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首页> 外文会议>International meeting on severe accident assessment and management 2012: Lessons learned from fukushima dai-ichi >HOW FUKUSHIMA DAIICHI SEVERE ACCIDENTS COULD BE AVOIDED
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HOW FUKUSHIMA DAIICHI SEVERE ACCIDENTS COULD BE AVOIDED

机译：如何避免福岛大地严重事故

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摘要

As a result of the very serious consequences of the Fukushima Daiichi core melts at Units 1F1,1F2, and 1F3 and of their significant implications to worldwide nuclear power generation, numerous assessments have been published to-date. There is general agreement about their three principal causes: the assumed tsunami design basis which was low by a factor of 2 to 3; the very difficult post-tsunami impact which led to quite poor site conditions and overstressed plant personnel and management; and the Japanese regulators decision to not consider beyond design basis station black out (SBO). It left Japan government, its regulators, plant owners, plant management, and operating personnel without necessary plans and procedures to deal with the extreme SBO at Fukushima. During SBOs, all water nuclear power plants require early cooling of the reactor cores to avoid core melts. In Boiling Water Reactors (BWRs), this need is satisfied for limited periods of time by isolation condensers (IC) as installed at 1F1 and by reactor core isolation cooling (RCIC) systems utilized at 1F2 and 1F3. If they stop working, provisions are installed to add fire water to the depressurized reactor pressure vessels (RPV) to insure that two critical conditions are avoided: (a) keeping the reactor water level above the middle of the reactor core to prevent zircaloy fuel cladding chemical reaction with steam producing hydrogen, accelerating decay heat, and invalidating reactor water level data; and (b) not allowing the containment pressure to reach excessive values in order to avoid radioactivity leakage to the environment and to permit the reactor to be depressurized to allow adequate fire water injection. It is the purpose of this presentation to show that those two critical safety conditions during SBO could have been predicted readily by an integral decay heat method which would have helped avoid the 3 core melts at Fukushima. At Fukushima, not enough priority was given to assure early and safe reactor cooling by adding fire water to reduced reactor pressure of their BWRs. In the case of Unit 1, the safe strategy would have been to restart IC after its loss of DC power, and, if that was not possible, to use the installed fire water system to provide water to the depressurized reactor. That action had to be carried out within 3 hours as determined by the proposed simplified integral decay heat method to avoid the critical reactor water level falling below its core midpoint. In the case of Units 2 and 3, RCICs were allowed to run too long without the foresight and a clear priority given to implement reactor depressurization and fire water addition. Unfortunately, also, it happened that preparations for 1F1,1F2, and 1F3 to carryout RPV depressurizations and fire water additions were disrupted by hydrogen explosions at 1F1 and 1F3 as well as by other unanticipated circumstances. It is important to note that the proposed strategy to avoid core melts would have required full delegation of authority to the sites with no time available for necessary approvals for fire water addition or containment venting as well as intensive training and very strong safety culture of plant managers and personnel. That necessary condition may not have been prevalent at Fukushima Daiichi and not in agreement with Japanese usual reliance upon consensus.
机译：由于1F1、1F2和1F3号机组的福岛第一核的严重后果，以及它们对全球核电的重大影响，迄今为止已发表了许多评估报告。关于它们的三个主要原因，人们达成了普遍共识：假定的海啸设计基准降低了2到3倍。海啸后造成的非常困难的影响导致现场条件相当恶劣，工厂人员和管理人员承受的压力过大；日本监管机构决定不考虑超出设计基准站的停电（SBO）。日本政府，其监管机构，工厂所有者，工厂管理人员和运营人员没有必要的计划和程序来应对福岛的极端SBO。在SBO期间，所有水核电站都需要及早冷却反应堆堆芯，以避免堆芯熔化。在沸水反应堆（BWR）中，通过安装在1F1处的隔离冷凝器（IC）以及通过在1F2和1F3中使用的反应堆堆芯隔离冷却（RCIC）系统，可以在有限的时间内满足这种需求。如果它们停止工作，则安装了向失压的反应堆压力容器（RPV）添加消防水的设施，以确保避免了两个关键条件：（a）将反应堆水位保持在反应堆堆芯中部以上，以防止锆合金燃料包层与蒸汽的化学反应产生氢气，加速衰变热，并使反应堆水位数据无效； （b）不允许安全壳压力达到过高的值，以避免放射性泄漏到环境中，并使反应堆减压以允许注入足够的消防水。本演讲的目的是表明，通过积分衰减热方法可以很容易地预测SBO期间的这两个关键安全条件，这将有助于避免福岛的3个岩心融化。在福岛，没有给予足够的重视，以通过增加消防水以降低其压水堆的反应堆压力来确保及早和安全地冷却反应堆。对于1号机组，安全策略将是在IC失去直流电源后重启IC，如果不可能，则使用已安装的消防水系统向减压反应堆供水。该行动必须在3个小时内完成，这是由拟议的简化积分衰减热法确定的，以避免反应堆的临界水位降至其核心中点以下。对于2号和3号机组，RCIC的运行时间过长，没有先见之明，并且明确优先考虑实施反应堆降压和添加消防水。不幸的是，也发生了1F1、1F2和1F3进行RPV降压和添加消防水的准备工作，但由于1F1和1F3处的氢气爆炸以及其他意外情况而中断。重要的是要注意，拟议的避免堆芯融化的策略将需要将权力完全下放到现场，而没有时间进行必要的批准以添加消防水或封闭安全性以及强化培训以及非常严格的工厂管理人员安全文化和人员。这种必要条件可能在福岛第一核电站并不普遍，并且与日本通常对共识的依赖不同。

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