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Proposal and application of ROM-Lasso method for sensitivity coefficient evaluation

感度係数評価に向けたROM-Lasso法の提案と適用

方野 量太   ; 山本 章夫*; 遠藤 知弘*

Katano, Ryota; Yamamoto, Akio*; Endo, Tomohiro*

ADS炉心核特性の反応断面積に対する感度係数評価を、炉心解析システムに大幅な変更を加えることなく効率よく行うために、ROM-Lasso法を提案した。ROM-Lasso法では、まず感度係数ベクトルはAcitve Subspace (AS)と呼ばれる部分空間基底に展開され、実効的な未知数を大幅に削減する。続いて、ランダムサンプリングを実行して得られる炉心核特性と展開係数との罰則化線形回帰分析を通じて展開係数を決定し、感度係数ベクトルを推定する。ROM-Lasso法ではASを用いることで必要な炉心計算回数を大幅に低減することができる。本発表では燃焼末期の冷却材ボイド反応度の感度係数評価を例に、サンプル数やASの取り方で推定精度がどのように変化するかを示す。

We have proposed the ROM-Lasso method to perform an efficient evaluation of the sensitivity coefficients of ADS core parameters to cross sections without major modification of the core analysis system. In the ROM-Lasso method, the sensitivity coefficient vector is expanded via the subspace bases so-called Active Subspace (AS), and the effective number of unknowns is reduced. Then, the expansion coefficients are determined via the penalized linear regression with the core parameters obtained by the random sampling, and the sensitivity coefficient vector is estimated. Owing to the AS, the required number of the core calculations is dramatically reduced in the ROM-Lasso method. In this work, we take the sensitivity coefficient evaluation of the coolant void reactivity at the end of the cycle for example and demonstrate how estimation accuracy depends on the number of samples and the AS.

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