Posted by: PARTHA DAS SHARMA | October 17, 2008

Nuclear Energy based power plants – Discussions on future dependability for production of cleaner power:

Nuclear Energy based power plants – Discussions on future dependability for production of cleaner power:

1. Some facts about nuclear reactor for power generation:

A. Understanding running of nuclear reactor (fission) for power generation –

(i) Nuclear power can come from the fission of uranium, plutonium or thorium or the fusion of hydrogen into helium. Today it is almost all uranium. The fission of an atom of uranium produces few million times the energy produced by the combustion of an atom of carbon from coal.

(ii) Natural uranium is almost entirely a mixture of two isotopes, U-235 and U-238. Today’s commercial nuclear reactor uses U-235 for fission reaction. Natural uranium has 99.3 percent of U-238 and only 0.7 percent of U-235.

(iii) Most nuclear power plants today use enriched uranium in which the concentration of U-235 is increased from 0.7 percent to (nowadays) about 4 to 5 percent.

(iv) The U-238 “tails” are left over for eventual use in “breeder reactors”. The Canadian CANDU reactors don’t require enriched fuel, but since they use expensive heavy water instead of ordinary water, their energy cost is about the same.

(v) Present reactors that use only the U-235 in natural uranium are very likely good for some hundreds of years.

(vi) A power reactor contains a core with a large number of fuel rods. Each rod is full of pellets of uranium oxide. An atom of U-235 fissions when it absorbs a neutron. The fission produces two fission fragments and other particles that fly off at high velocity. When they stop the kinetic energy is converted to heat.

(vii) The steam withdrawn and run through the turbines controls the power level of the reactor. The heat from the fuel rods is absorbed by water which is used to generate steam to drive the turbines that generate the electricity.

(viii) After about two years, when enough U-235 is converted to fission products and the fission products have built up enough so that the fuel rods must be removed and replaced by new ones.

(ix) Besides fission products, spent fuel rods contain some plutonium produced by the U-238 in the reactor absorbing a neutron. This plutonium and leftover uranium can be separated in a reprocessing plant and used as reactor fuel.

(x) Thus running a reactor for four years produces enough plutonium (about 1/4 as much as the U-235 that was in the fuel rods) to run it for one more year provided the plutonium is extracted and put into new fuel rods. Newer designs with higher “burn-up ratios” get more of their energy from plutonium.

B. Understanding nuclear waste –

(i) After the fuel has been in the reactor for about 18 months, much of the uranium has already fissioned.

(ii) A considerable quantity of fission products also have built up in the fuel.

(iii) The reactor is then refueled by replacing about 1/3 of the fuel rods. This generally takes one or two months. Canadian CANDU reactors replace fuel continuously.

(iv) When fuel rods are removed from the reactor they contain large quantities of highly radioactive fission products and are generating heat at a high rate.

(v) They are then put in a large tank of water about the size of a swimming pool. There they become less radioactive as the more highly radioactive isotopes decay and also generate less and less heat.

(vi) The fuel rods should then be chemically reprocessed. Reprocessing removes any leftover uranium and the plutonium that has been formed.

(vii) The fission products are then put in a form for long term storage.

(viii) A large reactor produces about 1.5 tonnes of fission products per year.

(ix) Economic advantages of reprocessing are great. If do not reprocess, we lose the economic benefit of the plutonium.

(x) At the same time, the spent fuel remains radioactive for longer duration and has to be better guarded, because it contains plutonium.

C. Understanding of future nuclear reactor – ‘breeder reactor’

(i) If the design of reactor is such that, enough U-238 can also be converted to plutonium so that after a fuel cycle there is more fissionable material than there was in the original fuel rods in the reactor. This system is more economical.

(ii) Such a design is called a ‘breeder reactor’.

(iii) Breeder reactors essentially use U-238 as fuel. Therefore, it is more advantageous and it is estimated that, there is 140 times more beneficial than the conventional reactor.

(iv) They are more expensive than present reactors.

(v) Breeder reactor will be reprocessing on site, so no plutonium will ever become externally available.

(vi) It is much safer system than the present one. It is hoped that it would address the proliferation concerns of the anti-nukes.

2. Discussion on advantages of environment-friendly Nuclear power:

Power from nuclear energy can prevent many of the environmental consequences arising out of the use of fossil fuels, hydropower etc. Below we discuss about the disadvantages of power generated from (a) burning of fossil fuels and (b) hydropower – two major sources of power available by many countries at present other than nuclear power.

A. Power generated by burning of fossil fuels (coal, petroleum and gas):

(i) The main drawback of fossil fuels is pollution. Burning any fossil fuel produces carbon dioxide, which contributes to the “greenhouse effect”, warming the Earth. The effect of rise in temperature is disastrous to environment. Agriculture is very sensitive to climate and hence is heavily affected, requiring shifts in crops that cannot be grown in different areas. Livestock also been affected through problems in breeding, diseases. Eventually, the melting glaciers will cause sea levels to rise – causes loss of habitat land, allows inland penetration of salt water which heavily impacts aquatic life. Burning fossil fuel also produces sulfur dioxide, a gas that contributes to acid rain. Acid rain is destroying forests, making lakes unlivable for fish and degrade ecosystem.

(ii) Mining of coal can be difficult and dangerous. Coal mining destroys large areas of the landscape.

(iii) Waste disposal for coal-fired power plant is a major issue. Coal-fired power plant produces large quantity of ashes, which is difficult to handle and store. It destroys and pollutes large areas of land. Dust is also generated, causing health problems to human being.

B. Hydropower: Although hydroelectric power is considered to be a clean, renewable source of energy, emitting a very low level of greenhouse gases when compared to fossil fuel plants; it has some disadvantages. Shortcomings of hydropower are listed below:

(i) The flooding of large areas of land means that the natural environment, forest etc., is destroyed.

