POITOU-CHARENTES chronology of major events at Civaux 1 plant 24 Dec. 1997. Civaux 1 was first connected to the grid. It operated in test mode into May. 7 May 1998. The reactor was taken off line for final testing [NucW 27.v.99]. 12 May 1998. Three hundred m3 of radioactive water leaked from the primary circuit into the reactor building. Subsequent investigation revealed a crack 18 mm x 0.2 mm on an elbow in a heat exchange bypass line in the residual heat removal system (RHR), a system that is used to remove heat from the core when the reactor is shut down. The reactor was still off line when the leak occurred. The cracking was found to be the result of thermal fatigue due to the mixing of hot and cold water just above the elbow [NucW 19.xi.98; Con viii.98]. Framatome, which designed the circuit, blamed the cracking on “layout, unusually large temperature gradient, and unpredictably frequent solicitation of the RHR systems as the [N4] plants remained down for various technical problems for many months.” The RHR system had operated for 1500 hours, a number of hours that would be normal for the entire lifetime of a reactor [NucW 12.vii.99]. 29 June 1998. As a result of the 12 May leak and subsequent tests, the operator began unloading the reactor’s fuel. Chooz B2 was shut down and its fuel removed, and the fuel was unloaded from Chooz B1. (The Chooz B reactors, like the Civaux reactors, belong to the N4 class.) The cracked section of the RHR was eventually redesigned and replaced in each N4 reactor. 4 Dec. 1999. A cracked weld was discovered in the residual heat removal pump bypass line at Civaux 1. Again the problem was caused by thermal fatigue [NucW 10.xii.98]. In each N4 reactor this section of piping was replaced but not first redesigned. 1 June 1999. The process of restarting Civaux 1 began. [Ouest 2.vi.99]. 16 June 1999. EDF announced that the restart had been postponed pending a decision of the Conseil supérieur d’hygiène de France in regard to measures to prevent the formation of amoeba in the cooling system [AFP 16.vi.99]. Certain power plants favor the development of pathogenic micro-organisms including Acanthamoeba and Naegleria Fowleri, which causes a lethal form of meningitis. The conditions that lead to this effect are present at Civaux: stainless steel condensers (copper condensers corrode and contaminate the cooling water with heavy metals but they do moderate the growth of amoeba) and closed cooling water circuits (a portion of the cooling water is confined for a considerable time at an elevated temperature that promotes the growth of toxic amoeba). The situation is aggravated at Civaux by the fact that the reactor can warm the water by 2 degrees Centigrade and that it is allowed to operate when the flow in the Vienne is as low as 9 m3/sec, allowing little dilution of any proliferation of amoeba [UFCV 99]. The Council recommended keeping the water in the system below 33 degrees C and treating it with ultraviolet rays, steps that necessitated additional preparations [AFP 18.viii.99]. 17 Aug. 1999. The designated measures for control of amoebas put in place, DSIN authorized the restart of Civaux 1. The reactor had been shut down since 12 May 1998 [AFP 18.viii.99]. |