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Extension of cross section homogenization method for particle-dispersed media to layered particles

粒子分散系での断面積均質化手法の多層粒子への拡張

山本 俊弘

Yamamoto, Toshihiro

Shmakovらによって開発され、その後山本らが改良を行った、粒子がランダムに分散した媒質に対する断面積均質化手法を高温ガス炉の燃料のような多層粒子に適用できるよう拡張を行った。ここでは二層からなる同心球の粒子に対して立式化を行った。これを連続エネルギーモンテカルロコードMCNPに組み込みを行い、単純化した高温ガス炉炉心を含む幾つかの計算例に対して適用を行った。二層粒子に対して拡張を行った本手法は、単層粒子に対する従来の手法とほぼ同等の結果を与える。単純化した高温ガス炉炉心に対する本手法の中性子実効増倍率は、二層粒子を直接燃料コンパクト中にランダムに分散させたときの参照解に対して数百pcmの範囲内で再現できる。従来の単層粒子に対する手法は解析的に解くことができたのに対して、本手法は数値積分を要するために計算効率が低下する。しかし、二層粒子を直接非均質でモンテカルロ法で解いたときに比べてはるかに短い時間で計算が可能である。

A cross section homogenization method for media containing randomly dispersed particles, which was originally developed by Shmakov et al., and then was improved by Yamamoto et al., is extended to layered particles, such as coated fuel particles of gas-cooled reactors. A new extended formulation is derived for concentric double-layered spherical particles. This formulation is successfully implemented into a continuous energy Monte Carlo code MCNP, and is applied to some examples including a simplified gas-cooled reactor core. The extended method for double-layered spherical particles provides as accurate results as the previously developed method for mono-layered particles does. For the simple gas-cooled reactor core, the new method reproduces keff within several hundreds of pcm as compared to the direct heterogeneous calculation in which double-layered spherical particles are explicitly distributed in the fuel compact. Whereas the previously developed method for mono-layered particles can be performed analytically, this new technique requires numerical integration, making the computation efficiency of the new method deteriorate. However, this method allows one to perform Monte Carlo criticality calculations for double-layered particle-dispersed media with much less computing time than direct heterogeneous calculations.

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パーセンタイル:79.37

分野:Nuclear Science & Technology

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