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ERF send date:
On March 11, 2016On March 11, 2016, at 0852 hrs, Kakrapar-1 experienced an event of leak from a pressure tube. Following the event, reactor underwent automatic shutdown and all the safety systems provided in design for core cooling and containment isolation functioned as intended. There was no fuel failure due to the event.
Following the event, at 0910 hrs, plant emergency was declared as per an established procedure. This was terminated after safely defueling and isolating the leaky pressure tube from primary coolant system on March 21, 2016. During the course of plant emergency, environmental survey within the site as well as in the off-site domain up to 30 km was carried out. No increase in air borne activity or radiation level was observed. There was no radiological impact on plant workers, public and environment due to the event. The event was categorised as ‘Small LOCA’.
Root cause analysis of the event revealed that Kakrapar-1 had operated with an unlisted impurity (ethylene) in carbon dioxide gas which is used in leak detection system of pressure tubes. This led to corrosion on the outer surface of all the pressure tubes in the reactor and leak from the affected pressure tube.
The event is rated at level 2 on INES.Kakrapar-1 was operating at 220 MWe. At about 0852 hrs, primary containment (pump room) pressure high alarm appeared in control room. Both fast acting reactor shutdown systems and liquid poison injection system actuated automatically and brought the reactor to long term sub-critical state. Emergency Core Cooling System (ECCS) actuated as per design and provided cooling to the core.
As per the established procedure, plant emergency was declared at 0910 hrs.
Shutdown cooling loop was taken in service and primary coolant temperature was brought to 45 °C. The core continues to be cooled by operation of shutdown cooling system and ECCS long term re circulation system.
After the event, radiological surveys of Reactor Building outer containment wall, operating island and outside operating island was carried out and no increase in air borne activity or radiation level was observed. Maximum radiation level of 10-20 microR/hr was observed at outside the main airlock of Reactor Building.
Plant emergency is still in place. Leaky location is yet to be identified.
Initial assessment has indicated that the leak is from primary coolant system and the leak rate corresponds to ‘Small LOCA’ category.
Based on the available information, the event is provisionally rated at level 1 on INES.
ERF rating date:
ERF contact person:
Ranjitsinh Udaysinh Parmar
Reported by Atomic Energy Regulatory Board of India on 14 Mar 2016. Last update on 19 November 2018
Atomic Energy Regulatory Board