Abstract
In a conceptual UK geological disposal facility for nuclear waste within a high-strength, crystalline geology, a cement-based backfill material, known as Nirex Reference Vault Backfill (NRVB), will be used to provide a chemical barrier to radionuclide release. The NRVB is required to have specific properties to fulfil the operational requirements of the geological disposal facility (GDF); these are dependent on the chemical and physical properties of the cement constituent materials and also on the water content. With the passage of time, the raw materials eventually used to synthesise the backfill may not be the same as those used to formulate it. As such, there is a requirement to understand how NRVB performance may be affected by a change in raw material supply. In this paper, we present a review of the current knowledge of NRVB and results from a detailed characterisation of this material, comparing the differences in performance of the final product when different raw materials are used. Results showed that minor differences in the particle size, surface area and chemical composition of the raw material had an effect on the workability, compressive strength, the rate of hydration and the porosity, which may influence some of the design functions of NRVB. This study outlines the requirement to fully characterise cement backfill raw materials prior to use in a geological disposal facility and supports ongoing assessment of long-term post-closure safety.
Highlights
IntroductionIntermediate Level Waste (ILW) comprises a significant proportion, approximately 450 000 m3, of the UK's projected inventory of radioactive waste (Nuclear Decommissioning Authority, 2015)
Intermediate Level Waste (ILW) comprises a significant proportion, approximately 450 000 m3, of the UK's projected inventory of radioactive waste (Nuclear Decommissioning Authority, 2015). This includes waste arising from the reprocessing of spent nuclear fuel and from the operation, maintenance and decommissioning of nuclear facilities (Hicks et al, 2008). This waste is destined for final disposal in a Geological Disposal Facility (GDF) (Nuclear Decommissioning Authority, 2010a), where the conditioned waste packages will be placed in vaults excavated in host rock, deep underground (Nuclear Decommissioning Authority, 2010b)
Most of the results presented in the above summary were reported on the basis of unspecified testing methods and precursor materials, and little other detailed information is available about the cement hydration and microstructure of Nirex Reference Vault Backfill (NRVB)
Summary
Intermediate Level Waste (ILW) comprises a significant proportion, approximately 450 000 m3, of the UK's projected inventory of radioactive waste (Nuclear Decommissioning Authority, 2015) This includes waste arising from the reprocessing of spent nuclear fuel (e.g. spent fuel cladding) and from the operation, maintenance and decommissioning of nuclear facilities (e.g. sludges from the treatment of radioactive liquid effluents) (Hicks et al, 2008). In a conceptual scenario where a high-strength crystalline rock will host the facility, the vaults will be backfilled with a cement-based material to provide a physical and chemical barrier to radionuclide release (Nuclear Decommissioning Authority, 2010b) For this purpose, the Nirex Reference Vault Backfill (NRVB) has been considered (Francis et al., 1997). These include (Crossland and Vines, 2001; Nuclear Decommissioning Authority, 2010c; United Kingdom Nirex Limited, 2005):
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
