaust ventilation of the other rooms through ducts leading to the building stack will be provided. Facilities for checking and eliminating radioactive contamination to hands or clothing, and for lockers, clothes-changing, scrubbing, etc., will be arranged near the normally used entrance to this wing. 3. The Student Wing. A second laboratory wing adjacent to another side of the Reactor Room (opposite the Research Wing) will be equipped for instruction and training of students in a wide range of nuclear techniques. The wash room ventilation and laboratory facilities of this wing will be similar to these in the research room. Activities of much lower level will normally be present in the student wing. The laboratory wings will be designed for later addition of second stories, if needed. 4. Control-Observation-Administrative Area. One uncontaminated area adjacent to the Reactor Room will house the control console, the calculations, records, operations offices, a conference room, storage rooms (for uncontaminated supplies and equipment), an observation room, and one or two offices for the reactor staff.

C. VENTILATION SEWAGE AND WASTE DISPOSAL 1. Ventilation

Large blowers located high above the reactor in the Reactor Room will draw air via ducts from all areas of the building through filters, and discharge it to the building stack which will in turn discharge the air into the atmosphere 25 feet above the roof of the highest buildings in the nearby area. Within the building, therefore, air will flow from areas of low radioactivity toward the area of highest activity. It is not intended that the stack will be used for routine disposal of radioactive gases into the atmosphere. These will normally be handled in other ways as described below. Traces of activity or occasional inadvertent small gas releases may accompany or contaminate the ventilating stream of the air through the blowers to the atmosphere. The stack discharge is placed high in the atmos- phere to provide safe disposal of these traces and infrequent inadvertent releases. Careful and continuous monitoring of the ventilating stream will be maintained. The source of any increase in activity will be promptly located and handled by prescribed methods.

2. Sewage

Radioactive liquids and solids will not be permitted to enter the city sewage system. Three separate sewage systems will be provided in the building. (a) Waste from the toilets, storm sewers, drinking fountains, etc., will go directly into the city sewage system. (b) Drain lines from the laboratories or any area in which radioactive materials are handled will go to one of two underground (but accessible) holding tanks, and from there to the city system. Radioactive solids or liquids will not normally be placed in these drain lines. It is possible, however, because of their proximity to working areas, that accidental spills or disposal of radioactive

materials may find their way into these lines. Therefore, continuous monitoring at the entrance to the holding tank will be maintained; and should appreciable quantities of radioactive material inadvertently reach the tank from the laboratories in the building, it will be held there and handled by prescribed methods, and then be allowed to enter the city sewage system only under predetermined safe conditions. Meanwhile the drainage from the laboratories will be switched to the second holding tank. (c) Short-lived radioactive materials may be dispatched down one or two special drains to an underground (but accessible) holding tank, which has no connection with the city sewage system. When the activity has decayed sufficiently, the material, by positive effort (not automatically), may be disposed of as non-active waste.

Long-lived materials of solid or liquid nature will be accumulated in closed, shielded, non-breakable containers designed for safe subsequent transportation to Oak Ridge, Tennessee for disposal. Radioactive gases will be accumulated in non-breakable cylinders, or absorbed in liquid or solid absorbents, and handled as above.

Thus, no activity whatever above trace level will enter the city sewage system, or be dispersed into the atmosphere or into the ground.

D. REACTOR DESIGN 1. General

The reactor assembly consists of the reactor itself which is a stainless steel cylinder containing a uranyl sulfate solution, the graphite reflector, a limonite or barytes concrete-lead shield, a graphite thermal column, sample exposure-neutron beam ports, control and safety rods, cooling coils, and auxiliary apparatus and systems. Each of the major component parts will be described separately below. The overall design is intended to produce a simple and relatively inexpensive instrument that will provide maximum useful- ness and flexibility, and minimum potential hazards. The water-boiler type of reactor was chosen because of its simplicity, its proven usefulness, its inherent safety characteristics, and the long experience of satisfactory operation of the Los Alamos unit. With this type of reactor, a relatively high radiation flux can be obtained with simple construction and equipment. The two chief disadvantages of the liquid-type of reactor are (1) the mobility of the fuel creates a design problem in avoiding loss if leaks should occur, (though the mobility is also an advantage in that fuel transport, handling, etc. by remote control, through pipes, pneumatic pressure, etc., is relatively easy,) and (2) decomposition by radiation of the fuel solution into gaseous products creates problems of gas disposal and solution replenish- ment.

Since this reactor will be operated in the relatively populous environs of a college campus and as an unclassified establishment relatively accessible to the public, an attempt has been made to incorporate into the design (1) exceptionally large safety factors against potential hazards and (2) unusually extensive precautions against sabotage.

2. Shielding Arrangement

The major volume of the reactor assembly consists of concrete shielding. The shielding is designed to perform the primary function of attenuating to a safe level all radiations from the reactor and its accessories. It is intended that a "heavy" concrete will be used; i.e. one in which the usual crushed stone or gravel aggregate is replaced with a metallic ore which possesses greater radiation attenuating ability. Limonite (iron ore) or Barytes (Barium Sulfate-Iron Oxide) aggregates are being considered.

A lead shield (described later) will surround the reactor inside the concrete shielding. Using shielding data empirically obtained at Oak Ridge and Los Alamos and calculating the attenuation of radiations expected from the reactor, it is found that a total of 30 inches is sufficient to reduce the reactor radiation to a safe level. However, because of various pieces of apparatus to be imbedded in the shield, and to provide an adequate margin of safety, the concrete around the reactor will be made 6 feet thick.

The concrete in this particular assembly performs several secondary functions in addition to the primary function of attenuation; (1) It provides security of the fissionable material against theft. Hence, the design must minimize accessibility to the interior in which all parts of the reactor system are enclosed. (2) It is the primary defense against possible attempts to sabotage the installation, hence, no openings may be left into which explosives or other damaging materials could be placed. (3) It houses the auxiliary systems of the reactor (exposure ports, control, cooling, gas disposal, etc.) and these much be reasonably accessible in proportion to their demand for use or maintenance.

Numerous channels and openings are provided in the concrete shield. The entire shield is octagonal in shape, 17 feet in diameter and 9 1/2 feet high. The assembly is composed of an octagonal poured concrete base, 18 inches

thick and 17 feet across and two poured concrete super-structure sections comprising three octagonal faces in each on opposite sides of the base. The super-structure extends 96 inches above the base slab, (Figure 4). Between the two poured concrete super-structures a large open channel is left. This opening is 5 feet wide and 92 inches deep and extends from one octagonal face across to the other. Inside this volume will be placed the reactor, the reflector, the gas handling system, the instrumentation-control mechanism, and the graphite thermal column. The remaining volume will be filled with slabs and blocks of concrete. Various holes, ports, and trenches are pro- vided in the poured concrete sections to accomodate various auxiliary apparatus of the reactor assembly.

