報告書番号

383043

タイトル（和文）

フォールアウト（放射性降下物）を利用したプルトニウムの地中移動の検討（その２）

タイトル（英文）

MIGRATION OF FALLOUT RADIONUCLIDES IN THE UNSAURATED SILTY LOAM LAYER OF NISHIYAMA IN NAGASAKI

概要 （図表や脚注は「報告書全文」に掲載しております）

放射性廃棄物の陸地処分時安全評価を精度よく実施するためには，実環境中での核種移行挙動現象を把握し核種輸送機構の解明を図り新たに得られた知見を基に評価モデルの改良およひ評価解析に必要な入力パラメータの収集を行う必要がある。本報告では，前報に引き続き，長崎原爆に起因するフォールアウト核種の地中移行を長崎市西山にて追跡調査し以下の結果を得た。１）押出し流れモデルにより降水浸透解析を行い，降水浸透速度として２００～３００ｃｍ／ｙを得た。２）核種の地中移行速度は，核種形態によって異なり，Ｐｕの１０％程度は地中を速く移動しておりそれらは非イオン状核種である。３）湧出地下水中に２３９＋２４０Ｐｕが０．６６±０．１３（ｆｃｉ／■）検出された。

概要 （英文）

IN A SERIES OF STUDIES,THE AUTHOR HAS OVSERVED A MIGRATION OF THE FALLOUT RADIONUCLIDES,ORIGINATED FROM THE DETONATION OF THE ATOMIC BOMB AT NAGASAKI IN 1945,DURING THE PAST 37 YRS.IN THIS WORK,THE FOLLOWING THREE FIELD SURVEYS WERE CONDUCTED;(1)A VERTICAL DISTRIBUTION OF A TRITIUM CONCENTRATION OF SOIL WATER IN THE NISHIYAMA LOAM LAYER,(2)A VERTICAL DISTRIBUTION OF FALLOUT PU-239 AND CS-137 IN THE LOAM LAYER,AND(3)CONCENTRATION OF PU-239 IN A SEEPED GROUNDWATER.THROUGH THESE RESULTS DERIVED FROM THE FIELD INVESTIGATION,THE AUTHOR FOCUSSED TO REVEAL THE INFILTRATING RATE OF RAINWATER IN THE AERATED ZONE OF THE NISHIYAMA LOAM AND THE CHEMICAL FORM OF MOBILE PLUTONIUM. 1.INFILTRATION ANALYSIS OF RAINWATER WITH THE DISPLACEMENT FLOW MODEL. THE INFILTRATION RATE OF RAINWATER IN THE NISHIYAMA LOAM WAS EVALUATED 200 300CM/YR FROM THE DISPLACEMENT FLOW ANALYSIS BASED ON THE TRITIUM DISTRIBUTION OF SOIL WATER IN THE SOIL LAYER. 2.VERTICAL DISTRIBUTION OF FALLOUT RADIONUCLIDES IN THE GROUND. MORE THAN 90% OF TOTAL PU-239 AND CS-137CONTAINED IN A NISHIYAMA SOIL WERE RETAINED TO A 50CM DEPTH FROM THE GROUND SURFACE.THE REMAINING 10% OF PU-239 AND CS-137 DISPERSED UP TO A 650 CM DEPTH ABOVE THE BED ROCK.FROM THESE OBSERVATIONS,CHEMICAL FORMS OF A MOBILE PU-239 AND CS-137 WERE INFERRED THAT THEY DID NOT MIGRATE IN A FORM OF ION BUT THEY WERE TRANSPORTED IN FIXED ON FINE SOIL PARTICULATES BY GROUNDWATER. FOR THE PURPOSE OF MEASURING AN UNDERGROUND MOBILITY OF PU-239 DEPOSITED AT THE NISHIYAMA DISTRICT,A CONCENTRATION OF PU-239 CONTAINED IN THE SEEPED GROUNDWATER WAS INVESTIGATED.PU-239 WAS DETECTED AT 0.66-0.13 - +0.13 FCI/L IN GROUNDWATER.THIS SHOWS THAT PU-239HAS MIGRATED IN A TRACE CONCENTRATION IN GEOENVIRONMENT.

報告者

キーワード