Microbial impacts on gas production in LLW/ILW

Gas production from low- and intermediate-level nuclear waste (LLW/ILW) is important to the safety of near surface and deep geological nuclear waste repositories in two main aspects. First, gaseous radionuclides such as 14C may be released from LLW/ILW and transported in the gas phase to the biosphere. Second, gas generation can lead to pressurization and gas-phase formation, which can affect the engineered barrier system, water flow, and hence the transport of radionuclides and other contaminants in groundwater. Gases may be generated from LLW/ILW by anaerobic corrosion of metals, generating hydrogen and in some higher activity wastes (ILW) by radiolysis of organic materials and water, which can generate a range of gaseous species of which hydrogen is again considered the most significant. Microbial processes are of principal importance in the generation of methane from cellulose-containing wastes, but also have other effects on gas production, such as by consuming hydrogen generated by corrosion and radiolysis. In this chapter, the complex role that microbes play in mediating and affecting gas generation from cellulose-containing LLW/ILW is discussed based around understanding gained from a long-term study of
gas generation from LLW arising from the nuclear power plants at Okiluoto, Finland.