BALANCE OF PLANT | STEAM GENERATOR UPGRADE
Switching up on steam
As plant owners increasingly look at plant life extension there are also options to increase the power output without changing the nuclear island. One opportunity comes from improving the steam generator and Framatome’s Charles Merlin tells NEI about their breakthrough design.
WITH NUCLEAR POWER PLANT OWNERS worldwide looking at extending the service life of their assets to 60, 80 years or even longer it’s clear that while the reactor itself is unlikely to change, key balance of plant components will need to be upgraded or replaced. One of the most important balance of plant elements is the steam generator and by uprating the design, important economic and performance opportunities potentially emerge. Steam generators have a typical service life of between 40 and 50 years, meaning their replacement is all but guaranteed during the extended lifetimes that are being commonly mooted today. However, since many of today’s operating large light water reactors were designed and built in the 1970s and 1980s, steam generator design and the materials used have seen a number of significant advances. Taking advantage of these breakthroughs, Framatome developed its axial economiser steam generator. With its improved thermal efficiency, this design can significantly increase the outlet steam pressure and thus boost electrical power produced by a nuclear reactor. Framatome states it can achieve these gains while also preserving the operating flexibility of the plant. Charles Merlin, who leads Framatome’s NSSS large
components business development in North America, explains to NEI that the origins of the new steam generator lie in the French N4 reactor: “It’s based on the steam generator design for the N4 reactor,” he says, noting that applying experience from these reactors commissioned in
the early 2000s the design has now evolved to become a standard feature on the French 1650 MW EPR design being built, for example, in the UK at Hinkley Point and elsewhere. “We came up with this design for the N4 originally as an improved steam generator. Afterwards it was deployed on the EPR platform as the only way to get such a high power rating on the four loop design without introducing a very large steam generator, like Combustion Engineering has been doing. Axial economiser steam generators are now installed in all our EPRs,” says Merlin. One the key technical developments in the axial
economiser is the design of a recirculation system which enables feedwater preheating. “There is a double wrapper around the steam generator shells, around the tubes in the bottom part. There is a second cylindrical part so we can inject cold water from the recirculation on the cold leg at the bottom of the steam generator where the tube starts. The effect is mainly to increase the thermal transfer by getting a much bigger temperature difference between the water in the tube and the water around it from the secondary loop. The recirculation is on the secondary side and the feed water is transformed into steam in the recirculation with pre-heating,” says Merlin. And, while he acknowledges that the idea to have an economiser and steam generator is not new, the Framatome design has a crucial difference with earlier attempts. “There was an attempt, for example, by others, where there was
Above: Although eight reactors now feature the Framatome axial economiser Ringhals 4 was the first retrofit project installed as part of a life extension programme
18 | January 2025 |
www.neimagazine.com
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