See glossary pages 33 to 36 Saint-Laurent-des-Eaux, two accidents in France The two accidents at the Saint-Laurent-des-Eaux Nuclear Power Plant (NPP) are the most serious nuclear events ever recorded in France. Retrospectively rated level 4 on the INES scale by ASN, they occurred on graphite-moderated Gas-Cooled Reactors (GCRs), which are currently being decommissioned as this technology has been abandoned. The Saint-Laurent-des-Eaux nuclear accident of 1969 On 17 October 1969, five fuel elements melted An error occurred during a loading operation on GCR A1. This error prevented proper circulation of the carbon dioxide which served as the coolant. This greatly reduced the cooling of the fuel elements present in a channel of the reactor core. The temperature of the magnesium alloy and zirconium cladding of five fuel elements increased, causing their deterioration. The rise in radioactivity in the reactor chamber caused an automatic reactor trip. The five fuel elements represented about fifty kilograms of uranium. The radiological consequences were limited: the level of irradiation of the uranium was very low given that the fuel elements had just been loaded into the reactor. Clean-up operations About ten days after the accident – the time necessary for the nuclear fuel to cool – the operations to clean up the melted uranium began. On completion of these operations, 47 kg of uranium had been recovered, essentially using remotely-operated equipment. Additional human intervention was nevertheless necessary to recover some of the debris. A full-scale mock-up of the area to clean up was built in order to train the operators tasked with the clean-up. Technological arbitration Two nuclear technologies were in competition at the time: the GCRs, considered to be the “French” solution, and the PWRs The President of the Republic at the time, Charles de Gaulle, preferred the GCR technology, whereas Georges Pompidou, his successor in 1969, preferred the PWR technology. Shortly after the accident, the GCR technology was abandoned in favour of PWRs. The GCR reactors The GCR reactors were the first generation of French nuclear power reactors. They used a natural (nonenriched) uranium fuel, moderated with graphite and cooled by carbon dioxide (CO2) gas. Just before the 1969 accident, EDF had announced that it was abandoning this type of reactor in favour of the Pressurised Water Reactor (PWR) for economic rather than technical reasons. Artist's rendition of Saint-Laurent-des-Eaux reactors A1 and A2. 8 • Les cahiers Histoire de l’ASN • November 2023
RkJQdWJsaXNoZXIy NjQ0NzU=