Prof.T.Shivaji Rao,
Director, Centre for Environmental Studies,
With the disastrous consequences of Chernobyl accident which led to the evacuation of 1,35,000 people from the 30km exclusion zone around the nuclear plant in Kiev people all over the world have begun to doubt about the safety of nuclear power. Experts in some countries like
1. Pollution: Radioactive residues discharged into the air, water and soil during routine operations of the nuclear power plant certainly pollute the environment. During accidents such contamination will become all the more dangerous with large scale emissions of Krypton, Xenon, Iodine, Strontium, Caesium and Tritium. Due to their half-lives extending over decades they enter into the food-chain and poison the plant, animal and human populations for centuries. Unfortunately, these are millions of times more hazardous that most of the toxic chemicals. And unlike many chemicals, their presence cannot be detected by smell, touch, taste or colour. These residues have a tendency to become accumulated. Radioactive zinc that was discharged, by a plant into Columbia river in the
| What are the Types of accidents in the Indian Reactors? Speaking at the Madras seminar on “Atoms for Peace power and prosperity” (October 28, 1988) the Chair person of AEC claimed that “because of inherent characteristics, an accident of the type that occurred at Chernobyl is not possible in Indian reactors” Perhaps not the Chernobyl type, but what other types of accidents are possible in the Indian reactors? Uranium 235 produces several highly toxic elements when it goes through an energy-producing fission process. Within a fuel bundle , these substances produce intense beams of radiation and even if only trace amounts escape into the environment they can find their way into the food-chain by contamination of water, vegetation cattle, fish and agricultural products. -- Dhirendra Sharma, HINDU, 14th March ‘89 |
2.Risk factors-Dosage: It is surprising that nuclear experts have so far, not attempted to present any scientific basis to convince the people about the impact of different levels of radiations on public health. For instance, according to the experts a radiation dosage of 30-70 rems/year was fixed as the tolerance level in 1928. This was reduced to 15 rems/year by 1950 and in 1956 it was further reduced to 5 rems/year. According to the International Council of Radiological Protection (ICRP) while the plant workers can be exposed to 5,000 millirem/year the dosage for the general public is restricted to 500 milli-rem/year. The US Environmental Protection Agency (EPA) has reduced the dosage near nuclear plants from 500 milli-rems/year to 25 milli-rems and the US Nuclear Regulatory Commission (NRC) has recommended 5 milli-rems/year for the public. It is absurd to presume that a nuclear power plant worker is less susceptible than a member of the public by 10,200 and 1000 times. According t Dr.Morgan, former chairman of ICRP, radiation damage can never be completely repaired. Children with allergies like asthma, have 300% to 400% more risk of dying from leukemia. Some experts feel that no radiation dose is so low that the risk of cancer is zero, based on the linear no-threshold hypothesis.
This assumes that the incidence of cancer at low-dosage is directly in proportion to its incidence at high dosages. Another group of experts, who contest that this hypothesis over estimates the risks of low level radiation, believe in the linear quadratic theory that predicts that the cancer incidence is proportionately lower at the low dosage because the body cells may repair themselves more easily at low-doses than at high doses. Other experts believe that the hypothesis under estimates the cancer risk by a factor of 10 or more. However, the US Governmental agencies like the USEPA use the no-threshold hypothesis as it provides reasonable guidelines for protecting the public health. The USEPA has specified 25 milli-rems/year for whole body dose and yet does not claim that this level is risk free …….Hence, there is nothing like a safe limit …………..Many people, therefore feel that all actions leading to nuclear power generation and weapon proliferation and testing are crimes against mankind. Infact Chernobyl proved that even an advanced country like the
| Disposal of Waste Suppose a meltdown proof and inherently safe reactor has been designed. Still the problem of dismantling and disposal of nuclear fuel waste will remain for any system based on uranium fuel produces thousands of tonnes of low, intermediate and high levels of waste. And no nation s yet demonstrated the capacity to dismantle and dispose of a reactor while the operational life of an inherently unsafe reactor is just about 25 years it takes 15 years to construct one at the capital cost of Rs.800 crores a station. Add to it the cost of about 600 tonnes of heavy water a reactor unit at Rs.15,000 a kg ( at 1985 price) But before dismantling a reactor, it is necessary to de-fuel its fuel core which takes about five years and after that it will take 10-15 years to dismantle it piece by piece with remote controlled and robotic systems. According to a -- Dhirendra Sharma, HINDU, 14th March ‘89 |
