Safe-to-fail: Accident-tolerant fuel cladding

传统的水冷核反应堆，包括目前的CANDU反应堆和计划在达林顿核电站建造的小型模块化反应堆（SMR），使用的氧化铀燃料被包裹在一种叫做锆锡合金的保护管中。然而，在反应堆中发生严重的冷却剂损失事故（LOCA）时，锆合金与高温蒸汽的反应会产生大量的氢气，这种气体与空气混合时会爆炸。2011年福岛第一核电站反应堆事故发生时，这种情况就曾出现过，导致多次氢气爆炸。已经探索了各种“事故耐受燃料”（ATF）概念，以帮助降低或消除在严重LOCA条件下导致氢爆炸的包层蒸汽反应的风险。这项研究的大部分集中在对锆合金施加保护涂层以降低其在严重LOCA条件下与蒸汽的反应性，或者用在事故期间不会发生危险反应的材料取代锆合金。不幸的是，目前的一套涂层和替代品不够耐用，无法承受LOCA而不发生显著退化。由于加拿大现在正准备建造新的SMR，因此在ATF覆层方面建立专业知识以与其他领先国家（如美国、法国和中国）相匹配具有相当大的价值。这些知识对于政府决策和管理监督以及SMR建设和运营的许可证发放特别有价值。欧洲议会最近规定，所有反应堆都必须执行各自国家监管机构批准的ATF，以符合“绿色能源”的要求。在加拿大实施这些政策和监管决定将需要通过研究现有的ATF包覆概念和开发新的加拿大解决方案，对与ATF包覆性能相关的各种因素有深入的了解。该研究计划旨在开发新型ATF包层，并对现有ATF包层概念进行基础研究，以消除严重LOCA期间发生氢爆炸的可能性。

Conventional water-cooled nuclear reactors, including the current fleet of CANDU reactors and the small modular reactor (SMR) planned for construction at the Darlington nuclear power plant site, use uranium oxide fuel that is clad in protective tubes of a zirconium-tin alloy called Zircaloy. However, during a severe loss-of-coolant accident (LOCA) in a reactor, the reaction of the Zircaloy with high-temperature steam can generate large volumes of hydrogen, a gas that is explosive when mixed with air. Such a scenario previously played out during the Fukushima-Daiichi reactor accident in 2011, resulting in multiple hydrogen explosions. A variety of "accident tolerant fuel" (ATF) concepts have been explored to help decrease or eliminate the risk of cladding-steam reactions leading to hydrogen explosions under severe LOCA conditions. Much of this research has focused on either applying a protective coating to the Zircaloy to decrease its reactivity with steam under severe LOCA conditions or replacing Zircaloy with a material that would not react so dangerously during an accident. Unfortunately, the current suite of coatings and replacements are not durable enough to withstand a LOCA without significant degradation. Since Canada is now preparing to build new SMRs, there is considerable value in building expertise in ATF cladding to match that of other leading countries, such as the USA, France, and China. This knowledge will be particularly valuable for government decision-making and regulatory oversight and licensing of SMR construction and operation. The European Parliament has recently mandated that all reactors implement ATFs approved by their respective country's regulators in order to qualify as "green energy" sources. Implementing such policy and regulatory decisions in Canada will require a robust domestic understanding of the various factors related to ATF cladding performance, established by studying existing ATF cladding concepts and developing novel Canadian solutions. This research program aims to develop novel ATF claddings and to perform fundamental studies on existing ATF cladding concepts meant to eliminate the potential for hydrogen explosions during a severe LOCA.