Bugey Nuclear Power Station

Bugey Nuclear Power Station is EDF's four-reactor pressurised water plant at Saint-Vulbas in the Ain department of eastern France, on the right bank of the Rhone roughly 35 kilometres upstream of Lyon. The four active units, Bugey 2, 3, 4 and 5, each generate in the 880 to 910 megawatt range, giving the site a combined capacity of around 3,580 megawatts. A fifth, older reactor, Bugey 1, a gas-cooled unit that entered service in 1972, was permanently shut down in 1994 and remains under decommissioning.

The station was built during France's 1970s nuclear expansion. Bugey 2 and 3 entered commercial service in March 1979, Bugey 4 followed in July 1979 and Bugey 5 in January 1980, making Bugey one of the older stations in France's operating fleet. Its Rhone-side siting means it is one of a handful of French plants subject to river thermal-discharge limits: units 2 and 3 draw direct river cooling while units 4 and 5 use cooling towers, a distinction that shapes how each pair copes with hot, low-flow summers.

That cooling constraint has become the station's live story. Bugey 3 was taken offline on 12 July 2026 after Rhone temperatures breached the regulator ASNR's 28C cooling-water limit during a heatwave, with its restart uncertain. Separately, ASNR granted Bugey 4 and 5 a temporary derogation from normal thermal-discharge limits, ratified by the economy ministry on 11 July and valid to 20 July, after the grid operator RTE said it needed minimum output from those units for grid security. The episode illustrates a recurring seasonal tension for Rhone-cooled reactors: environmental limits versus supply reliability.