報告書番号

U97106

タイトル（和文）

熱変成によるセメントの核種収着性能の変化

タイトル（英文）

CHANGE OF THE SORPTION PROPERTY OF CEMENT MATERIALS DUE TO HYDROTHERMAL ALTERATION

概要 （図表や脚注は「報告書全文」に掲載しております）

放射性廃棄物処分において，セメントには，核種閉じ込め性能が期待されている。ところが，長期に亘るセメントの化学的変質については依然不明点が多い。本報告では，セメントの水熱変成を取り上げ，それに伴う核種収着性能の変化を収着試験により実験的に評価した。結果は以下の通りである。（１）ＯＰＣ，ＢＦＳ混合セメントについて，７０度までの水熱変成試験を行った。ＣＳＨ－ｇｅｌ相など構成鉱物の結晶性の変化など，固相自体の熱変成を観察した。（２）熱変成後のセメントについて，Ｓｒ，Ｓｅの収着試験を行った。収着性能の熱変成による低下が観察され，構成鉱物の変化が原因であることが示唆された。以上より，セメントの化学的バリア性能の長期評価には，熱変成による，固相の変化を把握する必要があることが示された。熱変成と収着現象の関係について，更にアクチニド元素をも対象とし調べる予定である。

概要 （英文）

IN RADIOACTIVE WASTE DISPOSAL, CEMENT MATERIALS ARE USED AS AN ENGINEERED BARRIER. THEY ARE EXPECTED TO RETARD THE RELEASE OF RADIONUCLIDES AS A PHYSICAL AND CHEMICALLY ENGINEERED BARRIER. THE PERFORMANCE OF THE CHEMICAL BARRIER MUST BE A KEY ISSUE, ESPECIALLY IN THE DISPOSAL OF TRU WASTE WHICH CONTAINS LONG-LIFE RADIONUCLIDES. THES SORPTION PROPERTY OF THE CEMENT MATERIALS WOULD PLAY A VERY IMPORTANT ROLE. IN THE DISPOSAL ENVIRONMENT, THE CEMENT MATERIALS MUST BE ALTERED BY DISSOLUTION, HYDROTHERMAL REACTION, ETC. IF THE COMPOSITION AND CRYSTALLINITY OF MINERALS IN CEMENT ARE CHANGED, THE CHEMICAL PROPERTIES, ESPECIALLY THE SORPTION PROPERTY, MIGHT BE CHANGED. BUT THE ALTERATION PROCESS AND MECHANISM OF CEMENT HAVE NOT BEEN CLEARED YET. IN THIS REPORT, THE HYDROTHERMAL ALTERATION PROCESS WAS STUDIED EXPERIMENTALLY, AND ITS EFFECT ON THE SORPTION PROPERTY OF CEMENT WAS INVESTIGATED. THE RESULTS ARE THE FOLLOWING ;(1)OPC, BFS BLENDED CEMENT WAS HEATED INSYNTHETIC CEMENT EQUILIBRATED WATER AND DISTILLED WATER UP TO 70DEGREE. CHANGES IN THE CRYSTALLINITY OF THE MINERALS, FOR EXAMPLE, CSH-GEL, WERE OBSERVED. SOME MINERAL PHASES (EX.ETTRINGITE) DISAPPEARED BY HEATING. (2)IN THE SORPTION EXPERIMENT, THE DISTRIBUTION COEFFICIENT OF CEMENT DECREASED AS THE ALTERATION TEMPERATURE RAISED. THIS IS THOUGHT TO BECAUSED BY THE ALTERATION OF HYDRATED MINERALS, ESPECIALLY CSH-GEL, IN CEMENT. IN THE LONG-TERM ASSESSMENT OF THE CHEMICAL BARRIER PERFORMANCEOF CEMENT, THE CHANGE OF MINERAL PHASES IN CEMENT BY HYDROTHERMAL ALTERATION MUST BE CLEARED. MORE INVESTIGATION WILL BE REQUIRED BY SORPTIONTESTS WITH TRU ELEMENTS AND MODELING STUDIES.

報告者

キーワード