聚变堆失真空事故下氚的大气扩散模拟研究

Simulation study of tritium atmospheric dispersion of loss of vacuum accident of a fusion reactor

聚变反应堆发生失真空事故的情况下氚会泄漏到环境中,氚大气扩散模拟是聚变堆事故后果评价的重要内容。基于高斯烟团模型以及Pasquill稳定度分类方法,考虑重力沉降、烟气抬升、风速等因素的影响,建立了适用于事故下瞬态分析的大气扩散模型,在高斯烟团模型中加入修正了像源贡献的地面反射系数,提高了模型对于地面边界处干沉降的计算效果。选取加拿大氚气释放实验和美国萨凡那河工厂氚释放事故验证了所建立模型的准确性,模型的计算结果与HotSpot 3.0和UFOTRI软件的精度相当。选取国际热核聚变实验堆(International Thermonuclear Experimental Reactor,ITER)的失真空事故作为研究对象,分析了氚的分阶段释放、风速以及释放高度对氚扩散分布的影响。结果表明:氚的分阶段释放会导致沿下风向出现两个高放射性区域;释放高度和风速的增加会强化氚在大气中的扩散行为,从而减弱放射性在近场的积聚。

[Background]Tritium can be released into the environment in a loss of vacuum(LOVA)scenario in a fusion reactor.The simulation of the atmospheric dispersion behaviour of tritium is one of the core components of the assessment of the radioactive consequences.[Purpose]This study aims to analyse the behaviour of tritium dispersion in the atmosphere after a fusion reactor accident.[Methods]Based on the Gauss model and the Pasquill stability classification method,an analytical model of tritium dispersion was developed for transient cases considering the effects of gravitational settling,smoke lifting,and wind speed,etc.The calculation of the model for dry settling at the ground boundary was improved by adding ground reflection coefficients to the Gauss model.Finally,the Canadian tritium release experiment and the tritium release accident at the Savannah River plant in the United States were used to verify the applicability of the model.[Results]Verification results show that the accuracy of the developed model is the same as that of UFOTRI and the HotSpot 3.0 code.For the LOVA scenario of International Thermonuclear Experimental Reactor(ITER),the atmospheric dispersion behaviour of tritium is obtained for multiple release heights,different wind velocities and tritium phased releases.[Conclusions]The phased release of tritium results in two highly radioactive regions along the downwind direction,and the increase in release height and wind speed will enhance the atmospheric diffusion behaviour of tritium and thus reduce the accumulation of radioactivity in the near field.