严重事故时蒸汽发生器传热管蠕变断裂风险评估

Quantitative Risk Assessment of Induced Steam Generator Tube Rupture in Severe Accident

摘要: 严重事故时，一回路将会出现蒸汽自然循环冷凝回流现象；高温蒸汽不断进入热管段，波动管和蒸汽发生器传热管，最终可能导致蒸汽发生器传热管发生蠕变断裂失效。本文首先使用严重事故分析计算严重事故时传热管蠕变断裂参数和传热管断裂的概率。然后使用简化二级概率安全分析模型评估传热管蠕变断裂导致的大量早期释放频率。最后评价一回路卸压和恢复二次侧给水等严重事故缓解措施对防止蠕变断裂的有效性。可以发现在中压和高压的情况下，一回路卸压和恢复二次侧给水能够有效地防止传热管蠕变断裂，降低大量早期释放频率。

Abstract: Under severe accident conditions with countercurrent natural circulating high temperature gas in the hot leg, surge line and steam generator tubes, SG tubes integrity could be threatened by creep rupture, particularly if cracks are present in the tube walls. In this study, the first step we perform thermal-hydraulic analysis to predict the creep rupture parameter of the tubes in severe accident. The next step we apply the creep rupture models to test the potential for the degraded SG to rup-ture before the hot leg. Then, the mean of the SG tube rupture probability was applied to estimate large early release frequency in simplified Level-2 PSA model, and the overall LERF (Large and Early Release Frequency) risk due to the Induced SGTR was calculated. In the final step, imple-mentation of severe accident management guidance, such as the RCS depressurization and refilling to SG, is evaluated using PSA approach. It can be found that strategy of RCS depressurization and refilling to SG can mitigate the severe accident process under the condition of high and medium pressure, and reduce LERF effectively.