Cause of OL3 feedwater pump damage yet to be determined

Monday, 7 November 2022

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.

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 feedwater pumps were delivered for the turbine island by a proven pump supplier that has supplied pumps to several nuclear power plants," TVO noted.

It added that several different investigations, analyses and studies are currently being carried out.

TVO said one of the damaged impellers has been split into parts in a destructive test and the parts have been sent to several different laboratories for analyses. "The objective of this is to, for example, verify the quality of the material during manufacture and to identify the point of origin of the crack as well as to investigate the failure mechanism," it said.

The precise geometry of the impeller was determined for a 3D model by a laser scan. The 3D model is to be used in supplementary analyses related to stress technology and flow technology. The results of these analyses will be used to determine the causes of the failure and help in resolving the issue.

"The possible impact of the results on the [test production] schedule will be announced as soon as the investigations have been completed," TVO said.

OL3 attained first criticality on 21 December last year and was connected to the grid on 12 March. The 1600 MWe pressurised water reactor is currently in an ongoing test production phase. It was operated at full capacity for the first time in late-September and is currently scheduled to start regular electricity production in December.