Yuanzineng kexue jishu (May 2024)
Study on Shielding Benchmark Experiment of 238U Sample with D-D Neutrons
Abstract
238U regarded as not only one of the important materials in the design of advanced nuclear energy system, but also significant components of the nuclear fuel cycle, especially constitutes more than 90% in power reactor. Improving the accuracy of evaluated neutron data for 238U is essential for the design of reactor and nuclear devices, and fusion neutron integral experiment is one of the effective means to check the accuracy of nuclear data. The idea of this approach is to find out differences and deficiencies between measurement and prediction of different evaluated libraries, which can provide guidance for the adjustment of evaluated data. The leakage neutron spectra were measured at angles of 60° and 120° after the interaction of D-D neutrons with 238U samples in different sizes by time-of-flight method using the shielding integral facility of China Institute of Atomic Energy. The samples were rectangular slabs with a 30 cm square base and 3, 6 and 9 cm in thicknesses. A φ5.08 cm×2.54 cm BC-501A liquid scintillator was used to detect neutron in the measurement, and the gamma background can be removed by neutron-gamma discrimination. The leakage neutron spectra were simulated by Monte Carlo code using 238U data from the CENDL-3.2, ENDF/B-Ⅷ.0, JENDL-5.0 and JEFF-3.3 evaluated nuclear data libraries. The energy, angular flux and pulsed time distributions of source neutron were described carefully in the process of simulation, and the parameters of target structure material and detector efficiency were all taken into account. By comparing the calculated results with the experimental results, the shortcoming of 238U data in CENDL-3.2 library and the need for improvement were analyzed. The results show that the calculated result of CENDL-3.2 library in the fission reaction energy range is in good agreement with experimental result, but greatly overestimates in the elastic scattering energy range both at 60° and 120°, especially at 120°, there is also significant underestimation in the mixed energy range of 1.5-2.5 MeV for fission reaction and discrete level inelastic scattering.
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