報告書番号

U86011

タイトル（和文）

バッチ試験による粘土およびロームの核種吸着特性

タイトル（英文）

ADSORPTION CHARACTERISTICS OF COBALT AND STRONTIUM BY CLAY AND LOAM USING BATCH EXPERIMENTS

概要 （図表や脚注は「報告書全文」に掲載しております）

低レベル放射性廃棄物の陸地処分時安定評価にあたっては，地下水・土壌系での放射性核種の移行挙動の評価が重要となる。本報告は，移行挙動の中でも主要な現象の一つである土壌への核種吸着反応について，Ｃｏ，Ｓｒを対象各種としてバッチ試験により検討したものである。その結果，従来から安全評価コードの中で用いられている核種吸着等温式は，核種の初期濃度，共存イオンの種類と量，ｐＨ，温度等によって式中の定数が変化し一義的には決まらないことが明らかになった。しかし，土壌の主要吸着機構がイオン交換反応であることから，核種と地下水中の共存イオン（たとえばＣｏ２＋，Ｓｒ２＋と同一荷電を有するＣａ２＋イオン）とのイオン交換反応を想定し，その平衡定数である選択係数を求めると，その値は種々の因子の影響をうけて変化することがなく選択係数が安定な指標となりうることが判明した。

概要 （英文）

IT IS NECESSARY TO EVALUATE THE INTERACTION BETWEEN SOILS AND RADIONUCLIDES,IN PARTICULAR THE RETARDATION EFFECTS OF SOILS DEPENDING ON THEIR ADSORPTION PROPERTIES BECAUSE THE SAFETY ASSESSMENT ON LAND DISPOSAL OF LOW-LEVEL RADIOACTIVE WASTES PRODUCED FROM NUCLEAR POWER PLANTS HAS TO BE CONDUCTED. IN THIS REPORT,USING THE BATCH TECHNIQUE THE ADSORPTION OF NONRADIOACTIVE COBALT AND STRONTIUM TO CLAY AND LOAM WAS STUDIED UNDER THE COEXISTENCE OF MAJOR CATIONS CONTAINED IN GROUNDWATER. COBALT AND STRONTIUM HAVE BEEN REGARDED AS ONE OF THEREPRESENTATIVE NUCLIDES IN SAFETY ASSESSMENT ON LAND DISPOSAL. THE PRINCIPAL RESULTS WERE AS FOLLOWS. 1)THE COEFFICIENTS OF THE ADSORPTION ISOTHERMS WERE DEPENDENT UPON THE INITIAL CONCENTRATIONS OF NUCLIDES,SPECIES AND AMOUNT OF THE COEXISTING CATIONS CONTAINED IN SOLUTION,PH AND TEMPERATURE.2)THE CATIONS WHICH HAVE THE SAME VALENCE OF CO2+ AND SR2+,FOR EXAMPLE CA2+ AND MG2+,HADA POTENT INFLUENCE ON THE AMOUNTS OF NUCLIDES ADSORBED BY CLAY AND LOAM.3)THE EQUILIBRIUM COEFFICIENT OF THE ION EXCHANGE REACTIONS BETWEEN NUCLIDE AND COEXISTING CATION,THE SELECTIVITYCOEFFICIENTS,BECAME VERY STABLE INDICATORS INDEPENDENT OF THE CHEMICALCOMPOSITION OF SOLUTION,PH AND TEMPERATURE,EXCEPT THE SYSTEM COBALT-CALCIUM-KAOLINITE. 4)IN PRACTICE THE DISTRIBUTION COEFFICIENTS HAVE BEEN USED IN THE SAFETY ASSESSMENT. IF THE MAJOR MECHANISM OF ADSORPTION IS REGARDED AS ION EXCHANGE REACTION,THE DISTRIBUTION COFFICIENTS OF NUCLIDES CAN BE ESTIMATED BY USING A SET OF THE SELECTIVITY COEFFICIENT AND THE DISTRIBUTION COEFFICIENT OF MAJOR CATIONS GROUNDWATER WHICH HAD THESAME VALENCE AS THE NUCLIDES.

報告者

キーワード