The Site Ion Exchange Effluent Plant has been stripping radioactivity out of the water leaving Britain’s most hazardous nuclear site since 1985. It was designed for twenty-five years of service. It has now run forty-one, and it is a single point of failure for the entire Sellafield decommissioning mission, which is why its replacement carries a P50 sanction of roughly £1.007 billion. The SIXEP Continuity Plant is going up immediately north of the original so the old plant keeps treating effluent until handover. As of August 2026 the building is about 75% complete and weatherproofed.
Project Scope
Replacement of the 1985 SIXEP plant, built immediately north of it, with the original staying in service until transfer.
Mitigates failure of SIXEP’s Sea Discharge Treatment Plant, adds waste storage capacity and allows alternative ion-exchange media to be deployed.
Roughly 5,000 cubic metres of concrete in the foundation campaign alone, complete February 2022.
Fourteen pump and valve modules at about 16 tonnes each, craned into place.
A 55-tonne gantry crane with a 21-metre span installed inside the building.
Designed to operate to at least 2060 in support of site decommissioning; active commissioning targeted 2029.
Why It Matters
Nuclear effluent treatment is the least visible and least forgiving work on a decommissioning site. Everything else at Sellafield — retrievals from the legacy ponds and silos, the reprocessing shutdown, the waste packaging — depends on there being a functioning route for contaminated water to leave. That dependency is what turns a treatment plant into a billion-pound programme.
The delivery model is the other reason to watch it. Sellafield runs this through its Programme and Project Partners alliance, with KBR as integration partner, Amentum and Jacobs on design, Morgan Sindall Infrastructure on civils and Altrad Babcock on process construction. It’s an integrated alliance rather than a prime contract, and the UK nuclear estate is treating it as the template for the next decade of major projects. Whether the 2029 commissioning date holds is the number that will settle that argument.
Project Team & Details
| Developer | Sellafield Ltd |
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| Owner / Client | Nuclear Decommissioning Authority / Sellafield Ltd |
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| Consultants | KBR (Integration Partner)
Amentum (Design Partner)
Jacobs (Design Partner)
Altrad Babcock (Process Construction) |
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| General Contractor | Morgan Sindall Infrastructure |
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| Major Subcontractors | Ansaldo Nuclear (Tie-in Connection Works) |
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| Status | Under Construction |
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| Delivery Method | IPD |
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| Funding Source | Public (Federal) |
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