Nuclear Energy and nuclear power plants

Nuclear Energy and nuclear power plants – An overview and discussions on future dependability for production of clean electricity:

Introduction -

Out of two (fission and fusion) known technology, fission technology is used by nuclear power plant and fusion technology is under development stage.

Nuclear power plants generate electricity by using heat obtained from such fission reaction; usually use uranium-235 (U-235) as fuel. The nucleus of U-235 has 92 protons and 143 neutrons. When bombarded by extra neutrons on U-235, it loses atomic balance and becomes unstable to split into smaller pieces of fission products and releases more neutrons. This post splitting mass difference causes to release huge energy in the form of heat. The extra neutrons produced responsible for further chain reaction within the leftover mass of uranium.

Nuclear Fusion technology is to combine two light atomic nuclei to form one heavier nucleus. This process generates tremendous amount of energy - heat. As this technology generates enormous amount of energy, we are now struggling to control this quantum of energy obtained out of fusion reaction– thereby, not yet developed fully. Developed world is making every effort to make nuclear fusion technology workable. The energy released from atomic fusion can be unimaginably great - our celestial Sun and other stars shine through this fusion since their inception.

If fusion energy does become practicable it would offer the advantages such as:

(1) an effectively limitless source of fuel;

(2) it would be of inherent safety , as the amount of radioactive material present would be much low;

(3) as waste products that are less radioactive and simpler it would be easer to handle them than those from fission

Relevant facts about nuclear reactor for power generation and advantages of nuclear power over fossil fuels generated electricity:

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 fission starts. 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 "burnup 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.

D. Advantages of Nuclear power -

Power from nuclear energy can prevent many of the environmental consequences arising out of the use of fossil fuels. Below we discuss advantages of nuclear power vis-a-vis other energy options, especially fossil fuel.

(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. It 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. The disposal of radio-active waste which nuclear power plant generates, can be effectively organized as our technology is improving at a fast pace. Moreover, the quality of radio-active waste improved if we go for reprocessing of spent fuel.

(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.

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) For efficient community power backup environment-friendly Sodium-Sulfur (NaS) battery or equivalent should be used extensively along with nuclear power, wind power. (Refer: http://knol.google.com/k/partha-das-sharma/electric-cells-or-batteries/oml631csgjs7/5)

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

(vii) 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 bio-fuel means availability of agriculture for more food production – reduction of poverty.

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

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

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