Interactions between Simulant Vitrified Nuclear Wastes and high pH solutions: A Natural Analogue Approach
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Interactions between Simulant Vitrified Nuclear Wastes and high pH solutions: A Natural Analogue Approach Colleen Mann1, Clare Thorpe1, Antoni E. Milodowski2, Lorraine P. Field2, Richard P. Shaw2, Luke Boast1, Russell Hand1, Neil C. Hyatt1, John L. Provis1 and Claire L.Corkhill1 1
NucleUS Immobilisation Science Laboratory, Department of Materials Science and Engineering, The University of Sheffield, Mappin Street, Sheffield S1 3JD, UK 2 British Geological Survey, Environmental Science Centre, Nicker Hill, Keyworth, Nottingham, NG12 5GG, UK ABSTRACT This study details the characterization of a glass sample exposed to hyperalkaline water and calcium-rich sediment for an extended time period (estimated as 2 - 70 years) at a lime (CaO) waste site in the UK. We introduce this site, known as Peak Dale, in reference to its use as a natural analogue for nuclear waste glass dissolution in the high pH environment of a cementitious engineered barrier of a geological disposal facility. In particular, a preliminary assessment of alteration layer chemistry and morphology is described and the initiation of a longterm durability assessment is outlined. INTRODUCTION Owing to a long history of encapsulation of radioactive wastes in cementitious materials, the proposed geological disposal facility (GDF) of the UK will most likely incorporate a significant volume of cement. In addition to 450,000 m3 of cement-encapsulated waste [1], the facility may also use a cementitious backfill as part of the engineered barrier, which will be optimised to physically and chemically impede the transport of radionuclides to the biosphere [2]. Over geological time scales, groundwater will interact with the cementitious components of the facility resulting in high pH conditions in the repository [3]. Should vitrified intermediate level waste be placed in this environment, an understanding of the effect of cement leachates on the longevity of glass is required. We describe a new natural analogue site for long-term glass durability assessment in high pH, cement-like leachates, including a preliminary assessment of the physical and chemical conditions and their effects on glass samples recovered from the site. METHODOLGY Site and sample description The Peak Dale Tunnel site is a disused railway tunnel, constructed in the early 20th century, to link the Peak Dale limestone quarry to its associated limekilns. The waste produced from the limekilns is distributed in a thick layer (1 – 2 m) of lime (CaO) over the soil and bedrock of the surrounding area [4]. This has seeped through to the tunnel below, creating a naturally hyperalkaline ground water and Ca-rich sediment. Access to the tunnel was restricted to the
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public when a locked gate barred the entrance. A number of glass bottles were found to be exposed to these high pH co
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