Microbial Considerations and Studies in the Canadian Nuclear Fuel Waste Management Program
- PDF / 604,043 Bytes
- 8 Pages / 414.72 x 648 pts Page_size
- 16 Downloads / 178 Views
MICROBIAL CONSIDERATIONS AND STUDIES IN THE CANADIAN NUCLEAR FUEL WASTE MANAGEMENT PROGRAM
S. Stroes-Gascoyne and J.M. West*. AECL Research, Whiteshell Laboratories, Pinawa, Manitoba, Canada. *British Geological Survey, Keyworth, Nottingham, UK.
ABSTRACT AECL Research is developing a concept for the permanent disposal of nuclear fuel waste. A program to address the potential effects of microbial action on the integrity of the multiple barrier system, on which the disposal concept is based has been initiated. This microbial program focusses on answering specific questions in areas such as the survival and growth of microbes in compacted clay buffer materials and the potential consequences for container corrosion and microbial gas production; microbial effects on transport of radionuclides through the buffer into the geosphere; the presence and activity of microbes in deep granitic groundwaters; and the effects of biofilms on radionuclide migration in the geosphere. INTRODUCTION AECL Research is developing a concept for the permanent disposal of nuclear fuel waste in plutonic rock of the Canadian Shield [1]. The concept involves the disposal of nuclear fuel waste in an engineered excavation (vault), at a depth of 500 to 1000 m in plutonic rock. The disposal vault would consist of arrays of rooms, connected by access tunnels for transportation of the excavated rock, waste containers and backfill materials. Fuel wastes would be isolated in corrosion-resistant
metal
containers
(ASTM
Grade-2
titanium is
the reference material;
copper
is another option in the concept). The reference scenario is emplacement in boreholes drilled in the floor of the disposal rooms [2]. Another option in the concept is emplacement of the containers in the rooms [3]. A minimum container-design lifetime of 500 a has been specified in the reference disposal system to ensure isolation of the fuel waste during the period of high fission-product activity. The containers would be surrounded by a compacted buffer material (50 wt.% sodium bentonite and 50 wt.% silica sand) that would swell on saturation with groundwater and ensure that transport of contaminants from the containers was controlled by diffusion. A 5-cm thick compacted pure sand layer would separate the containers from the compacted buffer material. After the waste emplacement, the rooms would be backfilled with a mixture of 75 wt.% crushed and graded host rock and 25 wt.Z glacial lake clay. On completion of the vault operations (-70 a) the remaining volume, including all the shafts and exploratory boreholes, would be backfilled and sealed. Once the facility is sealed, no further actions would be required to ensure adequate isolation of the waste [4]. The awareness that microbial activity could potentially affect the performance of a system for the geological disposal of radioactive waste occurred in the late 1970's and as a result, many countries considering radioactive waste disposal have developed or are in the process of developing programs to study and quantify microbial ef
Data Loading...
