Abstract During the last decades, the substitution of passive safety systems instead of active safety systems has increased the reliability of new commercial nuclear power plants. This effort is much more significant for generation (Gen) III + reactors in comparison with Gen II and III reactors. Hydro-accumulators, as a part of the emergency core cooling system (ECCS), is a common passive system among different Gens to encounter the loss of cooling accidents (LOCAs). Recently, the application of advanced and multi-stage accumulators has become successful in GEN III + reactors. Bushehr nuclear power plant (BNPP-1) as a Russian VVER-1000 is somehow categorized between II and III Gens, but it is the first VVER-1000 equipped with two stages of accumulators. This article investigates the influence of Second Stage Accumulators (SSAs) of BNPP-1 on postponing the core damage time in an MB-LOCA with Station Blackout (SBO). Also, SSA's injection line is upgraded after the engineering judgments of start-up tests, and accordingly, each line was equipped with a Flow Restriction Component (FRC). Besides, the effect of FRCs on postponing of the core damage time is assessed in this work. Extracted results achieved from both start-up tests and RELAP5 simulations showed that, although the SSAs are useful in supplying water in MB-LOCA with SBO as a Design Extension Condition (DEC), the application of FRCs are much more effective in postponing the core damage time and without them, SSAs discharge instantly. The results of this study verify the utilization of SSAs with their associated FRCs. Also, the results confirm that some design modifications in BNPP-1 as a commercial reactor can provide resistance against a DECs. Moreover, this experience gained in BNPP-1 could be turned into a basis for safety systems designs in newer VVER-1000s and also VVER-1200 reactors.

中文翻译：

---

BNPP-1 二级蓄能器响应 MB-LOCA 与 SBO 的性能分析：支持注入线中的实际修改

摘要 在过去的几十年里，被动安全系统代替主动安全系统提高了新型商用核电站的可靠性。与第二代和第三代反应堆相比，这一努力对于第三代（Gen）+ 反应堆来说更为重要。蓄能器作为应急堆芯冷却系统（ECCS）的一部分，是不同发电系统之间常见的应对失冷事故（LOCA）的被动系统。最近，先进的多级蓄能器在第三代+反应堆中的应用取得了成功。Bushehr 核电站 (BNPP-1) 作为俄罗斯 VVER-1000 以某种方式归类在 II 和 III 代之间，但它是第一台配备两级蓄电池的 VVER-1000。本文研究了 BNPP-1 的第二级蓄能器 (SSA) 对在具有站停电 (SBO) 的 MB-LOCA 中延迟堆芯损坏时间的影响。此外，SSA 的注入线在启动测试的工程判断后进行了升级，因此，每条线都配备了限流组件（FRC）。此外，本文还评估了 FRC 对延迟堆芯损坏时间的影响。从启动测试和 RELAP5 模拟中获得的提取结果表明，虽然 SSA 在以 SBO 作为设计扩展条件 (DEC) 的 MB-LOCA 供水方面很有用，但 FRC 的应用在推迟堆芯方面更有效损坏时间，没有它们，SSA 会立即放电。本研究的结果验证了 SSA 及其相关 FRC 的利用。还，结果证实，BNPP-1 作为商业反应堆的一些设计修改可以提供对 DEC 的抵抗力。此外，在 BNPP-1 中获得的这一经验可以转化为新型 VVER-1000 和 VVER-1200 反应堆安全系统设计的基础。