The unit No 1 was in planned outage from April 20, 1996. On July 24, 1996 preparations for primary circuit hydro-testing were in progress. Due to mistake of the personnel, a nitrogen supply pipeline was filled with primary coolant. This pipeline is designed to supply gaseous nitrogen from special building (located on-site) to the reactor building. It results in radioactive contamination of the pipeline, equipment and ground at the special building. Dose rate at the contaminated area was monitored to be 60 - 100 microR /hour (microroentgen per hour).
The contaminated area was decontaminated, equipment decontamination is in the progress.
There was not overexposure to any personnel and off-site releases.
Justification of Rating: Off-site impact criterion is not appropriate for the event rating. Available information is not enough to estimate applicability of on-site contamination criteria (par. II-2.2 of User's Guide page 17: "contamination by liquids involving a total activity radiologically equivalent to a few hundred gigabecquerels of ruthenium-106". The event is provisionally rated level "1" under the degradation of defence in depth criterion in accordance to par. III-3.4. of User's Guide. The final rating will be made after the event investigation completion.
Event date: Wed, 24-07-1996