KUDANKULAM NUCLEAR SAFETY STUDIES OF 1990

SOME ENVIRONMENTAL ASPECTS OF THE NUCLEAR PLANT AT KUDANKULAM

(Extracted from “Religion and Society”, Vol.XXXVII, No.2, June 1990)

T.SHIVAJI RAO

INTRODUCTION:  Man requires energy for day-to-day requirements, transport, food production, economic growth and prosperity.   About 40% of the energy needs of the people are met from non-commercial sources like cow-dung, agricultural wastes, firewood and animal power, while the remaining 60% is met from commercial sources like coal, gas, oil and hydropower.  Among the commercial sources, electricity is the most important and convenient form of energy.   Electrical power constitutes 18% of the total power at present and it may go up to30% by 2000 AD.  Nuclear power contribution is less than one per cent of the total energy requirement of the country and it is proposed to establish about 20 more reactors estimated at Rs.15,000 crores to increase the nuclear power contribution upto 10% of the commercial power by 2000AD. Before embarking on such large scale expansion of nuclear power it is pertinent to discuss the environmental and safety aspects of proposed nuclear plants.

In order to discuss nuclear power and its environmental effects, it is necessary to understand the fundamentals of nuclear power. The atom which is the smallest unit of an element has a nucleus containing protons and neutrons encircled by electrons.  When the nucleus disintegrates radioactivity is set free producing L particles and X-rays which ionize the atoms of any substance through which they pass.  This ionization causes a chain reaction that damages the penetrated substances such as human cells.

In nature elements such as radium are unstable and tend to attain stability by disintegration or by emission of radioactivity in the form of  particles and X-rays.  On the other hand, any element can be converted by force into another, rearranging the atomic components.  During this conversion of an unstable element to a stable one enormous amount of heat is released and the same is used to heat water to produce steam and then electricity.  In this process a few neutrons and radio nuclides are released into the human environment and they often cause pollution problems.  When the nuclear fuel is fully utilized, radioactive wastes are produced.  Usually these radioactive wastes are dumped into the ocean or buried in thick containers in abandoned mines.  The only way to make a radio nuclide least harmful is to enable it to disintegrate naturally until a stable element is formed.  The radioactivity of an element disappears after an equivalent time-period of about ten times its half life period or when its radioactivity reaches 0.1%  of its original value.  For example, a millionth of a gram of plutonium causes lung cancer and it remains active for 2,50,000 years.  According to experts even natural radioactivity is both physiologically and biologically unsafe.

Different types of reactors are used for the generation of nuclear power.  In India, the boiling water reactor and pressurized heavy-water reactors are used at present.  However, it is proposed to import enriched fuel and the pressurized water reactor from USSR for the proposed plant in Tamilnadu.

OPERATION OF A PRESSURIZED WATER REACTOR:  A nuclear reactor like a coal-fired thermal power station used steam to generate electricity.  Instead of producing steam by burning coal, nuclear reactors are fuelled by uranium, an ore mined from the earth and refined by various processes.  Uranium has an unstable atomic structure which means that some of its atoms contain an unequal number of protons and neutrons in their nuclei.  In nuclear power, other neutrons are used to bombard these unstable nuclei, causing them to split and thereby release more neutrons,  a process called nuclear fission.  When the freshly released neutrons hit the other unstable nuclei in the fuel, a chain reaction occurs.  The massive heat energy released by this chain reaction is so intense that a single uranium fuel pellet of the size of a pencil eraser can produce as much heat as a tonne of coal.  For efficient operation, proper control of this energy is essential and adequate precautionary measures must be taken to ensure that there is  no disastrous core melt-down.  For the purpose, the operators control the reactions by packing the fuel pellets inside hollow metal rods which are assembled to form the core.  The fission process is  manipulated by the control rods in the core that can be raised and lowered to absorb the neutrons.  The reactor is filled with water to act as a coolant to absorb over 600^oF and this is used to generate steam which like its coal fuelled counterpart is used to drive turbines to produce electricity.  To prevent the escape of radioactivity the reactor core is shielded by a thick steel vessel, housed in an air tight steel containment structure which again is surrounded by thick walls of RCC (Double-containment)

