Establishment of NDA Measurement Technology for Heterogeneous Sludge Item containing Various Chemical Component

The plutonium Conversion Development Facility (PCDF) in Tokai Reprocessing Plant is the facility to convert from Plutonium (Pu) and Uranium (U) mixed nitrate solution to mixed oxide (MOX) powder using the microwave heating method. And the facility has a liquid waste treatment process to remove radioactivity in the liquid waste. This process uses a neutralization precipitation method to reduce radioactive materials from the liquid by adding sodium hydroxide and produces highly heterogeneous sludge. Since this sludge is heterogeneous mixture with multiple components that cause a large sampling uncertainty, we need to develop a measurement technology to determine Pu mass instead of conventional method using Destructive Analysis (DA). Japan Atomic Energy Agency (JAEA) and Los Alamos National Laboratory (LANL) jointly conducted a research to solve this subject. The purpose of this study is to establish a quantitative measurement technique of Pu mass in those heterogeneous sludge items and to reduce the measurement uncertainty using Non-Destructive Assay (NDA) technique for improving Nuclear Material Accountancy (NMA). In order to improve the measurement uncertainty of the Pu mass in those sludge items, the predelay of the Plutonium Scrap Multiplicity counter (PSMC) detector was appropriately optimized to reduce the uncertainty of multiplicity count rates for the items. In addition, we evaluated the key PSMC operating parameters to assure their validity for sludge and evaluated applicability of multiplicity counting and underlying assumptions for sludge measurements. Those influences for the Pu mass measurement were evaluated using various types of sample measurements and Monte Carlo N-Particle transport code calculations. The PSMC operating parameters were found to be valid for use with sludge items. As a result, it was confirmed that PSMC is capable of providing a reliable NDA assay of the sludge materials at a practical level. For the optimized PSMC/highresolution gamma spectrometry system for sludge items, a total measurement uncertainty was confirmed 6.5%. Based on the above results, JAEA and LANL conducted the acceptance test with the presence of IAEA, and this system was accepted.