Accident source terms for light-water nuclear power plants

Abstract

This paper presents a discussion of current U.S. Nuclear Regulatory Commission (NRC) activities regarding the proposed revision of accident source terms for light-water nuclear power plants, particularly since the issuance of draft revised source terms in July 1992. The NRC's current reactor site criteria require that an accident fission product release within containment, or [open quotes]source term,[close quotes] be postulated to occur and that its radiological dose consequences be evaluated. The current source term, derived from a 1962 report 2 TID-14844, postulates the instantaneous appearance within containment of 10% of the core inventory of noble gases, 50% of the core inventory of iodine (with half of this assumed to plate out very rapidly on interior surfaces), and 10% of the remaining fission products. This source term has also been used to evaluate other important plant performance requirements, such as control room habitability, postaccident access, and sampling and equipment qualification, and consequently has played an important role in nuclear power plant licensing. Aspects of this source term have long been recognized as being inconsistent with a realistic understanding of severe accident behavior. Because NRC review of advanced reactor designs showed the need for a more realistic understanding of accident mitigation capability,more » it became clear that the current source term should be updated.« less