Experimental Verification of Tritium Production Rate in CFETR Water Cooled Ceramic Breeder Blanket Mock up

As one of CFETR’s candidate blankets, water cooled ceramic breeder (WCCB) blanket undertakes important nuclear-related functions such as tritium breeding, nuclear heat extraction, and neutron shielding. The reliability of neutronics design directly affects the realization of CFETR tritium self-sustaining goal. In order to verify the reliability of the neutronics design tool, i.e. MCNP and FNEDL databases, in the WCCB blanket neutronics design, the WCCB scaling-down mock up was developed to carry out the neutronics experiment in the DT neutron environment, including two layers of lithium titanate, two layers of beryllium, three layers of cooling plate, and one layer of tungsten armor. The neutronics performance of the mock up are similar with the real blanket module. The mock up neutronics experiments were carried out using DT neutron generator, the simulated value (C) and experimental value (E) of neutronics parameters represented by tritium production rate (TPR) were analyzed. For TPR validation, two independent detection technologies were used, including the Li2TiO3 pellets as off-line TPR detectors, and the developed lithium glass detectors as on-line TPR detectors. The TPR validation was complemented by evaluating the predicted neutron-induced reaction rates of the Au, Zr foils. The experiments on the mock up were analyzed by MCNP-4C code and FENDL-3.0 nuclear data libraries, and the source term for Monte Carlo simulation was built using the custom-developed model based on depth profiling of tritium in the tritide target. The analysis results show that the C/E of TPR in the axis of two lithium titanate layers is 0.97 and 1.08 respectively, while there is a large deviation between the calculated and experimental values of TPR in the edge region of the mock up. According to the experimental results from Li2TiO3 pellets, the C/E of TPR at the edge of two lithium titanate layers is 0.65 and 0.82, respectively. The TPR is obviously underestimated by simulation at the edge of lithium titanate layers, confirmed by the C/E results of 197Au(n, γ)198Au reaction rate at the edge of lithium titanate layers, which are 0.72 and 0.90, respectively. It is indicated that there are unexpected scattered neutrons in the edge region of the mock up, resulting in the higher TPR than expected. The further experiments are needed to verify the influence of the scattered neutron on the TPR at the edge region of the mock up. To investigate the TPR gap between simulation and the experimental results from lithium glass detectors, the contribution of the fast neutrons on the 6Li(n, t)4He should be further studied. Also the other suggestions are provided for further experimental research, refering to the radiation protections and nuclear measurements.