A committee appointed by Atomic Energy Regulatory Board (AERB) after the Fukushima nuclear accident in March this year has recommended that India’s nuclear power plants (NPPs) should have an emergency facility that will remain functional during calamities like earthquake or tsunami.
The panel chaired by former AERB chairman S K Sharma has stressed the need to make additional design provisions so that the basic safety functions for the NPPs are not impaired even under extreme natural events.
The committee sought the need to give a conservative definition to the parameters for each postulated extreme natural event, using the best available analytical methods. While design-basis external events should govern the design of SSCs (structures, systems and components), functionality of the most safety relevant SSCs should still be maintained under extreme events. Further, submergence of the fuel in the pool water should be assured for a time period of at least one week under station blackout, even with the most conservative assumptions on the quantum of decay heat from the stored fuel and without any credit for operator action. There are currently 20 nuclear power plants with generation capacity of 4,780 Mw.
The panel at the outset observed that the design, operating practices and regulations followed in India have inherent strengths, particularly in case of pressurised heavy water reactors that account for 18 our of 20 currently operational nuclear power plants to deal with the natural events and their consequences. It noted that the Nuclear Power Corporation has already taken interim safety measures to enhance safety of the two older boiling water reactors which are operational at Tarapur in light of the Fukushima accident. The measures include provisions of continuous reactor cooling under prolonged SBO in which loss of both offsite and onsite power supplies is considered and preparatory work for inerting the containment with nitrogen to avoid hydrogen explosions as happened at Fukushima in Okuma on March 11, following a temblor that triggered a tsunami.
According to the committee, unlike in the Fukushima case, the simultaneous occurrence of a strong earthquake and a tsunami at Indian nuclear power plants was not foreseen as the submarine faults capable of generating tsunamis are located at very large distances of more than 800 km from the western coast and more than 1,300 km on the eastern coast.
The panel suggested that despite all the safety measures the extremely remote possibility of an accident leading to partial or total melting of fuel in the reactor core, called severe accident, due to unforeseen reasons should still be deterministically taken into consideration. In the area of severe accident management significant progress has been made in the country in terms of analysis and research and development. The committee recommended that it should be expeditiously translated into design provisions together with related procedures for operating as well as under construction NPPs.
