Steam generators

Pumping out RSGs: 32 in 6 years

14 February 2012

In September, the world’s largest nuclear utility, EDF, allocated a contract worth more than EUR 1 billion to Areva to supply 32 replacement steam generators for the utility’s operating fleet of twenty 1300 MWe reactors in France. As the delivery schedule is very tight, challenges for Areva promise to equal the importance of the contract.

Areva’s factories in Burgundy, France will be most called upon to hand over 16 of the 32 components in July 2016, eight in January 2017 and eight in January 2018. Areva’s long-term partner ENSA of Spain will also contribute to the order, particularly during the first term. This very tight schedule required the nuclear group to anticipate and make the necessary arrangements to be able to launch manufacturing of these heavy components as soon as the result of the call for tenders was announced.

Although rarely mentioned, documentation is key in the timely delivery of such heavy equipment as lead times largely depend on the time needed to obtain and validate the required documentation. Planning and scheduling must therefore be extended beyond the procurement of large forgings and the manufacturing of the components, and include the documentation process in order to guarantee the overall schedule of the project.

No less than 2000 documents must be generated to design and manufacture a steam generator, so total control over the documentation process is imperative. On the whole, including the phases of production, internal and external validations as well as the various revisions, an average of 8000 concurrent milestones must be met to produce all of the documentation. Areva’s integrated teams leverage common, standardized and proven methodologies throughout the 60-month project to ensure smooth project progression and timely delivery.

The manufacturing quality of steam generators, in particular the tube bundles they house, is essential for the safety and performance of a plant. They constitute the heat exchange area where the heat from the primary coolant system is transferred to the secondary coolant system. They must keep their integrity under all conditions to prevent any contact between the primary and the secondary coolant circuits. Preventing steam generator tubes’ rupture is thus part of Areva’s defence-in-depth approach. Using a different alloy—Alloy 690 instead of Alloy 600—Areva developed new steam generators with more robust tube bundles that are highly resistant to primary corrosion as well as other forms of corrosion.

In addition, to prevent degradation, steam generator tubes are subject to very close surveillance. Inspection and servicing is carried out by Areva subsidiary Intercontrole.

EDF instituted a special in-service monitoring programme for steam generators at its plants, which is periodically revised to factor in continuous improvements. The programme is required by French regulations and defines the level of degradation at which tubes must be plugged and taken out of service. The programme is submitted to the French Nuclear Safety Authority ASN, which can request utilities to perform complementary inspections and replacements.

EDF’s current 1300 MWe replacement programme will be subjected to the French regulatory order on nuclear pressure equipment (Equipements Sous Pression Nucléaires, or ESPN), an additional challenge for the suppliers.

Over the past five years, Areva defined a strict framework regarding regulatory monitoring and maintenance operations under this new regulation and acquired significant experience through similar orders.

Prior to this contract, in which Areva won 73% of the steam generators (and Westinghouse the remainder), Areva had already been awarded 75% of the replacement steam generator market for EDF’s fleet of 900 MWe reactors, and half of the US replacement market.

New steam generators

While replacing steam generators according to the ASN programme contributes to utilities’ first objective—safety—it is also a cost-effective operation. Maintenance costs are significantly reduced with new steam generators. As the number of welds on the reactor coolant channel head and the secondary containment was halved, the frequency and the scale of related regulatory inspections are therefore equally reduced. In addition, as replacement steam generators are equipped with more robust tube bundles, nuclear operators can step up plant power if required. At the same time, with forging techniques and capacities having evolved since the original steam generators were manufactured, new steam generators’ pressure vessel, that is their external shell, has been modernized to further reduce operating costs.

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This article was first published in the January 2012 issue of Nuclear Engineering International magazine

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