Abstract Reliable mechanical valves that can withstand the corrosive and high-temperature conditions in Molten Salt Reactors (MSRs) have not yet been demonstrated. In their place, freeze valves (sometimes called freeze plugs) represent a unique nuclear design solution for isolating salt flow during operations. Additionally, in some cases, they are intended to perform safety-related functions. As implied by the name, operation of a freeze valve depends upon the controlled phase change of salt, and the ability of increased reactor heat from transients to induce modulation of the “valve” has frequently been equated to safety function passivity. In this article, a review of literature pertaining to freeze valve design, performance, and thermodynamic analyses is presented first. The Molten Salt Reactor Experiment (MSRE) was the first MSR to implement the use of freeze valves and is the only liquid-fueled MSR with significant operating experience; yet, the success of the MSRE freeze valve to thaw on demand or remain frozen during power operation depended on two subsystems comprising power-operated sensors, mechanical valves, and other active components. Accordingly, as executed at the MSRE, the freeze valve system was not a fully passive safety feature. Performance of original Process Hazards Analysis (PHA) studies on an MSRE safety-related freeze valve design indicates failure of multiple individual active components could result in the impairment of the freeze valve function, such that the freeze valve itself is a system of components – rather than a single component. Fault Tree Analysis (FTA) based on PHA results provides estimated failure rates for two important failure modes of freeze valves. The results suggest that designers of freeze valve systems may face a trade-off between the reliability of the freeze valve to thaw on demand and the reliability of the freeze valve to remain frozen during normal reactor operations; however, a sensitivity study showed that the likelihood of a spurious thawing of the MSRE freeze valve system could have been reduced without significantly affecting the likelihood of a failure to thaw.

中文翻译：

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独特的熔盐反应堆特性——冷冻阀系统：设计、操作经验和可靠性

摘要 能够承受熔盐反应器 (MSR) 腐蚀和高温条件的可靠机械阀门尚未得到证实。取而代之的是，冷冻阀（有时称为冷冻塞）代表了一种独特的核设计解决方案，用于在操作期间隔离盐流。此外，在某些情况下，它们旨在执行与安全相关的功能。顾名思义，冷冻阀的操作取决于盐的受控相变，而瞬变引起的反应堆热量增加导致“阀门”调节的能力经常被等同于安全功能的被动性。在本文中，首先回顾了有关冷冻阀设计、性能和热力学分析的文献。熔盐反应堆实验 (MSRE) 是第一个使用冷冻阀的 MSR，也是唯一一个具有重要操作经验的液体燃料 MSR；然而，MSRE 冷冻阀能否成功按需解冻或在动力运行期间保持冷冻状态取决于两个子系统，包括动力运行的传感器、机械阀和其他有源组件。因此，在 MSRE 执行时，冷冻阀系统不是完全被动的安全功能。对 MSRE 安全相关冷冻阀设计的原始过程危害分析 (PHA) 研究的性能表明，多个单独活动组件的故障可能导致冷冻阀功能受损，因此冷冻阀本身是一个组件系统 - 而不是比单个组件。基于 PHA 结果的故障树分析 (FTA) 提供了冷冻阀两种重要故障模式的估计故障率。结果表明，冷冻阀系统的设计者可能要在冷冻阀按需解冻的可靠性和正常反应堆运行期间冷冻阀保持冻结的可靠性之间进行权衡；然而，敏感性研究表明，MSRE 冷冻阀系统虚假解冻的可能性本可以降低，而不会显着影响解冻失败的可能性。结果表明，冷冻阀系统的设计者可能要在冷冻阀按需解冻的可靠性和正常反应堆运行期间冷冻阀保持冻结的可靠性之间进行权衡；然而，敏感性研究表明，MSRE 冷冻阀系统虚假解冻的可能性本可以降低，而不会显着影响解冻失败的可能性。结果表明，冷冻阀系统的设计者可能要在冷冻阀按需解冻的可靠性和正常反应堆运行期间冷冻阀保持冻结的可靠性之间进行权衡；然而，敏感性研究表明，MSRE 冷冻阀系统虚假解冻的可能性本可以降低，而不会显着影响解冻失败的可能性。