Year
2015
Abstract
The Plutonium Inventory Measurement System (PIMS) used at RRP (Rokkasho Reprocessing Plant) is an assay system to quantify plutonium amount by means of total neutron count. JNFL started to monitor the Pu amount directly in each glovebox for the purpose of facility MC&A. However, it was found that PIMS counting increased unexpectedly and continuously during long time of inter- campaign although operator did not produce new MOX powder into the process. JAEA and JNFL jointly conducted several investigations to find out the potential causes of the increase. In the investigations, correctness of system, behavior of neutron generation focused on O/M and moisture change when MOX powder is stored in actual glovebox for a long time, and the behavior focused on the interaction between MOX powder and light element, such as fluorine included in the PTFE (polytetrafluoroethylene) which is used in many gloveboxes as packing of instruments) were experimentally confirmed. As a result, the same behaviors occurred in the actual PIMS were confirmed in the testing environment in which MOX powder coexists with fluorine, it is concluded that the essential cause for continuous increase of PIMS count rate is the increasing of the probability of (a, n) reactions by a contact between fluorine (PTFE) and MOX powder. In this paper, we present some experimental results related to the predicted neutron generation behavior from MOX powder inside glovebox.