Application of bias factor method with use of exponentiated experimental value to prediction uncertainty reduction in coolant void reactivity of breeding light water reactor

累乗化実験値の概念を用いたバイアス因子法の水冷却増殖炉心の冷却材ボイド反応度の予測誤差低減への応用

久語 輝彦 ; 小嶋 健介; 安藤 真樹  ; 森 貴正; 竹田 敏一*

Kugo, Teruhiko; Kojima, Kensuke; Ando, Masaki; Mori, Takamasa; Takeda, Toshikazu*

本研究では、実機炉心とは逆の符号を持つ反応度価値測定値、すなわち実機炉心とは逆の符号の感度係数を持つ実験値を使用する場合に従来バイアス因子法では予測誤差が増加する問題を解決するため、バイアス因子法に累乗化実験値の概念を導入し、これをFCA-XXII-1臨界実験を活用して水冷却増殖炉心の冷却材ボイド反応度の予測誤差低減へ応用した。数値計算結果から、従来法では予測精度の改善が見られなかったのに対し、累乗化実験値概念が予測精度を向上させることが確認された。よって、累乗化実験値概念が効果的に実験結果を活用するとともに、バイアス因子法の適用性を拡張するものであると結論づけられる。

We have applied the bias factor method to coolant void reactivity of a breeding light water reactor with use of FCA-XXII-1 experiment with introducing a concept of exponentiated experimental value into the bias factor method in order to overcome a problem caused by the conventional bias factor method in which the prediction uncertainty increases in the case that the experimental core has the opposite reactivity worth and the consequent opposite sensitivity coefficients to the real core. In the present study, we have formulated the prediction uncertainty reduction by the use of the bias factor method extended by the concept of the exponentiated experimental value. From the numerical results, it is verified that the concept of exponentiated experimental value can improve the prediction accuracy compared with the original uncertainty in the design calculation value while the conventional bias factor method cannot improve the prediction accuracy. It is concluded that the introduction of exponentiated experimental value can effectively utilize experimental data and extend applicability of the bias factor method.