Allaying fears in the minds of the public after the recent quake-tsunami-triggered explosion in a couple of nuclear reactors in Japan, Site Director, Koodankulam Nuclear Power Project (KKNPP) M. Kasinath Balaji has said the state-of-the-art safety measures in the 1,000 MWe capacity pressurised water reactors of KKNPP had made the reactors the safest units.
Speaking to reporters at Koodankulam on Tuesday, Mr. Balaji said the nuclear reactors there had been designed to be safe in all natural eventualities such as tsunami and earthquake. The buildings that house the reactor and its auxiliary equipment, reactor safety systems, safety diesel generators, the control room and other power generating equipment — all are designed to operate safely under seismic activity as “Koodankulam comes in a Very Low Seismic Category Zone 2 as per the seismic classification.”
While designing the Koodankulam reactors, the designers have considered the ground elevation of all the buildings to be starting from 7.50 metre (25 feet) above the Mean Sea Level (MSL) to preclude flooding due to any reason whatsoever, including tsunami. These design features got testified when tsunami struck the coast of Tamil Nadu in 2004. The Koodankulam site has been provided with a shore protection bund to a height of 7.50 metre from the MSL.
Third generation design
The reactors have the third generation safety design features, in terms of the various passive safety features backing up the active safety systems, ensuring that the core is always filled with water-containing boron and the temperature of water is well below the limits.
Twelve huge capacity water accumulators have been kept inside the reactor building to ensure that the reactor is filled with water with boron, in the eventuality of loss of water from the reactor core. In addition, the reactor is cooled by way of natural circulation in the event of loss of power supply to the recirculation pumps by the large capacity system generators which are kept at high elevation compared to the reactor.
Further, the steam generator water is cooled by a passive air cooling system which works on the principle of natural convection needing no external power. This ensures long term cooling of reactor core in the event of no power supply to the coolant pumps.
Each reactor at Koodankulam is provided with four redundant diesel generators of which only one is required to keep the reactor in cool state under shutdown condition. The diesel generators at KKNPP are located at a higher elevation of 9 metres (30 feet) above MSL, isolated from tsunami-like natural calamities.
The cooling water pumps for the diesel generators are also kept in secured buildings, capable of withstanding earthquakes. In the unlikely event of unavailability of all diesel generators, the passive heat removal system mentioned above, which is a unique feature of the KKNPP, will ensure cooling of the steam generator using the natural cooling by air. Thus the reactor core is kept in cool condition, ensuring that the fuel cladding temperature is within the limits.
In the most unlikely event of core melt, for which the probability is extremely low in this type of reactors in view of the above mentioned features, there is a special feature called ‘Core Melt Catcher' to contain the core melt if at all it occurs.
To convert any hydrogen formed in the above unlikely event, passive hydrogen re-combiners are provided in the containment to recombine the hydrogen back to water. This precludes the possibility of accumulation of explosive quantity of hydrogen in the containment.
Thus the events that had taken place in Japan would not happen in the Koodankulam reactors.
To verify the structural integrity of the above mentioned systems, the system circuits were hydro-tested and the result accepted by the Indian and Russian specialists as well as the Indian Atomic Energy Regulatory Board.
Safety drill soon
“Unit 1 of KKNPP is getting prepared for hot run in a couple of days when all the safety systems will be tested for its design capability during operation and power generation will start within three months,” Mr. Balaji said, adding that the safety drill rehearsal involving the local communities will be conducted soon.