Radiation Resistance of the Natural Microbial Population in Buffer Materials
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RADIATION RESISTANCE OF THE NATURAL MICROBIAL POPULATION IN BUFFER MATERIALS
S. Stroes-Gascoyne, L.M. Lucht, J. Borsa, T.L. Delaney, S.A. Haveman and AECL Research, Whiteshell Laboratories, Pinava, Manitoba, C.J. Hamon. Canada ROE ILO. ABSTRACT The radiation sensitivity of naturally occurring microorganisms in buffer materials was investigated as well as the sensitivity of Bacillus subtilis The D1 0 values spores and Acinetobacter radioresistens in a buffer matrix. obtained in our radiation experiments varied from 0.34 to 1.68 kGy and it was calculated that the surface of a nuclear fuel waste container would be sterilized in 9 to 33 d after emplacement, depending on the type of This suggests that formation of container, and the initial bioburden. biofilms and microbially influenced corrosion would not be of concern for The results also indicated that sterilization some time after emplacement. throughout a 25 cm thick buffer layer is unlikely and that repopulation of the container surface after some time is a possibility, depending on the mobility of microbes in compacted buffer material. INTRODUCTION AECL Research is developing a concept for the permanent disposal of nuclear fuel waste in an engineered vault 500 to 1000 m deep in plutonic The concept is based on a multi-barrier rock of the Canadian Shield [1]. The fuel waste, isolated in corrosion-resistant (ASTM Grade-2 system. titanium (Ti) or oxygen-free copper (Cu)) containers, would be emplaced in boreholes drilled in the floor of disposal rooms, or would be directly The containers would be surrounded by a emplaced in disposal rooms. compacted buffer material (50 vt.Z sodium bentonite and 50 wt.Z silica sand) that would swell on saturation with groundwater and ensure that transport of After waste contaminants from the containers was limited to diffusion.
emplacement, the vault would be backfilled with a mixture of 75 vt.Z crushed A disposal vault and graded host rock and 25 wt.% glacial lake clay [2]. would not be a sterile environment and microbial effects could potentially One of the concerns is that occur at many locations in such a vault [31. microbially influenced corrosion (MIC) may affect the integrity of the MIC of metals is either a direct reaction containers that hold the waste. in which microbes use the metal as an energy source, or an indirect process, in which microbes change the environmental conditions such that chemical and electrochemical corrosion processes are induced or enhanced. Of the commonly used engineering metals and alloys, Ti and its alloys are the only ones for which microbtally influenced corrosion has not been Titanium exists in aqueous solutions almost exclusively reported [4,5,6]. In the +4 oxidation state and its ions have a closed-shell configuration, which makes Ti unavailable for biologically supported redox chemistry and coordination reactions [7]. Titanium is not biotoxic and permits the growth of biofilms. that are known to act as crevice formers on other metals [4,8]. The possibility that microbial activity in the for
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