White paper on reactor vessel integrity requirements for Level A and B conditions

The purpose of the ASME Section 11 Task Group on Reactor Vessel Integrity Requirements was to examine the ASME Code requirements for reactor vessel integrity. As a part of this effort, the historical basis of the current ASME Section 3, Appendix G limits for plant operating criteria was revisited. With the benefit of advancing technology, the appropriateness of the existing Code requirements was reexamined. The goals of the Task Group were to: review current regulations for materials reference toughness, assumed reference flaw size and plant operating criteria, and identify areas of conservatism and potential nonconservatism; and provide recommendations for determining plant operating pressure-temperature limits while maintaining the necessary requirements to assure vessel integrity. This white paper is focused primarily on pressurized water reactors rather than boiling water reactors, although information is provided for both reactor vessel types. The white paper was prepared by the ASME Section 11, Task Group to document the basis for the current Section 11, Appendix G approach with recommendations for future Code improvements. The recommendations and conclusions provided, however, are generic and any application of these should be checked against plant specific considerations