Corus unit in risk reduction project at Sellafield nuclear plant

Sheffield, UK - Corus Process Engineering (CPE), part of Corus Northern Engineering Services (CNES), has completed sealing and deployment trials for Sellafield Ltd on two sludge and effluent lines. The project is to eliminate any potential fault scenarios on the plant and reduce operator dose uptake during implementation - as the effluent tank pipes no longer have to be drained of radioactive sludge before the sealing mechanism is deployed.

According to CPE, special sealing and deployment techniques deployed on the sludge and effluent lines will also accelerate the nuclear plant’s Effluent Tank remediation programme and deliver cost savings.

In April 2006, Sellafield commissioned CPE to provide a sealing solution for its two-off sludge and effluent (RESPS) lines, which connect the Magnox storage pond to the effluent tank. Due to the potential risk of a hydraulic ‘link’ between the two plants, the isolation or sealing of these lines is critical in order to enable the early start of the sludge and effluent removal from the Magnox Storage pond. The scope of work was to develop and demonstrate a method of sealing the RESPS lines, which are located approximately seven metres underwater, within the Effluent Tank Sludge Sump and four metres underwater within the Effluent Tank Inlet Chamber.

Sellafield and CPE used knowledge gained from a previous collaboration on the Magnox Pond RESPS project in early 2006, which involved the development of various grout and resin sealing techniques for other RESPS pipelines. After numerous trials, recommendations were made for the use of a special technique sourced from Steve Vicks International. This technique, which has proved successful for the RESPS project, was taken as the basis of the solution to be developed for the sealing of the RESPS lines into the Effluent Tank.

The challenge for CPE was to find a method of allowing all the new trialling work and safety case documentation to be completed within a certain timescale. In order to achieve this, it was decided to co-locate the project teams at CPE’s Workington test facility and use the existing test rig, which had been constructed for the previous RESPS project.

This strategy, said CPE, has delivered significant savings in terms of both the time and cost associated with constructing a brand new facility. All manufacturing, testing and development was carried out at CPE’s facility, again saving time and enabling immediate feedback on trialling and test data.

From the results of the initial trials at CPE Workington, it was quickly established that the initial technique identified would be suitable for the application. However, the dry foam bag sealing approach requires dry conditions within the pipework for the system deployment. To achieve this would require additional work and time by the implementation team in a hazardous environment at Sellafield.

Therefore, in parallel, the project team, in conjunction with CPE and Steve Vicks International, has developed a new system that gives greater confidence in the function of the seal and also greatly reduces the time it will take to perform the isolation on site and as such reduced the dose burden that make this such an onerous task.

Sellafield project manager Chris Cunningham said: “The project was very successful and represents a major risk reduction exercise for the Sellafield site. In terms of safety, the new sealing technique provides the plant with a step change in risk reduction and negates any potential fault scenarios with the effluent and sludge tank systems.”

The approach taken on this project will realise an acceleration of the Effluent Tank remediation programme of about two years, with corresponding cost savings. The solution will have additional safety benefits in terms of reduced operator dose uptake during implementation, as the pipes no longer have to be drained of liquor before the sealing mechanism is deployed.”

Stuart Pegler, project engineer at CPE added: “Potentially, the new sealing and deployment technique has many other plant applications at Sellafield and may offer opportunities as a technical solution in the remediation and decommissioning of facilities across the site.”

The work undertaken involved a large number of local suppliers, including Derwent Fluid Power, Unblock Cumbria, Hewdens Hire, REACT, PKA, Lloyds Kone Crane, Yarl Hydraulics, SLB Pumps, Tubros Engineering, Westlakes Engineering and Carlisle Hydraulics.