基于ASME规范的核石墨改进概率评价方法研究

Study on improved probability evaluation method of nuclear graphite based on ASME specification

核石墨作为慢化剂、反射层以及结构材料广泛应用于熔盐堆与气冷堆中,石墨构件的完整性对反应堆安全运行至关重要。脆性核石墨材料强度分散,相比于确定论方法概率论方法更适合对核石墨构件失效评定。本文基于ASME计算失效概率模型,改进了失效概率计算的分组标准,并运用有限元软件ABAQUS建立了NBG-18核石墨巴西圆盘劈裂模型加以验证。结果表明:与过于保守的ASME模型相比,改进的模型结果更接近于试验数据,同时比KTA3232规范更保守。改进后的模型对试件尺寸比较敏感,对网格敏感度不高。

[Background]Nuclear graphite,as neutron moderator,reflector and structural material,plays an important role in the molten salt reactor and high-temperature gas-cooled reactor(HTGR).The integrity of graphite component is crucial to the safe operation of the reactor.As a brittle material,the strength of nuclear graphite is dispersed,hence the probabilistic method is more suitable for failure assessment of nuclear graphite components.[Purpose]The study aims to propose a modified model to calculate the probability of nuclear graphite failure by modifying the ASME code.[Methods]Based on ASME calculation failure probability model,the grouping criterion of failure probability calculation is improved.A Brazilian disc was used to model the tensile strength of nuclear graphite NBG-18 by finite element method software ABAQUS.[Results&Conclusion]Compared with the overconservative ASME model,the results of revised ASME model is closer to experimental data,and more conservative than the KTA3232 specification.The modified model is sensitive to the size of the specimen and insensitive to the grid.