In these difficult hours in South Asia after the deadly tsunami, there is something to be proud of for India.

It's time to acknowledge the achievement of Indian scientists who designed and built the Kalpakkam nuclear power reactors without foreign assistance. The nuclear station withstood the devastation of the Big Wave because it is not even imaginable what would have happened had the tsunami damaged the two nuclear power units situated on the shore.

L V Krishnan, former director, safety research and health physics at the Indira Gandhi [Images] Centre for Atomic Research at Kalpakkam, explains how the great disaster was forestalled because of scientific planning.

A veteran of the Department of Atomic Energy for 40 years, he retired from Kalpakkam nine years ago and is a well-known safety expert on nuclear plants. For many years, Krishnan, has been closely associated with the Kalpakkam nuclear power generating plants. He continues to advise DAE in selective matters. He visited Kalpakkam immediately after the tsunami hit the town killing 56 people including 5 nuclear scientists.

In an interview to Senior Editor Sheela Bhatt, he not only gives his account of how the Kalpakkam nuclear power plant withstood the tsunami but also suggests how India's nuclear assets can be protected in the case of a similar disaster.

No, tsunami was not taken into consideration. Nowhere in India people had thought a tsunami could strike the Indian coasts. But we had taken into account the worst cyclonic storm surges. Before a cyclone hits, a storm surge comes. We had provided for the worst cyclone that could hit the coast looking at historical statistics.

The maximum water level that could be expected if the cyclone coincided with highest of high tides was estimated at 6 metres or so. The Kalpakkam plant site is built to withstand that. The construction of Kalpakkam began in about 1968 but it was completed in 1983 because around 1974 outside help was discontinued and we found that we will have to build the plant indigenously and that took some time.

The first unit of Kalpakkam was commissioned in 1983 and the second was commissioned in 1984. Since then, it is functioning extremely well.

The tsunami storm surge that we saw on that day was not much more than that, in fact it (intensity of tsunami storm surge) was less than that!

Yes. These nuclear reactors, for cooling purposes, draw water from the sea; that is why they are located in the coastal area.

In Kalpakkam, half a kilometre into the sea there is a huge well that has been dug. That well is connected to another well on the shore on land. These two wells are connected by an under seabed tunnel. As the storm surge comes in and the water level rises in the well in the sea, the level of water also rises in the well on the shore.

The moment the water level rises beyond prescribed limits in the well on the shore, the seawater pump trips. The moment it trips the operator sitting in the control room knows that something is wrong and he trips the reactors.

Even before the wave hits the shore, I would say, that the reactors were shut down. Imagine if the waves would have been higher than what was anticipated by planners and if they would have come in, then, what would have happened to the reactors? Nothing at all.

The well in the sea and well on the shore are also connected by a jetty. On the shore there is a horizontally spread building that has turbines installed inside. Behind the turbine building lie the domes of two reactors. Even if the tsunami waters had come in they would have hit the turbine building first, not the reactors. And the reactor buildings have walls that are one metre thick (http://www.npcil.org/maps.asp). So even if waves had affected the site, sea water simply could not have entered the reactors. The reactors are pretty safe. It so happened that this time the water didn't even enter the turbine building. Even the turbine building is so designed that the ground level is sufficiently raised to withstand earthquakes and storms.

Also, all our reactors have a buffer zone of one-and-a-half kilometres between residential localities and the reactor building. If that buffer zone had existed in Bhopal, the death toll would not have been so high. I know from my experiences that district collectors are worried more about oil refineries than the nuclear reactors' safety measures.

The casualties were not at the plant site at all. The causalities were in the township. In the construction of the township we have not taken into account all of these things.

We had no fears of radiation there. Second, as I said we had not anticipated a tsunami. As far as a cyclone is concerned, one always gets advanced warning. But in the case of a tsunami if you don't have any advanced warning, the sea comes in silently. Many more people would have died if the tsunami had hit at 5 am instead of 9 am.

All earthquakes don't cause tsunamis. Certainly we didn't take into account earthquakes of a magnitude of 8 or more. While planning, we take more into account the earthquakes on land. We thought the fault line near Indonesia is quite far away from the Indian coast. Also, historical statistical data didn't suggest that a magnitude of 9 is a possibility and we didn't anticipate it.

After this event I have read only two reports on the historical data of tsunami in the Indian context. R N Iyengar, professor at the Indian Institute of Science, said on November 28, 1945, Pasni, a trading town about 100 kms from Mekhran, was washed away by a wave of about 15 meters, after an earthquake measuring 6.7 on the Richter scale hit the coast which is now in Pakistan. But that could not have been the basis of our designers in Kalpakkam. Another report claimed that a tsunami once hit some parts of Bangladesh.

It is safe. I visited the plant site two days after the tsunami hit us. Water had come in some places but it had just wet the ground. It didn't enter the building, it came just outside it. There are two reactor units in the Madras Atomic Power Station at Kalpakkam. One unit was already shut down for maintenance and the other was operating and the sea water pump house of that unit had registered the higher level of water.

