ABSTRACT

The ‘perturbation source method’ (PSM) is a Monte Carlo perturbation method that calculates an exact k-eigenvalue change caused by cross-section changes. Although the PSM, which can consider the effect of fission source perturbation, was proposed long ago, it has garnered minimal interest as a Monte Carlo perturbation method. The applicability of the PSM has not been thoroughly elucidated hitherto. This study revisits the PSM and reviews the associated Monte Carlo algorithm. Some improvements have been made to improve the efficiency. The PSM is applied to some numerical tests that involve the replacement of a fuel material with light water, a density change in a water hole, an interface shift between a fuel and reflector, and an external boundary extension. The performance of the PSM for these tests is compared with that of another exact Monte Carlo perturbation method, which is the correlated sampling method. The PSM can yield an accurate k-eigenvalue change even for large cross-section changes such as the replacement of a material with another material. The PSM used in this study is the exact method except for the approximation related to the spatial discretization for fission source perturbation. Furthermore, it exhibits superiority in terms of accuracy and computational efficiency, particularly for large perturbations added in a small region.

摘要

“扰动源法”(PSM) 是一种蒙特卡罗微扰法，它计算精确的k- 截面变化引起的特征值变化。尽管可以考虑裂变源扰动影响的 PSM 很早以前就被提出，但它作为蒙特卡罗扰动方法的兴趣却微乎其微。迄今为止，PSM 的适用性尚未得到彻底阐明。本研究重新审视了 PSM 并回顾了相关的蒙特卡洛算法。已经进行了一些改进以提高效率。PSM 应用于一些数值测试，包括用轻水替换燃料材料、水孔中的密度变化、燃料和反射器之间的界面偏移以及外部边界扩展。将 PSM 在这些测试中的性能与另一种精确的 Monte Carlo 微扰方法（即相关采样方法）的性能进行了比较。PSM 可以产生准确的即使对于大的横截面变化（例如用另一种材料替换一种材料），k - 特征值也会发生变化。除了与裂变源扰动的空间离散化相关的近似外，本研究中使用的 PSM 是精确的方法。此外，它在准确性和计算效率方面表现出优势，特别是对于在小区域中添加的大扰动。