Year
1998
Abstract
Reprocessed spent nuclear fuel that has gone through various stages of chemical processing is currently stored at the INEEL. The material consists of three categories: “clean” U-235 with radiation readings in the mR/h range, U-235 and fission products up to 900 mR/h, and U-235 with U-232 from 100-200 mR/h. The material is contained in plastic bottles and stored in steel structures consisting of seven vertically arranged individual compartments. A total of forty “stacks” reside in individual concrete wells. This material is considered hard to measure due to excessive radiation exposure to personnel involved with handling the material during mass and NaI U-235 confirmation measurements for Safeguards inventory purposes. A U-235 confirmation method was developed to assay the individual items in place with the ability to discriminate one item from the other items in the stack. Equipment used with this method includes a portable high-resolution gamma-ray detection system, an appropriate tungsten shield and collimator, and a laser-positioning device. A discrimination control test was incorporated to compare the gamma-ray signal of an item in place to the background signal when the item is removed. Total discrimination of the 186-keV gamma ray signal was achieved.