Irradiation Test of Reluctance Type Pressure Sensor for Measuring Fission Gas Pressure

摘要

A reluctance type pressure sensor for continuous measurements of the fission gas pressure in fuel pins during irradiation was developed and irradiated in the JMTR. The pressure sensor is constituted of magnetic materials and electric wire, which may be affected by the effect of heat and radiation, and this in turn may impair the accuracy of the pressure sensor. An irradiation test was performed to obtain quantitative information on the accuracy of the pressure sensor itself and for examining its viability in actual use under radiation. The test was made during three cycles of operation of the JMTR at 30 MW reactor power. The calculated neutron fluence was about 4.2 x 1019n/cm2 (E>1.05 MeV) and 6.8 X 1020n/cm2 (E<1.05 MeV).It was found that the effect of heat was larger than that of radiation to a fluence of this order, but the former effect can be reduced by correction for temperature. The error due to radiation effect is estimated to be about ±1.0% at the limiting pressure of 50 kg/cm2G. The error at full power (30 MW), including the ±1.0% given above for the radiation effect, as well as other errors such as that of the pressure sensor itself and the temperature effect remaining after correction, is estimated to be about ±1.8% at the limiting pressure of 50 kg/cm2G when the neutron fluence does not exceed the values indicated above. In actual measurements of the fission gas pressures in fuel pins, the total error including those inherent in the apparatus for measuring the back pressure, is expected to be about ±2.8 %. Practical application in reactor of the reluctance type pressure sensor has been proved to be promising as a result of this irradiation test.