Finnish power company Teollisuuden Voima Oyj (TVO), owner-operator of the Olkiluoto NPP, has said that investigation of the supply water pumps of Olkiluoto 3 is continuing. “In October, damage was observed in the inner parts of the feed water pumps of the Olkiluoto 3 turbine plant. The survey work is still in progress and the date of the continuation of the trial operation program is not yet known,” TVO noted.

Cracks were found in all four feedwater pump impellers of OL3. The company that supplied the turbine plant's feedwater pumps is an experienced pump supplier and has supplied pumps to several nuclear power plants. Many different reports, analyses and studies are currently underway.

“In so-called destructive testing, one damaged impeller was split open and the parts sent to several different laboratories for examination. This ensures, among other things, the quality of the material during manufacturing and identifies the starting point of the crack, as well as elucidating the mechanism of the damage,” TVO said.

The exact geometry of the impeller for the 3D model was determined by laser scanning. The 3D model is used, among other things, in complementary strength and flow analyses. The results of these are used in the investigation of the causes of the damage.

“In addition, the operating history and operating conditions of the feedwater pumps during the commissioning of the plant have been explained in detail. With the help of investigations, we will get an answer to what causes the distortions and how to solve the matter. The possible effects of the results on the schedule will be communicated as soon as the investigations are completed.”

The Areva-Siemens consortium constructed the OL3 plant under a fixed-price turnkey contract. They have joint liability for the contractual obligations until the end of the guarantee period of the unit. Construction of OL3 began in 2005, with completion of the reactor originally scheduled for 2009, but the project has faced various delays and setbacks. OL3 achieved first criticality in December 2021 and was connected to the grid in 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.

Image: One of the feedwater pump impellers of OL3 (courtesy of TVO)