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

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II3.8.1

A Study on the Chemical Forms and Migration Behavior of Carbon-14 Leached from the Simulated Hull Waste in the Underground condition Satoru Kaneko*, Hiromi Tanabe*, Michitaka Sasoh**, Ryota Takahashi**, Takayuki Shibano**, Shinji Tateyama** *Radioactive Waste Management Funding and Research Center, 2-8-10 Toranomon Minato-ku, Tokyo 204-0001, JAPAN **Toshiba Corporation, 4-1 Ukishima-cho Kawasaki-ku, Kawasaki, 210, JAPAN 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, Fe3C, 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 Fe3C). 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]. INTRODUCTION

In the performance assessment of transuranic (TRU) waste disposal, from the Nuclear Fuel Reprocessing Facility, carbon-14 (C-14) in the hull (zircaloy cladding waste) and end pieces has been so far estimated to considerably contribute to the radiation exposure to the public[2]. In this performance assessment, however, the estimation is based on the fairly conservatively

II3.8.2

selected parameters for C-14, since the chemical forms of C-14 leaching from the hull are unknown[3]. For the performance assessment to be more realistic, the chemical forms of C-14 leaching from the hull should be identified. For example, the distribution coefficients of C-14 for barrier materials, example cement, bentonite and so on, would be low, if the form of C-14 is mainly organic. Thus, 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. To support the discussion for the speciat