Study on Assessment of Nuclear Data and Neutronics Calculations through Critical Experiments

通过装载铀燃料并经聚乙烯缓和的紧距晶格核的临界实验，对核数据和中子计算进行了评估研究。在利用京都大学临界装置（kuuca）进行的一系列临界实验中，系统地改变了慢速剂与燃料体积比（V_m/V_f比）和堆芯中铀的平均富集度^<235>，以获得核数据评估和中子计算的基准数据。用蒙特卡罗计算来评估核数据的有效性和中子计算中使用的计算方法。通过本研究发现，使用日本现行版本的评价核数据文件JENDL-3，与美国旧版本评价核数据文件ENDF/B-IV的测量值和计算结果相比，往往低估了有效乘法系数，而使用日本旧版本JENDL-2，则往往高估了有效乘法系数。对于有效截面的产生过程，应适当考虑相邻两区含铀共振自屏蔽的干扰效应。在扩散计算中不能忽略输运效应，在扩散计算的基础上，通过修正输运效应、能量群效应和网格效应，可以得到与准确输运计算相当的结果。

A study on the assessment of the nuclear data and neutronics calculations was performed through the critical experiments on the tight-pitch lattice cores loaded with uranium fuel and moderated by polyethylene.In this series of critical experiments using the Kyoto University Critical Assembly (KUCA), the moderator-to fuel volume ratio (V_m/V_f ratio) and the average enrichment of ^<235>U in the core were systematically varied to obtain the benchmark data for the assessment of the nuclear data and neutronics calculations. Monte Carlo calculations were executed to assess the validity of the nuclear data and the computational methods used in the neutronics calculation.Through the present study, it was found that the use of the current version of evaluated nuclear data file in Japan, JENDL-3, tends to underestimate the effective multiplication factor in comparison with the measured one and the cal-culated result by ENDF/B-IV which is a previous version of evaluated nuclear data file in the United States, whereas the use of a previous version in Japan, JENDL-2, tends to overestimate the effective multiplication factor. For the generation process of effective cross sections, it was found that one should properly take into account the interference effect in resonance self-shielding of uranium contained in two adjacent regions. It was also found that the trans-port effect can not be neglected in the diffusion calculation and the result com-parable to the accurate transport calculation can be obtained on the basis of the diffusion calculation by correcting the transport,energy group and mesh effects.