INES-event
INES 1

Degradation of essential service water (ES'W) for a year due to a defficient design modification

Over discussion with Spanish Regulator, licensee discovered that a design modification consisting of introduction of a new ESW automatic start up signal upon loss of conventional service water (CSW), could lead to loss of ESW in scenarios such as failure of CSW pressure control plus failure of any auxiliary contact of CSW breaker followed by a loss of off site power.

Rating Justification: Table I: Events without initiator:
Initiator: Loss of off-site power (high expected) safety function availability: adequate level 1 is chosen, instead of 2, on low probability of the scenario leading to ESW unavailability

Location: ASCO-1
Event date: Fri, 12-07-1996
Nuclear event report
Legenda & explanation