June 19: After the recent explosion at the Fukushima nuclear reactor in Japan, authorities are cautious about new nuclear power plants. The proposed 9,000 MW Kovvada Nuclear Power Project has been designed in such a way so as to fight against natural and man-made disasters, by following various principles of nature. It will have a gravity-based heat draining system, thermo-siphoning and natural circulation along with a multi-barrier safety system. The design will also enable the reactors to absorb shocks of an aircraft crash or a missile attack as well.
The explosion at the Fukushima nuclear reactor, due to the failure of its cooling systems, has led to a re-evaluation and revisit of the nuclear power plants in the country by the five central committees. The committees have recommended that the height of the diesel generator sets, (which are used for cooling off the reactors after they are shut down), be elevated to over 11 metres to avoid a repeat of Fukushima.
The Kovvada reactor will have a six-day window period where it will be able to cool itself without power in case of a plant blackout (automatic shutdown due to a natural tragedy). Huge DG sets will cool the decay heat, and they will be able to auto-start and continue running for 72 hours without any manual intervention and for another 72 hours (will require manual opening of valves). The problem at Fukushima was this inability to cool itself.
“The safety features of the Kovvada reactors are designed to allow them to remain unaffected by power supply, as the passive cooling systems work on principles of gravity draining, natural circulation and low thermo siphoning. The use of natural principles will allow cooling of decay heat to go on for six days without any intervention at the plants,” explains Kovvada Nuclear Power Project director, Mr G.V. Ramesh.
Meanwhile, 885 tons of water within each of the six reactors will ensure that the fuel rods to get exposed at least for two days, as it will take at least 49 hours for this huge amount of water to boil off. Also in case of exposure, a gravity-based system to pull down and seal off the fuel rods, to prevent radioactivity, is part of the design. Standby DG sets will also be installed at the reactors to give access to additional water for cooling when required.
Another point which shows the amount of thought behind this site, is that it falls under seismic zone two and stands negligible chances of an earthquake hitting it. The nearest active seismic fault line exists 1,300 km away, in the Bay of Bengal, between the Sunda Arc and Sumatra. The distance will ensure that even in case of a Tsunami, the intensity of the Tsunami will be very minute by the time it reaches Kovvada. Incidentally the Fukushima reactors lie at a distance of 80 km from the nearest active fault line.
“The design of the reactors will allow them to work, even if an earthquake of magnitude 7 on the Richter scale, hits the reactor. In case of an earthquake of magnitude 7.2, the reactor will auto-trip and the cooling process of the decay heat will begin immediately without any intervention required. The workers at the plant can escape in case of an emergency situation, like an earthquake or even a terrorist attack, and not worry about any damage for six days,” added the official.
As per the reports of the National Geophysical Research Institute and other seismology survey reports, Kovvada falls under zone two and is considered a non-seismic region, whereas, Fukushima stood at seven on the seismic region scale. Meanwhile, there is an ongoing debate on whether to term the six light water reactors, (to be designed by US-based General Electric Energy Services), coming up under the project, generation three or generation three plus as they have some safety features which measure up to the Generation three plus standards. Along with thermo siphoning and gravity-based draining systems, the reactors will have multi barrier safety systems in place. A fuel clad over the fuel, primary coolant inventory, primary containment and an exclusive boundary to prevent release of radioactivity are part of the reactor design.