Finnish EPR set to resume test operation

On 18 October, TVO announced that damage had been discovered in the internals of the feedwater pumps located in the plant's turbine island during maintenance and inspection work. Ten days later, it said cracks of a few centimetres had been identified in all four of the feedwater pumps. Earlier this month, TVO said the earliest date for resuming the production of electricity at OL3 had been moved back to 25 December, which would see regular electricity production due to start in February 2023.

The feedwater pumps are Olkiluoto 3's largest pumps and are used to pump water from the feedwater tank into the steam generators. TVO said the cracks detected in the pumps have no impact on nuclear safety.

"The investigation into the damage in Olkiluoto 3's feedwater pumps has mainly been completed," TVO said. "The cracks in the impellers of the feedwater pumps have most likely been caused by the test production, where the pumps are used in abnormal circumstances. The feedwater pumps have been operated outside the range of normal use during production tests, which has led to a higher-than-normal strain on the pumps. The recurrence of similar damage can be avoided by the optimal operation of the pumps as well as using impellers with more robust measurements."

The company said that, based on the results of the investigation and the planned inspection programme for the pumps, the plant's test production can be continued temporarily by using intact pumps of the current model together with cracked feedwater pumps. It said test production will be continued with two feedwater pumps which are using a spare impeller and two feedwater pumps with a cracked impeller. One of the pumps with a cracked impeller is used as a reserve.

"It is of course extremely unfortunate that Olkiluoto 3's test production was interrupted during late autumn when the feedwater pumps' damage was discovered," said TVO President and CEO Jarmo Tanhua. "This caused a long period of uncertainty relating to our production during the winter period. The investigations, which turned out to be especially challenging, have now been completed so that based on them, we can return to completing the last tests in the test production programme and proceed towards regular electricity production."

Test production will continue 27 December, with a test period of about 11 days, during which power levels vary significantly. TVO said around ten significant tests still remain to be conducted. After tests at full power, electricity production will be interrupted for around four weeks in order to inspect the feedwater pumps and restart the plant unit. After that, test production lasting about one month will follow, during OL3 will mostly be operated continuously at full power.

Impellers reinforced with a new design are being produced and are expected to be delivered in late-February or early-March 2023. TVO said time has been reserved in the test production programme to inspect the existing impellers as well as install the new impellers.

OL3 attained first criticality on 21 December last year and was connected to the grid on 12 March. The EPR, a 1600 MWe pressurised water reactor, was operated at full capacity for the first time in late-September. The Areva-Siemens consortium constructed the OL3 plant under a fixed-price turnkey contract. Construction began in 2005 but there have been various setbacks and delays. Once regular electricity production has started, OL3 will produce about 15% of Finland's total electricity consumption.