When the reactor assembly is complete, the concrete shielding will be so arranged that no access whatever to the interior can be accomplished ex- cept (1) through beam-ports which are closed when not in use by combination- lock safe doors, or (2) by removal of external slabs of concrete, which weigh not less than 5 or 10 thousand pounds each. The concrete slabs, in addition to their weight, are interlocked into the assembly in such fashion that their removal is impossible unless the "cap-slab" on top of the assembly is removed first. The "cap-slab", in turn, is securely bolted in position and the bolts are secured against removal by locks. A completed assembly of shielding components is shown in Figure 5.

3. The Fuel Container.

Figure 6 shows the fuel container and its attached components. Stainless steel (18 - 8), type 347 is used throughout the fuel system. and in all struct- ural parts in contact with the solution or its vapors. Thickness of the reactor walls is 1/16 inch. The fuel container is a cylinder of 27.2 cm. diameter and 27 cm. height. (See Nuclear Fuel, below.) There are no

openings in the bottom of the cylinder or on the vertical sides. There are 13 openings in the top surface of the reactor cylinder.

1. Six openings are for entrance and exit to three separate water cooling coils inside the reactor. 2. There are two 3/4" o.d., 1/16" walled, re-entrant tubes extending vertically from points 18" above the reactor to points inside the reactor, 8" below the top surface. These tubes serve respectively as guides or scabbards, for two control-safety rods. 3. One tube, 1 1/2" in diameter, projects vertically upward along the vertical axis of the reactor. This tube carries away the by-product gases from the reactor. 4. One 3/16" o.d., 1/32" walled tube, projects vertically downward 7" into the reactor. A thermocouple, for solution temperature measurement, is carried inside the tube. 5. One 3/8" i.d., 1/32" walled tube, projects downward into the reactor, very close to the bottom. This tube is used for admitting and removing material to and from the reactor. 6. One 1/2" i.d., 1/16" walled tube, projects 20" vertically upward from the reactor, and carries on its top end a sylphon bellows arrangement for measuring height of solution in the reactor. (To be described below.) 7. One 1" i.d., 1/16" walled re-entrant tube extending 8" downward into the reactor and 56" upward to a point just below a removable plug in the concrete shielding on top of the assembly. This tube is used for exposure of small samples in the interior of the reactor where the radiation level is highest.

All re-entrant and connecting tubes are welded into the reactor. All joints and connections in the reactor are welded. The entire assembly is built to withstand an internal pressure of 100 p.s.i.a. without rupture

and without leaks detectable with a helium mass-spectrometer leak-detector. The reactor must meet these specifications by actual test before initial use. All tubes connecting to the reactor project vertically upward for 18 inches. At this point, all except the exposure-tube, the control rod sheaths and the level indicator, turn through 80° or 90° to an approximately horizontal position. Beyond the bond or elbow, a leak-proof coupling is provided in each tube.

4. The Cooling System.

The heat generated in the reactor during operation must be removed. The cooling system designed to accomplish this consists of three helical coils of 1/4" stainless steel tubing of 30 feet total length inside the reactor cylinder. At maximum anticipated power level (10 K.W.), one gallon per minute of water from the city mains through each of the three coils, or a total of 3 gallons/minute will dissipate the heat. Since the coils are immersed in the corrosive uranyl sulfate solution, they must be made of stainless steel. Water comes from the city system to the three coils through separate automatic pressure reducing-regulating valves. A thermocouple indicates the water temperature. The pressure regulating controls for the valves are mounted on the Control Console. From the three valves, the water goes directly to the three coils inside the reactor. Thermocouples indicate and record the water temperature down stream of each coil. The exit lines from the coils join into one line at a point about 1 foot from the reactor, and through the single 3/4" tube the water flows downward inside the concrete shield to an underground pipe trench and along this trench to an underground holding reservoir outside the reactor building.

A small amount of short-lived activity is built up in the water during its passage through the reactor.

Data supplied by the City Public Utilities Department on water analysis made over a period of years indicate that the average mineral content of Raleigh city water is:

SiO29.8 p.p.m.S0411 p.p.m. Fe0.02Cl4.9 Ca8.7F0.1 Mg1.4NO30.1 NatK4.2HCO314.0 Mn0.0CO33.9

The number of atoms per cc of water of each of these chief constituent elements and the nuclear characteristics of the particular isotope of interest are indicated below. The calculations are based on a 2 second exposure in a thermal neutron flux of 1012.

IsotopeAtoms/cc of H20Slow neutroncross section x 1024Resultant halflife activityResultant Activ-ity Disinte-grations/cc/sec. F193.4 X 10150.0112s3.35 Si309.8 x 10150.122.8 hrneg Fe544.0 x 10132.14 yrneg Fe582.0 x 10120.3246 dneg Ca445.8 x 10150.4315 dneg Mg265.3 x 10154.810 m625. Na231.4 x 10170.514.8 hneg S241.5 x 10160.2687 dneg Cl351.2 x 101753.02 x 106 yneg Cl374.1 x 10160.637 m9.5 0187.5 x 10190.0002231 s110

Actually, the exposure of each cc of water should be less than 2 seconds, at normal cooling water flows of 1 gallon per minute through the 1/4" cooling pipe, and the average thermal neutron flux will probably be less than 1012.

The induced activity is therefore probably somewhat exaggerated. Even so, the resultant activity is less than 1000 disintegrations per second in each cubic centimeter of water. Much of this radiation is internally absorbed in the water.

Assuming no shielding and no internal absorption of radiation by the water, 10 gallons of freshly irradiated water would produce a radiation dosage at the rate of 0.08R/8hr. to a person standing 5 feet away. After one hour, this dosage rate reduces to 0.0008R/8hr. at 5 feet.

The water therefore is sent to a holding tank where the activity is allowed to die away before discharge into the sewers. The 1800 gallon holding tank is large enough to hold the water form 10 hours of maximum level operation.

Radiation detectors, with indicating meters on the Control Console, are placed at the entrance and exit of the holding tank. If any increase in activity should occur, the cause will be determined and escape of active material from the tank to the sewer will be prevented.

If a leak in the cooling coils inside the reactor should occur, the water will tend to flow into the reactor solution instead of the converse, because of the pressure in the coils. Should a leak occur, and sufficient water enter the reactor for the liquid level to rise, an interlock on the level indicator will operate and shut down the reactor and close the valves in the water line to the cooling coils.

5. The Nuclear Fuel.

The water boiler at Los Alamos operated first with uranyl sulfate solution and later with uranyl nitrate solution. The change was made primarily because it was expected that periodic chemical clean-up of the solution would be necessary, and the nitrate seemed much more amenable to this operation than the sulfate. After extended operation it has become

apparent that necessity for clean-up processing will be an extremely rare occurance, hence this reason for choice of nitrate is of little importance.

