Re-instrumentation technique of pressure gauge for irradiated fuel rod

The extention of the burnup of LWR fuel from an economical point of view is one of the current important issues. In order to study irradiation behavior of high burnup LWR fuel, re-instrumentation to LWR fuel irradiated in LWRs of fission product (FP) gas pressure gauge and thermocouple for center temperature measurement are being developed in the Department of JMTR Project. The re-instrumentation of fission product gas pressure gauge has been developed since 1985, and put into actual use currently through successful demonstration test done in 1990 using power ramping testing facility the BOCA (BOiling water CApsule). The fuel rod used for the demonstration test was a segment (length of 412mm) fuel rod irradiated up to about 25GWd/t in a BWR. The pressure gauge was attached to an end plug of the fuel rod by TIG welding. After that a perforation with diameter of about 1.5 mm was made on the end plug by electric arc discharge to lead the gas pressure from the inside of the fuel rod to the pressure gauge without gas leakage. In the demonstration test, electrical characteristics of the instrumentation such as resistance, insulation resistance and reluctance of coil of the differential transformer as well as out put of the pressure gauge corresponding to linear heat rate of the fuel rod were checked. (author)