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JAEA/FNSにおけるDT中性子源を用いた新たな銅ベンチマーク実験

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

権 セロム; 太田 雅之; 落合 謙太郎; 佐藤 聡; 今野 力

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

約20年前にJAEA/FNSで銅ベンチマーク実験が行われた、数keV以下の中性子に係る実験値と解析値に不一致がみられた。この原因の一つとして実験室の壁からのバックグラウンド中性子による影響が考えられるため、バックグラウンド中性子を低減させた銅実験体系を構築し、新たな銅ベンチマーク実験を実施した。解析はモンテカルロ中性子輸送コードMCNP5-1.40と最新の核データライブラリーのENDF/B-VII.1, JEFF-3.2, FENDL-3.0(ENDF/B-VII.0), JENDL-4.0で行い、反応率と核分裂率の計算にはドジメトリファイルのJENDL Dosimetry File 99を用いた。前回の$$^{197}$$Au(n,$$gamma$$)$$^{198}$$Auの結果に比べるとJENDL-4.0を用いた計算結果は若干改善されたものの、まだどの核データライブラリーを用いた解析値も実験値を大幅に過小評価し、この過小評価の原因が銅の核データにあることがわかった。

A benchmark experiment on copper with DT neutron source was performed 20 years ago at JAEA/FNS. However, the calculated results tended to underestimate the measured data related to lower energy neutrons below a few keV in the experiment, which suggested that the measured data might be affected by neutrons scattered in the concrete wall of the experiment room or other surroundings. Therefore, we have carried out an additional integral experiment on copper, where a copper assembly was covered with Li$$_{2}$$O blocks to reduce neutrons scattered in the concrete wall. We used the Monte Carlo neutron transport code, MCNP5-1.40 and the recent nuclear data libraries, ENDF/B-VII.1, JEFF-3.2, JENDL-4.0 and FENDL-3.0 (ENDF/B-VII.0) for the experiment analysis. JENDL/D-99 was used as dosimetry cross section data. The calculated reaction rates of the $$^{197}$$Au(n,$$gamma$$)$$^{198}$$Au reaction with all the nuclear data libraries still underestimate the measured data, although the underestimation was improved compared to the previous result with JENDL-4.0 in particular. We found out that the nuclear data of copper caused this underestimation problem.

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