The nitrate perhaps does have a lesser tendency to corrode than does the sulfate, but experiments at Los Alamos and Oak Ridge indicate that sulfate corrosion of stainless steel is extremely small at temperatures below 100°C.

The solubility of uranyl nitrate is loss than that of the sulfate. Once dissolved however there appears no difficulty in preventing precipitation of either the nitrate or the sulfate, provided the solution is kept sufficiently acid.

There are three chief advantages in using the sulfate solution: (1) the boiling point is somewhat higher for the sulfate solution than for the nitrate solution, (2) the radiation decomposition into gaseous products is much lower, is about half in fact, that of the nitrate, and (3) the neutron absorption is less in the sulfate than that in the nitrate.

It is intended, therefore, that the reactor described herein will operate with a solution of uranyl sulfate as the nuclear fuel. Uranium highly en- riched in U235 will be used. The amount of uranium needed and the dimensions of the cylindrical reactor are determined approximately by comparison with the amount and dimensions in the spherical Los Alamos Reactor, with appropriate conversion factors. A detailed, accurate evaluation of amounts and dimensions will be made later from considerations of reactor theory and nuclear constants when exact arrangements of reactor, reflector, etc. have been decided.

The Los Alamos Reactor contains 12,600 cc of uranyl nitrate in which 839 grams of U235 are dissolved. 764 grams are needed to produce criticality at 20°C, and the extra 75 grams are needed to overcome the negative temperature coefficients and provide a useful excess reactivity. A cylindrical reactor, because of its larger surface:volume ratio, requires 1.14 times as much

material as a spherical reactor, other conditions being equal. On this basis, the cylindrical reactor solution should have a volume of 12,600 x 1.14 = 14,360 cc. Using optimum height to radius dimensions for a cylinder of H/R 1.848, gives height 24.8 cm, and diameter = 27.2 cm. A cylinder of 27.2 cm diameter and 27.0 height would permit 2.2 cm depth of unoccupied volume in the top of the cylinder. This depth becomes 2.9 cm when the sulfate Solution and the difference in cooling coils is taken into consideration.

About 840 grams of U235 in the cylindrical reactor are required to produce criticality at 20°C, and about 60 grams more, or 900 grams, at 80°C. The negative temperature coefficient is such that the critical mass increases about 0.9 grams per degree centigrade. Fifteen additional grams are added to insure sufficient excess reactivity for useful experimentation. The total U235 required, therefore, will be about 915 grams.

6. The Reactor Envelope

The stainless steel reactor itself is surrounded by a second envelope made chiefly of aluminum (Figure 7). The 27.5 cm O.D, (diameter) cylindrical reactor is enclosed in a 28.3 cm I.D. cylinder which is closed at the bottom, underneath the reactor, and which extends upward 16" to a flanged connection in the lower surface of a much larger aluminum cylinder. The lower part of the smaller cylinder is made of stainless steel, so that it will not be chemically attacked immediately in case a leak should occur. The reactor itself rests on and is supported by the lower end of the Reactor Envelope. The larger upper cylinder, 48" in diameter and 42" high, flange- closed at top and bottom, together with the connecting smaller cylinder fitted around the reactor, constitute the Reactor Envelope.

The purposes of the Reactor Envelope are (1) to catch any liquid which should inadvertently leak from the reactor; (2) to retain for leisurely

disposal any radioactive gases which inadvertently escape from the reactor; and (3) to serve as a safety volume into which the reactor contents could expand without wide liquid or gas dispersal in case of rupture of the reactor system. This envelope-chamber is not absolutely vacuum-tight and does contain several imperfectly fitted joints through which gases under pressure inside the volume could slowly escape. The envelope, however, would reduce any leak to a very low rate so that the ventilation system could dispose of the escaping gases without permitting the room to become contaminated. The gases inside the envelope can be pumped out slowly through purge lines to absorption traps or pumped directly to the stack for disposal.

The volume of the envelope (exclusive of the space occupied by motors, etc.,) is about 40 cubic feet, or about 45 times the total volume of the reactor itself, hence any pressure inside the unfilled volume of the reactor should be tremendously reduced if it should expand into the envelope volume. The reflector around the reactor will be so arranged that the line of least resistance for a pressure release around the reactor. will be upward into the large volume of the envelope. That is, the 16" of graphite on top of the reactor, inside the reactor envelope is loosely packed powder which would be pushed aside by a pressure release below.

An atmosphere of inert gas under slight positive pressure will normally be maintained in the envelope. Periodic sampling will quickly reveal the pressure of any gases leaking from the reactor. The positive pressure will retard the escape of gases from the reactor through any leak which should occur.

The water lines to the cooling coils, the refueling sampling line to the reactor, the gas disposal tube, etc. from the reactor penetrate the wall of the reactor envelope through screwed-in, spring-tightened gas

seals. These seals are not vacuum-tight, but will only permit the escape of negligible amounts of gas unless the pressure inside becomes extremely large. These tubes are all arranged with union couplings in the lower 4" of the large cylinder of the reactor envelope. If these unions are uncoupled, and the lower flange seal of the large cylinder is broken (by removal of screws), the upper part of the reactor envelope, with the un- connected tubes and pipes, can be removed. This would only be necessary under certain emergency conditions, described later.

The reactor is not concentrically placed inside the slightly larger cylinder of its enclosing envelope. The reactor touches one side of its envelope, which leaves a gap of about 0.8 cm on the opposite side between the reactor and the envelope. In this space are located (1) a thin strip of cadmium which moves vertically in a guiding scabbard and serves as a shim- control rod, and (2) a small tube extending downward to the bottom of the reactor envelope, to the lower surface of the reactor, which provides a means of removing liquid from the envelope in case a leak in the reactor develops. The remaining space is filled with tightly packed graphite powder.

7. The Reflector.

The reactor envelope, immediately underneath the reactor, rests upon a 16" thickness of graphite blocks, and is also surrounded on the sides con- tiguous to the reactor by 16" of graphite blocks.

The reflector is placed around the reactor (a) to decrease the amount of U235 needed in the reactor and (b) to increase the value of the radiation flux at the surface of the reactor. Highly purified graphite, shaped from 4" x 4" rectangular bars to fit snugly against the reactor surface is used as the reflector. The graphite is placed both inside and outside the reactor envelope, so that a thickness of at least 16" is present on all surfaces of the reactor.

Inside the reflector envelope, above the reactor and in the narrow channel around the sides, powdered graphite to a depth of 16" serves as part of the reflector. This powder is packed sufficiently to prevent any effective shifting of the reflector during reactor operation.

8. The Second Liquid Catch Basin.

If a leak should occur in the reactor, the liquid will be caught in the bottom of the reactor envelope. Any liquid in the reactor envelope would be in close contact with the reactor, and part of the same nuclear fuel accumulation. The control and safety rods of the reactor, therefore, would serve to prevent inadvertent nuclear reaction because of accumulation of the leaked liquid.

