報告書番号

385027

タイトル（和文）

フォールアウトを利用したストロンチュウム－９０とセシウム－１３７の地中移動速度の検討

タイトル（英文）

ESTIMATION OF UNDERGROUND MIGRATION RATE OF FALLOUT CESIUM-137 AND STRONTIUM-90 IN SITU

概要 （図表や脚注は「報告書全文」に掲載しております）

本研究では，低レベル放射性廃棄物陸地処分時安全評価上の決定核種の１つであるＳｒ－９０，Ｃｓ－１３７の遅延係数，分配係数についてフォールアウトを用いて長崎市西山の未耕作地で測定した。１．フォールアウトＣｓ－１３７とＳｒ－９０の起源と降下量を貯水池底質中の鉛直濃度分布より推定した。西山土壌に吸着されているＣｓ－１３７，Ｓｒ－９０の各々５０％，４６％が長崎原爆フォールアウトであった。２．４０年間の浸透移動分布の調査結果を基に遅延係数，分配係数を求めた。それらは，Ｃｓ－１３７については各々５０００，１７００またはＳｒ－９０については，１０００，４００であった。室内実験で測定した分配係数は，フィールドで測定した値に比べ１桁小さい。３．陸地処分の安全評価に室内実験で測定した分配係数を用いることは，評価結果に大きな安全裕度を与え

概要 （英文）

TO ESTIMATE THE UNDERGROUND MIGRATION RATE OF CESIUM-137 AND STRONTIUM-90 IN SITU,THE PROFILE OF FALLOUT RADIONUCLIDES WAS OBSERVED AT THE NISHIYAMA DISTRICTIN 40 YEARS AFTER THE EXPLOSION OF ATOMIC BOMB FATTMAN. FOR THIS ESTIMATION,THE HISTORICAL RECORD OFANNUAL DEPOSITION RATE OF FALLOUT RADIONUCLIDES DURING 40 YEARS WAS APPRAISED IN COMPARISON OF THE VERTICAL DISTRIBUTION OF CESIUM-137 AND PLUTONIUM-239 IN THE SEDIMENTS BETWEEN NISHIYAMA AND KOGAKURA RESERVOIRS,WHICH HAD RECIEVED BOTH THE LOCAL FALLOUT OF FATTMAN IN 1945 AND GLOBALONE AND THE ONLY GLOBAL FALLOUT,RESPECTIVELY. FIFTY % OF CESIUM-137 AND FORTY SIX % OF STRONTIUM-90 RETAINED IN THE NISHIYAMA SURFACE SOIL DERIVED FROM THE ATOMIC BOMBING OF NAGASAKI,AND THE RESH OF CESIUM AND STRONTIUM FROM THE GLOBAL ONE. BASED ON THESE DEPOSITIONAL DATA FOR FALLOUT,THE MIGRATION ANALYSIS OF CESIUME-137 AND STRONTIUM-90 WAS DONE. THEMIGRATION RATE OF CESIUM-137 AND STRONTIUM-90 WERE INFERED RESPECTIVELY TO BE 1/5000 AND 1/1000 OF VELOCITY OF GROUNDWATER FLOW FROM THE COMPARISON BETWEEN THE MEASURED DISTRITUTION OF THESE RADIONUCLIDES IN THE GROUND AND THE SIMULATED RESULTS. THE DISTRIBUTION COEFFICIENT OF CESIUM-137 AND STRONTIUM-90 WERE CALCULATED FROM THE AFOREMENTIONED RETARDATION FACTORS,AND THEY WERE 1700 TO CESIUM-137 AND 400 TO STRONTIUM-90. THESE VALUES MEASURED IN SITU WERE ABOUT TENFOLDS GREATER THAN THOSE DETERMINED IN THE BATCH TESTS BY USING THE SAME SOIL COLLECTED AT THE NISHIYAMA AREA. TNE MAJOR DIFFERENCE BETWEEN THE IN SITU VALUE AND THE LOBORATORY ONE ARE ASCRIBED TO BE IN THE DIFFERENT LENGTH OF TERM TO REACH THE ABSORBED EQUILIBRIUM.

報告者

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