An ammonia leak was detected at 14:50 on a storage tank adjacent to the turbine building of one of two units of a nuclear plant. The operator evacuated employees from the building, staffed the emergency response facilities and made immediate notifications to the state and local authorities. Because some vital areas within the turbine building had become inaccessible, the event was classified as an “Alert” (second of four emergency declaration levels – actual or potential decline in the level of plant safety). Local authorities activated their crisis center preventively. The two units continued to operate normally.

The leak was stopped at 17:25, the alert was terminated at 18:00. One hundred liters of ammonia were recovered from the berm.

The ammonia was leaking from an overflow vent valve of an ammonia tank used to control secondary plant water chemistry. The overflow was caused by the failure of an isolation valve that allowed excessive ammonia to enter the tank.