Year
1999
Abstract
A Spent-Fuel Coincidence Counters (SFCC) singles and doubles (coincidence) neutron rates were measured as a function of plutonium content and fuel pin geometry by placing various arrangements of fresh mixed oxide (MOX) and depleted uranium pins inside the counter. These experimentally determined rates were in good agreement with Monte-Carlo N-Particle (MCNP) calculations of the singles and doubles rates multiplied by 1.12 and 0.97, respectively. These scaling factors were used, along with MCNP, to predict the singles and doubles neutron rates for various nuclear reactor fuel assemblies with various mixes of the important isotopes. These MCNP calculations led to a prediction of p and the effective 240Pu calibration constant, K, for each assembly type. These calibration constants can be used, in conjunction with a calculation of the density of the neutron-emitting isotopes as a function of the plutonium density, to convert measured singles and doubles neutron rates into the total plutonium content of an assembly. To test the calibration procedures, we made measurements of the total plutonium content of 64 fat breeder reactor assemblies of different types and compared these measurements with facility-declared values. Our measurements are in excellent agreement with the facility declaration.