Small leak of primary coolant water at NPP Temelin - update
At about 3.00 a.m., January 25, 2006 a small leak was identified by operating personnel inside the containment of Temelin NPP Unit 2. At the time of event the unit was in preparation for restart after approx. 3 weeks maintenance outage.
As the most probable resource of leak the venting pipeline of the steam generator (SG) No.2 or SG No.3 was identified. Unit 2 preparation for start-up was immediately stopped and the unit was cooled down. The leakage was correctly identified by information system and subsequently confirmed by humidity inside of containment and by inlet to primary circuit floor drainage system, which is designed for drainage of leaks.
Event was notified to SUJB in accordance with rules as unusual event.
After decreasing of primary circuit parameters the leak was finished at about 1.00 p.m., January 25, 2006. Magnitude of the leakage was estimated by balance of primary circuit charging between 3 to 5 m3 per hour however this value cannot be taken as approximate due to insufficient stability of parameters.
The investigation determined as the most probable reason the internal valve leakage on the venting pipeline of SG 2, which was caused by temperature increasing. The leakage was not caused by any material defect. On the basis of following investigation results the technical modification was carried out to prevent repeating of such leak during loss of internal valve tightness.
The event did not cause leakage of radioactive substances into environmental surroundings and health of NPP staff also was not jeopardised.
Because the event occurred in time of minimum presence of gaseous fission products in primary coolant, the event did not affect values of gaseous radioactive releases.
SUJB immediately launched investigation by the team of specialists on the correctness of procedure during operator investigation and causes determination of the event and assignment of proper corrective measures.