Abstract
Cementitious grouts are being developed for use as sealing and support matrices (SSMs) in deep borehole disposal (DBD) where temperatures do not exceed 190 °C. They will seal radioactive waste containers into the bottom 2 km of holes drilled up to 5 km deep into the crystalline basement. The temperature and pressure is likely to be similar to those in hydrocarbon and geothermal energy wells, where grout placement and durability are affected. This paper reviews the potential cementing systems suitable for this application and explains why a single solution of a formulation of Class G oil well cement, silica flour, water, fluid loss additive, and retarding admixture has been selected. This type of formulation has been used extensively for over 100 years in well cementing. It should provide the short-term performance and durability required for an SSM, maintaining the seal around the waste packages within the disposal zone long after the boreholes are sealed back to the surface, and thus augmenting the safety case for DBD.
Highlights
Deep borehole disposal (DBD) of high-level radioactive waste (HLW, including spent nuclear fuel) is seen as a viable alternative to the use of mined repositories located only a few hundreds of meters deep [1,2,3,4,5,6,7]
Borehole will be very similar to those encountered in hydrocarbon and geothermal energy wells, suggesting that cement grouts that perform satisfactorily in those situations should be appropriate for deep borehole disposal (DBD) applications
Cementitious grouts based on Class G oil well cement have been shown to be suitable for providing low temperature sealing and support matrices (SSMs) for deep borehole disposal (DBD) applications
Summary
Deep borehole disposal (DBD) of high-level radioactive waste (HLW, including spent nuclear fuel) is seen as a viable alternative to the use of mined repositories located only a few hundreds of meters deep [1,2,3,4,5,6,7]. The DBD Research Group at The University of Sheffield in the UK has been pioneering the development of DBD for more than 25 years ([8] and references therein) It is envisaged waste packages will be placed and sealed into the bottom of a 5 km deep borehole drilled into basement granitic rock (called the disposal zone) [4,9,10,11,12]. A key component of the Sheffield DBD concept is the use of a sealing and supporting matrix (SSM) in the disposal zone which provides two principal functions, both of which will augment the DBD safety case:. The details and justification for the selection of a Portland cement system are explained
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