The unit with the fast breeder reactor was operating at rated power (600 MWe). At 11:19 a.m. local time personnel scrammed the reactor manually due to activity increase in the air duct of the exhaust ventilation system from the compartment (unattended while operation). The cause of activity increase was a leak in the auxiliary system - primary coolant (Na) cleanup system. Personnel isolated components of this system after identification of the leak indications.
Activity increase in the ventilation system and contaminaton of the unattended compartment did not lead to change of the radiological situation on-site and off-site. Radioactive release through vent stack was a little more than for the unit normal operation, but did not exceed maximum permissible level and was mainly conditioned by Na-24 isotope. Radiological situation in some unit rooms was degraded for a short time due to transportation of Na-24 aerosols via the ventilation system. Personnel overexposure did not occur.
The event is preliminarily rated at level 1. Final rating will be performed after more detailed analysis of the event causes and quantitative data on the radiological situation at the plant.
Event date: Thu, 07-10-1993