A New integral experiment on copper with DT neutron source at JAEA/FNS

JAEA/FNSにおけるDT中性子を用いた銅の新積分実験

権 セロム; 佐藤 聡; 太田 雅之; 落合 謙太郎; 今野 力  

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

JAEA/FNSのDT中性子源を用いて約20年前に行われた銅核データのベンチマーク実験で報告された低エネルギー中性子に係る実験データの過小評価の原因究明のため、我々は同施設のDT中性子源を用いて新たに銅の積分実験を実施した。実験体系は20年前と同じ半径315mm、深さ608mmの模擬円筒の銅体系で、バッググランド中性子を排除するため、その実験体系の前方とサイドに51mm、後方に153mmの酸化リチウムブロックで囲んだ。5種類の反応の反応率とU, Uの核分裂率を測定し、MCNP5-1.40と最新の核データライブラリーENDF/B-VII.1, JEFF-3.2, JENDL-4.0を用いて解析を行った。その結果、Au(n,)Au反応の反応率のC/Eが前回の実験結果より10%改善し、JEFF-3.2のCuデータ、JENDL-4.0のCuデータの組み合わせで更に10%程度過小評価が改善した。共鳴領域の弾性散乱断面積, 捕獲反応断面積を10%程度変えたところ、過小評価がほぼ解消した。銅の核データの共鳴領域のデータの再評価が必要である。

A benchmark experiment on copper with the DT neutron source at JAEA/FNS was performed over 20 years ago. The experiment showed that ratios of the calculated values to the experimental ones (C/Es) related to lower energy neutrons were drastically smaller than unity. In order to reveal reasons of the small C/Es, we performed an integral experiment on copper with the DT neutron source at JAEA/FNS. A quasi-cylindrical copper assembly of 315 mm in radius and 608 mm in depth was covered with LiO blocks of 51 mm in thickness for the front and side parts and 153 mm in thickness for the rear part to exclude background neutrons. We measured the reaction rates of 5 reactions and the fission rates of U and U. The experiment was analyzed by using MCNP5-1.40 with the recent nuclear data libraries, ENDF/B-VII.1, JEFF-3.2 and JENDL-4.0. As a result, the C/E of the reaction rate of the Au(n,)Au reaction was improved by 10% from the previous result and the combination of the Cu data in JEFF-3.2 and Cu data in JENDL-4.0 increased the C/E by more 10%. Moreover, the calculated result with modified elastic scattering and capture cross section data by 10% resolved the underestimation. The copper data should be reevaluated.