Olkiluoto 3 EPR’s test production to continue

The investigation into the damage in Olkiluoto 3’s feedwater pumps* has mainly been completed. 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.

– It is of course extremely unfortunate that Olkiluoto 3’s test production was interrupted during late autumn when the feedwater pumps’ damage was discovered. 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, says President and CEO Jarmo Tanhua.

Based on comprehensive investigations and the planned inspection programme for the pumps, the plant unit’s test production can be continued temporarily by using intact pumps of the current model together with cracked feedwater pumps. 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. The feedwater pumps are located in the turbine island, and they are not significant in terms of nuclear safety. However, their role in electricity production is central.

Test production continues on Tuesday, 27 December, with a test period of approximately 11 days, during which power levels vary significantly. 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. The aim is to carry out the inspections in as swift a schedule as possible, and there are still uncertainties related to the duration of the required interruption in production. Thereafter, before the start of regular electricity production, an approximately month-long production phase will still follow in the test production, where Olkiluoto 3 will produce electricity at mostly full power 24/7. Impellers reinforced with a new design are being produced and are estimated to arrive at the end of February or beginning of March 2023. Time has been reserved in the test production programme to inspect the existing impellers as well as change the new impellers. Even during test production, the plant unit produces about 15 percent of Finland’s electricity demand at full power.

The plant supplier is obligated to complete the plant unit in accordance with the Plant Contract and settlement agreements.

Information on electricity production during the test production phase is published on TVO’s website at www.tvo.fi/ol3forecast. A market message is published in NordPool regarding any significant changes.

*In October 2022, cracks of a few centimetres were identified in all four of Olkiluoto 3’s feedwater pumps. The root cause of the impeller cracks was not known, and comprehensive investigations into the matter were initiated. One of the impellers was split and sent to three different laboratories for examination. The laboratory results were verified with mathematical modelings and analyses. The operational history of the pumps was investigated thoroughly, and experiences with similar pumps around the world were researched. Possibilities for starting electricity production were investigated simultaneously. Several different options were assessed, and they were investigated thoroughly e.g. with the help of different modelings. Investigations were carried out into the suitability of existing spare parts, operational possibilities of the cracked pumps, fixing the cracked pumps, and the design and durability of new spare parts. Several representatives of the scientific community from Finland and abroad have taken part in the investigations in addition to the plant and equipment supplier and TVO’s specialists.

The OL3 EPR plant supplier consortium is constructing the plant unit under a fixed-price turnkey contract. The supplier consortium companies, AREVA GmbH, AREVA NP SAS, and Siemens AG, have joint and several liability for the contractual obligations until the end of the guarantee period of the plant unit.