British Energy expects AGRs to restart later this year

Following investigations into an issue with corrosion of wire windings of boiler closure units at four of its Advanced Gas-cooled Reactors (AGRs), British Energy (BE) said that all four units would be able to return to service by the end of 2008 after repairs.

In an Advanced Gas-cooled Reactor (AGR) eight boilers are within the concrete pressure vessel that safely contains the reactor core and potentially dangerous materials. The steel and concrete boiler closure units (BCUs) form part of the reactor pressure boundary and are pre-stressed with nine layers of wire windings. It is an issue with corrosion of this wire that forced BE to take the Hartlepool units 1 and 2 and Heysham units 1 and 2 out of service in October 2007.

The problem was first identified in Hartlepool 1. BE also chose to shut down Hartlepool 2 and Heysham 1, which share the same design of BCU. Heysham 2 was undergoing refuelling when the potential problem was discovered and BE decided to postpone its restart.

The company has now concluded that 'remedial engineering work' is required before the four reactors can operate again. BE said that it has identified a number of engineering modifications that will be needed to reduce the reliance on the current wire windings. These include: a mechanism to lock in the existing pre-stress in the BCUs; improvements to the structure of the BCUs; upgrades to BCU cooling systems; and enhancements to instrumentation to monitor the BCUs whilst in operation.

Return to service requires regulatory approval of the appropriate safety case for each reactor. BE said that the regulator, the Nuclear Installations Inspectorate (NII), continues to be closely involved in the process.

British Energy said that it currently expects that the restarts of the four units will be achieved in a phased process over the second and third quarters of financial year 2008/09 (1 April 2008 to 31 March 2009). T he cost of the remedial engineering work is not expected to exceed GBP50 million ($100 million). This is in addition to the costs of around GBP20 million ($40 million) of inspection and assessment of the units.