Pressure vessel fluence dependence on fuel management

One of the suggested remedial actions for reducing the rate of embrittlement of PWR pressure vessels; and, hence, their vulnerability to severe thermal shock transients, involves the application of fuel management schemes incorporating low leakage loading patterns. The low leakage concept makes use of either low enrichment or high burnup fuel assemblies at some or all of the grid locations on the periphery of the reactor core. This approach effects a reduction in the fast neutron flux at the pressure vessel via a decrease in the power density in the peripheral fuel assemblies along with an accompanying decrease in fast neutron leakage from the core. In many instances, low leakage fuel management has been implemented because of fuel cycle economics with no driving force from pressurized thermal shock considerations. This widespread incorporation of low leakage loading patterns, therefore, can pose problems for the radiation analyst that may or may not be directly related to the pressurized thermal shock issue. This paper deals with some of the ongoing analytical efforts at Westinghouse and Babcock and Wilcox that is geared toward resolving the issues of pressure vessel integrity projections and plant scheduling and operation