Backup issues put Swedish units out of action

Concerns over diesel backup generators have forced two of OKG's three units at Oskarshamn off line as Sweden prepares for the coldest months of the year. Oskarshamn 1 is likely to remain off line until mid-January.

Concerns over diesel backup generators have forced two of OKG's three units at Oskarshamn off line as Sweden prepares for the coldest months of the year. Oskarshamn 1 is likely to remain off line until mid-January.

Two of Oskarshamn's three BWRs are off line (Image: OKG)

Oskarshamn 1 had only recently restarted after over a year out of service, following problems with vibrations in the turbine system and the detection of damage to reactor vessel internals during the plant's regular maintenance outage. The unit was resynchronised to the grid on 29 November and undergoing final tests prior to resuming full operation. Earlier that month, OKG had anticipated having all three of its reactors online ready for the approaching winter.

However, in-service tests revealed problems with one of the unit's diesel generators, which failed to start in the specified time frame. Emergency back-up generators must be able to start up reliably at a moment's notice. To address the problem, OKG says it will either replace or reconstruct the generators' starter motors, but warns that whichever option is followed the work will take at least one month to complete, and has notified the Nordpool Nordic power exchange that the unit will be out of operation until 15 January.

Meanwhile, Oskarshamn 2 is being kept off line for work on its backup generators after Swedish regulators ordered an immediate shutdown of the unit. The Swedish Radiation Safety Authority issued its instruction on 6 December on the grounds that OKG had not been able to demonstrate that "equipment essential for ensuring safe operation" fully met requirements for operability and reliability. More specifically, the regulator said in a statement that one diesel generator was not serviced as scheduled in 2011, and it therefore instructed OKG to carry out extra maintenance and tests on both the unit's backup generators and related equipment.

OKG says the work at unit 2 is proceeding on schedule, and has notified Nordpool that it anticipates Oskarshamn 2 to come back into service on 21 December.

Researched and written
by World Nuclear News