UNIQUE CHALLENGES IN MAKING A REGULATORY DECISION REGARDING THE COMBINED EFFECTS OF BORIC ACID PRECIPITATION AND GSI-191

摘要

Long term core cooling is defined as maintaining the temperature of the core at an acceptably low value while removing decay heat for an extended period of time. It begins after the core has been reflooded following a loss of coolant accident and continues until the plant is sustained in a cold shutdown condition. Debris accumulation, on the recirculation strainers or in the core, following a loss of coolant accident could potentially challenge a nuclear power plant's capability to provide adequate long term core cooling. In addition, boric acid, already present in the core, as well as that injected from emergency core cooling systems may precipitate due to boiloff potentially causing an interference with long term core cooling. The effect of debris on long term core cooling is a challenging topic. It requires consideration of debris accumulation on the recirculation strainers and in the reactor vessel, and debris effects on boric acid precipitation. The challenging nature of this issue has resulted in difficulty establishing regulatory guidance on resolution of the issue. Research testing done in the past has resulted in an inconclusive basis for regulatory decisions. Additional research testing, as well as computational studies are essential tools in making a final regulatory decision regarding the combined effects of boric acid precipitation and Generic Safety Issue 191.