A safety research on nuclear reactors based on the microscopic reactor physics

在核反应堆安全分析中，“反应性系数”和“动力参数”等物理量的评价是非常重要的。特别是多普勒反应性在反应堆事故序列估计中起着重要的作用。多普勒反应度是重核素的单位升温引起的多普勒展宽效应与燃料平均升温的乘积。因此，在动态计算的每个时间步长，都需要精确地处理详细的温度分布。一般来说，这种计算是可以通过使用现有的代码应用详细的时间步长模型来实现的，但是由于计算的需要，这种计算是不现实的。在本研究中，采用并行计算算法来解决这一问题。相比之下，在测量领域，动态棒值作为一种测量反应器控制棒值的新方法被引入。该方法可以减少对程序和时间的要求，因此被认为是有前途的。实际上，美国核管理委员会已经批准它作为反应堆启动测试的标准措施。尽管如此，还没有详细的研究来支撑其合法性。为了澄清这一点，采用同时考虑中子通量局部依赖性和时间依赖性的动态计算模型进行了详细的分析。分析了在近畿大学训练反应堆中进行的不同插入速度下的控制棒下降测量，但新方法与传统方法之间没有明显差异。

It is highly important to evaluate the physical quantities such as 'reactivity coefficient' and 'dynamic parameters' in nuclear reactor safety analysis. Especially, the Doppler reactivity plays an important role in the estimation of reactor accident sequences. The Doppler reactivity is given as the multiplication of effect of Doppler broadening of heavy nuclides due to unit rise in the temperature, and the average temperature rise in the fuel. Thus the exact treatment of the detailed temperature distribution is necessary at each time step in the dynamic calculations. Generally, such calculations are possible by application of detailed time step models using existent codes, however, the requirement of calculation makes such calculations unrealistic. In the present study, the parallel computation algorithm was applied to resolve the problem.In contrast, in the field of measurements, the dynamic rod worth was introduced as a new method to measure the control rod worth of a reactor. This method enables to reduce the requirement in both the procedures and time, thus considered as promising. Actually, the U.S. Nuclear Regulatory Committee has approved it as a standard measure used in reactor startup testing. Despite the fact, detailed researches have not been made to backbone the legitimacy yet. In order to clear the point, a detailed analysis was performed using a dynamic calculation model that treats the local dependence of neutron flux and its time-dependency at the same time. The analysis was done for the rod drop measurements with different insertion speeds of the control rods, which were performed in Kinki University Training Reactor, however, any distinct difference was not observed between the new method and the conventional method.