Olkiluoto 1 wins the gold

The Eurajoki, Finland nuclear power reactor is a Westinghouse Atom BWR type, owned and operated by utility Teollisuuden Voima Oyj (TVO). It began commercial operation in 1979, with major modernisation and upgrades in the periods 1994-8 and 2005-6. The reactor is also a high performer in operation; it was ranked number 20 (out of 407) in lifetime load factor (88%) in NEI’s full-year 2010 load factor league tables, and remained in the 2010 top 100 for annual load factor, despite this outage.

Olkiluoto’s 20 MW mini-uprate was enabled by replacement of the low pressure turbine. That work involved installing four new rotors with new blade wheels, new casings with lead blade supports, and lead blades. The new turbine increased plant unit efficiency by approximately 1%, generating a power increase of about 20 MW across units 1&2.

The turbine swap was not the only work performed. A new generator cooling water system was installed in preparation for future replacement of the generator’s water-cooled stator and rotor. The cooling power was increased from 9.6 MW to 11.6 MW.

Four 8 m3/s seawater pumps were modernised; they were equipped with new blade wheels, shafts, diffusors, bearing cups and seals, and new motors were installed. This work increased plant output by approximately 2 MW.

Also replaced were extraction pipes that carry steam from the LP turbine to the condensate pre-heaters. The swap-out, from carbon steel to stainless steel piping, was carried out at the same time as the LP rotor replacement to save time and money.

As part of an ongoing project at the station where a third (38%) of switchgears will be replaced between 2010 and 2015, workers also made some low-voltage switchgear replacements.

On the reactor side, inner main steam line isolation valves inside containment were also replaced. Also, 104 fresh fuel assemblies were taken into the core, 751 fuel assemblies were moved around, and 63 control rods were tested.

The outage work was performed by 1444 people, split between employees and 90 contractors, working a total of 277,000 hours. That total workforce is double TVO’s entire workforce of 790. Total dose accumulated during the work was 638.6 man-mSv. The largest individual dose received was 8.95 mSv. There were no cases of internal contamination.

Although the Olkiluoto 1 outage won the most votes, all of the shortlisted outages were worthy of mention. In second place was a February-July refuelling and maintenance outage at Tsuruga 2, which included water- and laser-peening to mitigate stress corrosion cracking. In third place was an April-May refuelling and maintenance outage at Grand Gulf that included an N1 suction plug swap-out. In fourth place was a September-October outage at North Anna 1 that included a main generator replacement. Thanks go to all of those who sent in entries.