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Harwell, LETP
The Challenge:
The Liquid Effluent Treatment Plant (LETP) served 14 nuclear reactors from the main Harwell site. All reactors are no longer in service with all but three successfully decommissioned. The site is contaminated with a mix of low and very low level radioactive material as a result of processing and handling of radioactive effluent. In order to delicence the site Magnox contracted Cognition to demolish, segregate and assay the waste in order that it could be safely consigned to licenced nuclear waste facilities. The objective was to remove all structures and made ground and return the land back to its former natural state, where future development would then be permittable.
The Approach
Cognition was contracted by Magnox to remove all slabs and below ground structures, including tanks, drains, catch pits, pipework and interceptors associated with the treatment works and previous land use. The key elements of the works included;
- Division of site into zones, each with a unique radionuclide fingerprint;
- Carry out site characterisation and investigation works;
- All structures and contaminated made ground were broken up, excavated and bagged into 0.9m2 bulk bags, using telehandler mounted hoppers;
- Demolition of above and below ground structures using 360 excavators with pulverisers, breakers and shear attachments;
- Robust dust suppression techniques to mitigate any potential airborne alpha particles and minimise dust nuisance for operatives;
- Segregation of materials into material types, such as concrete, subsoil, metal etc. in order to help with the assay operation and waste disposal;
- Background air monitoring using static air samplers (SAS);
- Each bag is assayed using High Resolution Gamma Spectrometry (HRGS) to determine whether the material is either Out of Scope (OOS) thereby below Very Low Level Waste (VLLW) levels or In scope either VLLW or Low Level Waste (LLW);
- Inscope material is kept inside a separate storage facility and repackaged for disposal to nuclear licenced disposal facilities.
The Outcome
Cognition is successfully remediating the Harwell site with strict H&S and environmental controls in place; Health Physics supervisors ensure that there is no risk to operatives whilst dismantling and removal of materials and concrete containing very low levels of radiation. The assay work helps to segregate waste streams to ensure that only radiologically contaminated material is taken to nuclear waste facilities. The project is the largest nuclear decommissioning and delicencing project in the UK and has attracted global interest. Upon complete removal of the LETP structures the site will be validated to ensure there is no residual radiological contamination and successfully delicence the site for redevelopment.
