An Evaluation of Hydrogen Evolution from Corrosion of Carbon Steel in Low/Intermediate Level Waste Repositories
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AN EVALUATION OF HYDROGEN EVOLUTION FROM CORROSION OF CARBON STEEL IN LOW/INTERMEDIATE LEVEL WASTE REPOSITORIES FUMIO MATSUDA*, RYUTARO WADA*, KAZUO FUJIWARA**, AND Al FUJIWARA*** * Kobe Steel Ltd., 2-8, 4-Chome, Iwaya-Nakamachi, Nada-ku, Kobe, **
*
657, Japan. Kobelco Research Institute Inc., 2-8, 1-Chome, Wakinohama-cho, Chuo-ku, Kobe, 651, Japan. Radioactive Waste Management Center.,2-8-10, Toranomon, Uinato-ku, Tokyo, 105, Japan.
ABSTRACT As a sequence of studies to evaluate the quantity of gas evolution from low/intermediate level waste repositories,hydrogen gas evoluted from corrosion of carbon steel in simulated repository environment was evaluated by laboratory experiments. The experimental results on the hydrogen gas evolution both in air purging condition simulated oxidizing environment and nitrogen purging condition simulated reducing environment, are summarized as follows. (1)Hydrogen gas evolution enough to analyze quantitavely by gas chromatography (>5ppm) has been recognized under almost all test conditions except reducing equilibrium cement water. (2)Effects
of purging gas (airnitrogen) on the hydrogen gas evolution
and the corrosion rate calculated from weight loss were air purge > nitrogen purge. On the other hand, the contribution ratio of hydrogen evolution reaction in corrosion rate was nitrogen purge > air purge. (3)Effects of test solution on the hydrogen evolution rate were as follows. * Air Purge Equilibrium Bentonite Water z Equilibrium Cement Water > Synthetic Sea Water * N2 Purge Synthetic Sea Water > Equilibrium Bentonite Water >> Equilibrium Cement Water (4)No distinct effect of crevice geometry of test specimen on hydrogen evolution rate was recognized. Only under the reducing equilibrium cement water, however, the increase of hydrogen evolution was confirmed after the immersion of several hundred hours. (5)Hydrogen evolution rates tended to decrease with testing time except in the reducing equilibrium cement water. (6)No distinct difference of hydrogen evolution rate between steels (SPHC, SPCC) was observed.
Mat. Res. Soc. Symp. Proc. Vol. 353 0 1995 Materials Research Society
720
INTRODUCTION Gas generation from the waste itself and other components of the nearfield of a repository is assumed to be an important issue in the design and safety analysis of deep repositories, especially for the case of low/ intermediate level wastesEl]. It has been shown that in this type of waste the corrosion of metals, particularly of iron and steel (such as drums and rebars), will be the dominant gas generation mechanism even for general corrosion rates between 1 and O.1gm/year. The gas generation rate in this case will be such that the other near field components (backfill,cement covering) have to be specially designed to ensure that this gas can leave
the near-field before an appreciable gas pressure build-up[2]. This study intended to evaluate the hydrogen gas evolution rate caused by the corrosion of carbon steel in simulated repository environments.
EXPERIMENTAL PROCEDURES Test Speci
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