EDF Energy puts Sizewell B back to work

01 October 2010

Sizewell B came back online yesterday after a six-month outage for repairs inside the reactor building. 


The 1188 MWe power reactor had been offline since 16 March when a slow water leak of less than five litres per minute was noticed from the pressurizer. The Health and Safety Executive (HSE) said there were no radiological consequences for the public or workers as a result and, "The actual leak that occurred was only marginally above a level at which operators are required, under the safety case, to shut down the reactor."


The pressurizer is a large component containing water and steam that regulates the pressure with the reactor system's primary water coolant loop. The model at Sizewell B contains 78 electric heaters in tubes that keep the water inside at a slightly higher temperature than the rest of the primary circuit. It was one of these tubes that had cracked, leading to the development of a path for water to escape the circuit into the containment building.


Sizewell B (British Energy) 
Sizewell B 


Repairing the reactor took EDF Energy around six months and involved a remote video analysis of the constrained repair area, the development of specialist equipment and testing on a replica. Sizewell B is the only pressurized water reactor in the UK and EDF Energy said it drew on the experience of its owner Electricité de France, that recently redesigned the pressurizers used in France's 58 power reactors.


In its justification to the HSE that the reactor was safe to bring back into operation the company also promised to replace the rest of the heater tubes over time with a design less susceptible to cracking. Extra instrumentation has also been installed to give early warning of degradation in future.


Overall, the HSE said it had "sufficient confidence that the modification to the pressuriser have been adequately conceived and executed and that the Sizewell B ins safe to operate." It granted consent for the reactor to restart on 17 September and EDF Energy brought the unit back online yesterday. In mid 2008 Sizewell B completed a breaker-to-breaker run, operating for 516 days without interruption between refuelling outages.
Researched and written
by World Nuclear News