Les ouvrages de prise et de rejets de la centrale nucléaire de Gravelines

Water intake and outlet structures of Gravelines power station

¹ E.D.F., Direction de l'Équipement
² E.D.F., Laboratoire Nationale d'Hydraulique

Abstract

Gravelines power station is situated on the coast just beyond the western end of the new outer harbour. Gravelines itself lies on the North Sea between Dunkirk and Calais. The power station will eventually consist of four 900 MW pressurized-water and four 1,350 MW generating plants. The total once-through cooling-water requirement will be 400 m³/s. Water inlet and reject structure layout was dictated in large measure by the presence of the new outer harbour. The structureses were designed by the Laboratoire National d'Hydraulique in collaboration with the Dunkirk Harbour Authority. The intake structure was sited at the edge of the outer harbour so that deep water not exposed to large waves would be available close by. Design was based on model tests, the principal objective being to minimize currents in the immediate vicinity of the oil tanker jetties. The outlet structure backs up against the breakwater of the outer harbour and discharges off the beach by the generating plant. Reject at this point minimizes recycle from outlet to inlet but exposes the structure to waves. The outlet structure was also studied on a scale model. The design of the bank protection is similar to that chosen by the Dunkirk Harbour Authority for the new outer harbour, viz. (a) rockfill laid on fascines and polypropylene fabric and (b) superstructures faced with bituminous concrete. The floor protection will be reinforced or repaired as required by erosion and the commissioning of new plant. Inlet and outlet structures are linked to the power station by canals. The canal floors consist of rockfill. Walls are constituted by rockfill embankment, sheet-piling or concrete. The second part of the article deals with intakes and outlets located on beaches not comprising any kind of harbour installation. Theoretical studies were undertaken to identify valid designs for the cooling water structures required by power stations near beaches similar to the one at Gravelines, i.e. without breakwaters, etc. Two schemes appeared feasible. The first, based on Gravelines, consists of two "artificial harbours", one each for the intake and outlet. This keeps the structures separate and enables water to be pumped from calm, offshore water. Cooling water in the second scheme is withdrawn via one or more towers a considerable distance out to sea. It is then fed to the power station through an underwater tunnel system. The reject structure is similar to the Gravelines outlet.