SIXEP CONTINUITY PLANT

Infrastructure and Construction

Record date: 31 March 2026

Whole-life cost: £1.1bn
Published schedule: 25/05/2013 – 21/10/2031
NISTA delivery confidence: Not disclosed
Senior responsible owner: Jeremy Hunt

What the project is for

The SCP project will design, construct, inactively commission and handover a new radioactive effluent treatment facility, which is a mission critical requirement for Sellafield. Without this facility critical work at Sellafield would cease, most importantly the retrieval of legacy high hazard materials. Through spent nuclear fuel and waste management operations Sellafield site produces liquid effluent which requires treatment to remove radioactivity before discharge into the sea. This capability is currently delivered by the Site Ion Exchange Effluent Plant (SIXEP). The continued availability of effluent treatment via SIXEP is a regulatory compliance requirement and is essential for delivery of the site missions including high hazard and risk reduction activities (HHRR), underpinning the Government’s UK Discharge Strategy and OSPAR commitments. Continued effluent treatment through SIXEP (or SCP when available) is fundamental to the NDA Mission to “deliver safe, sustainable and publicly acceptable solutions to the challenge of nuclear clean-up and waste management.”

Departmental delivery commentary

Compared to financial year 24/25 Q4, the NISTA/SRO Delivery Confidence Assessment (DCA) rating at 25/26 Q4 remained at GREEN. This is primarily due to the following factors: The Project is currently in the execution stage, being delivered by the Programme and Project Partnership (PPP,) and is showing no significant threat to the overall P80 schedule which was also supported by the annual NISTA Gate 0 review undertaken in July 2025 which gave a GREEN Delivery Confidence Assessment, noting that delivery of the project “within the P80 schedule was assessed as highly likely."

Schedule

Compared to financial year 24/25-Q4, the project's end-date at 25/26-Q4 has increased from 23-Jan-2031 to 21-Oct-2031. This is primarily due to the following factor: Change in legislation relating to Passive Fire Protection Standards; the new requirements are more onerous than the original design specification. Due to the required design updates a number of critical path scope packages have been impacted and subsequently the project completion date has been delayed, which remains within the P80 schedule.

Cost

The increase to the project's departmentally agreed Whole Life Cost at 25/26-Q4 is primarily due to: Annual Indexation, in line with the agreed indices, and the impact of the agreed contractual adjustment event for Passive Fire Protection legislative change.

Benefits

Compared to financial year 24/25-Q4, the project's departmentally agreed Benefits at 25/26-Q4 (measured in £m) remained 0. This is primarily due to the following factors: There are no monetised benefits within the SCP project however, it will provide key capabilities which in enables the following benefits: • Allows the Site Licence owner to meet its requirements in the regulatory permit. • Provides effluent abatement to 2060 in support of site missions. • Provides an opportunity to deploy an Alternative Ion Exchange (IX) media that improves abatement performance, following the consideration of best available technique (BAT). • Maintaining unconstrained Site Ion Exchange Effluent Plant (SIXEP) waste material storage capacity.