Safety concerns

Nothing left to chance

Print edition : August 09, 2013

The elevation of the KKNPP structures well above the mean sea level protects the plant from the effect of tsunamis.

A cross section of the reactor vessel.

Nuclear reactors at Kudankulam will not harm marine life or displace any more people, say experts. The plant is also designed to withstand disasters, natural or otherwise.

IN the din whipped up by the agitation led by the People’s Movement Against Nuclear Energy (PMANE) against the two Russian reactors at Kudankulam, important observations made by the Muthunayagam Committee on the great lengths to which Nuclear Power Corporation of India Limited (NPCIL) has gone to incorporate a bank of safety features in the Kudankulam reactors have not got the attention they deserve.

The primary concern of the fishermen in the coastal villages around the plant is that the hot condenser water that would be let into the sea from the reactors would kill the fish in the sea and harm other marine life and thus ruin their livelihood. The Muthunayagam Committee’s report makes light of this fear. The coolant water let out into the sea will not have any significant adverse effect on the fish in the Gulf of Mannar and so there is no threat to the fishing community’s livelihood, it asserts.

An important conclusion in the report is that “the KKNPP is designed and engineered to the state-of-the-art nuclear reactors in line with the current international safety requirements and principles”. The report says PMANE members “were not prepared for any discussions” on the safety features of the reactors but were “repeatedly demanding the closure of the KKNPP project without justifying their demand”.

On October 20, 2011, the Centre constituted a 15-member experts’ group headed by A.E. Muthunayagam, former Secretary, Department of Oceanography, and former Director, Liquid Propulsion Systems Centre (LPSC), Indian Space Research Organisation, to interact with the local people around Kudankulam and dispel their fears about the safety of the reactors.

This reporter found that in all the villages around the nuclear plant, the fishermen are scared of the possible effect of the condenser water on the fish in the sea. However, there has been no agitation at all by the fishermen living around the Kalpakkam or Tarapur nuclear power station, built on the shores of the Bay of Bengal and the Arabian Sea respectively. They have not complained about a drop in the catch in either of these two places. Nowhere in the world have fishermen protested against coolant water being pumped from reactors into the sea, lakes or rivers.

In a nuclear reactor, the heat generated converts water into steam, which drives the turbine-generator to produce electricity. The unused heat in the turbine is 66 per cent of the total heat. This heat is discharged in the condenser, which becomes hot in the process and so cooled by water. In coastal nuclear power stations, the water to cool the condenser is drawn from the sea by pipelines laid on the seabed. This water becomes hot and is discharged back into the sea. While the seawater that comes in has a temperature of around 32 Celsius, the water that is pumped back into the sea is around 37 C. This is well within the Tamil Nadu Pollution Control Board’s stipulated maximum of 7 C for protecting the fish population in the sea. The Gidroproekt Institute, a reputed institute in Moscow, designed the cooling water system for Kudankulam after studying several variants.

Fish are safe

In view of the fears of fishermen around Kudankulam, the Department of Atomic Energy initiated a study headed by the DAE’s Board of Research in Nuclear Sciences. It involved seven universities, including Manonmaniam Sundaranar University, Tirunelveli. (The Kudankulam reactors are located in Radhapuram taluk in Tirunelveli district.) The universities were asked to do thermal ecological studies.

These studies, which took five years, were done not only near Kalpakkam and Tarapur but in the Kali river, on whose banks the Kaiga nuclear power station in Karnataka has been built. The studies found that the discharge of condenser water could cause a maximum rise of 5-6 C in the temperature of the seawater. Within a short distance from the landfall point of the discharged water, the temperature got homogenised because the sea was such a large body and there was a good mixing zone in it. In fact, Anil Kakodkar and Srikumar Banerjee, both former Chairmen of the Atomic Energy Commission, were confident that there was “absolutely no cause for concern” on this issue.

The Kudankulam station has an innovative fish protection facility. Since the plant uses seawater for cooling the condenser, pipelines made of concrete bring the seawater by gravity to the pump-house on the shore. But small fish may get trapped in the water and enter the cooling facility. At the place where the pipelines are laid on the bed, compressors blow air into the tunnels and create an air-bubble curtain and waves on the sea surface. So the fish will move up and float on the surface and not go down to enter the pipeline. These fish are then thrown out further into the sea by hydraulic ejectors. This fish protection facility was qualified by an actual test in a facility in Russia.

No more land acquisition

Residents of villages near Kudankulam are also agitated about supposed plans to evict those living within a radius of 30 km from the station. But NPCIL officials have made it clear that enough land, about 400 hectares, had been acquired for building six reactors and that there would be no further acquisition. S.K. Jain, former Chairman and Managing Director, NPCIL, had said that there would not be any evacuation or displacement of people. He was “dismayed”, he said, by the “rumour-mongering that people in villages over a distance of 30 km of the KKNNP will be permanently evacuated” ( Frontline, October 21, 2011).

