Validation and Performance Test of Plutonium Inventory Measurement System(PIMS) at the Rokkasho Reprocessing Plant(RRP)

摘要

At RRP,MOX powder is converted from Plutonium-Uranyl nitrate solution by microwave heating. In this process,large amounts of bulk plutonium material is transported within the plant.JNFL have introduced highly accurate measurement systems for material accountancy purposes and a multinational forum,LASCAR(Large Scale Reprocessing Plant Safeguards)recommended the need for additional safeguards measures to detect on a continuous basis both the normal movement and possible diversion of material. As a result,JNFL installed the Plutonium Inventory Measurement System(PIMS)developed by the BIL Solutions division of BNGPS.The JNFL-PIMS continuously measures plutonium masses inside pipes and vessels within the RRP gloveboxes utilizing the total neutron counting method. PIMS consists of 142 neutron detectors deployed external to the gloveboxes.By use of a 3D matrix-driven mapping algorithm the count rates are translated into real-time mass data for a total of 83 process vessels.This system operates 24 hours a day and does not interfere in any way with the continuous nature of the process. The JNFL-PIMS system was extensively modeled by BIL Solutions to determine optimum detector positions for the accuracy required,and verified in two stages.Firstly,an inactive calibration campaign in 2003 used a neutron source to simulate neutron emitting material.Secondly,an active campaign compared actual known masses of material with the results obtained from PIMS measurements.In this test U-Pu nitrate solution was introduced into the MOX conversion area in October 2006.Validation tests using the MOX powder were performed in order to check the accuracy and derive any further optimization parameters.This test was conducted by JNFL in cooperation with BIL Solutions and inspectorate. Although there was some minor optimization required,good correlation was obtained between PIMS measurements and expected values.The results confirmed that PIMS could measure the masses in the process to the required accuracy providing an effective and transparent additional level of continuous Safeguards protection.It was also shown that PIMS reflected the process operation very well,demonstrating useful capabilities as an additional means of monitoring plant operation. This paper describes the validation results and demonstrates the monitoring capability of PIMS.