3.Emergenc-Coolant Hazards: If the main pipe in the primary cooling circuit 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 650 MW plant the heat formation by radioactive disintegration 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 of fuel rods remains at 2,200oC. If the cooling liquid is lost, the outer surface of the rods heat up rapidly, within 10 to 15 seconds the fuel casing would begin to breakdown and within a minute the casing would melt. Unless the emergency cooling system comes into operation within a few minutes, the fuel (approximately 100 tonnes) and the supporting structure would all begin to melt, leading to a major accident. At a later 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 the heat from the fission products adds to it, thus sinking the molten core to the ground. In a 1000 MW nuclear reactor radioactive fission products accumulated after one year would be equivalent to the amount released by approximately 1000 atom bombs of the
| The Civilization is at stake The longest recorded civilization, is that of Egypt-5000 years but nuclear wastes are dangerous for more than 25,000 years. This poses an extremely complex theoretical problem of warning new civilizations on the earth. Enormous costs not withstanding, the scientists have yet to learn how to design and construct a nuclear waste structure which can survive for more than 20,000 years. |
Since the reactor pressure vessel contains the core, any leakage in the pressure vessel in excess of the supply from ECCS lead 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 Emergency core cooling system releases the cool water from the accumulators intended to cope with such emergencies. But the environmental experts and opponents of Nuclear power emphasize that by the time the Emergency Coolant Water gets into 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 on the Emergency Core Cooling system at the National Reactor Testing Station in
Subsequent tests at Oak-ridge National Laboratories indicated that the Zircaloy clad fuel rods may swell, rupture and obstruct the Cooling channel and thereby prevent the Emergency Cooling Water from reaching the reactor core. Fuel-rod swelling commenced at about 1400oF and at 1800oF 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 outside the design basis of the plant such as a molten fuel coolant explosion or the gross failure of the vessel support system.
4. Un-Resolved Safety issues: Steam generators also cause problems due to deformation of the tubes because of corrosion of the support plate materials. Some generators have experienced fretting, fatigue failures, tube-pitting and erosion-corrosion problems.
The feed water system piping is exposed to the problem of water hammer, leading to excessive pipe-movements and damage to the valves. The valves themselves face problems including those from packing gasket or seat leakage, galling and erosion.
In 1978 the US Congress directed NRC to solve the outstanding issues on safety. The most important issues were designated “un-resolved safety issues” (USI) which were defined as “a matter affecting a number of nuclear power plants that pose important questions concerning the aqequacy of existing safety requirements for which a final resolution has not been developed and that involve conditions not likely to be acceptable over the life time of the plants affected”. About 500 less important generic issues and issues specific to one or a few nuclear power plants were identified by 1980. By the end of 1984, a further 150 less important issues have arisen. Although most of these minor issues were resolved, there is never the less a large backlog awaiting solution. Unless these are resolved, it would be impossible to convince the public that nuclear power is the safest among all sources of energy.
In designing absolutely safe reactors a number of systems, like the air-tight containment dome and fail-safe features were originally proposed. But these only helped reduce the probability of accidents rather than eliminate them altogether. In fact no human activity is entirely free from risks and the greater the rector size the more should be the effort to assess the probabilities and magnitude of accidents before reactors are made operational and to initiate necessary design changes to make the probability sufficiently low. Unfortunately industrialists prefer the alternative of building the plants first and then making changes later (presumably after an accident).
| Search for alternatives The Soviets have now given up the RBMK and it is also reported that the VVER-1000 reactor will no more be permitted operation in the - Dhirendra Sharma – HINDU, 14th March, 1989 |
5.Concept of Risk: Nuclear scientists point to the safety aspects of their plants by restricting their considerations to risks of death comparing it well to losses due to causes such as fire, electrocution, lightning, road accidents etc. Although these latter accidents cause instant deaths, unlike the radio-active pollution they do not cause genetic mutations with long-term repercussions. The traumatic experiences of Europeans under the
| Who bear the Decommissioning cost? In the - Senator Lorenzo M.Tanada (Phillippines) |
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