In case a leak or rupture should occur in turn in the reactor envelope, a second catch basin for liquid is placed underneath the first. The secondary catch basin has an upper and a lower part. The upper part is an aluminum cylinder, open at the top, into which the lower end of the reactor envelope loosely fits. The cylinder is filled to within 2" of its upper end with snugly packed graphite blocks. The reactor envelope rests solidly on this graphite for support. Small channels through the graphite permit any liquid leaking from the reactor envelope to trickle down through the graphite to the lower part of the catch basin. Calculations show that a nuclear chain reacting condition in the graphite below the reactor will not be closely approached, even if all the solution from the reactor is thoroughly and uniformly inpregnated throughout the graphite, which is not likely to occur.

The lower part of the catch basin consists of a broad shallow chamber in which the liquid from above may be caught. There are no control rods in this vicinity, hence the unfavorable geometry of the flat catch basin is necessary in order to prevent uncontrolled nuclear reactions in case all of the nuclear fuel should leak down to this location.

9. The Lead Shield.

An aluminum cylinder, 52 inches (O.D.) in diameter and 48" high, open at the top, but lined on the sides and bottom with 2 inches of lead, encloses the reactor. Holes are cut in the sides for the passage of exposure parts to the reactor. An additional layer of lead, unattached to the cylinder, is placed externally around the sides of the cylinder. The purpose of this heavy metal layer is two-fold: (1) The metal acts as an attenuator for the gamma radiation from the reactor, thus reducing the amount of concrete shield- ing needed; and (2) in case the reactor must be removed from the assembly while it is highly radioactive from undecayed fission products, it may be removed inside the metal lead-lined cylinder, which then serves as a shielding container for the transportation or storage of the reactor. The "port holes" may be easily filled and a cover may be placed on the top to provide a complete shield after the upper part of the reactor envelope is removed.

The cylinder serves incidentally as a tertiary catch basin for leaked solution, in case the first and second catch basins fail.

10. Safety and Control Rods.

The reactor is provided with two identical boron rods and one cadmium "rod". One of the boron rods serves as a safety rod and the other as a control rod. The cadmium "rod", a 0.02" thick, 2" wide strip of cadmium mounted flat against the outside vertical wall of the reactor, serves as a shim control rod. The boron rods each consist of 8" of enriched (B10) sintered boron (ρ = 1.5 - 1.7) inside of a 5/8 o.d. thin walled stainless steel tube. The boron tubes are mounted vertically inside of stainless steel scabbards which are re-entrant through the top surface of the reactor, 8" down into the reactor. The boron rods are located 4" from the central vertical axis of the reactor and approximately 100 radial degrees from each other.

In these positions the boron rods are each "worth" about 80 grams of U235 in the solution. Thus either rod alone is equal to the total excess U235 in the solution above that required for criticality at room temperature. The shim rod is "worth" about 10 or 12 grams.

The stainless steel tubes containing the boron in their lower ends extend upward inside the (re-entrant) scabbard tubes about 18" to an electromagnet connection to vertical, motor driven "rack and pinion" rods. The "rack and pinion" rods may be raised or lowered by signals to their respective motors from the Control Console. The boron rods, likewise, through the electromagnet connection, are raised and lowered with the "rack and pinion" rods. Should current to the electromagnet be interrupted the connection is broken and the boron rod drops 8" into the reactor inside the re-entrant scabbard tube. The shim rod is likewise raised and lowered by motor drive.

In normal operation, one boron rod (safety) is hoisted completely out of the reactor to a poised position from which it can drop back into the reactor. The shim rod is partially removed, and in that position oscillates up and down in response to electronically amplified signals which attempt to move the shim rod to counteract fluctuations in the operating level of the reactor. The other boron rod (control) is partially withdrawn to such level as will cause the reactor to operate at the desired level.

11. Instrumentation and Control.

The instrumentation included in the reactor installation is intended: (1) to provide the operators with knowledge of all relevant conditions and processes occurring in the assembly and to record such information when desirable; (2) to furnish the operators with means of guiding, controlling, and regulating all processes.

The chief components of the instrumentation system are: (1) the sensi- tive devices: thermocouples, pressure guages, radiation detectors, etc., in and around the reactor assembly; (2) the signal transmitting system: cables, pressure leads, etc.; (3) the indicating and recording mechanisms at the operator's location; and (4) the controlling, regulating devices at the operator's location.

A control console will be located outside the reactor room in such a position that an operator at the console can view the inside of the reactor room through a large water window, 16 inches thick, (as protection from stray radiation). On the console will be located the indicating, recording, and con- trol-regulating mechanisms. Trenches under removable sections of the floor, loading from underneath the reactor to a point underneath the console, will provide the location of the signal transmitting devices.

The measurement and control of the operating level of the reactor is by far the most important component of the instrumentation system. Temperatures, pressures, water flow, gas disposal, monitoring data, etc., are also of vital importance. The vaious important components of the instrumentation system are described below:

A. Control (1) Detectors A total of six fission chambers are to be used in measuring and controlling the activity of the reactor. These are to be placed within the concrete shielding just outside the lead shield, and are to be placed symetrically around the reactor core so that any one chamber can be used to perform any of the control or measuring functions. These chambers are to supply the signals to the amplifiers and associated equipment, which normally perform the following functions:

Chamber No. 1--indicating and recording neutron flux level on linear scale. Chamber No. 2--indicating and recording neutron flux level on three decade logarithmic scale. Chamber No. 3--reactor period recording and indication. Chamber No. 4--neutron flux level for automatic rod control. Chamber No. 5--reactor period for automatic rod control. Chamber No. 6--neutron flux level and period for safety trip. The circuits of chambers 1 and 4 will also be used for tripping the safety releases at preset neutron flux levels.

Additional channels with proper amplification and metering will be supplied for inclusion of scintillation detectors to supplement the fission chambers.

The activity of the coolant is to be monitored continuously by means of a scintillation counter which measures the activity of the coolant as it enters the hold-up tank. A similar detector is to be placed at the exit of the hold-up tank.

The activity of the stack gases will also be monitored by detectors having indicating meters and recorders on the control console.

(2) Amplifiers and Recorders

The associated equipment of the fission chambers will be made up of stabilized low-drift D C amplifiers used in conjunction with necessary networks to produce the linear logarithmic and period functions

In addition to the above mentioned recorded information, the following data will also be recorded automatically:

(a) Position of the control rod and the shim rod. (b) The coolant temperature at inlet and outlet of reactor.

