報告書番号

N07039

タイトル（和文）

地下水年代測定評価技術の開発(その9) －溶存有機物を用いた14C地下水年代測定方法の開発-

タイトル（英文）

Research and development on groundwater dating No.9 -Deveropment on groundwater dating with dissolved organic radiocarbon-

概要 （図表や脚注は「報告書全文」に掲載しております）

JAEA瑞浪において，地下水に溶存する有機物の一種であるフルボ酸に含まれるC-14を用いて地下水年代測定を行った。その結果，同時に採取した溶存Heによる年代測定結果と近い年代値を得ることができた。一方，今後検討すべき課題を抽出することができた。現状のフルボ酸採取方法ではトン単位の地下水を揚水する必要があること，地下水にトレーサー物質として蛍光染料が含まれている場合に，フルボ酸の採取ができなくなること，デッドカーボンの混入量評価を行う必要があることである。

概要 （英文）

Groundwater dating is important technique for assessing the safety disposal of high level radioactive waste. In this paper, the authors applied the groundwater radiocarbon dating with fulvic acid in the granitic rocks area at the Tono study site, central Japan, and the problems under conducting the groundwater dating using the fulvic acid are pointed out.
The results of radiocarbon groundwater dating by fulvic acid indicated plausible ages compare to groundwater-dissolved helium gas ages sampled at the same time. However, more investigations were needed to elucidate the dating results: initial 14C concentration of fulvic acid has to be investigated in the recharge area, and the affect of mixing the sedimentary organic matter on fulvic acid age have to be evaluated.
The other problems are in the collecting method to obtain humic acids and fulvic acids. The humic acids and fulvic acids were obtained by passing the acidified groundwaters (pH~2) using hydrochloric acid through the supelite DAX-8 resin stuffed column. To obtain a few mg of fulvic acid, over the tons of groundwater was needed. Especially, in the case of humic acid, although passing over 10 ton of groundwater through the column, only a few mg or less was obtained. The organic carbons from collecting device, groundwater lifting pump and hoses, and instruments on purification process might be contaminated to the fulvic acid. The authors could evaluate the high concentrations of 14C were not contaminated but the contamination of dead carbons could not evaluate. The evaluation methods have to be developed. Some groundwater contained residual fluorescence agent (uranin) which was added to the drilling fluid when the well was bored. The uranin was adsorbed on DAX-8 and collected together with humic and fulvic acid. The collecting method have to be altered for collecting the humic and fulvic acid effectively and avoiding the fluorescence agent.

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