CHALMEX FS-13 investigations for process implementation

Licentiate thesis, 2020

From successive neutron absorption by uranium in nuclear reactors, transuranic elements such as neptunium, plutonium, americium and curium are produced. These elements are the main reason for the long-lived, highly radiotoxic and heat-producing nature of spent nuclear fuel. To reduce the strain on a final repository, the concept of partitioning and transmutation (P&T) has been developed. In P&T, the transuranic elements are partitioned from the nuclear fuel prior to final storage and transmuted into shorter-lived and far less radiotoxic elements. If the transmutation is facilitated in a nuclear reactor, as compared to in an accelerator driven system, further benefits include a more sustainable nuclear fuel cycle due to a reduced need for mining.

One partitioning option being developed is the Grouped ActiNide EXtraction (GANEX) process, which is a liquid-liquid extraction concept. In the Chalmers GANEX (CHALMEX) version, two extractants, tri-n-butyl phosphate (TBP) and 6,6’-bis-(5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-benzol-[1,2,4]-triazin-3-yl)-[2,2’]-bipyridine (CyMe4-BTBP) are combined for the direct separation of the transuranic elements from a spent nuclear fuel solution. The extractants are dissolved in phenyl trifluoromethyl sulfone (FS-13). The focus of the work presented in this thesis has been the optimisation and evaluation of the CHALMEX system for scaled up operations. Knowledge required for later process simulations, such as distribution ratios of all relevant elements over a range of acid concentrations, has been established. A fission product handling strategy using bimet and mannitol as masking agents has been suggested, although an efficient nickel and cadmium handling strategy is still required.