(c) The coolant rate of flow. (d) Radiation level in the coolant before and after the hold-up tank. (e) The temperature of the reactor solution. (3) Control Process. The control mechanism consists of a safety rod, which in normal operation is completely removed from the reactor; a control rod and a shim rod, which can be positioned automatically or manually. Separate positioning controls will be available for each rod. (a) Safety rod. The safety rod consists of a lower boron filled section, a connecting part and an upper gear drive section. The lower portion of the rod is held to the connecting rod by means of an A C operated holding coil which may be deenergized by various signals to be described later. The position of the rod is indicated on the control console. Limit switches, upper and lower, operate indicating lights on the panel. The rod is driven up or down by means of a two phase motor; the speed and direction of the the motor drive may be controlled from the panel. The gear reduction from the motor to the rod is such that a predetermined maximum rate of with- drawal cannot be exceeded. (b) The control rod is of the same construction as the safety rod. The drive mechanism in the manually operated function is the same ex- cept for the fact that the gear reduction system has very low backlash and the position can be read more accurately. For automatic operation, servo units controls the position of the control rod and the shim rod so as to maintain the neutron flux at a desired level. The shim rod is used to compensate for small fluctuations in the neutron level.

(c) The operator has before him at all times a three-decade presen- tation of the neutron flux variations as well as an expanded picture of the power level at the operating point. The rate of increase or decrease of the neutron flux is also metered at the operator's position. A galvanometer type of meter will show the operator at any time during automatic operation the difference between the desired flux level and the actual level. This meter will serve in similar capacity during manual operation as well. (d) Besides the above mentioned meters, operation of the holding magnets will be monitored so that the operator will know when the magnet current is on, and when each of the two rods has been picked up by its magnet. Limit switches on the upper and lower travel of the rods operate indicator lights on the control panel. This is a safety factor as well as a means of checking the position of the rods against the selsyn indicating system. (4) Interlocks.

A system of interlocks is provided to assure proper sequence of operation of the reactor.

The power going to the rod holding magnets is interlocked with reactor shield doors, water flow, amplifier rack doors and recorder chart motor drive as well as the main power supply to all instruments.

(5) Automatic Safety Mechanism. The automatic safety mechanism can be divided into two classes: 1.) safety devices which indicate faulty equipment or sequence of operation, and 2.) devices which deenergize the holding magnets and give indication when some level or rate has deviated from its normal

course. In the first class are the above mentioned interlocks, and the following items. In the cases where the signals from the fission chambers are amplified as a linear function, their outputs will be compared so that indication can be made when one deviates from the mean. If desired, this differential can be used to trip the holding magnet. Where possible, failure of other primary equipment will be indicated on the control console. In the second class of automatic safety mechanism are the following functions which can operate to trip the mechanism of the holding magnets: (a) An excessive neutron flux level in the reactor. (b) An excessive rate of rise of the neutron flux in the reactor. (c) A failure of water flow. (d) An excessive coolant temperature differential. (e) Accidental opening of any of the interlocks. (f) Failure in the main power supply. (g) Travel of the control rod to its top limit. (h) An excessive radiation in the coolant. (i) Manual trip from the control panel. B. Control Console. The control console consists of three divisions: (1) the central primary indicating and control panel, (2) the secondary indicating panels, and (3) the recording panels. (1) The central panel will contain the following instruments: (a) Indication of the neutron flux level on a three-decade scale. (b) Indication of the neutron flux level on a linear multi-range meter. (c) Indication of the rate of change of the neutron flux level.

(d) Safety rod position control. (e) Safety rod position indicator. (f) Control rod position control. (g) Control rod position indicator. (h) Shim rod mean position control and indicator. (i) Neutron flux level desired. (j) Difference between neutron flux desired and actual level indicator. (k) Maximum rate of change of neutron flux desired. (2) The secondary panel will include the following indicators: (a) The holding magnet current control and indicator. (b) Interlock indicating lights. (c) Instrument failure indicating lights and differential control. (d) Holding magnet trip indicator lights. (c) Indicating instruments to duplicate the recorded functions. (f) Recorder chart speed change control. (g) All power supply switches and indicator lights. (h) Room monitor level indicator. (i) Reactor solution temperature. (j) Stack monitoring indicator. (k) Coolant flow regulation. (3) The recording panel will contain the following recorders: (a) Neutron flux level on a three-decade range scale. (b) Neutron flux level on a linear multi-range scale. (c) Neutron flux power period (or rate of change of flux). (d) Control rod position. (e) Shim red position. (f) Coolant temperature.

(g) Coolant flow. (h) Coolant radiation. (i) Reactor solution temperature. 12. Operating Level; Radiation Fluxes; Reactivity of Solution.

All component parts of the reactor involved in determining the power level of operation (shielding, cooling coils) have been designed to permit steady state operation at 10 Kilowatts. It is probably that, in actual operation, power levels in excess of 5 KW may not be desired for a long time. Indeed, a great deal of work will be performed at 1 KW or less.

Table 1 lists the estimated and calculated radiation fluxes at various points in and about the reactor at 10 KW power output.

TABLE 1. VARIOUS FLUX DENSITIES AT VARIOUS POSITIONS (10KW)

1. Surface of Reactor Vessel.

From experimental work on a reactor similar to the one described in this report estimates of radiation fluxes on the surface of the reactor are:

Gamma rays5.4 x 1011γ's/cm2sec.2Mev. Neutrons fast1 x 1011n/cm2sec. Neutrons slow3 x 1011n/cm2sec.

2. Re-entrant exposure tube inside the reactor.

Based on the neutron distribution in the cylindrical reactor the above figures would require the following values at the center of the cylinder which we will consider as the values in the re-entrant exposure tube.

Gamma rays5.4 x 1011γ's/cm2sec.2Mev. Neutrons fast5.5 x 1011n/cm2sec. Neutrons slow1.5 x 1011n/cm2sec.

3. Experimental Port.

At the external end of port the flux can be estimated by assuming only in- verse square law acting. This will be approximately true even for γ rays. On this basis, the calculated values are:

Gamma rays2.0 x 109γ's/cm2sec.2Mev. Neutrons fast2.0 x 108n/cm2sec. Neutrons slow1.2 x 109n/cm2sec.

4. Thermal Column.

At external surface of column (5 ft from reactor) the slow neutron flux will be 3 x 107 n/cm2sec. with about 5.2 x 102 fast neutrons, (i.e., 60,000:1). There will be γ rays which will come from the absorption of slow neutrons when Cd sheet is in place to absorb slow neutrons.

Gamma raysfrom Cd(n,γ)when Cd in place Neutrons slow3 x 107n/cm2sec. Neutrons fast5 x 102n/cm2sec.

