Comparison of Conventional and Advanced Nuclear Fuel Performance

事故容忍燃料(ATF)是提高核工业安全的一个关键概念。2011年福岛第一核电站事故突出了当前UO2-Zr系统的热限制，因此，正在投入大量精力研究事故容错替代方案。为了被广泛采用并抵消任何研发成本，ATF理想情况下应该以增加铀密度的形式提供一些经济效益，允许更高的燃耗或更低的燃料浓缩。根据定义，事故容忍燃料(ATF)是指与传统的UO2-Zr系统相比，能够承受较长时间冷却剂显著损失的燃料和覆层，同时在正常运行期间保持或改善燃料性能。这一特殊特征往往是燃料先进的热性能的结果。从燃料组件中疏散热能的能力可能会在冷却剂丢失事故(LOCA)的情况下允许更长的“宽限期”，从而减少氢气和铯的产生。目前被认为是事故容错替代燃料的两个主要竞争者是氮化铀(UN)和硅化铀(U3Si2)，因为它们具有高导热系数、高熔点和高铀密度。每种事故容忍燃料的薄膜样品将使用布里斯托尔大学提供的直流磁控溅射设备进行工程设计。薄膜是进行辐射研究的理想样品。有限的样品厚度使得可以使用离子辐照来诱导均匀的损伤分布，从而能够精确地测量对热导的影响。本项目着眼于所建议的ATF的性能，特别关注将U3Si2和U3Si2的热行为与传统的陶瓷氧化物化合物进行比较，并研究作为辐照的函数的热行为是如何变化的。

Accident Tolerant Fuels (ATF) are a key concept in the drive to improve safety in the nuclear industry. The 2011 Fukushima Daiichi accident highlighted the thermal limitations of the current UO2-Zr system and as such, significant effort is being invested in researching accident tolerant alternatives. In order to be widely adopted and offset any R&D costs, ATFs should ideally offer some economic benefit in the form of increased uranium density, allowing for either higher burn-up or lower fuel enrichment.By definitions, accident tolerant fuels (ATFs) are fuels and claddings that can withstand a significant loss of coolant for a prolonged amount of time when compared to conventional UO2-Zr system, whilst maintaining or improving fuel performance during normal operation. This particular feature is often a result of the fuels advanced thermal properties. The ability to evacuate thermal energy from the fuel assembly could potentially permit for an extended 'grace period' in the case of a loss of coolant accident (LOCA) and, as a result, mitigate against the production of hydrogen and corium. The two leading contenders currently considered as accident tolerant replacements fuel are uranium nitride (UN) and uranium silicide (U3Si2) due to their high thermal conductivity, high melting point, and high uranium density. Thin film samples of each accident tolerant fuel will be engineered using DC magnetron sputtering facilities available at the University of Bristol. Thin films make ideal samples for irradiation studies. The limited sample thickness enables homogenous damage profiles to be induced using ion irradiation, allowing for precise measurements of the effect on thermal conductivity.This project looks at the performance of the proposed ATFs, with a specific focus on comparing the thermal behaviour of UN and U3Si2 against conventional ceramic oxide compounds and investigating how the thermal behaviour changes as a function of irradiation.