Extensive tests are to be carried out on the pressure vessel “heart” of the Sizewell B reactor as the power station closes down next month for refuelling and maintenance.

Anti-nuclear groups had pressed for an earlier examination of the vessel after faults were found in two similar power stations in Belgium in 2012.

However, the Office for Nuclear Regulation (ONR), the UK safety watchdog, ruled there was no need for early testing at Sizewell and the work could be carried out this year when the vessel is scheduled for its routine 10-year inspection.

However, EDF has pledged to carry out extra ultra-sonic tests to establish beyond doubt that the Sizewell B vessel is safe.

Pressure vessel faults at Belgium’s Doel and Tihange reactors, both of which were temporarily shut down as a precaution, are thought to have occurred during the manufacturing process. Both the ONR and EDF point out that the Sizewell B vessel came from a different manufacturer and underwent most exhaustive testing before and during installation in the Suffolk plant.

Pressure vessel tests will be among more than 13,000 individual jobs scheduled from next month when about 1,500 contract workers will join Sizewell B staff during a six-week refuelling shutdown known within the industry as an “outage”.

One of the biggest maintenance jobs will involve work on both turbine generators, which during operation convert steam into enough electricity to meet demand from more than two million homes.

It is the 14th routine outage at the power station since it began generating electricity in 1995 and has been planned in consultation with National Grid to try to ensure there is no risk to national electricity supplies.

EDF said the arrival of the huge number of contract workers would provide a boost to the area’s hotels and businesses.

Peter Lanyon, spokesman for the Shut Down Sizewell Campaign, said the risks of nuclear power had increased since the discovery of defects in reactor steel previously thought to be invulnerable.

“As times change so do risk perceptions. It is incumbent upon EDF Energy to subject the Sizewell B reactor to all the most modern checks possible,” he said.