Lessons Learned from the Development of Cementitious Grouts for Deep Borehole Disposal Applications

A Review of Potential Cementing Systems for Sealing and Support Matrices in Deep Borehole Disposal of Radioactive Waste

“…The radiation durability of an oil well cement system is likely to be high in this DBD application in the short-term [102]; a typical surface radiation dose rate expected from containers of vitrified UK HLW is an order of magnitude less than that used during the radiation durability testing of the UK ILW encapsulation grouts where no significant detriment to composition or microstructure was observed over a 2-year period.…”

“…Significant differences are likely to exist between cementing a hydrocarbon or geothermal well and deploying or placing a DBD grout [102]. In the former, the grout is pumped down through a tube in the centre of the well, returning to the surface up the annulus outside the casing.…”

“…When the points in Sections 2 and 4 are considered and following discussions with well operators, a generic formulation based on API Class G cement has been selected. The Sheffield DBD Research Group has recently demonstrated that Portland cement-based systems show great potential to perform as required under the conditions likely to be experienced in DBD [17,18,102]. However, their performance as sealing matrices still needs to be assessed.…”

Deep borehole disposal grouts – are inorganic retarders appropriate?

“…Both elevated temperature and pressure accelerate cement hydration reactions, reducing the time for the grout to thicken and set (Bensted, 2008;Collier et al, 2017a;Jupe et al, 2008;Nelson and Guillot, 2006;Scherer et al, 2010;Shariar and Nehdi, 2014;Taylor, 1997;Zhang et al, 2010), with temperature having greatest influence (Jupe et al, 2008;Nelson and Guillot, 2006;Scherer et al, 2010). Temperature also has a greater effect on the main cement hydrate phases formed (Collier et al, 2017a;Nelson and Guillot, 2006;Taylor, 1997) along with the calcium/silicon ratio. The limit of pumpability in well cementing grouts is considered to be the maximum consistency at which a grout can be pumped, and is reported to be 70 Bc (Bearden units) (Nelson and Guillot, 2006).…”

“…However, organics may complex radionuclides and adversely influence solubility, so their use in both radioactive waste immobilisation and in mined repositories is discouraged. This influence is less important in DBD because (a) any radionuclide releases are only likely many years after borehole sealing and the geological barrier re-established and (b) the elevated temperature and pressure and high pH of the cement grout will quickly decompose organic compounds (Collier et al, 2017a;Glasser, 1992Glasser, , 1993. However, to address concerns about any possible impact of organic compounds, inorganic retarders are being investigated.…”