(ii) It requires water at a certain volume and speed. Rain fall or lack thereof can affect the efficiency of this type of energy source.

(iii) Dams are extremely expensive to build and must be built to a very high standard. The high cost of dam construction means that they must operate for many decades to become profitable.

(iv) People living in villages and towns that are in the valley to be flooded, must move out. This means that they lose their farms and businesses. In some countries, people are forcibly removed so that hydro-power schemes can go ahead. Most of the time rehabilitation of such large number of people becomes very much problematic and some time not possible for whole mass of persons destabilized because of creation of dams.

(v) The building of large dams can cause serious geological damage. There are many examples when big dams are created; it aggravated the chances of earthquake. For example, the building of the Hoover Dam in the USA triggered a number of earth quakes and has depressed the earth’s surface at its location.
(vi) Building a large dam alters the natural water table level of the area.

(vii) Dams built blocking the progress of a river in one country usually means that the water supply from the same river in the following country is out of their control. This can lead to serious problems between neighboring countries.

(viii) It alters the ecology upstream and downstream of the dam, although fish-ladders have some moderating effect on migratory species going upstream, but can chew up the fish on the way down. The diversion of water can impact stream flow, or even cause a river channel to dry out, degrading both aquatic and streamside habitats.

C. Discussion on advantages of nuclear power:

(i) One of the greatest advantages of nuclear power is that it avoids the wide variety of environmental problems arising from burning fossil fuels – coal, oil, and gas. Nuclear energy does not produce smoke or carbon dioxide, so it does not contribute to the greenhouse effect. Thus ‘global warming’ process can be minimized – changing the earth’s climate, acid rain, which is destroying forests and killing fish; air pollution etc. Nuclear power checks degrading our quality of life; i.e., the destructive effects of massive mining for coal; and oil spills which do great harm to ecological systems can be prevented.

(ii) It is possible to generate a high amount of electrical energy in one single plant using small amount of fuel.

(iii) Nuclear power is reliable. This technology is readily available; it does not have to be developed first.

(iv) Produces small amounts of waste. As the quantity of waste generated by nuclear power plant is very small, the disposal of radio-active waste can be easily contained so they can be buried deep underground. Also, more effective ways can be found out as our technology is improving at a very fast pace. Moreover, the quality of radio-active waste improved if we go for reprocessing of spent fuel and reuse of plutonium is incorporated.

(v) Nuclear power is also not so expensive as compare to power from coal. Reprocessing and reuse of plutonium from spent fuel makes it even cheaper than coal based power plant. The concern about proliferation should be taken out of mind as there are much easier, faster, and cheaper ways for a nation to develop nuclear weapons than through a nuclear power program.

D. Discussions on future dependability for production of clean electric power:

(i) As observed from above, nuclear power has advantages in many areas, including some that have been traditionally viewed as problem areas. It averts the pollution, environmental degradation and above all retards generation of greenhouse gases responsible for global warming. It also solves difficult waste management problems.

(ii) In my opinion, the generation of nuclear power should be given most priority, to combat environmental degradation and global warming issues. Wherever there is stagnation in implementing new nuclear power projects, those should be sorted out immediately to get the benefits of nuclear power and to mitigate the global warming process. Any step which mitigates the global warming process has to be adopted immediately, without wasting time, as we may not sustain any more the adverse impact of global warming. Survival of human race is at stake due to global warming.

(iii) In my opinion, if we can generate sufficient clean nuclear power so that our dependence on fossil fuel is reduced to shear minimal – whether for generation of electricity or for transport – the overall environment would be much cleaner.

(iv) Nuclear power may be supplemented by other form of clean energy such as wind energy and solar energy.

(v) The coal industry’s woes have risen as worries over climate change have increased. Today’s coal-fired plants emit copious amounts of carbon dioxide, a major greenhouse gas. At the heart of the ‘Clean Coal’ campaign are two ideas: (a) We can’t stop using coal because it is abundant and cheap, and non-polluting sources like wind and solar power can’t meet our needs; (b) Technology will fix everything. Thus, the savior of the Earth will be a collection of technologies that will enable plants to capture the carbon they currently send into the air. The carbon would then be stored underground. Earlier also, there were lots technological challenges coal and power sector faced worldwide and technology has solved the majority of problems. Present problems also will be solved as well.

(vi) Of late, algae based bio-fuel is becoming very much promising source of green energy. This source of energy is to be developed for future use and a great deal of investment towards research and its implementation are necessary to obtain its advantages.

(vii) For efficient community power backup environment-friendly Sodium-Sulfur (NaS) battery or equivalent should be used extensively along with nuclear power, wind power and other renewable sources of energy.

(viii) Transportation including motor vehicles should be run only on clean electric power.

(ix) Another advantage of producing enough nuclear power for the requirement of almost every industry and day-to-day consumption is lesser dependence on bio-diesel, bio-ethanol and other bio-fuel. Use of less agricultural based bio-fuel means availability of agriculture for more food production – reduction of poverty.

(x) Research activities should be enhanced in the areas of development of efficient environment-friend batteries and other aspects of nuclear technology.

(xi) As technology advances, we hope to switchover to more environment-friendly nuclear reactor – ‘breeder reactor’ – soon; reducing radio-active waste disposal problem.

(xii) Moreover development of FUSION TECHNOLOGY successfully is also not very far; once we do that we have sufficient energy.

3. Conclusion It has become essential to every nation to access to cheap energy for their smooth functioning and uplifting their economies. However, the uneven distribution of energy supplies among all the nations and the critical need for energy has led to significant vulnerabilities. Global energy security has become synonymous to political stability and good administration.

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