Читать книгу Industrial and Medical Nuclear Accidents - Jean-Claude Amiard - Страница 37

During a loading operation of the no. 1 graphite-gas reactor (SLA1) in Saint-Laurent-des-Eaux, France on October 17, 1969, the fuel loading and unloading apparatus in the operating reactor was controlled by a programmable displacement system. By mistake, a flow control valve was introduced over already-loaded fuel elements into one of the reactor core channels. This resulted in a drastic reduction in the cooling circuit of the fuel elements and a subsequent rise in temperature at the level of the magnesium and zirconium alloy sheaths of five fuel elements and their degradation. The reactor was automatically shut down due to the rise of radioactivity in the reactor vessel. These five fuel elements corresponded to about 50 kg of uranium dioxide that melted in the reactor core [IRS 15a].

The contamination would have been limited to the site. But because of its seriousness, it should have been classified at level 4 on the INES. However, EDF described it as an incident because it would not have caused any damage to persons, property or the environment outside of the site.

Clean-up operations began 1 year after the accident, while the nuclear fuel cooled and a full-scale model was built. These cleaning operations were mainly carried out using remote-controlled means. To finish this operation, several hundred (300–400) “cleaners” were mobilized, each one being able to intervene for only about 10 minutes, even 2 minutes for some. At the end of the clean-up operations, only 47 kg of uranium was recovered and the reactor was restarted on October 16, 1970.

The second graphite-gas reactor in Saint-Laurent-des-Eaux (SLA2) was automatically shut down on March 13, 1980 following a sudden increase in radioactivity in the reactor vessel. The next day, EDF estimated that a significant amount of spent uranium had melted. From March 22 to 26, after checking the proper operation of the iodine traps, decompression of the reactor vessel to the atmosphere was carried out in order to return to atmospheric pressure. This same reactor suffered several incidents during the same quarter of 1980 [GUI 16].

Examinations undertaken on March 27, 1980 showed that the accident originated in a total or partial plugging of six channels by a metal sheet detached from the fairing device due to its corrosion. Two fuel elements melted (about 20 kg of uranium) and two others showed significant traces of fusion. The cleaning was very difficult and took more than three and a half years [IRS 15a].