The UK’s Office for Nuclear Regulation (ONR) has granted permission for three advanced-gas cooled reactors at Hartlepool and Heysham 1 to return to service.

The reactors, operated by EDF Energy, were shut down as a precautionary measure in August 2014, following discovery of a crack in a boiler spine at Heysham 1 Reactor 1.

On 21 November, ONR said that it had completed an independent assessment of a safety justification for the return to service of Heysham 1 Reactor 2 and the two reactors at Hartlepool, and that it was ‘satisfied’ that EDF has demonstrated the continued safe operation for the reactors. The reactors were expected to resume operations on 22 November, according to EDF’s website.

EDF intends to present a separate safety justification for Heysham 1 Reactor 1, which will be subject to independent assessment. Formal permission will also be needed before that reactor can return to service, ONR said. EDF Energy anticipates that Heysham 1 Reactor 1 will return to service by the end of the year.

The Heysham 1 and Hartlepool reactors share boiler designs. Within each unit the boiler tubes are assembled in a coil formation around a central forged metal tube called a boiler spine. The boiler spines support the weight of the tubes around them.

The other UK AGRs have a different boiler design without a boiler spine and they are manufactured from different materials, so will not suffer from the same issue.

Photo: Drawing of pod boiler (Source: EDF Energy)