A moisture probe using neutron moderation for PuO2 canister inspection

We have been developing a sensor to quickly and nondestructively measure th e moisture content of canisters containing PuO2. These canisters will be re tained in longterm storage facilities and, for stability reasons, must have moisture contents <0.5 wt%. The technique relies on the moderation of neut rons emitted by a radioisotopic source (Cf-252) to determine the hydrogen c ontent of the material. Modeling was used to help optimize the sensor desig n and to predict the sensitivity to moisture content. A benchmodel was firs t constructed and tested at SAIC with simulated PuO2 using Fe3O4 and B4C; m oisture was simulated with nylon rods. The benchmodel was also tested at Lo s Alamos National Laboratory (LANL) using actual PuO2-filled canisters modi fied to accept polyethylene rods to simulate moisture. The results indicate d that the detection limit tone statistical standard deviation) for a 10 mi nute inspection was less than 1.2 g of water, or 0.04wt%, in 3 kg of PuO2. A prototype system was recently constructed for testing a variety of PuO2 s amples with various material matrices. Here we present the calculations, se nsor designs, tests, test results, and discuss future plans.