基于散热的高放废物处置库废物罐间距研究

Canister spacing in a high level radioactive nuclear waste repository based on heat conduction

高放废物处置库废物罐间距设计的核心问题之一是处置库的温度场演化规律。在建立单个废物罐分层热分析模型的基础上,通过叠加原理给出处置库任意位置岩体温度增量表达式,并通过Crump方法对拉普拉斯域解进行数值反演,得到多废物罐放热体系下处置库近场温度演化规律。在相邻隧道间距40 m的条件下,由废物罐表面峰值温度-岩石导热系数-废物罐间距变化图确定废物罐间距的初始预估值,最后分析了相关参数对废物罐表面温度的影响。结果表明,单废物罐放热条件下,废物罐表面峰值温度出现在第6年,而在多废物罐放热体系下,峰值温度出现在第80年;以岩石导热系数2.4,2.8 W/(m×K)为例,废物罐的合适间距分别为12.2,13.5 m;废物罐间距越大,膨润土和岩石导热系数越大,废物罐表面峰值温度越小。膨润土层越厚,废物罐内部热量越不易向外扩散。研究成果可为处置库的尺寸设计以及安全评估提供参考。

One of the core problems in the design of canister spacing in the repository for disposing high-level radioactive waste is the evolution of the temperature field.On the basis of the layered thermal analysis model for a single waste canister,the expression for temperature increment at any position of surrounding rock in the repository is obtained through the superposition principle.The Laplace domain solution is numerically inverted by the Crump method,and the near-field temperature evolution of the repository under multi-waste canister exothermic system is obtained.Under the adjacent tunnel spacing of 40 m,the initially estimated value of the waste canister spacing is determined by the line graph of the peak temperature of the waste canister surface,the thermal conductivity of the rock and the waste canister spacing.Finally,the influences of the relevant parameters on the surface temperature of the waste canister are analyzed.The results show that the peak temperature of the waste canister surface appeares in the 6th year under the exothermic condition of a single waste canister,and the peak temperature appeares in the 80th year under the multi-waste canister exothermic system.Taking the thermal conductivity of 2.4 W/(m×K)and 2.8 W/(m×K)for the rock as examples,the appropriate spacing of waste canisters is 12.2 and 13.5 m,respectively.The greater the waste canister spacing,the greater the thermal conductivity of bentonite and rock,the smaller the peak temperature of the waste canister surface will be.The thicker the bentonite layer,the less the heat flux inside the waste canister will spread out.The research results can provide a reference for the dimensioning design and safety assessment of the repository.