Use of a decision tool for assessing nuclear reactor vessel embrittlement options

This paper reports on neutron embrittlement of the reactor pressure vessel in nuclear power reactors which is often the most life-limiting aspect for the entire plant in terms of safety and economic impact, especially when considering license renewal. In order to respond to the accumulating damage imposed in the reactor beltline region, may options are available to utilities for proper management of the embrittlement process. These options include various fuel management schemes, shielding of critical regions on the vessel wall, physical changes to the plant, operating procedural changes, thermal annealing, and enhanced evaluation procedures which may involve a supplemental surveillance testing program. The most feasible of these options have been analyzed for a test case of accumulated radiation embrittlement, and a decision analysis model has been utilized to produce financial numbers for a variety of these options which can be initiated at different times during the operating life of the plant. Depending upon the desired operating life of the vessel, the timing in which the options are involved, and the specific expected benefit from the various options, different strategies can emerge