EDF Energy has shut down two reactors, Heysham 1 and Hartlepool, following the discovery of a defect in a boiler unit of Heysham 1 Reactor 1 in Lancashire, UK.

During the Heysham 1 Reactor 1 planned statutory outage in 2013, the company identified an unexpected result during a routine ultrasonic inspection of a boiler spine.

EDF Energy has now decided to close the Heysham 1 Reactor 2 and Hartlepool Reactors 1 and 2, which feature a similar design, in order to conduct further inspections over the next few days and to install equipment to monitor the condition of the boiler spines.

The inspections will satisfy the UK nuclear regulator before the planned return to service of the four reactors.

Each reactor at Heysham 1 and Hartlepool has eight boiler units, which are arranged around their associated reactor in four quadrants, with each quadrant containing two boiler units.

EDF Energy said in a statement: “Subsequent more detailed inspections commenced in June 2014 on the affected boiler spine during an outage on Heysham 1 Reactor 1, and confirmed a defect in the location indicated by the initial findings.”

The Heysham 1 Reactor 1, located on the north-west coast of England near Lancaster, will remain closed while work to characterise the nature of the defect continues.

The investigations are expected to take around two months.