Benchmark experiment on copper with graphite by using DT neutrons at JAEA/FNS

核融合DT中性子源FNSを用いたグラファイト付銅ベンチマーク実験

権 セロム*; 太田 雅之*; 佐藤 聡*; 今野 力  ; 落合 謙太郎*

Kwon, Saerom*; Ota, Masayuki*; Sato, Satoshi*; Konno, Chikara; Ochiai, Kentaro*

磁場閉じ込め式核融合炉システムの超伝導コイルやIFMIF加速器中性子源でよく使われる銅の核データベンチマーク実験を原子力機構の核融合DT中性子源FNSで実施したが、閾反応以外の結果で計算値が実験値を大きく過小評価しており、共鳴領域で銅核データの弾性散乱、捕獲反応断面積に問題がある可能性を指摘した。そこでグラファイト付銅実験体系を提案し、低エネルギー成分を増やした入射中性子場を設けて新ベンチマーク実験を実施した。放射化箔を用いて反応率を測定し、この実験解析をMCNPコード、最新の核データライブラリーを用いて行った。しかし、未だに低エネルギー中性子に感度を有する反応の反応率は計算値が実験値を大幅に過小評価した。銅核データの詳細検討より、前回試験的に作成した修正核データを用いることでこの過小評価の解消できることを明らかにした。この結果で低エネルギー中性子成分が多い中性子場でもこの断面積の修正の妥当性を確認できた。

Copper is used as a material for superconducting coil in magnetic confinement fusion reactor and for accelerator-driven neutron source such as IFMIF. In our previous copper benchmark experiment, we had pointed out that the elastic scattering and capture reaction data of the copper had included some problems in the resonance region, which had caused a large underestimation of reaction rates of non-threshold reactions. In order to corroborate this issue, we carried out a new benchmark experiment on copper with graphite in the neutron field with more low energy neutrons. We measured reaction rates using the activation foils. We analyzed the experiment with MCNP code and the latest nuclear data libraries. As a result, the calculated reaction rates related to low energy neutrons, still excessively underestimated the measured ones as in the previous benchmark experiment. We also tested the nuclear data of copper modified in the previous study, where the elastic scattering and capture reaction cross section of copper. Then the calculated reaction rates with the modified copper nuclear data reproduced the measured ones well. It was revealed that the modification of the specific cross sections had been sufficient in the neutron field with more low energy neutrons.