5. Along Thermal Column.

Tabulated below are the neutron flux available at points along column:

Distance fromLead Shield1 foot2 feet3 feet n(slow)5 x 1010 n/cm2sec.1.2 x 1010 n/cm2sec.3.5 x 108 n(fast)4 x 106 n/cm2sec.5 x 105 n/cm2sec.1 x 104

As the reactor is operated, the fuel solution and surrounding materials become radioactive. The total radiation from the reactor derives from three sources: (1) fission of uranium, which instantaneously releases neutrons and gammas, with relatively fewer alpha and beta particles; (2) fission products, which are highly radioactive when first formed, and they release a few "delayed" neutrons and many beta and gamma particles; and (3) radioactive

materials artificially (activated by the radiation from (1) and (2). This induced activity consists chiefly of betas and gammas. When the reactor is not in chain reacting condition, radiation is not produced by (1) fission, but does continue from (2) and (3): fission products and induced activities. Both these latter materials decay in activity with half lives characteristic of the particular isotopes involved. The composite total of the half lives involved results in a characteristic decay pattern for the reactor contents. The "composite" half life has been found to be about 55 seconds.

When the reactor is brought to a chain reacting condition at a certain fissioning rate, after a period of inactivity during which the previousl induced activity decayed to a low level, radiation from the fissioning atoms is immediately produced and fission products begin to accumulate. Induced activity in the surrounding materials also begins to build up. assuming that the fissions continue at a constant rate, the total radiation steadily in- creases due to the contribution of the fission products and the induced activities. The increase continues until the decay of the non-fission sources is equal to the rate of formation. This will require a very long time, for a small fraction of the fission products are very long-lived. Thus, a "steady state" condition involves a small but gradual rise in total radiation from the reactor, even though the fission rate remains constant.

Table 2 below contains calculated values of the total activity of the fuel solution at various elapsed periods after shut down from various operating levels. It is assumed that the gaseous fission products escape from the reactor as they are formed.

TABLE 2. ACTIVITY IN CURIES OF FUEL SOLUTION

OperationTime (days)PowerTime in Days After Shut Down 0.0010.1151520 110KW2.1x1044.3x1033.1x1021.8x1020.52x1020.38x102 10102.4x1046.7x1032.6x1031.0x1034.0x1023.0x102 100101.8x1051.0x1044.3x1032.3x1031.4x1031.2x103 112.1x1034.3x1020.31x1020.18x1025.23.8 1011.8x1041.0x1034.3x1022.3x1021.4x1021.2x102

13. The Thermal Column.

A large portion of the neutrons emerging from the surface of the reactor are "fast" neutrons, i.e., their energies and velocities are high. A great deal of interesting research, however, involves the use of "thermal," or slow neutrons. Fast neutrons may be slowed by collision with light, low neutron- absorbing atoms, of which carbon is an excellent example.

The neutrons from one side of the reactor, therefore, are allowed to penetrate several feet of graphite, highly purified to remove neutron absorbing contaminants and, as they emerge, a large percentage have velocities in the thermal region.

The thermal column of graphite is shown in cross-section in Figure 8. Four exposure ports into the graphite are provided. Table 1 lists the anticipated values of the radiation flux at various positions in the graphite

14. Sample Exposure Ports.

It is anticipated that several sample ports may be used simultaneously for exposure of samples to the radiation from the reactor. Also, it may be desirable to "tie-up" permanently the bean from one or more ports with a

large piece of special apparatus. Hence provision is made for a large number of exposure-bean ports through the shielding into the region of the reactor, though only one or a few of these may be in use at any given time.

There are altogether 12 exposure ports. (Figure 9 )

Seven extend horizontally from the outside surface of the concrete shield inward to the surface of the reactor envelope, along extended diameters, respectively, of the reactor, of these seven, one runs along the horizontal axis of the thermal column.

Four exposure ports extend entirely through the assembly, from the out- side surface on one side through the interior of the assembly, to the outside of the shield on an opposite side. Three of those four traverse the thermal column, perpendicularly to the horizontal asix of the column. The fourth is tangent to the surface of the reactor envelope.

The twelfth exposure port extends vertically downward through the top surface of the concrete shield to the top surface of the reactor itself as a one inch tube, which continues downward into the reactor as a re-entrant tube to a depth of 8". Small samples in this tube are exposed to the highest possible radiation flux.

In order to achieve economy and convenience in construction, all exposure ports are standardized to a single pattern (except the 1" vertical port).

A 3.5" i.d. metal tube in the concrete is placed in position and permanently secured there by surrounding it with the poured concrete of the reactor shielding. Subsequently, the 3" i.d. "lining tube" is inserted into the first tube so that it provides a continuous passage from the outside of the shielding to the surface of the reactor envelope. The "lining tube" can be removed should it interfere with repair work around the reactor inside the concrete shield.

The external end of each exposure port terminates in a heavy "burglar- proof", combination-locked safe door. When not in use, the beam ports are plugged by inserting successively smaller telescoping tubes inside the "lining tube" until the passage is closed. The safe door is then closed and locked.

All exposure-ports emerge horizontally from the shielding at a level of 24" above floor level. The emergent beams thus would strike a person who carelessly stepped into the beam path on the legs, rather than in a more vital region. Radiation beams from the ports traverse paths across the Reactor Room 24" from the floor level, to respective openings in the building wall which lead to underground radiation traps outside the building.

To permit usage of lager apparatus than could be accomodated at the 24" level from the floor, trenches four feet wide and two feet deep, ex- tending from the respective faces of the reactor to the wall of the room, are provided. These trenches are normally covered when not in use by movable sections of the floor of the room.

15. Sampling-Replenishing Lines.

For the purpose of adding solution to the reactor or withdrawing solution (samples, or complete removal) a Sampling Line is included in the reactor design. (Figure 7). A 3/8" stainless steel tube, re-entrant into the reactor, extends from. the inside bottom of the reactor upward through a coupling in the wall of the reactor envelope, then at a slight incline from the horizontal, through a submerged trench in the concrete, to terminate at a cutoff valve just underneath a combination-lock safe-door in the top surface of the concrete shield.

By unlocking and opening the safe door, the end of the sampling tube is exposed. Addition of fluid can be readily accomplished by gravity flow into the reactor. Also, by simple connection to a vacuum pump, preceded by a liquid trap, solution may be quickly removed from the reactor.

A second tube, the Liquid Salvage Line, lies closely beside the first, but extends to the bottom of the reactor inside the reactor envelope enclosing the reactor. With this tube, liquid can be removed from the reactor envelope in case of leaks, etc.

16. Solution Level Indicator.

For measuring the level of liquid in the reactor two methods amy be used: (1) The pressure required to bubble air (or other gas) backwards through the sampling lines to the bottom of the reactor can be measured and, knowing the specific gravity of the liquid, the solution level can be calculated. (2) A liquid level indicator is provided for accurate level measurement when the reactor is nearly full. The latter instrument is described below.

