 INES 3 |
RADIOACTIVE CONTAMINATION IN THE REACTOR BUILDING |
On November 27, 1995, a considerable contamination of reactor hall floor was detected. Average contamination level was monitored to be 15000-20000 beta-part./(cm2 X min.), maximum level monitored - 126000 beta-part/(cm2 x min.). The examination revealed a few more rooms with radioactive contamination, in one of them highly-radioactive emitters (black crumbs, the largest one was about 5 mm in diameter) were detected. Maximum dose rate (measured at the crumbs surface) was equal to 100 R/hour.
A worker, who visited this room for a short time, received 4.09 rem dose which resulted in this annual dose to become 5.5 rem, that was an exceedance of a statutory dose limit (5 rem/hr). The event investigation showed that radioactive contamination was caused by a damaged fuel assembly, which earlier had been taken out of the reactor by on-line refueling machine. The fuel assembly was taken out on a supposition that it had a tightness failure.
After decontamiantion of rooms and equipment had been completed, the contamination level was decreased to a prescribed level.
Justification: Part II-2 of the User's Manual "on-site impact". Contamination spread criteria. The event has been rated level 3, because contamination level in one of the rooms "could result in a worker receiving a dose greater than a statutory dose limit in a period of about 1 hour" (see part II-2.2 of the User's Manual Definition of Levels).
Event date: Mon, 27-11-1995
