New replacement steam generator for Gravelines 5

Steam generators are used in pressurised water reactors. They act as heat exchangers between the water circulating in the reactor's primary coolant circuit and the water in the secondary circuit that supplies steam to the turbines. Their domed lower head is part of the primary circuit and therefore has an important safety role in ensuring cooling water is always available.

EDF had originally planned to replace all three steam generators at Gravelines 5 during its third 10-year in-service inspection, which began in April 2016. The 10-year inspection is a comprehensive check-up that allows many maintenance operations, reloading of fuel and conducting a safety review.

However, when the original replacement steam generators were delivered from Areva's Le Creusot facility ahead of the inspection outage, discrepancies were found in their manufacturing records. The replacement of the components was therefore postponed until this year. The unit was eventually allowed to restart in late July 2017 after EDF made repairs to certain tubes within the existing steam generators. These repairs involved almost 1800 'sleeves' over the affected tubes. These sleeves were deemed strong enough by the French regulator, Autorité de Sûreté Nucléaire, to guarantee the tightness of the primary circuit and meet the production standards.

EDF is now taking delivery of new replacement steam generators for Gravelines 5, one of which arrived by ship at Dunkerque on 13 March. The utility said the new components will be installed during the next inspection outage.

All six 900 MWe units of the Gravelines plant were commissioned between 1980 and 1984.