The nuclear operator said early last month that it plans a “phased return” of the Heysham and Hartlepool nuclear units between the end of October and the end of December 2014, but added on Friday that the units would only return to between 75-80 per cent of their full capacity.
The constrained supply will knock a further 240MW off the UK’s total available capacity for this winter, following a string of unplanned outages in the months leading up to winter.
The nuclear operator lost 2.5GW of nuclear capacity over the summer after a crack was found in a boiler at Heysham-1. As a safety precaution all units of the same design were removed from service for safety inspections.
As a further safeguard the generating capacity will be capped to reduce the temperature of the units and prevent further cracks from forming, EDF Energy said.
“As boiler spine defects can only develop into cracks at very high temperatures, two reactors at Hartlepool and one at Heysham 1 could be returned to service at 75 per cent – 80 per cent power to reduce the temperature to which the boiler spines are exposed. Specific modifications would then take place during planned maintenance periods in 2015 and 2016 to allow a return to full power for these three reactors,” the operator said.
Heysham-1 will return to service with the affected boilers isolated, the company said, so that the necessary modifications can take place while allowing its other boilers to operate at full power. It will therefore return to service at 75 per cent by the year’s and reach full power at some point in 2015.
EDF Energy initially gave a mid-October restart date for its Heysham-1 and Hartlepool nuclear power plants but later delayed the returns saying it would instead opt for a “phased return” between the end of October and the end of December 2014.