Development of numerical simulation method to evaluate molten material behaviors in nuclear reactors

原子炉内の溶融物挙動解析手法の開発

山下 晋   ; 吉田 啓之  

Yamashita, Susumu; Yoshida, Hiroyuki

過酷事故時の炉内の溶融物の移行進展挙動を機構論的に把握するために、原子力機構ではJUPITERと呼ばれる3次元多相多成分熱流動シミュレーションコードを開発している。本報告では、ペデスタル内部の燃料デブリの堆積状況の推定に対するJUPITERの適用性を確認するために、ペデスタル内部へのコリウムの広がり・堆積挙動予備シミュレーションを行った。解析パラメータとして、コリウムの流入境界条件を、鉛直下方と斜め横方向の2通り設定し、それぞれにおいて燃料デブリの体積形状に大きな違いが生じることを確認した。また、燃料デブリの構成成分(UO, SUS, Zry, BC)は複雑に分布することを確認した。従来手法に比べて、機構論的かつ現実的な燃料デブリ分布を予測することができる見通しを得ることができた。

In order to simulate the relocation phenomena phenomenologically around the reactor core and inside pedestal without assumptions, inputted information, empirical knowledge and given scenarios, a numerical simulation code based on computational fluid dynamics, JUPITER, that can phenomenologically evaluate the melting phenomena has been developed in JAEA. We confirm the applicability of JUPITER to the corium spreading process inside the pedestal by simulating corium spreading behaviors and its distributions under several parameters such as the corium inflow condition. And we investigated detailed fuel debris distribution inside the pedestal and the cavity named sump pit located on the lower part of PCVs, that is distribution for each component of core materials such as stainless steel (SUS), bron carbide (BC), zircaloy (Zry) and uranium dioxide (UO). As a result, since JUPITER uses interface capturing scheme which can treat complicated behavior of interfaces such as a large deformation and a complicated separation among interfaces, the corium was spread with complicated mixing behavior and the distribution of fuel debris tend to accumulate complicatedly inside sump pits. Since existing SA analysis codes difficult to treat such complicated phenomena and the complicated fuel distribution, those result might be contributed to an understanding of circumstances inside PCV and, ultimately, also contributed to reactor decommissioning process.