報告書番号

U97044

タイトル（和文）

核種吸着性に及ぼす天然有機物の影響に関する調査

タイトル（英文）

SURVEY OF EFFECTS OF NATURAL ORGANIC SUBSTANCES ON SORPTION OF RADIONUCLIDES

概要 （図表や脚注は「報告書全文」に掲載しております）

天然有機物の核種吸着性への影響に関する現状の知見と今後の検討課題を明らかにするため，内外の既往文献を調査した。その結果，以下の点が明らかとなった。（１）アクチノイドと遷移元素の吸着性は，可溶性のフミン酸やフルボ酸と核種との錯体形成により，低下する可能性がある。しかし，アルカリ金属やアルカリ土類金属の吸着性は，有機物の影響を受け難い。（２）不溶性の高分子有機物は，コロイド形成により核種を取り込み，コロイド自体の不溶化と，不溶性有機物への核種の吸着により，核種吸着性が高まる可能性がある。（３）有機物と核種の錯体及びコロイド形成，環境中での錯体やコロイドの安定性，有機物共存下での核種吸着性の変動の程度は，定性的・定量的に十分解明されていない。従って，有機物と核種の相互作用及び核種吸着性の変動を定量化する為の実験方法と評価方法の検討が今後必要である。

概要 （英文）

TO CLARIFY THE EFFECTS OF NATURAL ORGANIC SUBSTANCES ON SORPTION OF RADIONUCLIDES, WE SURVEYED TECHNICAL AND RESEARCH PAPERS. THE FOLLOWING CONCLUSIONS WERE OBTAINED. NATURAL ORGANIC SUBSTANCES ARE IMPORTANT IN RADIOACTIVE WASTE DISPOSAL PROGRAMS FOR PREDICTING THE FATE AND LONG-TERM PERFORMANCE OF RADIONUCLIDES IN THE ENVIRONMENT. FOR EXAMPLE, THE SORPTION RATIO OF TRANSITION ELEMENTS(FE, MN, CO, AND NI)AND ACTINIDE ELEMENTS(TH, U, PU, AM, AND NP)IN GEOLOGICAL MEDIA IS SUSCEPTIBLE TO DECREASE BY FORMATION OF COMPLEXES WITH SOLUBLE HUMIC AND FULVIC ACIDS. HOWEVER, ALKALINE METALS(K, CS)AND ALKALINE-EARTH METALS(CA, SR)ARE ALMOST UNOFFECTED BY SOLUBLE ORGANICS. CONVERSELY, THE SORPTION RATIO OF RADIONUCLIDES MAY BE INCREASED BY FORMATION OF COLLOIDS WITH INSOLUBLE AND POLYMERIC NATURAL ORGANICS. IN PARTICULAR, TRANSURANIC RADIONUCLIDES(PU, AM, AND NP)ARE MORE LIKELY TO BE ADSORBED BY REDUCING FORMS OF ORGANICS AND CARBONATES. IN ADDITION, SOME ADSORBEDCHEMICAL FORMS OF RADIONUCLIDES IN GEOLOGICAL MEDIA HAVE BEEN INDICATED, SUCH AS ALUMINUM SILICATES, AND OXIDIZED FORMS OF FE AND MN. AS MENTIONED ABOVE, THE REMARKABLE CHARACTERISTICS OF NATURAL ORGANICS SUGGEST THAT THEY CAN PROMOTE THE MOBILITY AND/OR IMMOBILITY OF RADIONUCLIDES. NEVERTHELESS, THERE ARE STILL QUESTIONS. WHAT IS THE INTERACTION BETWEEN NATURAL ORGANICS, RADIONUCLIDES AND GEOLOGICAL MEDIA? WAHT IS THE GEOCHEMICAL AND GEOMICROBIAL ROLE OF NATURAL ORGANICS? WHAT IS THE STABILITYOF RADIONUCLIDES OF COLLOIDAL AND COMPLEX FORM IN THE ENVIRONMENT? HOWCAN WE ASSESS THE BEHAVIOR AND MIGRATION OF RADIONUCLIDES IN THE ENVIRONMENT? FURTHERMORE, IN CHEMICAL REACTIONS IN THE PRESENCE OF ORGANICS,RADIONUCLIDES, AND GEOLOGICAL MEDIA, THE IMPORTNAT FACTORS AFFECTING THE ADSORPTION OF RADIONUCLIDES ARE AS FOLLOWS: REDOX CONDITION, PH AND IONIC STRENGTH OF SOLUTION, DIFFERENCES INCONCENTRATION BETWEEN DISSOLVED ORGANIC LIGANDS AND REDIONUCLIDES, SPECIES OF GEOLOGICAL SORBENTINITIAL CHEMICAL FORM OF RADIONUCLIDE. HOWE

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