压水堆内钍-铀增殖循环研究——乏燃料特性分析

摘要

利用ORIGEN-S程序对压水堆钍基乏燃料的特性进行分析,揭示了钍基乏燃料在放射性毒性、衰变热、γ射线等方面的特性,相关结果可为钍基乏燃料的贮存、后处理和地质处置提供必要的参考.研究的乏燃料是压水堆内钍-铀增殖循环堆芯设计方案中的4种,包括UOX(铀氧化物)、MOX(钚铀混合氧化物)、PuThOX(钚钍混合氧化物)和U3ThOX(工业级233 U-钍混合氧化物).研究结果表明:1)由于超铀核素的含量极低,在卸料后1000年内,U3ThOX的放射性毒性显著低于超铀核素含量高的乏燃料；2)由于232U衰变链中208T1的贡献,钍基乏燃料中2.6 MeV能量附近的γ射线强度明显高于铀基乏燃料,而这一能量附近的γ射线强度在卸料后约10年达到局部峰值,所以,钍基乏燃料的后处理最好避开此时间.%Spent fuel characteristics analyses of thorium-based fuel were investigated using ORIGEN-S code compared with uranium-based fuel. Such parameters as radioactivity, radiotoxicity, decay heat, and gamma ray were considered. Relative results in this work could provide some reference informations for storage, reprocessing and disposal of thorium-based spent fuel. Four type fuels, thorium-based fuel U3ThOX (mixed reactor grade 233U-thorium oxide), PuThOX (mixed reactor grade plutonium-thorium oxide) , uranium-based fuel UOX (uranium oxide) and MOX (mixed reactor grade plu-tonium-uranium oxide) , on the basis of core designs for thorium-uranium breeding recycle in PWRs were investigated. The calculated results show that: 1) Due to extremely low content of transuranic nuclides, the radiotoxicity of U3ThOX is dramatically lower than that of three other types of spent fuel in 1 000 years after discharge; 2) In thorium-based spent fuel the intensity of gamma ray near 2. 6 MeV mainly generated by 208Tl in 232 U decay chain is much stronger than that in uranium-based fuel. The intensity of y ray near 2. 6 MeV reaches a local peak in about 10 years after discharge when the reprocessing should not be performed for thorium-based spent fuel.