MONITORING METHOD OF CRITICAL APPROACH AND MEASURING JIG FOR MONITORING

摘要

PROBLEM TO BE SOLVED: To provide a monitoring method of critical approach of neutron multi plication system capable of automatically judging whether a system including nuclear fuel approaches the criticality or not and preventing a criticality acci dent, and a method capable of estimating the generation ratio of neutron and the outline of the change with time, even if the criticality accident has ocurred, from the outside of a building in the accident site. SOLUTION: A neutron detector is arranged on the side surface or inner part of a fuel container. When the relation of a neutron flux (0) with a large effective magnification to an effective multiplication factor (k0) is 0=a0+b0/(1-k0), and the relation of a neutron flux () in a small effective magnification with an effective multiplication factor (k) is =a+b/(1-k) (wherein a0, b0, a and b are constants), the area where (0/) and 1/0 (wherein 0=(1-k0/k0) have a substantially linear relation is determined from the relation of (0/) with 0, , k0, and k, 0 and are measured to monitor the change of k0, and when k0 exceeds a fixed value, an alarm is issued.