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Development of a SH wave single unit electromagnetic acoustic transducer (EMAT) for MONJU reactor vessel in-service inspection

「もんじゅ」原子炉容器廻り供用期間中検査装置用SH波電磁超音波探触子(EMAT)の開発

Xu, Y.*; 田川 明広; 藤木 一成*; 上田 雅司; 山下 卓哉

Xu, Y.*; Tagawa, Akihiro; Fujiki, Kazunari*; Ueda, Masashi; Yamashita, Takuya

高速増殖炉「もんじゅ」では、原子炉容器に対し供用期間中検査として体積検査を実施する。その検査中の環境は温度が200$$^{circ}$$C,放射線線量率が10Gy/hrと非常に過酷である。体積検査は、電磁超音波探触子(EMAT)を用いて実施されるが、これまではPPM構造の磁石配置のEMATを用いていた。PPN構造とはS極とN極を交互に組合せた構造である。本研究では、PPM構造の縦磁化磁石の間に横磁化磁石を入れ込んだHalbach構造を採用した。これにより磁束密度はPPMに比べ1.4倍に向上した。さらに、新しい信号処理方法を用いることで4倍の感度向上を達成した。さらに、200$$^{circ}$$Cで200時間の耐久性試験も実施した。

In-service inspection is carried out to confirm the integrity of the main components of "MONJU". The ambient temperature during the inspection is 200 $$^{circ}$$C and the irradiation field is 10 Gy/hr. A Periodic Permanent Magnet (PPM) structure has been used for electromagnetic acoustic transducer (EMAT). The PPM structure is the structure of putting in order alternately the S pole and N pole laterally magnetized magnets. A Halbach magnet structure is the structure which sandwiched the longitudinally magnetized magnets between each magnet of PPM structure. Thereby, magnetic flux density is improved 1.4 times. Moreover, it also checked aiming at 4 times as many improvement in detection sensitivity as this by a new signal processing method. The high temperature characteristic and high temperature durability of Halbach type EMAT in 200 hours which corresponds the twice of inspection time under the 200 $$^{circ}$$C inspection environment are reported.

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