ヘリウム蓄積法による中性子照射量の測定精度に関する研究

Accuracy of neutron dosimetry system by Helium accumulation method

鷹尾 良行*; 神田 幸則*

not registered; not registered

本研究は、動力炉・核燃料開発事業団が新ドシメトリー手法として開発中の、高速炉用ヘリウム蓄積型中性子照射量モニタ(HAFM)の精度評価を中性子照射試料を用いて行ったものである。具体的には、九州大学の微量He原子測定装置(HAMS)で、東京大学の高速中性子源炉「弥生」の標準照射場で校正照射されたHAFM試料のHe含有量測定を行い、測定結果を、同時に作製された校正照射済みHAFM試料の動燃のHAFM測定装置による測定結果及び多重放射化箔法により求めた各HAFM試料中でのHe生成量評価値と比較した。使用した校正照射済み試料は、HAFM試料6点、天然ホウ素チップ2点、TLD素子2点の合計10点である。HAFM試料は、バナジウムキャプセルに濃縮ホウ素1mg、天然ホウ素10mgまたは濃縮ホウ素40mgを封入した物で、各2点づつの合計6点である。また、未照射のダミー試料を試料測定におけるバックグラウンド決定に使用した。測定の結果、各試料のHe含有量を誤差+-3%で得ることが出来た。また、未照射試料測定により決定されたバックグラウンドは、中性子照射試料の1%未満であった。本測定結果および動燃測定値は概して良く一致した。また、多重放射化箔法によるHe生成量評価値は本測定結果を支持するものであった。これらの結果より、HAMSおよびHAFM測定装置によるHe量測定の信頼性とHe集積法による中性子線量測定の有効性が確認された。

Accuracy of the Helium Accumulation Fluence Monitor (HAFM) developed by Power Reactor and Nuclear Fuel Development Corporation (PNC) was experimentally estimated by using neutron irradiated HAFM samples. Samples were irradiated by neutrons in the standard neutron spectrum fields of the Fast Neutron Source Reactor of "YAYOI" at university of Tokyo. The amount of Helium produced in the samples was measured by the Helium Atoms Measurement System (HAMS) at Kyushu University and by the HAFM measurement system at PNC. Both experimental results and the values estimated by the multi-foil activation method were compared. The neutron irradiated samples measured by the HAMS were two 1 mg enriched boron HAFM samples (boron chips were enveloped in a vanadium capsule), two 10mg natural boron HAFM samples, two 40 mg enriched boron HAFM samples, two natural boron chips and two TLD chips. Several dummy samples, which were not irradiated by neutrons, were also measured to estimate the amount of background helium at sample measurements. The overall errors for the helium measurements of samples by the HAMS were estimated to be less than 3%. The amount of background helium determined by the dummy sample measurements was less than 1% of helium contained in the neutron-irradiated samples. Our results by the HAMS were mostly in good agreement with the results by PNC. The estimated values supported our results. Reliance of helium measurement by the HAMS and by the HAFM measurement system, and validity of the neutron dosimetry by the helium accumulation method were consequently confirmed.