Transmutation of 135Cs in a single‐fluid double‐zone thorium molten salt reactor.

Summary: The single‐fluid double‐zone thorium molten salt reactor (SD‐TMSR) allows for online reprocessing fission products and adding nuclear fuel, which provides a high Th‐U breeding capability for thorium utilization. Although 135Xe in the core can be online extracted by the helium bubbling system during reactor operation to improve the reactor neutron economy, it would decay to the long‐lived 135Cs with a half‐life of 2.3 × 106 years, which is undesired from the viewpoint of the development of nuclear energy. The total production of 135Cs decayed from the extracted 135Xe is about 1.83 tons for the SD‐TMSR after 60 years operation. To reduce the significant accumulation of 135Cs, we propose a cooling transmutation method, by which the produced 135Cs is reinjected into the core for transmutation. First, a separation and multigroup cooling system in the SD‐TMSR is adopted to enhance the mass fraction of decayed 135Cs in the total Cs isotopes from 29% to 75%. Then, the separated Cs isotopes with optimized mass fraction of 135Cs are online injected into the core for transmutation. The total transmuted mass of 135Cs is about 0.61 tons after 60 years operation, corresponding to the transmuted fraction of about 37.42% and the transmutation rate of 10.17 kg/(GWe y). Moreover, the net 233U production is about 2.03 tons which is much larger than the initial 233U loading inventory of the SD‐TMSR, indicating that the Th‐U breeding mode for the transmutation of 135Cs in the SD‐TMSR can be achieved over 60 years. Novelty Statement: "Transmutation of 135Cs in a single‐fluid double‐zone thorium molten salt reactor" was investigated by Kunfeng Ma, Chenggang Yu*, Jingen Chen*, and Xiangzhou Cai. A cooling transmutation method is performed to reduce the 135Cs decayed from 135Xe outside of core. It is found that a separation and multigroup cooling system improves the mass fraction of 135Cs in the total Cs isotopes from 29% to 75% and an online returning 135Cs transmutation scenario transmutes about 0.61 tons of 135Cs over 60 years. [ABSTRACT FROM AUTHOR]