A terrible earthquake has damaged Japan?s nuclear power plants. We explain why this should not make India reconsider plans to increase its own nuclear power capacity 13-fold

Are Indian nuclear reactors located in earthquake-prone zones?

India currently operates 20 nuclear reactors, only one of which (Narora in UP) is located in a seismically active area. Six more are under construction and several more planned. Depending on susceptibility to earthquakes, places are classified into different zones, with zone 1 being the least susceptible and zone 5 the maximum. Nowadays, no place is classified as zone 1, and it is considered that every location would have some chance of getting an earthquake sometime. Narora is located in a zone 4 area, while the rest of Indian reactors are in zone 2.

Can these reactors withstand earthquakes?

All nuclear reactors, including those in India, are designed to withstand earthquakes of very high magnitude, up to 7 on the Richter scale. Seismologists say it is theoretically not possible to design a building that can withstand earthquakes more than 7.5 on the Richter scale. While selecting the site for a nuclear plant, the seismic activity of the place is one of the biggest factors in decision-making. While the nuclear reactors generally have a life-cycle of 60-80 years, they are usually designed in such a way that they should be able to withstand quakes at least twice in strength to the biggest that the place has seen in a 1,000 years.

Then what has happened in Japan?

Nuclear reactors are designed to automatically shut down operations when they feel an earthquake. Then starts the process of cooling down where the very high temperatures in the reactors are gradually brought down. Because of a power breakdown at the Fukushima Daiichi nuclear plant in Japan, the cooling process was being carried out by emergency power from diesel engines. The process was going on as expected till the diesel engines started malfunctioning, possibly because of flooding. In order to prevent an explosion inside the overheated nuclear reactor that had not been sufficiently cooled down, the authorities resorted to a mechanism of controlled release of radiation in the environment. This controlled release is done in quantities that are not harmful for human beings.

In light of what has happened in Japan, is it safe to operate nuclear power plants?

Japan was struck with an earthquake measuring 8.9 on the Richter scale (now revised to 9), which triggered a tsunami. Such strong earthquakes are extra-ordinarily rare even in Japan, which is seismically one of the most active places on Earth. The earthquake was the fourth strongest ever recorded. Japan has 54 nuclear reactors located in zones 4 and 5. The US also has reactors located in zone 5. According to the World Nuclear Association, an estimated 20% of nuclear reactors worldwide are operating in areas of significant seismic activity. Globally, countries have felt satisfied with nuclear technology?s ability to handle earthquakes.

How prone is India to earthquakes?

The Himalayan region and the Northeast happen to be the most seismically dangerous parts of the country. In recent memory, the 2001 earthquake in Bhuj in Gujarat is the strongest recorded in the country. It measured 7.2 on the Richter scale. The 1993 earthquake in Latur in Maharashtra was 6.1 on the Richter Scale while the Uttarkashi quake in 1991 was measured at 6.5. The southern part of India is known to be seismically benign, although there are some areas that are in zones 3 and 4. Most of India?s nuclear installations are located in southern India near the sea coast. South India is not likely to have earthquakes of more than 6 in magnitude. Experts say that chances of a Latur-like earthquake happening in southern India is about once in 100 years.

How different is a quake of intensity 6 on the Richter scale from that of intensity 7?

Ten times. An earthquake of magnitude 7 would be 10 times more in strength than an earthquake of magnitude 6. In terms of energy, it would release 32 times more. The difference would be the same between the measurements of 7 and 8 on the Richter scale. This is because the Richter scale is not a straightforward measurement but based on the logarithmic scale. As it goes higher up, a difference of even one decimal point can mean a huge variance in terms of destruction. What the Richter scale measures is the vertical ground movement of the Earth. For example, a magnitude 3 earthquake on the Richter scale results in about 1 mm of vertical movement in the Earth?s surface at a distance of 100 km from the epicentre.

What has been the track record of Indian reactors in the face of nuclear disasters?

In 2004, the Kalpakkam nuclear installation near Chennai had been affected. While the residential colony of the nuclear facility had been flooded and some people had even lost their lives, the reactor itself remained unaffected. It went through the automatic shut down process and was restarted after a few days, following a regulatory review.

In the 2001 earthquake in Bhuj, the Kakrapar atomic power station had, in fact, continued to operate throughout, supplying power to the region.