Keeping Sellafield ponds chilled and clean

05 November 2009

Schneider Electric has bolstered the reliability of Sellafield with the upgrade of the PLCs (Programmable Logic Controllers) and software which control the Ion Exchange Effluent Plant. The facility is responsible for safely carrying out the decommissioning of the UK's nuclear legacy as well as reprocessing and nuclear waste management.

Keeping Sellafield ponds chilled and clean

Built in 1984, Sellafield was the first commercially successfully nuclear power station and is one of the most complex, yet compact, sites in the world. The Sellafield Ion Exchange Effluent Plant (SIXEP) features a waste matter process that removes radioactivity from a number of outlets across the site and is critical to the facility's operations. The waste material is kept in ponds, which generate heat and need to be chilled to be kept at a consistent temperature. Schneider Electric's PLCs have been controlling the chillers that maintain the temperature of the water since the site was first commissioned 25 years ago.

However, BNFL (British Nuclear Fuels) wanted to explore the various solutions that modern, innovative technology offers and were keen to upgrade the PLCs to reduce the risks associated with the potential failure of ageing control equipment.

As the original provider, Schneider Electric was called in to manage the upgrade project. Despite providing the existing PLCs, there were new challenges the team had to overcome as Phil Woods, services & support manager for Schneider Electric explained: "The system was previously controlled by five Modicon 684 PLCs, which were installed when the plant was built. One of the biggest issues on the new project was the requirement to create software that closely resembled the original version so that it was familiar to Sellafield's process engineering team. This was necessary to ensure minimum disruption to the plant and reduce the need for radical retraining. At the same time we had to implement programs that are compatible with IEC61131-3 open control system standards, bringing it in-line with modern regulations."

IEC61131-3 governs control system programming language specifications to ensure a consistent approach throughout the industry. To offer a solution, the team deployed Schneider Electric's Unity programming platform to build the application in a generic ladder format, similar to the original one. Five of the latest Modicon Quantum PLCs were installed, fitted with Cablefast 'plug and play', a pre-wired, fast slot cabling system, which enabled the system to be efficiently installed and commissioned following the factory acceptance tests.

Woods continued: "Essentially the five Quantum PLCs are arranged as two pairs that perform identical functions and the fifth as an individual unit, carrying out different functions from the others. One pair of PLCs is in use at any time and while this is not a truly dual redundant system, the operator can switch between the two pairs of PLCs. We recommended Quantum PLCs as they have a high level multi-tasking operating system but remain compact, and are particularly at ease in extended architectures where various networks are built on top of each other.

"By upgrading the PLCs within the SIXEP, any future spare or replacement components can be easily sourced and installed, helping to minimise downtime and supporting the system's long-term worth as an integral component of the Sellafield site."

Mark Duffy, project engineer for BNFL, commented: "We have a very open and collaborative relationship with the team from Schneider Electric. We are delighted they were not only able to deliver the project on time, but provided a solution which improves our system reliability and yet is flexible enough to easily adapt to future process changes."