An Investigation of Microbial Effect as Biofilm Formation on Radionuclide Migration
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An Investigation of Microbial Effect as Biofilm Formation on Radionuclide Migration H. Yoshikawa 1 , M. Kawakita2, K. Fujiwara2, T. Sato1, T.Asano2, and Y. Sasaki1 1 Japan Atomic Energy Agency, 4-33 Tokai-mura, Naka-gun, Ibaraki 319-1194, Japan 2 Chugai Technos Corporation, 9-12 Yokokawa-shinmachi, Nishi-ku, Hiroshima-shi, Hiroshima 733-0013, Japan ABSTRACT It is well discussed about biological effect to high-level radioactive waste (HLW) disposal and known that the biofilm is considered to be the uncertain factor to estimate for migration of radioactive elements. The objective of this research is to estimate the microbial effect of Cs migration in groundwater interacted with rock surface. Specially, we focus on Cs behavior at the rock surface surrounded by biofilm. The most important factor is the Cs sorption and diffusion to the microbe and/or their biofilm. Generation of bio-colloid absorbed with Cs and retardation of Cs by their matrix diffusion in rock will be influenced by these phenomena. We introduce about scenario analysis for biofilm and a simple Cs diffusion test with and without sulfur reducing bacteria (SRB) which is well known as easy to produce biofilm on the rock surface in order to clarify the existence effect of the bacteria at the rock surface. The Cs diffusion experiment, using Desulfovivrio desullfuricans as SRB, indicated that microbial effect was less to through their biofilm in the experimental condition. We consider that Cs is easy to contact the rock surface even if surrounded biofilm and not effect to retardation by matrix diffusion scenario. INTRODUCTION The various events including microbial effect are required to quantitatively assess to reduce the uncertainty of performance assessment (PA) for high-level radioactive waste disposal system. As one of the events, we interested in microbe behavior in deep groundwater or crack of base rock estimated as natural barrier system. The microbe will effect in groundwater chemistry, e.g. chemical components and/or redox condition, which is important for radionuclide migration. The radionuclide migration is considered to be retarded by interactions with the groundwater, minerals, and microbe present at the transport pathways in the matrix. When discussing radionuclide retardation by matrix diffusion, it is important not only to consider surface of the rock, but also phenomena such as formation of biofilm at the surface and the diffusion of the nuclide in the biofilm onto rock surfaces. The microbe usually attach to rock with some organic material like as extracellular polysaccharide (EPS) and they are defined as biofilm. The microbe will formed biofilm in following steps; (1)free microbe in groundwater contact to the surface of a rock and absorb on it in a monolayer, (2)the microbe grow up at the surface make their colonies, (3)generate EPS, increase their volume, and form biofilm, (4)some of the biofilm exfoliate from the surface to ground water flow as bio-colloid, and (5)the remaining biofilm
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decline and dead(Fig1).
Fig.1 Biofilm deve
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