Quintessa Presents Modelling of Borehole and Shaft Seals at the International DOPAS 2016 Seminar, Turku, Finland

Richard Metcalfe participated in the final meeting of the EC-supported project “Full-Scale Demonstration Of Plugs And Seals” (DOPAS), which was organised by a Posiva-led consortium in Turku, Finland from the 24th-27th May 2016. The meeting was attended by about 130 people who represented around 50 organisations from 15 countries, including many radioactive waste management organisations.

The conference provided a forum at which the DOPAS partners could present their results to an audience from beyond the project consortium, and at the same time allow contributors from outside the consortium to share outputs from other projects and other sectors. Quintessa belonged to the latter group and contributed the following presentations:

  • Towards robust models of well seals and plugs in CO2 storage sites, which concerned Quintessa’s modelling of cement evolution in well plugs and seals within CO2 storage sites (authored by Richard Metcalfe, James Wilson and Steven Benbow of Quintessa); and
  • Reactive transport modelling of bentonite shaft seals under hyper-saline conditions, which concerned Quintessa’s modelling of bentonite-quartz sealing components in the shaft seal for the Deep Geologic Repository (DGR) for LLW/ILW being proposed by OPG for development at Bruce in Ontario, Canada (authored by James Wilson, Steven Benbow and Richard Metcalfe of Quintessa, and Helen Leung of NWMO).
Volume Fraction vs Distance from centre of shaftEach of these presentations illustrated novel coupled modelling approaches using Quintessa’s QPAC software in conjunction with the Pitzer approach for calculating aqueous activity coefficients. Both presentations showed how water / seal interactions under the modelled conditions are likely to result in sealing of porosity over time and would not compromise sealing function. Example outputs from the DGR shaft seal models are shown above and show a marked decrease in porosity of the sealing material near the interface with the host shale, which contains hyper-saline porewater.

In addition, Nick Jefferies of Amec Foster Wheeler presented work on borehole seals for RWM, to which Quintessa is contributing. A presentation by Steve Reece of Tellus concerning the Chandler salt mine project in Australia included draft results from the post-closure risk assessment that Quintessa is currently undertaking.

DOPAS was coordinated by Posiva and has been undertaken by 14 nuclear waste management organisations, research institutes and consultancies from 8 European countries. The aim of DOPAS was to test plugging and sealing systems for underground radioactive waste repositories by means of 4 full-scale demonstrations, plus associated laboratory experiments, and performance assessment studies.  The four in-situ demonstrations were the:

  • Posiva Plug (POPLU) underground test in the ONKALO URL, Finland;
  • Dome Plug (DOMPLU) underground test in the Aspo URL, Sweden;
  • Experimental Pressure and Sealing Plug (EPSP) experiment in the Josef Mine, Czech Republic; and
  • Full-Scale Seal (FSS) experiment, which involved a full-scale mock-up, constructed in a surface facility, of a tunnel in ANDRA's proposed Cigeo repository.

In addition, DBE TEC and GRS, together with  the  Technical  University  of Freiberg and associated partners contributed outputs from the German ELSA project. This is a programme of laboratory and in-situ experiments that aims at further developing the reference shaft seal for the German disposal concept for a repository in rock salt and at developing reference shaft seals for a repository in clay host rocks.