Adjacent to the Madras Atomic Power Station a new fast breeder reactor is under construction. To make such vital buildings withstand earthquakes, first a large concrete base mat is built. So if the structure moves it will move all together without getting cracked. On the location of the fast breeder reactor they had dug up a huge area several metres below the ground level for the base mat. Sea water have flooded that place. Now, they will have to pump out the waters and start construction again.

There is no need to have operators present in the pump house all the time. Once the water level goes up there are water level indicators that trip the pump. And once the pump trips the reactors have to be shut down. As the water level rose in the well on the shore, the pump tripped and the operator saw it and he tripped the reactors. The operator's action is automatic.

I have not been there but Mr S K Jain, chairman and managing director of the Nuclear Power Corporation of India, was present at Kudankulam when the tsunami struck. The Kudankulam Atomic Power Project is under construction with the help of Russian scientists and he said the same thing -- that none of the building is affected.

If somehow the water had entered the turbines building what would have happened

In the turbine hall there is no radioactivity. The turbines are at a high level. Waters could only enter in the condensers and not in turbines. Now, if any part of the entire system is affected reactors will automatically shut down. And once the reactors stop functioning there is no risk.

And if tsunami waves would have entered the nuclear reactors building, then?

There is no way waters could get into the reactors buildings. The reactor will shut down automatically before water enters the building. The in-built system is such. We know nature is mighty. But we know the upper limit of what all nature can do. At least we can estimate. I agree scientists didn't anticipate a tsunami so the devastation has followed. But the cyclone was well anticipated and was taken into account. We anticipate something and then built the building. In Japan [Images] earthquakes are common but their nuclear reactors are safe and ongoing because of their designs of structures. Because man can anticipate safety is possible.

Yes. We too think like laymen and ask questions. Somebody designs the reactors. Another group builds it. And another group which is independent of it keeps asking questions as you do. What if the instrument fails? What if the operator makes mistakes? What if the back-up system fails too? We make sure that even if all these errors occur together the reactors will not release radioactive material.

The tsunami has hit India in the most vulnerable part. But if you are well protected you are safe. It so happened that our plants were well protected but our township was not so we lost 30 people. We didn't anticipate a tsunami but we anticipated a cyclone of this nature and it helped us tremendously. This time the velocity of water may not be as much as it is during cyclones but the volume of water was tremendous. See, the cyclone will have much higher wind speed as well. In Kalpakkam, the massive turbine building is able to protect the reactors.

I can assure you on the safety of Kalpakkam because often I am asked to assess the safety by the Atomic Energy Regulatory Board. I cannot afford to be lax on safety issue. I have to speak honestly.

I don't see any problem at Kalpakkam in the post-tusnami period too. I don't know however, what will be the case if an earthquake of magnitude 10 occurs in the Sumatra region. It is not enough to anticipate an earthquake, it is not enough to predict that an earthquake can cause a tsunami. It is also necessary to find out the impact of the tsunami along the coastline.

If you have an earthquake there, its effects may not be uniform everywhere on our coast. Along the coastline the depths of the sea are different. At some places sand gets piled up forming contours. The depths can be shallow there. The energy of the tsunami waves can be focused differently at particular point because depth varies along the coastline.

In India's coastline, the intensity of the tsunami is variable at different points along the coastline. Now, it is important to find out if there is likelihood of magnified impact because of the contour of the seabed underwater. Now the measurement of depth in the sea is necessary.

The bathymetric data of the sea ahould be available. We need to have it now to estimate wave heights and design accordingly. India will have to measure the depth of the sea and contours on the seabed. Then, we will be able to project the severity of waves and its impact at any particular point.

I am sure the Atomic Energy Regulatory Board will begin a review of the safety aspects. It is their objective. Every event of the country where unforeseen things have occurred, they assess and take corrective steps if necessary.

Even in our reactors when some surprises are noticed or when some component fails, immediately we shut down all other reactors which may have similar components. Only when we have understood why it failed, we restart the reactors. This is a common practice, everywhere in the world.

In this case, an earthquake of magnitude 9 will have to be taken into account. The mean return period of earthquakes of these magnitudes will be calculated. If something is likely to happen in the next thousands years we take that into account.

But something is likely to re-occur in say the next 5,000 years, you have to give less importance because somewhere you have to draw a line. On the basis of historical data, we will have to project the future of tsunami re-occurrences and also have to look at the possibility of an earthquake measuring 9.5. This is called extreme value analysis.

As I told you we will have to take into account seabed contours and its effect on the tsunami wave height. I am sure AERB will re-examine seismic designs of all the vital structures. Importantly, we will have to review the communication network.

Meanwhile, what we can do best is to observe also the movement of the seabed. There we should have buoys that have sensors on the seabed. If the seabed sensors move up because of earthquakes then they immediately relay the information to you. We don't have this system yet.

We should also be prepared for the events we cannot anticipate. We didn't anticipate a magnitude of 9. It's a huge earthquake. The fault lines off Sumatra extend from 2 degree to 10 degree north latitude. All along the fault line there is a disruption. It's mind-boggling. Nobody disputes that nature is superior to man but preparedness is possible. Safety is a question of attitude. When I visited Kalpakkam, scientists were happy that the design has withstood the tsunami and the reactors could be brought back in line. They had full faith in their own systems.