Nuclear plants in India: Designed to resist,at least probable quakes

India currently operates 20 nuclear reactors of which only one,Narora in Uttar Pradesh,is in a seismically active area. Six more are under construction and several more planned. Depending on susceptibility to earthquakes,places are classified into zones,with zone 1 the least susceptible and zone 5 the most vulnerable. No place is classified as zone 1 any longer; every place,it is felt,has some chance of having an earthquake sometime. Narora is in a zone 4 area,the rest of India’s reactors are in zone 2.

Can these withstand earthquakes?

All nuclear reactors,including those in India,are designed to withstand earthquakes of very high strengths,up to 7 on the Richter scale. Seismologists say it is theoretically not possible to design a building that can withstand earthquakes measuring more than 7.5. Seismic nature is a major factor in selecting the site. Nuclear reactors generally have a life cycle of 60-80 years; they are designed in a way that they can withstand quakes at least twice as strong as the largest the place has seen in 1,000 years.

What then has happened in Japan?

The way nuclear reactors are designed,they automatically shut down operations when an earthquake happens,then start a cooling process with the reactor shifting to emergency power. In Japan,this had started when some of the engines providing emergency power tripped,apparently because of damage caused by ocean water.

In light of this,is it safe to go for nuclear power?

Japan was struck with an earthquake measuring 9,which triggered a tsunami. Such strong earthquakes are rare,even in seismically active Japan. The earthquake was the fourth strongest ever recorded. Japan has 54 nuclear reactors in areas falling in zones 4 and 5. The United States too has reactors in areas in zone 5. According to the World Nuclear Association,an estimated 20 per cent of reactors worldwide are in areas of significant seismic activity. Yet,most countries are satisfied with their technology’s ability to handle earthquakes.

How does one read the Richter scale?

An earthquake of magnitude 7 would be 10 times larger than an earthquake of magnitude 6,in terms of vibrations caused. In terms of energy,it would release 32 times more. The Richter scale,which gives an indication of vibrations,is not linear but logarithmic. As it goes higher,a difference of even one decimal point can mean a huge variation. Earthquakes are measured in terms of ground movement of the earth. For example,a magnitude 3 earthquake on this scale results in about 1 mm vertical movement in the earth’s surface at a distance 100 km from the epicentre.

How prone is India to earthquakes?

The Himalayan region and the Northeast are the most prone. In recent memory,the 2001 earthquake in Bhuj in Gujarat is the strongest recorded at 7.2. The 1993 earthquake in Latur in Maharashtra was 6.1 while the Uttarkashi earthquake in 1991 was 6.5. The southern part of India is known to be seismically benign though there are some areas in zones 3 and 4. Most of India’s nuclear installations are in southern India near the sea coast,an area not likely to have earthquakes more than 6 on the scale. Experts say that chances of a Latur-like earthquake happening in southern India is about once in 100 years.

What happened to Indian reactors in 2004?

When that tsunami struck,the Kalpakkam nuclear installation near Chennai was affected. The residential colony of the nuclear facility was flooded and some people died but the reactor itself remained unaffected. It went through the automatic shutdown process and was not operated for the next few days.