SOME NUCLEAR EXPERIMENTS ON THE SRE

Subcritical assembly experiments were conducted by loading fuel elements in a SRE core and determining the critical mass from the counting rate data obtained from fission counters placed in the fuel channels. A plot of the normalized inverse count rate as a function of the number of the fuel elements loaded indicated a critical mass of 22.2 dry fuel elements at room temperature and 32.64 plus or minus 0.10 fuel elements at 400 deg F using a sodium coolant. The reactivity of the subcritical SRE was estimated from subcritical multiplication measurements, and the results were used to evaluate the worth of various fuel elements and poison elements. The total reactivity change caused by replacing each uranium element with a thorium-5% uranium element was determined. Flux mapping studies were made of the dry subcritical SRE using cadmium-covered and bars gold foils in the core and reflector. The results of the flux msasurements are given graphically. (B.O.G.