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Separate-Effects Tests for Studying Temperature-Gradient-Driven Cracking in UO2 Pellets
Nuclear Science and Engineering ( IF 1.2 ) Pub Date : 2021-07-27 , DOI: 10.1080/00295639.2021.1932223
S. Patnaik 1 , B. W. Spencer 2 , E. Roberts 1 , T. M. Besmann 1 , T. W. Knight 1
Affiliation  

Abstract

A variety of normal operation and accident scenarios can generate thermal stresses large enough to cause cracking in ceramic fuel pellets. Cracking in fuel pellets can lead to reduced heat removal, higher centerline temperatures, and localized stress in the cladding—all which impact fuel performance. It is important to experimentally characterize the thermal and mechanical behaviors in the pellet both before and after cracking, which would help to improve cracking models in fuel performance codes such as BISON. However, in-reactor observation and measurement of cracking are very challenging due to the harsh environment and design of the fuel rods involved. Recently, an experimental pellet-cracking test stand was developed for separate-effects testing of pellet cracking under normal operations and accident temperature conditions using thermal imaging to capture the pellet surface temperatures in order to evaluate the thermal stresses and optical imaging to capture the evolution of cracking in real time. Experiments were performed using depleted uranium dioxide (UO2) pellets, which are useful for collecting valuable data for development and validation of cracking models. A combination of induction and resistance heating was used to create thermal gradients similar to those seen in a reactor environment. Characterization of the pellets was conducted both before and after cracking. The cracking patterns are moderately different from those expected in a typical reactor because of the variations in the thermal conditions and pellet microstructures. However, when the actual conditions of these experiments are reproduced in computational models with sufficient precision, such out-of-pile testing on UO2 pellets provides relevant data for modeling purposes.



中文翻译:

用于研究 UO2 球团中温度梯度驱动开裂的独立效应试验

摘要

各种正常运行和事故情况会产生大到足以导致陶瓷燃料芯块开裂的热应力。燃料芯块中的裂纹会导致散热减少、中心线温度升高以及包壳中的局部应力——所有这些都会影响燃料性能。重要的是在开裂之前和之后对芯块中的热和机械行为进行实验表征,这将有助于改进燃料性能代码(如 BISON)中的开裂模型。然而,由于所涉及的燃料棒的恶劣环境和设计,反应堆内观察和裂纹测量非常具有挑战性。最近,开发了一个实验性弹丸开裂试验台,用于在正常操作和事故温度条件下对弹丸开裂进行单独效应测试,使用热成像来捕获弹丸表面温度,以评估热应力,并使用光学成像来捕捉弹丸开裂的演变即时的。使用贫化二氧化铀 (UO2 ) 球团,可用于收集有价值的数据以开发和验证开裂模型。感应加热和电阻加热的组合用于产生类似于反应堆环境中所见的热梯度。在裂化之前和之后进行粒料的表征。由于热条件和球团微观结构的变化,裂纹模式与典型反应器中预期的模式略有不同。然而,当这些实验的实际条件在计算模型中以足够的精度重现时,这种对 UO 2颗粒的堆外测试为建模目的提供了相关数据。

更新日期:2021-07-27
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