A Study of applicability of JENDL-4.0 to the HTTR criticality analysis

HTTR臨界計算へのJENDL-4.0の適用性評価

後藤 実  ; 島川 聡司; 橘 幸男 

Goto, Minoru; Shimakawa, Satoshi; Tachibana, Yukio

炭素の捕獲断面積の精度は、高温ガス炉の核特性を行ううえで重要であるが、これまで長期にわたり更新されてこなかった。2010年5月に公開されたJENDLの最新版であるJENDL-4.0では、この値が最新の測定データに基づき更新された。その結果、従来の核データライブラリをJENDL-4.0に換えることで、これまで解決できなかったHTTRの臨界ベンチマーク計算における過剰反応度の課題評価の問題が解決され、HTTRの臨界計算に対する高い適用性が示された。

In the past, benchmark calculations of criticality approach for the HTTR, which is a Japanese HTGR, were performed by research institutes in several countries, and almost all of the calculations overestimated the excess reactivity. In Japan, the benchmark calculations were performed by JAEA, and were also resulted in overestimation. JAEA improved the calculations by revising the geometric model and replacing the nuclear data library with JENDL-3.3, which was the latest JENDL at that time. However, the overestimation remained and this problem has not been resolved until today. We performed calculations of the HTTR criticality approach with several nuclear data libraries, and found that slight difference in the neutron capture cross section of carbon at thermal energy among the libraries causes significant difference in the values. The cross section value of carbon was not concerned in reactor neutronics calculation because of its small value of the order of 1E-3 burn, and consequently the cross section value had not been revised for a long time even in the major nuclear data libraries: JENDL, ENDF/B and JEFF. We thought that the cross section should be revised based on the latest measurement data to improve the accuracy of the HTGR criticality analysis. In May 2010, the latest JENDL (JENDL-4.0) was released by JAEA, and the capture cross section of carbon was revised. JENDL-4.0 yielded 0.4-0.9%k/k smaller values than JENDL-3.3 in the criticality calculations for the HTTR critical approach, and consequently the problem of the overestimation of the excess reactivity in the HTTR benchmark calculation was resolved by replacing the nuclear data libraries with JENDL-4.0.