Surveillance Program for Irradiation Embrittlement of Reactor Pressure Vessels in Japan

Abstract

The surveillance program for neutron irradiation embrittlement of reactor pressure vessel (RPV) steels is specified in Japan Electric Association Code (JEAC) 4201 [1]. The first version of the code was issued in 1970 to prescribe the baseline requirements for the surveillance program. A method for predicting a shift in the transition temperature due to neutron irradiation embrittlement (i.e., embrittlement trend curve [ETC]) for Japanese RPV steels was first introduced in 1991. This code was revised in 2007 to incorporate the methods for reconstituting surveillance test specimens and a withdrawal schedule of surveillance capsules beyond 40 years of operation. The ETC was revised in 2007 and again in 2013 to improve the correlation between the measured and calculated shift of the transition temperature. After the Fukushima accident, the Japanese Nuclear Regulatory Agency (NRA) demanded that additional surveillance tests be conducted if a utility wants to operate their plants beyond 40 years. This paper describes the details of the current JEAC 4201 specifications and NRA requirements as well as additional industry practices for addressing RPV embrittlement.