A welder or stainless steel tube of 3/8" inside diameter projects 24" above the top surface of the reactor (Figure 10). At this point the 3/8" tube is flange sealed with an insulator gasket to a 2" x 3" stainless steel sylphon bellows. From the movable top end of the sylphon bellows a 1/8" steel rod projects 25 inches downward to make contact, on its sharpened point, with the liquid in the reactor. The sylphon and its attached contactor, being in- sulated by the gasket from metal contact with the reactor, may be made the anode of a low voltage electrical circuit of which the reactor and its electro- lyte liquid is the grounded portion. The sylphon bellows may be compressed by means of pneumatic pressure inside a sealed-on metal chamber enclosing the sylphon. When pressure is exerted, the sylphon is compressed and the pointer lowers to make contact with the liquid. When this occurs, an electrical signal appears on the operators control console. The position of the pointed is calibrated against the pneumatic pressure. The distance of vertical travel is three inches. When the liquid is within 3 inches of the top surface of the reactor, therefore, its position may be determined with high accuracy.

17. Gas Disposal.

When the reactor is in operation, a very small volume of gaseous fission products will be released. These gases result from the fission of uranium into elements of gaseous nature near the middle of the periodic table. Most of the gases will be highly radioactive, but most of the radioactivity will be quite short lived.

Estimates have been made of the gaseous fission products expected from the reactor, calculations of the total radioactivity expected, and of the decay of the radioactivity Figure 11). About 2.5 x 1014 disinte- grations per second, or 7000 curries, occur initially from the atoms of the fission product gases produced per kilowatt minute. After 4 hours, however, the activity is 5.0 x 109 disintegrations per second, or 0.15 curios from a kilowatt minute of fission product gas, a decrease in activity by a factor of over 50,000 in 4 hours.

The fission product gases will be accompanied by much larger volumes of other gases resulting from the radiation decomposition of the water molecules in the fuel solution into hydrogen and oxygen. The hydrogen and oxygen will have negligible radioactivity, but these gases do constitute a mixture of explosive proportions.

The "gas problem" for the reactor in maximum normal operation (5 KW) consists therefore in disposal of 40 liters per hour of a hydrogen-oxygen mixture in which a trace of highly radioactive fission products gases are intermixed. There are several possible means of disposing of these gases:

(a) The gases can be swept out of the reactor as they are formed with, say, flushing air, conducted via ducts and blowers to a stack and thereby

dispersed into the atmosphere. This is the method used at Los Alamos, quite satisfactorily.

The flushing air dilutes the H2-O2 mixture to non-explosive pro- portions; the large blowers at the stack (8-10,000cfm) dilute the small amount of active gases to extremely samll parts of the volume blown into the upper atmosphere, and the release occurs adequately high (100 feet or so) to prevent ground contamination. This method, however, is not satisfactory as a routine disposal method in a thickly inhabited are, for several obvious reasons.

(b) The gases, undiluted, can pass to an underground holding tank large enough to require, say, 10 days for the gases to traverse, and then be dispersed via P stack to the atmosphere. The holding tank required would need only a 3500 liter capacity, and the gases, at dispersal, would be very low in activity. The only difficulty with this method is, the gases are potentially explosive, and storage of 3500 liters of an ex- plosive gas in an underground tank is not a desirable procedure. If the mixture is first diluted with inert gases to prevent explosions, the total volume would become at least 6 times as great, or 21,000 liters for the holding tank. This is not an impossibility, of course. For smaller volume of gas, this method would constitute a very desirable means of disposal.

(c) The gases can be diluted with an inert gas to prevent explosion, say, nitrogen or helium, and then the H2 and 02 can be combined, by ignition or catalytically. The resulting water can then be condensed and removed, and the diluent gas, with its slowly but gradually in creasing increment of fission product gas contamination, can be recirculated.

This is not a desirable process, chiefly because the condensing, re- circulating equipment, etc. would be rather complex.

(d) The gases can be diluted with steam to prevent explosion (at least 3:1 steam; H2-O2 mixture) and then ignited or catalytically combined to form water vapor. The diluent steam and the recombined water vapor is then condensed and the water sent to a holding tank for eventual disposal. The small fraction of uncondensed, non-explosive gases are then sent to a holding tank for radioactive decay and eventual disposal via stack to the atmosphere. Alternately, after removal of the explosive components, the small fraction of remaining gases may be absorbed in activated carbon traps and absorbed there until radioactive decay is sufficient. Then the gases may be released by heating the carbon, and dispersed into the atmosphere. (e) It may prove feasible simply to absorb all gases evolved, radio- active and otherwise, on activated carbon, hold for radioactive decay, and then release to the atmosphere by heat. (f) Another very promision method of handling these gases is now under investigation. This consists of preferential removal of hydrogen from the mixture, and storage of the non-explosive residue until sufficiently decayed to permit atmospheric dispersal. The hydrogen can be removed by passage of the gas mixture through a vacuum jacketed tube having porous walls, the pores being of sufficient size to permit passage of hydrogen but not large enough to permit passage of the ether gases. This can be accomplished by a thin, heated polladium tube, (which is also highly corrosion resistant), though the area needed for complete hydrogen removal is rather large. Certain other porous materials are now being investigated.

It is quite certain that some method or combination of methods can be devised to provide a completely satisfactory system of handling the gases. No dispersal to the atmosphere will be permitted until the activity is decayed sufficiently to be harmless.

If the system were to be built at the time of the present writing, the combination of methods described below would be used. It may be possible to improve the system considerably before the reactor is built as a result of studies now in progress.

As now visualized, the reactor gases would be handled by one of two methods (See Figure 12): 1) For product gas volumes below 500cc/min, which would be the case for a major portion of the "in" time, the gas would be diluted with 6 times as much air, to produce a non-explosive mixture, and sent to a 3000 gallon underground holding tank for radioactive decay. Ten days would be required for traversal of the baffled interior of the holding tank, during which time the activity would decay by a factor of 5 x 105 (Section 5 ). The gas emerging from the holding tank (500cc/min, maximum) would be diluted with 10,000 cfm of air and blown up the building stack. With uniform mixing, the gases emerging from the stack would have an activity of 2.5 x 10-4 microcuries.

2) For product gas volumes from 500cc/min to 2000cc/min (maximum for 10KW operation), steam at 100°C is used for dilution, 4:1. The resulting non-explosive mixture is passed through a stainless steel wool-packed preheater, where a hydrogen-oxygen combining reaction is initiated. The reacting gases are swept into a "converter" chamber where the exothermic H-O reaction is controlled by cooling coils. The total water vapor, both from the recombined H-O and the dilution steam, is condensed and sent to a holding tank where the short-lived activity decays. The small volume of non-condensed gases are then sent (a) to the 3000 gallon holding tank for radioactive decay before atmospheric dispersal, or (b) to a cooled activated carbon absorption trap where they are absorbed until radioactive decay is adequate for atmospheric dispersal.

If at any time an unsafe quantity of radioactivity is found in the gases being dispersed into the atmosphere, the reactor will be closed down until the situation is rectified. If an inadvertent power flash in the reactor should occur (a sustained high power is impossible) and create suddenly a volume of product gases, these would be diluted with air and swept to the holding tank where they would be held as necessary for radioactive decay.

