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Hunterston 'A' Nuclear Power

The client:Magnox
Services:Cut-off/barrier wall, nuclear waste segregation, stabilisation/encapsulation.

The Challenge:

An historic leaking active effluent drain on the site resulted in a sub-surface plume of radiological contamination. Also running through the area was a network of land drains that essentially acted as a pathway for mobilising Caesium137 contamination to the foreshore. Cognition designed a containment system comprising a barrier wall keyed into the natural clay beneath the site and capped with stabilised site-won material to reduce permeability and prevent surface water ingress into the contaminated plume area.

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The Approach

Cognition was contracted by Magnox to remediate the contaminated area between the Hunterston ‘A’ and ‘B’ stations, known as the Catch-pit 7 (CP7) compound. Due to the radioactive nature of the site, the level of precision required during excavation and remediation was crucial. The key elements of these works included:

  • Specialist training and inductions for site team;
  • Excavation, slurry wall and capping installation;
  • Excavation, testing and removal of 2000m3 of overburden soil;
  • Testing and disposal of Very Low Level Waste;
  • Design and testing of a slurry and capping material to meet the permeability and unconfined compressive strength specification;
  • Mixing of slurry using a modular slurry plant;
  • Frequent testing of slurry as part of high level of quality assurance programme;
  • Installation of a 1m wide, 311m long slurry wall around the contaminated effluent pipe and soil;
  • Excavation of the wall using specialist monitoring equipment (GEM and HIRAM) to test and segregate each excavator bucket of soil and reduce disposal;
  • Use of site won screened material to save costs and meet sustainability targets;
  • Cement stabilised cap installed across remediation area;
  • Radiological and geotechnical testing as part of verification process.

The Outcome

The slurry wall and cap was installed successfully and fully compliant with the Client’s tight design specification and delivering a highly sustainable and robust solution.  The project demonstrated Cognition’s ability to meet very high standards expected within the nuclear industry. Cognition has since been awarded three further remediation    projects for the nuclear industry in the UK.

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