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 600oF
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 4100oF (2250oC) while the
metal casing around the fuel is kept at 650oF (350oC) 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 1800oF
(1000oC) and melts at 3350oF (1850oC) 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 350oC,
while the interior fuel rods remain at 2220oC. 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 1400oF
and at 1880oF 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.
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 3300o.
Since the maximum temperature that the fuel grains can obtain in the spheres
is limited to about 3000oF 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 4100oF at
the core while the casing temperature is maintained at 650oF 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 1800oF
and melts at 3370oF. 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 3000oF (1648oC)is less than the fuel
casing failure temperature of 3300oF (1815oC)in a safe reactor,
the maximum fuel temperature of 4100oF(2260oC) is more
than twice the fuel-casing failure temperature of 1000oF(538oC)
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.
|
