Читать книгу Industrial and Medical Nuclear Accidents - Jean-Claude Amiard - Страница 44

Before the two most serious accidents, a first accident occurred in the La Hague fuel reprocessing plant on October 2 and 3, 1968. It resulted in an atmospheric release of 185.10⁹ Bq of iodine 131 (Scheidhauer et al., 1971, in [AMI 80]).

The breakage in the offshore discharge pipeline from the La Hague reprocessing plant

The estimated date of this breakage was between early September and late November 1979. This resulted in an increase in radioactivity in the marine environment (seawater, sediments, algae, mollusks, crustaceans, fish) of many radionuclides (⁹⁰Sr, ¹⁰⁶Ru, ¹³⁷Cs, ²³⁸Pu, ^239Pu, ²⁴⁴Cm) between 1980 and 1981 [GRN 99, BAR 00]. For example, for ⁹⁰Sr in 1979, 1980 and 1981 respectively, the concentrations in sediments were 122, 823 and 71 Bq.kg⁻¹ wet weights and those in mollusks were 41, 274 and 24 Bq.kg⁻¹ wet weights.

The fire at silo 130 at the La Hague facility

On January 6, 1981, a fire broke out in silo 130 of the La Hague plant, where waste from the reprocessing of spent fuel from the “natural uranium-natural graphite-gas” process was stored in the UP2-400 plant, causing cesium 137 to be released into the environment for several hours. It took more than 24 hours to control this fire [JAC 14].

Between 1973 and 1981, silo 130 received a total of 518 tons of waste, mainly graphite, magnesium and uranium. The radioactive substances present in silo 130 were mainly the activation products contained in graphite liners and magnesium caps after their passage through the reactor, and the fission products (in particular cesium 137) contained in uranium metal after their passage through the reactor and uranium metal. In addition, between December 11 and 15, 1980 (a few days before the fire), cotton used for decontamination operations (cotton soaked in phosphate degreaser) was dumped into the silo.

The last waste container was emptied into silo 130 on January 5, 1981 at 6:30 p.m. It mainly contained magnesium caps and uranium metal. Between recovery and disposal in silo 130, this waste remained dry for several days, but previously the last waste dumped was uranium from a water pit. The most plausible hypothesis is that this uranium, which is most likely present in the form of hydride (UH3) as a result of its prolonged contact with water, is highly pyrophoric, especially when it has been dry for several days, which was the case here.

On January 6, 1981, at 4:00 a.m., air contamination was detected approximately 800 meters from silo 130 at the AT1 building. Cesium 137 was mainly present in these discharges, which directed research attention towards the silo.

The resulting contamination inside the site on about one hectare affected building 130 overlooking the silo and outside areas. The maximum values recorded were 111.10³ Bq. m-² in cesium 137. Off-site, contamination remained low and did not exceed 3.7.10² Bq.m⁻² in cesium 137 [JAC 14].

Silo 130 now contains the same substances as those present at the time of the fire, as well as effluents from fire suppression (600 m³) and rainwater infiltration (800 m³). It will be necessary to dismantle this silo despite all the difficulties involved.