Assessment of emergency core cooling system effectiveness for light water nuclear power reactors

摘要

The effectiveness of Emergency Core Cooling Systems (ECCS) for light water nuclear power reactors was the subject of lengthy, controversial and technically complex hearings conducted by the AEC over the two years from 1971 through 1973. An independent, objective review and assessment of the technical issues associated with ECCS effectiveness was conducted in a study performed at the Environmental Quality Laboratory of the California Institute of Technology. The review was based upon the testimonies and supporting technical documentation of the principal participants in the hearings: the AEC, utilities, reactor manufacturers, and intervenors. ududFrom the review, the critical technical parameters influencing ECCS performance, which were at issue, are identified. Of fifteen parameters cited by the Advisory Committee on Reactor Safety in the hearings as being of unproved conservatism, essentially all are reviewed in detail, including, for example, the initial stored fuel energy, fuel rod gas gap conductance, fluid flow rates through broken pipes, metal-water reaction energy release and fuel rod embrittlement, reflood/core-spray heat transfer, and reflooding rates, as well as the adequacy of ECCS analytical models and numerical methods. ,The relative influence of uncertainties in the performance criteria associated with these parameters is assessed. Based upon the relative importance of these parameters, alternative responses to resolution of the ECCS problem are analyzed. The importance of the core reflooding rate in resolving the technical issues of the problem is emphasized. The conservatism of the proposed criteria (current and past) is reviewed. Recommendations are made for improvements in criteria conservatism, especially in the establishment of minimum reflood heat transfer rates (or alternatively, reflooding rates). Several new and/or accelerated research programs and additional large scale testing programs are also recommended. Suggestions are also made for areas in which design improvements would help to achieve greater ECCS reliability.