Debris-simulated core analysis under fuel procurement constraints in new STACY experiments

STACY更新炉における燃料棒本数制限下におけるデブリ模擬炉心の検討

荒木 祥平   ; 郡司 智  ; 新垣 優; 吉川 智輝 ; 村上 貴彦; 小林 冬実 ; 井澤 一彦 ; 須山 賢也

Araki, Shohei; Gunji, Satoshi; Arakaki, Yu; Yoshikawa, Tomoki; Murakami, Takahiko; Kobayashi, Fuyumi; Izawa, Kazuhiko; Suyama, Kenya

福島第一原子力発電所で発生した燃料デブリの臨界管理に資するため、STACY更新炉においてデブリ模擬炉心の検討を進めている。燃料輸送の問題から実験に利用可能な燃料棒本数に制限がある中で、低減速条件の炉心を構成するため、テスト領域とドライバ領域からなる2領域炉心を検討した。中性子スペクトル及びコンクリート模擬体を装荷した際の感度をMCNPとENDF/B-VIIを用いて計算した。テスト領域が1717の炉心は1313サイズの領域において低減速条件のスペクトルをRMSPEが5%以下で模擬できることを明らかにした。

New experiments simulating fuel debris in the new criticality assembly, STACY, are designed to contribute to the validation of criticality calculations for criticality control of the fuel debris in the Fukushima Daiichi Nuclear Power Plant accident. In the new STACY experiment, a two-region core consisting of a driver region and a test region was investigated in order to configure a debris-simulated core with under-moderation condition (lattice pitch 1.27-cm) having the constraint of available fuel rod number. The test region with a 1.27-cm lattice pitch is surrounded by the driver region, in which fuel rods are arranged in a checkerboard pattern on a 1.27-cm lattice plate, with a 1.80-cm lattice pitch. Neutron spectra and sensitivity were calculated by using MCNP6 and ENDF/B-VII. The core which has a 1717 test region with 373 fuel rods is the largest two-region core under the constraint. It was found that the core which has a 1717 test region can simulate the neutron spectra of under-moderation condition in a 1313 region inside the test region with the root-mean square percentage error of less than 5%. It was also confirmed that the sensitivity of Si and Ca (n,) reactions when the concrete simulant, was loaded could be simulated.