Periodic level measurements of Materials and Life science experimental Facility in J-PARC

J-PARC物質・生命科学実験施設における定期水準測量

原田 正英   ; 酒井 基亘*; 黒澤 卓史*; 羽賀 勝洋  

Harada, Masahide; Sakai, Motonobu*; Kurosawa, Takashi*; Haga, Katsuhiro

J-PARCのMLFは、3GeV、1MWの陽子ビームを利用する大強度核破砕中性子源及びミュオン源を有している。ビーム損失を減らすために、陽子、中性子、ミュオンの各ビームライン機器は、精密にアライメントされている。しかしながら、設計当初、建屋建設、重量遮蔽体の設置、地震、基盤の圧密化、多くの機器の設置により、MLFの沈下が生じる可能性があった。そこで、設計期からMLFの定期的な水準測量を始めた。MLFの内外に数十箇所の水準測量点を設け、建設期には1回/月、建設後には1回/年、測量を行ってきた。MLFの建設期には、建屋の建設と多くの遮蔽体の設置により、大きく沈下したことが確認された。2011年3月11日の東日本大震災では、MLFに付属する建屋が大きく沈下したことが確認された。その後、現在では、局所的には、多少の沈下が生じているが、全体として、問題となる大きな沈下は確認されていない(年に1.0mm程度の変化)。

Materials and Life science experimental Facility (MLF) in J-PARC has a high-intense spallation neutron source and a high-intense muon source induced by 3-GeV and 1MW proton beam. To reduce beam loss, components of proton, neutron and muon beam lines are precisely aligned. However, a settlement of MLF caused by a building construction, installation of heavy shields, earthquakes, consolidation of basement, instrument installation (weight increase), and so on, was assumed in the design stage. Therefore, periodic level measurements in MLF was started from the design stage. A few tens of level measuring points are installed inside and outside MLF. The level measurements were done once per month in the construction stage and per year after operation start. In the construction stage of MLF, it was found that the MLF building largely settled by construction of the building and installation of many shields. And it was also found that The Great East Japan Earthquake on March 11, 2011, caused large settlements of MLF attached buildings. Figure 1 shows fluctuations of measured levels at representative points in each area from December 2011. No critical deterioration (small changes within 1.0 mm) could be detected. However, a few local settlements are found in the MLF building. In the presentation, periodic level measurement results at MLF will be introduced.