Effects of neutron irradiation on resistivity of reactor pressure vessel steel

Abstract

The embrittlement of reactor pressure vessel (RPV) steel owing to fast-neutron irradiation is one of its primary failure mechanisms. In this work, neutron irradiation tests were performed on an RPV steel at a high temperature (565 K) using a neutron irradiation test reactor. In addition, resistivity measurements were performed on the RPV steel both before and after irradiation in a hot laboratory using the four-probe method. The results showed that the resistivity of the RPV steel exhibits nonlinear behaviour with respect to the radiation fluence and that the nonlinearity becomes more pronounced with an increase in the radiation fluence. For instance, when the radiation fluence is 0.1540 dpa and the excitation current is increased from 0.2 mA to 200 mA, the resistivity of the RPV steel decreases by as much as 67.12%. During irradiation embrittlement, the resistivity increases with the fluence. When the radiation fluence is greater than 0.116 dpa, the increase in the resistivity accelerates. When the radiation fluence is less than 0.116 dpa and when an excitation current of 2 mA or 20 mA is used, the relationship between the resistivity and the radiation fluence for the RPV steel is a quadratic one, whereas that between the rate of change in the resistivity and the radiation fluence is a linear one. Thus, the resistivity of RPV steel can be used to characterise its degree of irradiation embrittlement, and resistivity measurements can be employed as a nondestructive evaluation technique for monitoring the degree of irradiation damage experienced by in-service RPV steel.