PRESSURISED WATER REACTORS: In a pressurized water reactor, the pressure vessel of the reactor is packed with the uranium fuel rods and is filled with water which not only transfers the heat generated during the fission chain reactions in the core to the heat exchanger but also sustains the chain reactions in the fuel rods.  The heat released from the fuel rods is carried by the coolant in the primary water loop to the heat exchanger where it is used to convert the water in the secondary water loop into steam which in turn runs the turbo-generator to produce electricity.  As the fission products from the fuel are radioactive and emit particles and rays and neutrons that cause damage to living cells, they produce immediate somatic and long-term genetic damage among people exposed to the radiation (Table-I).  Hence extensive precautionary measures are to be taken to ensure that the radiation from the fuel rods does not break the barriers of safety and get into human environment.

EACTORS AT KUDANKULAM: In order to utilize the heat generated during the fission of uranium, the Atomic Energy Commission proposed to establish a 2 x 1000MW water-cooled and water-moderated (VVER) reactor at Kudankulam in Tamilnadu. Here nuclear fission occurs in 100 tonnes of uranium oxide fuel in 50,000 close-packed fuel rods, the zirconium alloy tubes of half-inch diameter.  These fuel bundles, the reactor core, sit in a thick steel pressure vessel through which cooling water is pumped at 18tonnes per second to carry away the heat generated during nuclear fission and use it to produce steam and electricity through a turbo generator.  The fuel gets yellow-hot at its core, attaining a temperature of 4100^oF (2250^oC) while the metal casing around the fuel is kept at 650^oF (350^oC) by the cooling water.  If due to an accident the coolant water gets interrupted for just a few seconds the fuel temperature rises rapidly and the zirconium casing begins to break at 1800^oF (1000^oC) and melts at 3350^oF (1850^oC) The actual danger comes when the hot fuel begins to lump together in a molten mass that can explode the containment or seep into the ground, a process known as “Chinese-Syndrome”, and release massive quantities of radioactivity into the air, water and soil environment.

SAFETY OF REACTORS:  In order to avoid the core melt-down, experts have provided a series of safety devices.  One major line of defence is emergency core cooling system (ECCS) which provides an instantaneous water supply that keeps the core from melting.  Another line of defence is the concrete containment that surrounds the core and the pressure vessel so that even during a loss of coolant accident, no radioactivity will escape into the outside environment.  Such engineering safety measures also fail sometimes.  If the main pipe in the primary cooling breaks, immediately the control rods eliminate the nuclear fission process, halting the activity.  But the radioactivity  in the  already disintegrating fission products cannot be arrested.  In a 650MW plant, the heat formation by the radioactive disintegration process amounts to roughly 200MW three seconds after the reactor is switched off, 100 MW after one minute, 30MW after one hour and 12MW after 24 hours.

Under normal operating conditions, the reactor has an external fuel casing temperature of about 350^oC, while the interior fuel rods remain at 2220^oC.  If the cooling liquid is lost, the outer surface  of the rods heats up rapidly within 10 to 15 seconds, the fuel casing will begin to break down and within a minute, the casing will melt.

Unless the emergency cooling system comes into operation within a minute, the fuel (approximately 100 tonnes) and the supporting structure will all begin to melt, leading to a major accident.  At this stage even if the emergency cooling system works, it will make the situation worse.  The molten metals react with the cooling water to produce steam and hydrogen and heat from the fission products adds to this, thus  sinking the melten core to the ground.  In a 200MW nuclear reactor radio-fission products accumulated after one year would be equivalent to the amount released by approximately 1000 atom bombs of the Hiroshima variety.  Since the reactor pressure vessel contains the core, any loss in the pressure vessel in excess of the supply from ECCS leads to the escape of the coolant, thereby exposing the core that gets overheated within seconds.   The failure of the vessel can inflict serious damage to the core and also break the containment.

