Experiments on Concrete-loaded core in the modified STACY

STACY更新炉におけるコンクリート模擬体を装荷した実験

荒木 祥平  ; 新垣 優; 前川 知之; 神川 豊; 長谷川 健太; 吉川 智輝 ; 多田 裕太; 住谷 正人; 関 真和; 會澤 栄寿; 石井 淳一; 井澤 一彦 ; 岩橋 大希*; 柴 茂樹*; 郡司 智  

Araki, Shohei; Arakaki, Yu; Maekawa, Tomoyuki; Kamikawa, Yutaka; Hasegawa, Kenta; Yoshikawa, Tomoki; Tada, Yuta; Sumiya, Masato; Seki, Masakazu; Aizawa, Eiju; Ishii, Junichi; Izawa, Kazuhiko; Iwahashi, Daiki*; Shiba, Shigeki*; Gunji, Satoshi

燃料デブリの臨界安全管理に資するため、STACY更新炉にコンクリート模擬体を装荷した実験を実施した。炉心は4.98wt%のUO燃料と軽水及び、デブリ構造材模擬体(コンクリート)で構成され、デブリ構造材模擬体(コンクリート)の装荷本数が9,25,69本である3種類の炉心を構成した。これらの炉心の臨界水位データを取得し、MCNP6.2及びJENDL-4.0をはじめとした核データライブラリで解析を実施した。解析の結果、計算値はデブリ構造材模擬体(コンクリート)の装荷量に従って、実験データを過大に評価する傾向があることが明らかとなった。

In order to investigate the effect on criticality characteristics of fuel debris containing concrete composition in the Fukushima Daiichi Nuclear Power Plant, critical experiments loaded concrete rods were conducted in the modified STACY. The experimental cores of the modified STACY were composed of light water, fuel rods, and concrete rods with grid plates with 15.0-mm lattice intervals in the core tank. Each fuel rod consisted of a zirconium alloy clad tube (9.5-mm outer diameter) and UO pellets (8.2-mm diameter) with 4.98wt.% 235U enrichment. Each concrete rod was composed of concrete simulant pellets (7.0-mm diameter) and an aluminum alloy clad tube (9.5-mm outer diameter). The concrete simulant pellets were fabricated using an aggregate-free mortar in order to ensure a uniform composition of the pellets, and the composition was evaluated by chemical analysis. Three experimental cores were configurated with 9, 25 and 69 concrete rods. The critical water level data were obtained. An effect of composition uncertainty of the concrete simulant pellet was estimated by sensitivity analysis using MCNP6.2 with JENLD-4.0. The sensitivity analysis estimated the effect to be less than 3 pcm. The calculation results performed using MCNP6.2 with ENDF/B-VII.1, JENDL-4.0, and JENDL-5 libraries showed a tendency to overestimate the multiplication factor according to increasing the loading amount of the concrete rods.