Development of numerical simulation method for melt relocation behavior in nuclear reactors; Validation and applicability for actual core structures

原子炉内溶融物移行挙数値解析手法の開発; 実機炉内構成材に対する検証と適用性

山下 晋   ; 徳島 二之*; 倉田 正輝 ; 吉田 啓之  

Yamashita, Susumu; Tokushima, Kazuyuki*; Kurata, Masaki; Yoshida, Hiroyuki

過酷事故時の炉心溶融物の移行挙動を詳細に評価するために、数値流体力学的手法に基づく3次元多相多成分熱流動解析手法JUPITERを開発している。BWRの制御棒、燃料支持金具、燃料集合体といった複雑構造物やその溶融移行挙動を表現するために精度、効率、安定性及び堅牢性に優れた数値計算手法を適用した。本論文では、実機炉内構造物へのJUPITERの適用性と妥当性を評価するために、実機炉内構成材中の溶融移行予備解析を実施すると共に、基礎的な問題と、複雑な実験解析によりJUPITERの妥当性を検証した。その結果、予備解析では多成分での溶融移行挙動と凝固挙動を安定的評価できることを確認した。また、検証解析では、実験結果と良好な一致を示した。これらの結果から、JUPITERは、RPV内における溶融物移行挙動評価手法としてポテンシャルを有していることが明らかになった。

In order to precisely investigate molten core relocation behavior in severe accidents, we have been developing the detailed and phenomenological numerical simulation code named JUPITER for predicting the molten core behavior with melting and solidification based on computational fluid dynamics (CFD) including the three-dimensional multiphase thermal-hydraulic simulation models. In order to treat complicated core structures, e.g., boron carbide (absorber), stainless steel (control rod, fuel support structure, etc.), Zircaloy (channel box and fuel cladding) and to deal with complicated melt relocation behaviors, high accuracy, efficient, stable and robust numerical schemes are implemented. In this paper, in order to evaluate the validity and applicability of the JUPITER for actual core structures, we perform the preliminary melt relocation analysis in the control rod and fuel support piece and also verify the validity of the JUPITER regarding the melt relocation and solidification processes by the fundamental numerical problem and the experimental analysis. As a result, the preliminary analysis showed that multicomponent melt flow and its melt and solidification were stably worked in the melt relocation simulation. In the validation analysis, the numerical results were in the reasonably agreement with experimental results. Therefore, it was confirmed that the JUPITER has a potential to calculate the core melt relocation behavior in RPVs.