At 11:52 am in the reactor no. 2 building at a nuclear power plant, an oil leak was detected on the motor of pump 1 in the reactor’s cooling water circuit by means of a low-level alarm; 2 min later, fire outbreaks were detected in the corresponding utility room. Coincidentally, at 12:12 pm, an abnormal rise in pump motor temperature caused the pump to turn off, triggering automatic shutdown of the reactor due to a lack of flow in loop 1 of the primary circuit. Technicians applied the set of instructions aimed at keeping the reactor cooled in the event of an incident.
The internal emergency plan was activated at 2:10 pm. Both internal and external first responders entered the building reactor; they extinguished 3 ignited oil pools and removed the adjoining heat insulation. During this response effort, one fire-fighter was slightly injured but no contaminations were reported.
Around 6 pm, the plant operator logged an abnormally high water discharge rate on the primary pump’s 1st joint. The deployment of joint 2, designed to remediate the deficiencies of joint 1 as needed, provided a seal: water remained where it was normally collected by the designated circuit. Technicians then applied instructions to lower the primary circuit water pressure and temperature, thus restoring water discharge rates around the joints to their design values.
The idled reactor stabilised at 4:40 the next morning and the emergency plan was lifted at 5:15 am.
The Nuclear Safety Authority conducted an inspection on 6th April and requested from the operator a technical analysis of this event, along with an expert appraisal of the disabled pump. Moreover, reactor restart was made contingent upon their authorisation.
The operator proceeded by: replacing deteriorated equipment (all of pump 1 except for its volute casing, heat insulation, etc.), and performing all inspections required to demonstrate the absence of residual damage on the primary circuit. A detailed analysis of this event indicated to the operator the 3 following areas of emphasis:
- prevention of subpar maintenance and operations ;
- control room monitoring ;
- decision-making protocols.
