Fire broke out at 10:30 p.m. on production unit No. 2 of a nuclear power plant. The incident on the reactor occurred during a scheduled maintenance outage. The outbreak was located in the turbine hall in the non-nuclear part of the facilities. The site’s internal emergency plan (PUI) was initiated. The personnel in the turbine hall and the adjacent buildings were evacuated. The firefighters located the seat of the fire inside one of the condensers. A large firefighting system was set up: four fire hoses, two hose reels and a water cannon. As there was a risk of exposure to fine particles, the firefighters intervened with the appropriate protective gear (breathing apparatus and paper suit).

The fire then spread to a 2nd condenser. The firefighters consulted with experts to define an alternative method to extinguish a metal fire using an appropriate extinguishing agent. The technique chosen was similar to that used to extinguish silo fires. The fire was brought under control the following day at 8:00 a.m. Operations were maintained, and the temperature of the equipment was monitored at 14 locations. The fire was declared extinguished at 10:50 p.m. The internal emergency plan was lifted at 11:40 p.m. and the firefighters left the site at noon on 04/07. The operator continued to monitor the temperature of the equipment. The extinguishing water was collected.

Hotspot work was implicated

At the time of the incident, the unit was undergoing its ten-year inspection. The condenser was being completely overhauled, consisting in the replacement of all the titanium tubes. A procedure for cutting internal structures of the condenser using a plasma torch was underway when the fire started. According to the initial analyses conducted by the operator, these hotspots may have been responsible for the accident.

The nuclear safety inspectors visited the site on 08/07. They noted that the presence of titanium did not appear to have been identified before the works began. Furthermore, they noted that the analysis of the associated risks did not mention the use of a plasma torch for the cutting operations, but only an electric grinder. Based on their conclusions, the French Nuclear Safety Authority (Autorité de Sureté Nucléaire, ASN) has asked the operator to conduct a detailed study of the event to define corrective actions to take the risk of metal fires into account during hotspot operations. The ASN also asked the operator to ensure the completeness of the risk analyses before conducting operations and of the fire permits issued for hotspot operations. These elements, as well as the analysis of the fire’s impact on the protection-related elements, will be examined by the ASN within the framework of the reactor’s restart authorisation.