The control and safety rods at Los Alamos have a maximum speed of 9.6 inches/minute, enabling a skilled operator to bring the reactor to full power of 25 KW in about three minutes. Safety controls are not associated with the rod removal rate but with the more realistic concept of power rise rate. At Los Alamos the power is allowed to rise on a 5 second period before [unclear]

This is necessary since the temperature of the reactor, the power region in which you are working, and the flow rate of the cooling water all effect the rate at which the power rises and not the control rod alone. This point was illustrated in the region of 1 KW power for a cold reactor. In this case the rod removal rate was about 3.5 inches/minute because of the practically constant temperature of the reactor (water flowing at a rate such that a very small differential in temperature would dissipate the 1 KW) and therefore practically all of the control was in the rod. At higher powers the temperature increases more rapidly and the rod must be removed much faster to allow the same power increase rate. The condition for constant power rise is

At Los Alamos the hydrogen and oxygen are recombined by a catalyst method and the remaining gas is allowed to pass up the stack after a "hold-up" of about one week. The system is shown schematically below with approximate dimensions.

When the reactor is to be filled it will be necessary to first fill the reactor with pure H2O and obtain a zero reading for the chambers. Then approxi- mately 50 cc of the H2O is removed and replaced by 50 cc of concentrated soup. This process is repeated with the necessary re-concentration of removed soup until the reactor becomes critical.

It was emphasized by Dds. Evans and Zabel to have sufficient chambers (> 4) placed at different positions so that the true 1/C curve can be bracketed (See Figure below.) and thereby determined.

It was suggested that B4C be obtained from Norton Abrasive Co., Worcester, Massachusetts of 60# grade. This should be mixed with hot paraffin and the excess paraffin drained off. The remaining mixture has about the consistency of fresh concrete and can be placed in a form for cooling. The form used for the curtain at Los Alamos was of Al and the curtain proper was about 1/2" thick. A different process will have to be developed in our case since the boron is to be placed against the concrete slabs forming the door to the thermal column.

The cooling coils consist of three 20 ft sections of 1/4" I.D. stainless steel (347) having 1/32" wall thickness. The total flow through these tubes is 3.2 gal/min with a pressure of 60#/in2 required to obtain this flow.

The water is cooled to 19°C at the inlet and at 25 KW the water exit reaches a temperature of 71°C. At Los Alamos if the outlet temperature reaches 85°C the control rods are dropped.

It is very important to avoid cracks in the graphite about the reactor. This is due to the presence of fast neutrons. The standard graphite blocks are held together by the use of Al pins. Detail plans for this stacking is to be obtained from Los Alamos which will help in our design.

The exposure ports at Los Alamos were in all but one case rectangular. The rectangular ones had a 1/8" shoulder to prevent the radiation from having a direct path to the outside of the reactor shield. The retangular ones were lined with steel and plugged with Bi, Fe, graphite, Pb all sandwiched to produced sufficient shielding. These sections were easily removed.

The question was raised regarding the advisability of using the uranyl sulphate. It was suggested that we contact Oak Ridge concerning this.

(1) In the thermal column Bi should be used instead of Pb. An increase in the flux of a factor of ten is obtained by its use. This should be studied in some detail.

(2) The bubbling effect has been measured but can be neglected in comparison with temperature coefficient. They do not ever consider it at Los Alamos.

(3) The temperature coefficient is 0.72 gm/degrees at low temperatures and 0.95 gm/°C at high.

(4) Total uranium content is 970 gram, with about 100 gm excess when the reactor is cold.

(5) Lower power level for automatic control is 50 milliwatts with fluctuations of less than 1%. No information was available on frequency of these.

(6) The neutron source is Ra - Be and has a strength of 200 millicurries. It is placed about 1 foot from the reactor sphere,. If Sb - Be source is used it will be necessary to use Ra - Be to start after long shut-down.

(7) Cooling water activity is very low, only slightly above background after reaching counting room.

(8) Use iron-constantan thermocouples of 24 gauge glass installation with glyptal used as cement

(1) Portable Beam Traps Several beam traps were constructed of discarded oil drums. These were mounted horizontally on casters and were filled with B4C and paraffin in granular form with 4" of lead in the rear. The size of the drums used was about 2 ft long x 18" in diameter. These have proved to be very useful. Larger sizes were also noted.

(2) Portable Neutron Shields Borax and paraffin make very good portable shields. This should probably be placed in metal cans to reduce fire hazard of too much exposed paraffin.

(3) Specimen Holders The specimen holders should be of either Be, special magnesium free iron or Al. Plastic holders are not too good. The special magnesium free iron is obtained from iron carbonyl and is very good. Al is fair but builds up quite a bit of induced activity.

The exposure holes are 4" from reactor and are placed in a 1 1/2" x 4" opening in the graphite as indicated in sketch below. These holes are worth less than 0.1 gram of U235.