 INES 2 |
VIOLATION OF SAFETY REGULATIONS AT A WORKSHOP IN THE FUEL FABRICATION PLANT |
On Tuesday, 4 June, inspectors from the safety authority (Department for the Safety of Nuclear Installations - DSIN - and the Rhone-Alpes regional division) reported that two incidents involving a criticality risk had taken place on 29 and 30 April 1991, in the plant's workshop for the oxide production process.
This plant fabricates fuel assemblies, particularly for pressurized water reactors, and uses slightly enriched uranium. The criticality ;risk must therefore be taken into account, owing to the presence of a large amount of enriched uranium in one place. Under certain conditions there could conceivably be concentration of this uranium which would reach criticality, resulting in the onset of a chain reaction and a high level of radiation in the vicinity. Very strict regulations have therefore been imposed to avert this danger.
On 29 April an open container filled with enriched uranium oxide powder was overturned, causing oxide powder to be spilled in thepacking area. A maintenance worker recovered the powder with a vacuum cleaner designed for that purpose, but the amount of uranium oxide powder recovered during this operation was 33 kg - greatly in excess of the 15 kg level authorized by the technical regulations. This excess of weight was noted by a plant safety official immediately after the operation; but, though the incident was a significant event, it was not reported to the safety authority (DSIN), although such action was required by the regulations.
On 30 April, five containers 30 cm in diameter filled with enriched uranium oxide pellets were set down on the floor rather than on the storage table provided for that purpose where they are normally left until used in uranium pellet fabrication operations.
The storage table is equipped with a device which keeps the containers at a minimum distance of 15 cm from each other to prevent criticality. However, the movement of a fork-lift truck brought the five containers on the floor into contact with each other. This second significant event was not reported to the safety authority, in violation of the regulations.
In view of this double violation of the safety regulations, the DSIN ordered the immediate shutdown of the facility. Restarting of the plant is subject to approval by the safety authority, following consideration of the operator's suggestions to improve operating procedures and personnel safety culture.
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Event date: Mon, 29-04-1991
