INES-event
INES 2

Exposure of two workers in excess of statutory annual dose limits

On 31 July 2009, Unit 2 of the Beznau NPP was shut down for maintenance. As part of the scheduled maintenance, it was planned to test the pressure in the primary circuit – this is done every 10 years – and as preparation for the later use of a camera two employees were installing lamps in the enclosed space beneath the reactor pressure vessel. Running through this space are double-walled tubes through which probes can be fed to measure the neutron flux in the core. Whilst the two employees were working under the reactor pressure vessel, the inner tubing was withdrawn from the reactor pressure vessel by employees located in a different room so that other work could be carried out. The tubing and probes in the reactor normally emit high levels of radiation and so the resultant local dose rate beneath the reactor suddenly jumped to a dose rate of probably more than 1,000 mSv per hour. The two employees left the scene as quickly as possible. One employee received an individual dose of 37.8 mSv and the other a dose of 25.4 mSv.

For radiological protection reasons, the two tasks - the installation of the lamps and the withdrawal of the tubing - should have been done consecutively. Based on investigations to date, it would appear that the work was not properly coordinated and so a time overlap occurred. As a result two employees were exposed to radiation in excess of statutory dose limits.

Location: BEZNAU-2
Event date: Mon, 03-08-2009
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