EMERGENCY COOLANT FAILS: According to the advocates of nuclear power when the primary coolant comes out of the major pipe break in the coolant water loop, the control rods are immediately driven into the core to stop the fission reaction and the ECC system releases the cool water from the accumulators intended to cope with such emergencies.  But the environmental experts and opponents of nuclear power emphasise that by the time the emergency coolant water gets in the core, the temperature in the core would become so high that the water turns into high pressure steam, either obstructing the entry of more coolant or forcing it to exit through the breakage in the pipes  so that the reactor core gets overheated to cause a major disaster.  When the Aerojet Nuclear Company conducted tests of ECC system at the National Reactor Testing Station in Idaho, USA, mechanical failure occurred.  Subsequent tests at Oakridge National Laboratories indicated that the Zircalloyclad fuel rods may swell, rupture and obstruct the cooling channel thereby preventing the emergency cooling water from reaching the reactor core.  Fuel rod swelling commenced about 1400^oF and at 1880^oF the coolant channels were blocked by 50 to 100 percent and such a blockage could be catastrophic.  The combined effect of the rapid cooling during an emergency core cooling with the rapidly rising pressure in a reactor vessel could lead to its rupture, an accident that no nuclear plant is designed to cope with.  Failure of the vessel could occur due to inherent weakness in the construction of  the vessel itself or due to factors such as molten fuel coolant explosion or the gross failure of the vessel support system.  Steam generators also cause problems due to deformation of tubes  because of corrosion of support of plate materials, fatigue failures and tube pitting problems.  The feed water system piping is exposed to water-hammer, leading to the damage of valves.  These valves on their own face problems from packing, gasket leakage and erosion.
Places to be evacuated during accident at Kudankulam: When an accident at a nuclear plant releases enormous quantities of radioactivity into the air, water and soil environment, there will be immediate fatalities and long-term genetic damage among the exposed populations.  All the people within the zone of influence from the reactors must be evacuated.  Evacuation must be completed within 6 hours for 2 to 5km, 12 hours for 5 to 25km, 24 hours for 25 to 75km and 40 hours for over 75kms downwind from Kudankulam as per the British Accident scenario for the 1100MW, Sizewell reactor, based on a wind speed of 5m/sec rainfall of 1mm/hour and natural stability conditions of the atmosphere.  After thorough scrubbing and decontamination of lands, equipment and residences due to radioactive pollution from an accident, people may be permitted  to return to their original residence along with their cattle and other properties after three weeks upto 170kms, one year upto 140km, from 5 years upto 115km, 10 years upto 98km and 20 years upto 77kms distance from the nuclear plant.  Depending upon the weather conditions during the accident, certain places will be more affected than others.  Many villages of Ramanathapuram, Tirnelveli and Kanyakumari of Tamilnadu and Trivandrum and Quilon districts of Kerala will be affected seriously.  Killakkarai, Sattirakudi, Abiramam, Virudhnagar and Watrap of Tamilnadu and Gudalur, Thekkadi, Vengamala, Pantalam and Karunagapalli of Kerala lie within 170kms.  Sayalkudi, Nattakkadu, Sivakasi and Sattur of Tamilnadu, Edathora, Aruppokottair, Srivilliputtur and Rajapaliyam lie in between 140km and 170kms.  Karilgatti, Kalugumala and Puliyangudiof Tamilnadu, Tenmala, Kadakkal, Attingal and Kadiamkulam of Kerala lie within 115km.  Taruvaikulam, Kadambur, Tirumalapuram and Tenkasi of Tamilnadu and Palad and Attipara lie within 98kms.  Tuticorin, Kayattar and Trivandrum lie in between 98kms and 77kms, Sayarpuram Pudukkottai, tirunelveli, Ambassamudram, Mannar, Balaramapuram, Neyyattinkara, Nanguneri, Panakudi, Kolachel, Nagercoil and Cape Comorin lie within 77kms from the nuclear plant site. 

CHERNOBYL TURNS PUBLIC ATTENTION TO SFE REACTORS:

B.Scherbin, Deputy Prime Minister of USSR has said, “No amount of safety precautions can rule out an unfortunate combination of mechanical failures or human errors.  In future therefore, we must pay equal attention to nuclear plant safety and to effective ways of dealing with nuclear plant accidents.

The tragedy of Chernobyl must stimulate research into what should be a fundamentally new generation of advanced reactors with built-in-self-protection systems

When the accident at the reactor at Three Mile Island occurred in 1979, Dr.David E.Lilienthal, the first Chairman of the US Atomic Energy Agency demanded that since all the existing reactors are inherently unsafe, the experts all over the world must concentrate their energies in producing an inherently safe reactor.  In pursuance of this demand the Swedish, German and American experts began to work on the development of the safe reactors.  Today the experiment is a success.

