BALANCE OF PLANT | STEAM GENERATOR UPGRADE Given that this is potentially a more compact solution
it was considered an option for the Ringhals 4 upgrade because while there wasn’t available space to put in a bigger steam generator it was nonetheless possible to increase output from the reactor.” “Ringhals 4 is a very classical Westinghouse three loop design, like North-Anna, Surry, Beaver Valley etc…This is the same design family. We did a steam generator design, which was the same volume as the original one but with this economiser which created a large margin compared to the original steam generator,” Merlin says. The new steam generators, each of which weighs some
300 tonnes and is about 20 metres long, were transported by ship from the port of Videbergshamn on Sweden’s west coast to the Studsvik harbour at Nyköping on the country’s east coast ahead of their final journey to the plant. During the summer of 2011 refuelling and maintenance outage at the plant, the three new axial economizer steam generators and the new pressuriser and new high-pressure turbines were installed. Replacing the original steam generators with the axial economizer design led to an 18% increase in plant capacity. The new high-pressure turbines added a further 30 MWe, boosting the unit’s rated power output from 930 MW up to 1130 MW with the new steam generators adding a substantial proportion of the increase alone. The capacity uptick was confirmed in early 2015,
after testing and a safety audit, when the Swedish nuclear regulator, Sweden’s Radiation Safety Authority (Strålsäkerhetsmyndigheten, SSM) approved the 1130 MWe output, equivalent to adding 200 MWe. The replacement of the three steam generators was the largest single project in the unit’s modernisation and life extension programme. In January 2012 the three old steam generators were
transported to the Studsvik plant, where they were processed for recycling and disposal. In the wake of the upgrade, in 2017 Ringhals decided
to invest in further subsequent improvements with an independent core cooling system in units 3 and 4. With this investment, totalling around SEK 900 m (US$82 m), the plant will be able to supply electricity into the 2040s.
Future steam generator replacement market Looking ahead, Merlin sees much more scope for uprating reactor power ratings by retrofitting axial economiser
steam generators. “From all this family of reactors the one in Sweden is definitely by far the one with the highest power rating so this is the biggest opportunity, given those other design families also have opportunities to increase output by using this better steam generator design,” he says. Although acknowledging that the gains achieved may be less than that at Ringhals 4, Merlin is nonetheless clear that there are substantial benefits: “We couldn’t necessarily expect 18% everywhere, that would be unrealistic and will also depend on the balance of plant. Not all the reactors from this generation are really standardised too, even if the core could be the same sometimes the geometry is a bit different, so we’d need to study the opportunity on a case- by-case basis. But, in the general case it will create quite a large margin to operate, which is usually the thing you want to increase for operational and maintenance flexibility. This provides a future opportunity to uprate the steam turbines and other balance of plant equipment to get that extra leap in power depending on life expectancy,” he says. Merlin also points to broader macro-economic trends that point to life extension and capacity increases across the global reactor fleet: “For reactors which have very old steam generator designs with alloy 600 tubing, replacing them, especially if they want to go to 80 or even 100 years of operation, is a no regret option because the steam generator would have to be replaced at some point in the lifetime of the plant because the tubes are from earlier alloys that are not as good so they’re being replaced everywhere,” he says. In addition, “It goes well with the current paradigm,
especially in the US where there is an incentive for major investment plans to maximise lifetime and production. Under the IRA, because the steam generator allows operational improvements, such upgrades are therefore eligible for funding,” he says. There are also underlying drivers such as growth in the
data centre sector and elsewhere that favour the continued operation of nuclear power plants beyond their original lifespan. “I would say the climate around this changed quite quickly. This is something we weren’t hearing before that much. There is a demand for increased power and our steam generator technology is definitely suitable for this so that potentially also bodes well for uprating and life extension,” Merlin concludes. ■
Above: The Framatome economiser steam generator design is deployed in all the EPR units, such as the UK’s Hinkley Point C Source: EDF
20 | January 2025 |
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