Interest in evaluation of severe accidents induced by extended station blackout (ESBO) has significantly increased after Fukushima. In this paper, the severe accident process under the high and low pressure induced by an ESBO for a small integrated pressurized water reactor (IPWR)-IP200 is simulated with the SCDAP/RELAP5 code. For both types of selected scenarios, the IP200 thermal hydraulic behavior and core meltdown are analyzed without operator actions. Core degradation studies firstly focus on the changes in the core water level and temperature. Then, the inhibition of natural circulation in the reactor pressure vessel (RPV) on core temperature rise is studied. In addition, the phenomena of core oxidation and hydrogen generation and the reaction mechanism of zirconium with the water and steam during core degradation are analyzed. The temperature distribution and time point of the core melting process are obtained. And the IP200 severe accident management guideline (SAMG) entry condition is determined. Finally, it is compared with other core degradation studies of large distributed reactors to discuss the influence of the inherent design characteristics of IP200. Furthermore, through the comparison of four sets of scenarios, the effects of the passive safety system (PSS) on the mitigation of severe accidents are evaluated. Detailed results show that, for the quantitative conclusions, the low coolant storage of IP200 makes the core degradation very fast. The duration from core oxidation to corium relocation in the lower-pressure scenario is 53% faster than that of in the high-pressure scenario. The maximum temperature of liquid corium in the lower-pressure scenario is 134 K higher than that of the high-pressure scenario. Besides, the core forms a molten pool 2.8 h earlier in the lower-pressure scenario. The hydrogen generated in the high-pressure scenario is higher when compared to the low-pressure scenario due to the slower degradation of the core. After the reactor reaches the SAMG entry conditions, the PSS input can effectively alleviate the accident and prevent the core from being damaged and melted. There is more time to alleviate the accident. This study is aimed at providing a reference to improve the existing IPWR SAMGs.

中文翻译：

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ESBO情景下小型IPWR的严重事故管理评估

福岛事故后，人们对评估由扩展车站停电（ESBO）引发的严重事故的兴趣大大增加。在本文中，使用SCDAP / RELAP5代码模拟了小型综合压水堆（IPWR）-IP200的ESBO在高低压下引起的严重事故过程。对于这两种选定的情况，无需操作员就可以分析IP200的热液压行为和堆芯熔化情况。岩心退化研究首先关注岩心水位和温度的变化。然后，研究了反应堆压力容器（RPV）中自然循环对堆芯温升的抑制作用。此外，分析了芯降解过程中的芯氧化和氢生成现象以及锆与水和蒸汽的反应机理。得到了芯熔化过程的温度分布和时间点。并确定IP200严重事故管理准则（SAMG）的进入条件。最后，将其与大型分布式反应堆的其他堆芯退化研究进行比较，以讨论IP200固有设计特性的影响。此外，通过比较四组情景，评估了被动安全系统（PSS）对减轻严重事故的影响。详细的结果表明，对于定量结论，IP200的低冷却液存储量使铁心退化非常快。在低压情况下，从核心氧化到真皮迁移的持续时间比高压情况下的快53％。低压情况下液态皮质的最高温度比高压情况下的最高温度高134K。此外，在低压情况下，岩心在2.8小时之前形成熔池。与高压情况相比，高压情况下产生的氢气更高，这是因为岩心的降解速度较慢。在反应堆达到SAMG进入条件后，PSS输入可有效缓解事故并防止堆芯损坏和熔化。有更多的时间来减轻事故。这项研究旨在为改进现有的IPWR SAMG提供参考。与高压情况相比，高压情况下产生的氢气更高，这是因为岩心的降解速度较慢。在反应堆达到SAMG进入条件后，PSS输入可有效缓解事故并防止堆芯损坏和熔化。有更多的时间来减轻事故。这项研究旨在为改进现有的IPWR SAMG提供参考。与高压情况相比，高压情况下产生的氢气更高，这是因为岩心的降解速度较慢。在反应堆达到SAMG进入条件后，PSS输入可有效缓解事故并防止堆芯损坏和熔化。有更多的时间来减轻事故。这项研究旨在为改进现有的IPWR SAMG提供参考。