American experts have recently developed such safe reactors for which probability of a serious accident is zero, that is a reactor whose ‘safety depends not on the active intervention of safety systems but on physical principles that ensure the reactor’s safety without mechanical or human intervention but upon immutable physical principles that even in an emergency could not be abrogated.

Enlightened nuclear and environment experts have been warning the industry and the government to renounce the current generation of reactors stating that no matter how extensive the safety measures are, the reactor machines are disasters, ‘writing in the wings’.  In fact General Atomics, an American firm, is building a (MHTGR) modular high temperatures gas cooled reactor in Idaho falls,  to produce tritium  for nuclear weapons and to serve as a basis for a civilian reactor that will generate electricity.  In this reactor, the core size and the reactor output has been restricted to 140MW.

The secret of a safe reactor lies in its sand-grain sized fuel particles encapsulated in multi-layered glassy carbon spheres that trap radioactive fission products but transmit heat while remaining intact upto 3300^o.  Since the maximum temperature that the fuel grains can obtain in the spheres is limited to about 3000^oF the uranium fuel will not melt through the spheres under any kind of accident.

The pressurized water reactors proposed to be built at Kudankulam in Tirunelveli District of Tamilnadu are inherently unsafe.  In these reactor, fuel rods of about ½ inch thickness attain a temperature 4100^oF at the core while the casing temperature is maintained at 650^oF  by the cooling  water.  If the pipe breaks, water supply fails for just a few seconds and the hot fuel can destroy the metal casing which begins to break at 1800^oF and melts at 3370^oF.  back up systems such as the emergency core-cooling system(ECCS) and concrete containment are expected to ensure that no radioactivity will escape into the outside environment during an accident.  In spite of this core-melt accidents occurred at Three Mile Island and Chernobyl plants.  While the maximum fuel temperature of 3000^oF (1648^oC)is less than the fuel casing failure temperature of 3300^oF (1815^oC)in a safe reactor, the maximum fuel temperature of 4100^oF(2260^oC) is more than twice the fuel-casing failure temperature of 1000^oF(538^oC) in an inherently unsafe reactor.

CONCLUSIONS: Since the present generation of nuclear reactors are inherently unsafe it is essential to make detailed environmental impact reports, risk analysis and emergency evacuation and disaster management plans before clearance is given for locating a nuclear plant at a given place.  The environmental impact reports must be prepared for various alternate locations and they should be presented to the public for organizing scientific debates so that constructive suggestions from the experts and the public can be received for incorporation in the final reports on which appropriate decisions can be taken by the government.

Whether the same economic goals can be achieved through alternate methods of generating the energy including the option of no nuclear power should also be considered.  If at all nuclear plants are considered essential for the production of plutonium for national security, the use of safe integral reactors (SIR) under development and the modular high temperature gas cooled (MHTGR) reactors under construction in countries like USA must be given preference over the present generation of light water and heavy water pressurized reactors.  Even if the inherently hazardous reactors have to be inevitably used, they should be located underground or in mountain caverns in coastal belts or Islands so that the damage and critical impacts due to air-plane crashes, sabotage, human or mechanical failures are minimized.

TABLE No.1  HARMFUL EFFECTSOF RADIATION

A.  Dosage and damage to public Health
DOSE(rems)	EFFECTS
0-50	No visible symptoms except change in blood
80-220	Vomiting and nausea for one day plus symptoms of radiation sickness in 10% upto 120 rems; 25% upto 170 rems, 50% upto 220rems
270-500	Vomiting and nausea on first day plus sickness amaong all people with 20% deaths within six weeks upto 330 rems and 50% deaths in 1 month upto 500 rems
550-750	Vomiting and nausea within 4 hours and death upto100%
B. Single high dose and late effects
Cancer	Blood, nervous system, thyroid in excess of 100 rems, Leukemia rises correspondingly.
Cataracts	Lenses of eyes become increasingly opaque at 200 rems
Fertility	Brief sterility at 150rems
Degenerations	Impairment of organ functions.
Mutations	Rate doubled between 20 and 200 rems.
Life-shortening	Radiologists have 5 years lowered life-span
C. Chronic low doses	Cancer, immune deficiency, mutations, stillbirths, abortions etc.