Accident safety measures

Informed NPCIL officials said that when a supplementary agreement was signed in 1998 to the earlier Inter-Governmental Agreement of 1988 on buying the Russian reactors, the DAE and the NPCIL had specifically wanted to buy the VVER-1000 reactors because they were among the safest in the world. The NPCIL also insisted on additional safety features in the VVER-1000 that it was going to buy. These features which were incorporated into the reactors, included the core-catcher, the passive heat removal system and the hydrogen recombiners.

The VVER-1000 reactors at Kudankulam belong to the latest Generation 3 Plus category, which incorporates the most advanced safety features to combat failure of supply of the coolant or a station blackout, to mitigate a fuel core meltdown, and to withstand earthquakes, tsunamis, cyclones and a small aeroplane crash, said N. Nagaich, Executive Director (Corporate Planning and Corporate Communications), NPCIL.

The reactors have many active and passive, inherent and engineered, safety features to cool the fuel core in case of an accident, that is, to prevent the enriched uranium fuel from melting and ensure that no radioactivity escapes into the atmosphere. The innovative passive heat removal system (PHRS) will ensure that the uranium fuel core does not melt in case of an accident or a station blackout. NPCIL engineers conceived its design and the Russians polished it up. It is called a passive system because it has no moving parts, it needs no electricity to be activated, and works automatically on the thermo-syphon principle. It is a box-like structure which sits on top of the reactor building. The PHRS consists of several heat exchanges and steel pipes three metres in diameter. While the PHRS will allow the hot air inside the reactor building to go out into the atmosphere, air will come in from outside to cool the reactor core.

Another safety feature special to the reactors is the core-catcher situated on the floor of the reactor building. It is a huge vessel, weighing 101 tonnes and made of stainless steel. In case of a loss-of-coolant accident (LOCA, that is, where there is no supply of light water coolant to circulate around the core) and fuel meltdown, the highly radioactive molten fuel core will drop down into the core-catcher. The core-catcher is filled with bricks of ferrous oxide and aluminium oxide, which absorb the heat from the molten uranium. The molten fuel and the bricks form a lump over a period of time. The catcher itself is surrounded by several lakh gallons of water. Extensive research was done at the Kurchatov Institute in Moscow before the catcher’s design and the bricks’ composition were finalised.

Again, to ensure that the reactor core is kept cooled in case of an accident, each reactor building has 12 huge water tanks, called hydro accumulators. In case of an LOCA, this water, mixed with boron, will douse the fuel core and keep it cool.

Hydrogen accumulation will not take place in the reactor building at Kudankulam as had happened at Fukushima because hydrogen recombiners have been installed for hydrogen and oxygen to combine to form water. At Fukushima, hydrogen formed when the zirconium cladding around the fuel assemblies reacted with air and there was a hydrogen explosion.

To prevent this from happening at the Kudankulam reactors, 154 box-like structures, installed at vantage locations inside the reactor buildings, are filled with chemicals, including palladium. If the fuel core melts and the hydrogen level in the atmosphere rises to more than 4 per cent, the palladium will force the hydrogen to combine with oxygen and form water. Thus, a hydrogen explosion will not take place.

The reactor building itself is “a dome within a dome”. The reactor is housed inside a 1.2-m-thick wall made of pre-stressed and reinforced concrete and called primary containment. Its inside has a steel lining, 6 mm thick. The outer, secondary containment wall is 60 cm thick and made of reinforced concrete.

These two walls are topped with domes, and hence called “a dome within a dome”. The primary and secondary containment walls, with their domes, will prevent radioactivity from escaping into the atmosphere in case of an incident or accident. These walls and domes will protect the reactor building during tsunamis, cyclones or a small aeroplane crash.

Safe from tsunamis

The KKNPP design takes into account the rise in water level in the event of a tsunami. “The ground elevation of all buildings at the Kudankulam plant starts from 7.5 metres above mean sea level (MSL), which precludes flooding even by a tsunami. This design feature passed the test during the tsunami of December 2004,” said Nagaich.

The tsunami ravaged the Kanyakumari coast, about 25 kilometres away, but no water entered the KKNPP site because it was 7.5 m above MSL. The tide level during the tsunami was only 5 m high. While the pump houses are located 7.65 m above MSL, the turbine building is 8.1 m above it, and the reactor building is 8.7 m above. The four diesel generator (DG) sets, which will erupt into life in case of a station blackout, have been installed 9.3 m above MSL. At Fukushima, the DG sets were knocked out by the tsunami waves because they were not situated at an elevated level.