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Microtransport with small size and a wide range of applications is very attractive for the utilization of future reactor modularization. A microreactor uses a closed Brayton cycle (CBC) to achieve high conversion efficiencies at low specific mass. The recuperator is one of the key components of CBC system which recovers heat exhausted from the turbine. A printed circuit heat exchanger (PCHE) is currently the preferred type of recuperator for the closed Brayton cycle due to its high heat transfer efficiency, high compactness, and high pressure and temperature resistance. This work intends to analyze different geometry configurations of a zigzag PCHE to increase its heat transfer efficiency while reducing its weight and size. The effect of geometric structure parameters such as channel diameter, zigzag pitch length, and zigzag angle on the Nusselt number and Fanning friction factor is investigated using a zigzag PCHE unit model. Based on the numerical simulation, the principle of least squares is employed to carry out a nonlinear fitting of the flow and heat transfer criterion correlation equations. Besides, the maximum value of the Nusselt number and minimum value of the Fanning friction factor are optimized as two conflicting objective functions using the nondominated sorting genetic algorithm-II (NSGA-II), with which a set of optimal solutions is obtained. Meanwhile, the shortest normalized distance is used to determine the compromised solution on the Pareto optimal points, and the independent variable's sensitivity analysis is performed. Finally, a multiobjective optimization analysis is conducted for the PCHE to achieve lightweight and the high heat transfer efficiency design requirements of SIMONS. [ABSTRACT FROM AUTHOR]

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]

Summary: An increasing number of countries have taken nuclear energy as a preferred approach in response to the environment deterioration and energy supply deficit. The rapid expansion of nuclear technologies, however, would pose a great challenge to nuclear non‐proliferation, especially for the Generation IV nuclear reactor systems, which significantly differ from current nuclear fuel systems. This paper gives an overview of non‐proliferation research activities worldwide and outlines the existing problems, especially in non‐proliferation assessment. Because of numerous processes and various types of variables involved in nuclear fuel cycles (NFC), it is difficult to obtain a quantitative and objective assessment on non‐proliferation. In addition, the influences imposed by national nuclear policy on non‐proliferation have been rarely studied because of their large uncertainties, which may not precisely reflect the real non‐proliferation status in a specific country. In view of the above issues, we put forward an assessment framework by considering impact factors of national nuclear policy and by employing multi‐mathematical models to address some of the issues including subjectivity and uncertainties in the current assessment methodologies. [ABSTRACT FROM AUTHOR]