Study on Micro Reactor Physics for Improvement of Neutronics Calculation

1）建立了考虑微堆物理效应的瞬态分析理论，并在此基础上编制了相应的计算程序。当前的耦合碰撞概率方法（CCCP方法）在所发展的理论中被采用，因为CCCP方法可以严格地模拟燃料组件中的非均匀性，例如针电池结构，并且可以在计算有效截面时处理非均匀性：提出了一种新的CCCP方法，该方法能及时处理瞬态过程，2）基于微堆物理的分析表明，中子注量率角分布受周围几何结构和成分的影响很大。因此，我们考虑了测量堆芯中子通量角分布的技术。该技术采用光纤探测器和镉管。将该技术应用于KUCA C堆芯容器堆芯角分布的测量，结果表明该技术能有效地测量中子注量率角分布。3）开发了中子热力学耦合程序，用于评价瞬态过程中燃料棒温度分布的影响。利用所开发的程序对冷、热备用状态下的控制棒落棒事故进行了分析，直接模拟了燃料棒内温度分布的不均匀性等。结果表明，基于微堆物理的分析方法对于考虑瞬态条件下燃料棒内复杂的温度分布是必要的，也是有效的，但由于燃料棒内温度分布的复杂性，采用有效温度模型时，燃料棒内的温度分布较为平坦，从而带来了复杂的结果。

1)We have developed the theory for transient analysis with the consideration of Micro-reactor physics effect, and have developed the calculation code based on the developed theory. The current Coupling Collision probability method (CCCP method) is adopted in the developed theory because the CCCP method can strictly model the heterogeneity such as a pin cell structure in a fuel assembly and can treat the heterogeneity in calculating the effective cross sections: New CCCP method, which can treat the transient in time has been developed, because the conventional CCCP method does not consider the transient2)The analysis based on Micro-reactor physics shows that the angular distribution of neutron flux is greatly affected by the surrounding geometry and composition. Therefore, we considered the technique to measure the angular distribution of neutron flux in the core. The designed technique uses the optical fiber detector and Cd tube. The technique was applied to the measurement of the angular distribution in the core assembled in C-core tank at KUCA, and the technique was found to be effective to measure the angular distribution of neutron flux.3)The neutronics-thermodynamics coupling code has been developed to evaluate the effect of temperature distribution in fuel rods during the transient phenomena. The developed code was used to analyze the control rod drop accidents at the cold and hot stand-by states with the direct modeling of the heterogeneity of temperature distribution etc. in fuel rods. As the results, it is found that the analysis based on Micro-reactor physics is necessary and useful to consider the complex temperature distribution in fuel rods at a transient, and also the effective temperature model, which has a flat temperature distribution in fuel rods, bring the miscellaneous results because of the complex temperature, distribution.