Verification Test for Methods of Criticality Safety Control Based on Neutron Moderation Management
Investigation for Water Content of UO₃ Powder Stored for a Long Term and Development of the System which Continuously Measures Water Content of UO₃ Powder with Infrared Moisture Meters

Abstract

  In consideration of applying methods of criticality safety control based on neutron moderation management to a new uranium oxide storage building which Japan Nuclear Fuel Ltd. (JNFL) plans to construct at the Rokkasho Reprocessing Plant in the future, it is necessary to verify that water content of UO₃ powder controlled by the process will not increase, (1) on condition that, after it is filled to storage canisters, which are sealed and stored for a long term, and (2) in the process that it is filled to these canisters. Then, concerning the former (1), we investigated operations in the uranium denitration facility at Japan Atomic Energy Agency similar to the one at JNFL and the actual values of water content of UO₃ powder about its storage. On the other hand, concerning the latter (2), it is possible to verify that basically by sampling and analyses of water content of UO₃ powder in the filling process. But, for the purpose of increasing reliability for criticality safety control more, we newly developed the system which continuously measures water content of UO₃ powder with infrared moisture meters and we confirmed the effectiveness in a mock-up test. As a result, it was found that water content of UO₃ powder in the filling process was stable below 0.5% and that it did not tend to increase even after storage for about 15 years. Furthermore, we developed two systems which continuously measure water content of UO₃ powder with infrared moisture meters, and then we got prospects to apply to the real plant. Based on these results, we suggested a basic policy of criticality safety control based on the neutron moderation management for the new uranium oxide storage building as an example.