Sellafield chills after upgrade

London - British Nuclear Fuels Ltd (BNFL) has improved the reliability of Sellafield with an upgrade of the PLCs 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.

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 PLCs have been controlling the chillers that maintain the temperature of the water since the site was first commissioned 25 years ago.

However, BNFL wanted to explore the various solutions that modern 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, according to Phil Woods, services & support manager for Schneider Electric

“The system was previously controlled by five Modicon 684 PLCs, which were installed when the plant was built," said Woods. "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’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.

The five 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, explained Woods.

Schneider recommended Quantum PLCs as a high level multi-tasking operating system. The units, it added, remain compact, and are particularly suitable for 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,” concluded Woods.