The Introduction of Microbial Nutrients into A Nuclear Waste Disposal Vault during Excavation and Operation

Abstract

AECL has developed a concept for permanent geological disposal of used nuclear fuel waste in Canada. This concept would involve disposal of the waste in corrosionresistant metal containers, surrounded by compacted claybased buffer and backfill materials, in a vault 500-1000 m deep in granitic rock of the Canadian Shield. Such a vault would not be a sterile environment. Microbial activity would be expected in those areas of a vault where effects of heat, moisture content, and radiation would not exclude microbial life and where sufficient nutrients would be present. Although the granitic rock environment is naturally nutrient-poor, a substantial amount of nutrients could be introduced from residues of explosives used in the excavation of a vault. Using standard rock leaching techniques, measurements of the concentrations of such residues were made in excavated rock, tunnel walls and mine service-water supplies at AECL's Underground Research Laboratory. The effects of these residues on the bacterial population size in groundwater were also determined.Results showed that the largest potential nutrient addition (both N and C) to a vault would result from using untreated broken rock as part of the backfill. Nitrate in the residues could increase groundwater bacterial populations by several orders of magnitude.

Microbial corrosion of metallic materials in a deep nuclear-waste repository

“…Na nutnost přítomnosti organických nutrientů upozorňuje [29]. Jejich obsah se většinou sleduje pomocí TOC (total organic carbon) [43,44] a v úložišti pocházejí hlavně z bentonitu [45]. Přestože nutrienty zvyšují obsah bakterií na cca dvojnásobek [31], nejsou pro životnost bakterií nutnou podmínkou.…”

Review of Microbial Responses to Abiotic Environmental Factors in the Context of the Proposed Yucca Mountain Repository

“…For instance, explosives may be encountered as residue in a geological repository, depending on the mining techniques that are used. Stroes-Gascoyne et al (1996a) and Stroes-Gascoyne and Gascoyne (1998) determined the potential introduction of large amounts of easily usable nutrients into a Canadian nuclear fuel waste repository in granite as a result of excavation with explosives (ammonium nitrate and diesel fuel). Large amounts were mainly associated with the excavated rock, and leachates from this rubble enhanced bacterial population by as much as two orders of magnitude.…”

Identification of Groundwater Nitrate Contamination from Explosives Used in Road Construction: Isotopic, Chemical, and Hydrologic Evidence

“…Fragmentation of bedrock with explosives for construction and mining projects is a potential source of nitrate (NO 3 – ) contamination of groundwater. − Hundreds to tens of thousands of kg of NO 3 – are typically used at a construction site. Nitrate is a component of ammonium nitrate (NH 4 NO 3 ), which is approximately 90% of commonly used commercial explosives by weight .…”

“…High NO 3 – concentrations in groundwater affected by explosives could be related to several different processes, including (1) leaching of NO 3 – from unexploded NO 3 – -bearing explosive compounds such as NH 4 NO 3 ; (2) oxidation (nitrification) of reduced N components of explosives such as NH 4 NO 3 , TNT, RDX, etc. ; and (3) injection of soluble NH 3 or NO x gases into the subsurface by blasting . The mass of explosive N remaining in the ground after blasting is unknown; estimates suggest that up to 6% of ANFO slurry may escape detonation, , which could be a substantial contribution to groundwater recharge locally.…”