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

通过对装有铀燃料和聚乙烯慢化的紧节距晶格堆芯的临界实验，对核数据评估和中子学计算进行了研究。在这一系列利用京都大学临界组件(KUCA)进行的临界实验中，系统地改变了慢化剂与燃料体积比(V_m/V_f比)和堆芯中^&lt；235&gt；U的平均浓缩度，以获得核数据评估和中子学计算的基准数据。通过蒙特卡罗计算评估了核数据的有效性和中子学计算中使用的计算方法。通过本研究发现，使用日本当前版本的评估核数据文件JENDL-3，与实测值和美国评估核数据文件的先前版本ENDF/B-IV的计算结果相比，倾向于低估有效乘积因子，而使用日本先前版本的JENDL-2，则倾向于高估有效乘积因子。对于有效截面的产生过程，发现应适当考虑相邻两区铀的共振自屏蔽中的干扰效应。在扩散计算中，输运效应是不可忽略的，通过对输运效应、能团效应和网格效应的修正，可以在扩散计算的基础上得到与精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.