The problems were first discovered last week during an annual maintenance outage at OKG’s Oskarshamn 3, where a fracture was discovered in a control rod shaft. Similar cracks were subsequently discovered in six more control rods, and the company is now extending its maintenance outage to enable it to carry out fuller tests and to determine the root cause of the problem, WNN said.

 No problems have been found at the other two Oskarshamn units, but OKG has notified Nordic power exchange Nordpool that it does not expect unit 3 to restart until 3 December. The boiling water reactor normally supplies 1153 MWe, the agency said.

In the light of the Oskarshamn discovery, Swedish radiation safety authority SSM called for immediate inspections at Swedish plants sharing similar control rod designs. Inspections at Forsmark 3 have revealed similar problems to those at Oskarshamn, said WNN. No problems were found in the other two units at the site, which have a different control rod design to the affected plants.