Development of improved gamma thermometer (GT)

In boiling water reactors (BWRs), traversing incore probes (TIPs) are used for the continuous measurement of the axial distribution of neutron flux in a reactor and the calibration of local power range monitors (LPRMs). One of candidates for a substitute for TIP is gamma thermometers (GTs). Some researches have been conducted so far for the verification of applying GT to BWR plants. In the research initiated in 1996, the applicability of hardware of GT was confirmed. In the next research initiated in 2000, the applicability of GT to Core Monitoring System (CMS) in BWR plants was confirmed. Considering the results of these two researches, we manufactured GT assembly with improved structures and installed 2 of them in Kashiwazaki-Kariwa 6 (ABWR) to conduct a verification test and acquired GT signal data for 1 cycle of the plant operation. We compared the reactor power distribution calculated from TIP data with that calculated from the acquired GT signal data. The average Root Mean Square (RMS) value between these two reactor power distributions was 3.5%, and it is well consistent compared with the result of the past two researches. So we had verified the applicability of the improved GT assembly from the result of the in-plant test. (author)