A Study on the Chemical Forms and Migration Behavior of Carbon-14 Leached from the Simulated Hull Waste in the Underground condition

Abstract

The chemical forms of carbon leaching from carbon-containing Zr and Fe-based metallic materials have been investigated to improve the estimation of the contribution of C-14 in the performance assessment of TRU waste disposal. Both organic and inorganic carbons were identified in the leached solution with carbon containing zirconium and steel, and the concentrations of total carbon (organic plus inorganic) in the leached solutions increased with time. The carbon concentrations in the leached solution for both metallic samples were higher at higher pH. With High Performance Liquid Chromatography (HPLC), organic carbons were identified to be low-molecular weight alcohols, carboxylic acids and aldehydes.To explore the chemical state of carbon in the matrix materials, the leaching experiments were carried out also for ZrC, Fe 3 C, the powder mixtures of carbon and zirconium, and of carbon and iron. The low-molecular weight organic carbons were detected only in the case of carbides (ZrC and Fe 3 C). The chemical forms of carbon in the zirconium alloy were suggested to be carbide or carbon by H.D.Smith [1]. The present result suggests that the chemical forms of carbon in zirconium or iron are mainly in the form of carbide.In the interest of performance assessment, the distribution coefficients of the organic carbon species identified in the leached solution for cement were obtained. As expected, some of them were shown to be larger than the values assumed in the performance assessment of Progress Report on Disposal Concept for TRU Waste in Japan [2].

Partitioning of14C into Solid, Liquid, and Gas Phases in Various Paddy Soils in Japan

“…The mean value was about 10 times higher than that of the previous report. 2) Experimental conditions between the present study and the previous study were quite different. For example, cement materials were used as a solid phase sorbent in the previous study, and these solid materials were in contact with alkaline water (pH 12.5) under anoxic conditions for 100 days.…”

“…These wastes contain significant amounts of 14 C. 1) Recently, the possibility of leaching of organic carbon compounds from simulated hull wastes has been reported, and carboxylic acids such as formic acid and acetic acid were identified as dominant forms among the radioactive organic carbon compounds. 2) Because there is little information regarding reliable migration and realistic transport models for such organic 14 C, the possible migration of organic 14 C from a TRU repository site to the biosphere through groundwater presents some concern. Therefore, it is necessary to understand the behavior of 14 C in the human habitation sphere on the assumption that the 14 C derived from TRU wastes migrates to the biosphere.…”

“…As an organic 14 C form, [1, 2-14 C] sodium acetate was used because acetic acid is one of the dominant chemical species in TRU waste. 2) Since a repository site in Japan for TRU waste has not been selected yet, paddy soils for this study were collected throughout the country, and the ranges of each partitioning ratio (solid, liquid, and gas phases) in paddy fields were determined. The relationships among the partitioning ratios and selected soil properties were also discussed.…”

Environmental Transfer of Carbon-14 in Japanese Paddy Fields

“…Our value, however, was higher than expected from the chemical form of 14 CH 3 14 COO À . For example, Kaneko et al [1] obtained the K d value of 9.5 ml g À1 for the sorption test of acetic acid using cement materials. The reason for our high K d value is explained next.…”

“…Group two waste includes hull and end piece wastes with relatively high amounts of 14 C, and leaching of low molecular weight 14 C organic materials from simulated hull wastes has been reported [1]. The 14 C organic materials have very few sorption properties to clay and rock, and 14 C has a relatively long half-life of 5,730 years.…”