CONFIDENTIAL III. REACTOR HAZARDS A. NORMAL HAZARDS.

In the routine operation of the reactor and its associated facilities, certain hazards to personnel will exist. The situation is quite analogous to that existing in an x-ray laboratory or in a chemicals manufacturing plant where toxic gases, say, fluorine, is handled. In those and all similar situations, safety or personnel is insured by (1) proper design of equipment, (2) adequate monitors and safety devices and (3) continuous education and emphasis on safe practices. The normal hazards of operating this establishment are listed below, together with the means of insuring safety of personnel.

1. Radiation

Radiation may come from two sources: (1) open ports in the reactor shielding from which a direct beam may emerge. Anyone entering the path of such a beam would receive a dose of radiation of greater or lees magnitude, depending on many factors. The beam of maximum possible intensity as it emerged from a 3" hole at the surface of the shielding would contain

6 x 1010 2mev γs 6 x 109 fast ns 3.5 x 1010 slow ns.

This beam would cause a radiation exposure over a 3" circular area of approximately 2.0x103R/second. At the wall of the reactor room, due to attenuation and "inverse square" spreading of the bear, the radiation ex- posure would be about 1.3x102R/second over a 12" circular area. If the beam

CONFIDENTIAL

strikes an object in its pathway, considerable amount of scattered radiation over the reactor room may result. (2) Radioactive sources, e.g. irradiated samples, etc., could cause irradiation of persons in the vicinity.

The following means, among others, will be followed as precautions against excessive radiation exposure:

(a) All beans from the reactor emerge horizontally at a height of 24 inches from the floor so that exposure, if any, will normally occur on the legs instead of in some more vital region. (b) Exit holes in the wall of the buildings leading to underground radiation traps will be provided opposite each beam port in the reactor. Thus, the emergent beams will not be scattered inside the reactor room. (c) Occupancy of the reactor room when the reactor is in operation will be kept to a minimum. (d) The reactor room is provided with 12" - 16" masonery wall, except at one place, to prevent scattered radiation reaching personnel in other parts of the building. On one side a large water observation window, 16" thick, permits external observation and simultaneously prevents exposure by stray radiation. Openings from the reactor room are pro- tected by "Chinese screens" to prevent escape of stray radiation. (e) A bank of tubes of assorted sizes project outward and downward a height of 4 - 6 feet on one wall of the reactor room (hence they are underground externally) in which all radioactive sources and irradiated samples are stored when not in use. Thus, persons in the area are not exposed to radiation from these stored materials. (f) Radiation monitors, equipped with visible and audible warning signals, will be placed in strategic positions in the building to provide warning when radiation tolerance limits are being approached.

(g) All personnel in the building will be required to wear personnel electroscope monitors, film badges, and other radiation recording devices as necessary, to provide knowledge of routine exposure history. (h) Constant vigilance and emphasis on safety will be practiced and demanded of all persons engaged in activities in the vicinity. 2. Radiochemical and Radiophysical Hazards.

In pre- and post-exposure handling of samples and specimens, considerable manipulation of radioactive materials, largely beta and emitters, will be involved. Handling, chemical processing, measuring, weighing -- all these and similar operations may involve hazards of exposure, ingestion and personal contamination. Various precautions will be followed to insure the safety of personnel.

(a) No person will be permitted to engage in radiophysical and radio- chemical activities who has not satisfactorily demonstrated adequate training in this type of work. (b) The very best type of radiochemical equipment and facilities will be provided. Ventilation will provide motion of air from areas of low activity toward those of higher activity. In hoods and on chemical benches ventilators will move air away from the operator. Adequate tools, tongs, shielding brick, radiation monitors, etc. will be provided in the laboratories. (c) No smoking or eating in radioactive areas will be permitted. (d) Lockers, showers, clothing change rooms, scrubbing facilities, hand, foot, and clothing monitors will be provided and their use will be required.

B. EMERGENCY HAZARDS.

In this category are listed inadvertent, unexpected, unplanned and ab- normal occurences and accidents which could or might result in personnel hazard or area contamination of less than catastrophic proportions.

1. Leak or Rupture of the Reactor.

If a leak in the reactor occurs, radioactive liquid and radioactive gases may be released. The reactor envelope is provided for just this occurence. The released liquid and gas will be contained in the envelope. The Liquid Salvage Line (Section II, D, 15) and a vacuum pump may be used to withdraw the escaped liquid from the reactor envelope into shielded, "always safe" containers. The gases may be pumped from the envelope via the purge lines to absorption traps or to a gas holding tank and subsequent- ly to the stack for disposal.

When the liquids and gases have been removed from the reactor and reactor envelope, the fluids and the contaminated parts of the system needing repair will be handled as any other similar material. If the parts to be repaired cannot be decontaminated; i.e., if the activity is due to the metal itself, radioactive decay must be permitted or the part must be discarded.

The graphite blocks immediately below the reactor but included in the envelope contain small drain holes to allow the fluid, in case of leakage, to flow freely to the bottom of the reactor envelope. The possibility of a sustained reaction in this region, however, was considered assuring that the U235 was distributed uniformly throughout the graphite in the cylindrical volume just below the reactor. Calculations show that such a reaction would be impossible.

2. H2-02 Explosion.

The hydrogen and oxygen resulting from the radiation decomposition of the fuel solution recombine with violence when ignited under certain con- ditions. Should this occur, pressures up to 20 atmospheres may result if all the gas in a given volume engages instantaneously in the reaction. The pressures actually resulting, which may be considerably less than 20 atmospheres, night cause rupture of the gas disposal tube or of the reactor itself. Damage to the reactor envelope almost certainly would not occur. Hence the most serious result would be a leak or rupture of the reactor, which would be handled as above.

3. Inadvertent Removal of Control and Safety Rods.

The anticipated behavior of the reactor has been determined for the case in which the control rods are removed completely from the reactor in a five second period and also for the more extreme case in which the rods are re- moved instantaneously. In both cases it has been assumed that the reactor fluid was at an initial temperature of 20°C.

The constants used were (20°C): Neutron cycle time, 1p = 5 x 10-5secs. Multiplication constant for infinite size = 1.74 Excess reactivity at 20°C = 0.0157 The solution constants at 20°C are: Density = 1.1 g/cc. Mass = 15,800 gm. Specific heat = 0.95 Gas formation rate = 2 cc/KW sec. Temperature coefficient -2.0 x 10-4/°C.

Case I - Removal of Rods in Five Seconds

In this case it was assumed, due to the Blow removal of the rods, that the delayed neutrons wore all of one period and group. The value used for the percentage of delayed neutrons was 0.65% and for the period, 1/6 second. This assumption results in a simple power equation which can be integrated numerically to obtain the general r