弥生炉の標準照射場を用いたHAFM等の校正照射

Irradiation test of HAFM and tag gas samples at the standard neutron field of "YAYOI"

井口 哲夫*

not registered

高速炉の新型中性子ドシメトリー手法であるヘリウム蓄積型中性子フルエンスモニター(HAFM)の測定精度評価、及びタグガスの放射化分析による高速炉の燃料破損検出法への適用性評価を目的として、東京大学工学部附属原子力工学研究施設の高速中性子源炉「弥生」の標準照射場を用い、これらの試料の校正照射を行った。HAFM試料の照射では、炉心中央(Gy孔)に、93%濃縮ボロン1mg入りバナジウムカプセル、また高速中性子柱実験孔(FC孔)に、同仕様の濃縮ボロンカプセル、天然ボロン10mg入りカプセル、天然ボロンチップ、96%濃縮6LiF熱蛍光線量計素子が装荷された。これらの照射場の中性子束及び中性子スペクトルは、Al, Fe, Co, Ni, Cu, Ti, In, Au, 235U, 237Np等を用いた放射化箔法でモニターされ、平成8年3月末現在、照射された0.1MeV以上の中性子フルエンスは、Gy孔で1.010の17乗n/cm2(積算炉出力78kWh相当)、またFCで3.410の14乗n/cm2(積算炉出力160kWh相当)に達している。一方、ステンレス鋼製カプセルに封入されたKr、Xeベースのタグガス試料(単体型と小径型の2種類)について、Gy孔で、積算炉出力9kWh及び7kWhの2回の標準照射を行い、照射直後から各試料のガンマ線スペクトル測定を行った。タグガスの封入されていないダミーカプセルの測定スペクトルと比較した結果、タグガスの放射化で生成された79Krや125Xeなどの放射性核種からのガンマ線光電ピークを明確に同定でき、燃焼計算の精度評価に有用なベンチマーク実験データが得られた。

To check the accuracy of helium accumulation neutron fluence monitoring (HAFM) technique and the applicability of tag gas activation analysis to fast reactor failed fuel detection, these samples were irradiated at the standard neutron field of the fast neutron source reactor "YAYOI" (Nuclear Engineering Research Laboratory, University of Tokyo). The HAFM samples of 93% enriched B powder of 1 mg contained in a V capsule were set up in the reactor core center (Glory hole :Gy) and another samples including V encapsulated natural B powder of 10 mg, natural B chips and 96% enriched LiF thermoluminescence dosimeters were in the leakage neutron field from the reactor core (Fast column :FC). These neutron fields were monitored by the activation foils consisting of Al, Fe, Co, Ni, Cu, Ti, In, Au, U, Np etc., which were used to derive the neutron flux and spectrum. At the end of March in 1996, the irradiated neutron fluence in the energy more than 0.1Mev reached up to 1.110 n/cm at Gy and 5.410 n/cm at FC, respectively. Two kinds of tag gas samples, which are the mixed gases of isotipically adjusted Xe and Kr contained in stainless steel (SUS) capsules, were irradiated twice at Gy; one is up to 9kWh and the other 7kWh, and after the irradiation, -ray spectra were measured for each sample. Through comparison with the -ray spectrum from dummy capsule of no tag gas, the -ray peaks of Kr, Xe etc., which would be produced from tag gas activation, were able to be clearly identified.