%MurNBdesign021651; ]> Memorandum from Raymond L. Murray and A. C. Menius, Jr. to C. K. Beck [a machine-readable transcription] Murray, Raymond L. Menius, A. C., Jr. Creation of machine-readable version: Russell S. Koonts Creation of digital images: Russell S. Koonts Conversion to TEI.2-conformant markup: NCSU Science and Technology Electronic Text Center. ca. 9 kilobytes NCSU Libraries. Raleigh, NC. Modern English, MurNBdesign021651

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 2000

Nuclear Reactor Digitization Project

Raymond L. Murray Reactor Project Notebook

 Illustrations have been included from the print version. Scanned by Russell Koonts with Photoshop 5.0 software. Memorandum from Raymond L. Murray and A. C. Menius, Jr. to C. K. Beck <author>Raymond L. Murray</author> <author>A. C. Menius, Jr.</author> <respStmt> <resp/> <name/> </respStmt> </titleStmt> <editionStmt> <p></p> </editionStmt> <extent>2 pp.</extent> <publicationStmt> <publisher></publisher> <pubPlace></pubPlace> <date></date> <idno>Manuscript copy consulted: NCSU Libraries call number UA105.16</idno> </publicationStmt> <seriesStmt> <p/> </seriesStmt> <notesStmt> <note></note> </notesStmt> </biblFull> </sourceDesc> </fileDesc> <encodingDesc> <projectDesc> <p>Prepared for the NCSU Libraries Science and Technology Electronic Text Project.</p> </projectDesc> <editorialDecl> <p>Spell-check and verification made against printed text using Notetab spell checker.</p> <p>The lineation of the manuscript has been maintained and all end-of-line hyphens have been preserved.</p> <p>The images exist as archived TIFF images, one or more JPEG versions for general use, and thumbnails.</p> <p id="ETC">Keywords in the header are a local Electronic Text Center scheme to aid in establishing analytical groupings.</p> </editorialDecl> <refsDecl> <p>ID elements are given for each page element and are composed of the text's unique cryptogram and the given page number, as in NEprop033050a for the title page of Clifford Beck's Proposal.</p> </refsDecl> <classDecl> <taxonomy id="LCSH"> <bibl> <title>Library of Congress Subject Headings 1951, February 5 English non-fiction; prose LCSH 24-bit color; 400 dpi Memorandum from Raymond L. Murray and A. C. Menius, Jr. to C. K. Beck Typescript 2 pp. Feb. 16, 1951 MurNBdesign021651

NCSC-3 OFFICIAL USE ONLY Feb 16, 1951 To: C. K. Beck CC: Members of Reactor Committee

COMMITTEE REPORT

Internal Design of Reactor

The program to date has consisted of determining best values of critical numbers; these should allow the design to proceed with less fear of serious error. Those chosen are:

1. Thickness of concrete shield 2. Reflector size 3. Thermal column length 4. Lead shielding for x-rays

Auxiliary information to the above includes:

5. Thermal neutron flux at reactor core surface; same for γ rays 6. Attenuation of neutron flux in various materials; same for γ rays 7. Tolerances

Flux: Two-group reactor theory was applied to the water-graphite system as if it were a sphere. Since this method lumps all fast neutrons into a single "group", the predicted critical U235 mess of 0.96 kg (compared with the Los Alamos value of .87kg) is rather good. The thermal flux at the edge of the core computed was 3.75 x 1011 neutrons/cm2/sec as compared with tho Los Alamos value of 3 x 1011. The theoretical attenuation in the graphite of the reflector and thermal column was

; empirical treatment of actual data gives
. The Los Alamos values are adopted without reservation on the basis of this agreement.

The γ-flux may be estimated from the 10 kw power level, the number of γ's per fission and the area of the container. A figure of 5.4 x 1011/cm2/sec of 2 MoV energy is used.

Tolerances: The present accepted levels are: slow neutrons 1500/cm2/sec; 2 MoV γ rays 1050/cm2/sec. Those correspond to a 0.1 r/8 hour day.

Attenuation of γ rays: Inverse-square spreading exponential attenuation is assumed, with absorption coefficients (μ in o-μx, where x is in cm) as follows:

graphite0.064 lead0.51 concrete0.09for ordinary type 0.19for "heavy" type

Attenuation of slow and fast neutrons: Data from various sources diff or widely. All predictions, however give safety with a 6' Shield if the concrete is "heavy". Further investigation is needed.

Thickness of concrete shield: A tentative choice of a 5 ft diameter central cavity filled with graphite relector end the core, with the overall dimension of 17 feet, leaves a shield thickness of 6 feet. This is proposed as fixed unless safety is questionable, which is not the case. From the standpoint of γ rays, the effects of reflector graphite, shield concrete (ordinary type) and

distance, reduce the flux from 5.4 x 1011 to less than 1 γ/cm2/sec. From another viewpoint the necessary thickness to reach tolerance levels is approximately 4 ft, so a two foot safety margin is provided.

Thickness of reflector: In order to satisfy two requirements (a) a low critical U235 mass and (b) a maximum thermal flux at the core surface, the largest practical thickness is used. This seems to be 20". The rate of change of critical radius and the rate of change of the ratio of wall flux to central flux were computed by one-group theory. With this thickness, the critical volume differs by only 3% from that for infinite graphite; the flux is within 5% of the ultimate.

Thermal column length: To achieve a length compatible with the Los Alamos reactor, it is indicated that the end should be located near the out- side surface of the octagon, with a movable concrete slab external to the reactor shield. If the Cd shield at the end is used, a built-in Pb block shield is needed to stop the γ's from Cd; if Boron instead were the neutron shield, the Pb could be eliminated. A 7 foot thermal column can easily be obtained in the space.

Load shield outside the reflector: If the thermal neutron flux from the end of the column is to be free of reactor γ's a lead shield must be inserted, presumably next to the reflector. One question that must be decided is - What is γ free? A slab 2" thick will cut the flux to ≃ 1400/cm2/ sec, slightly above health tolerance; a 4" slab will cut it to ≃ 110 or 1/60 tolerance. It is found that little thermal neutron absorption is encountered in either case. Even in 4" of Pb the flux is reduced by only 6%. (The alternative, Bi, absorbs 93% in a 4" section.)

Problems yet to be looked into further by means of calculations are listed:

Type of concrete needed for neutron absorption (moderately heavy is probably adequate) Effect of open exposure ports (At present, estimates are no better than 80 grams of U235 per port, comparing reactor cores with and without reflector, and 5 grams, on the basis of a fractional solid angle for escape. A guess would give 20 grams.) Decision on Cd vs. B for end of thermal column Neutron source strength, location and adjustment

Raymond L. Murray A. C. Menius, Jr.

Soodak, H., Campbell, E. C., <hi rend="underline">Elementary Pile Theory</hi>, Wiley (1950), p. 56.