INES-event
INES 0

Unexpected closure of the main steam line isolation valve caused reactor trip

On August 27 at 09:15 after three months of stable operation since last refueling outage in May 2003, reactor trip with safety injection actuation occurred. Reactor trip and safety injection was initiated by main steam line Lo-Lo pressure signal as the consequence of unexpected closure of the main steam line isolation valve while performing surveillance testing. All safety, control systems and plant equipment responded in accordance with design requirements. Unusual event was declared based on rapid depressurization on secondary side of the plant. Unusual event was terminated after two hours. Plant was stabilized at "No-load" parameters and restarted after 19 hours and connected to the power grid.
Preliminary analysis and evaluation indicates failure of limit switch which caused closure of the main steam isolation valve.
There was no impact to the environment or plant personnel.

Location: KRSKO
Event date: Wed, 27-08-2003
Nuclear event report
Legenda & explanation