Institute of Nuclear and New Energy Technology, Tsinghua University, Beijing 102201, China.
J Hazard Mater. 2012 Nov 30;241-242:456-62. doi: 10.1016/j.jhazmat.2012.09.072. Epub 2012 Oct 6.
High-temperature gas-cooled reactors (HTGRs) are advanced nuclear systems that will receive heavy use in the future. It is important to develop spent nuclear fuel reprocessing technologies for HTGR. A new method for recovering uranium from tristructural-isotropic (TRISO-) coated fuel particles with supercritical CO(2) containing tri-n-butyl phosphate (TBP) as a complexing agent was investigated. TRISO-coated fuel particles from HTGR fuel elements were first crushed to expose UO(2) pellet fuel kernels. The crushed TRISO-coated fuel particles were then treated under O(2) stream at 750°C, resulting in a mixture of U(3)O(8) powder and SiC shells. The conversion of U(3)O(8) into solid uranyl nitrate by its reaction with liquid N(2)O(4) in the presence of a small amount of water was carried out. Complete conversion was achieved after 60 min of reaction at 80°C, whereas the SiC shells were not converted by N(2)O(4). Uranyl nitrate in the converted mixture was extracted with supercritical CO(2) containing TBP. The cumulative extraction efficiency was above 98% after 20 min of online extraction at 50°C and 25 MPa, whereas the SiC shells were not extracted by TBP. The results suggest an attractive strategy for reprocessing spent nuclear fuel from HTGR to minimize the generation of secondary radioactive waste.
高温气冷反应堆（HTGR）是一种先进的核系统，将在未来得到广泛应用。开发适用于 HTGR 的乏核燃料后处理技术非常重要。本文研究了一种用含有三正丁基膦（TBP）的超临界 CO₂从三结构各向同性（TRISO）包覆燃料颗粒中回收铀的新方法。首先将 HTGR 燃料元件的 TRISO 包覆燃料颗粒粉碎，暴露 UO₂ 芯块燃料核。然后将粉碎的 TRISO 包覆燃料颗粒在 750°C 的 O₂气流下处理，得到 U₃O₈粉末和 SiC 壳的混合物。在少量水的存在下，通过 U₃O₈与液体 N₂O₄的反应将其转化为固体硝酸铀酰。在 80°C 下反应 60 min 后即可实现完全转化，而 SiC 壳则不会被 N₂O₄转化。将硝酸铀酰转化混合物用含有 TBP 的超临界 CO₂萃取。在 50°C 和 25 MPa 下在线萃取 20 min 后，累积萃取效率超过 98%，而 SiC 壳则不会被 TBP 萃取。这些结果为从 HTGR 乏核燃料后处理中最小化二次放射性废物的生成提供了一种有吸引力的策略。
