NUCLEAR RESEARCH
NUCLEAR RESEARCH
INTRODUCTION :
Nuclear Technology deals with the changes in the nuclei of an atom. The changes result in release of energy from the nuclei which can be trapped for human betterment.Nuclear Technology is of utmost importance due to the multifarious applications associated with it. It is used in energy, medicine, agriculture, industry, defence etc which serves the humanity in multitude of ways. It was Henri Becquerel in 1896 who was investigating phosphorescence in uranium salts discovered a new phenomenon which came to be called radioactivity. Then it was Marie curie and Pierre Curie who isolated the radioactive element called radium. They also discovered that radioactive materials produce intense, penetrating rays of several distinct sorts, which they called alpha rays, beta rays and gamma rays. Some of these radiations could pass through ordinary matter, and all of them could cause damage to a larger extent.
In India the commendable contribution of Homi.J.Baba gave way to the three-stage nuclear energy programme which gave the vision for our energy security. Infact the Indo-US nuclear deal in many ways will support our indigenous nuclear programme which is one of the unique programs in the world. As India is resolute about nuclear technology for peaceful purposes, the advancement in this technology in India will help all the third world nations as well.
NEED FOR NUCLEAR ENERGY
As the developing world tries to meet the energy needs of its growing population and support its development aspirations, the global energy consumption would double over the next three decades and will rise further subsequently. Only power of the atom can, in principle, realize this. Without a central role for nuclear power this could lead to a catastrophe both in terms of sustainability of energy resources with enhanced level of conflicts to grab the residual resources and, even more importantly, in terms of global climate. As we move forward in time, the crucial importance of nuclear power would be increasingly felt not only for supporting economic growth but also for some basic human needs such as availability of clean air and water. In fact, the day is not far off when we would need to view nuclear energy as not just a source of electricity but a primary energy source which could assure our sustainable future. Looking from India’s perspective, development of nuclear energy based on a closed cycle approach enabling fuller use of uranium and thorium is inevitable for development aspirations of over a billion people.
With the domestic oil production barely meeting one third of the country’s requirement so India’s energy security strategy should include alternative fuels and technologies. Let us examine the fuel resource situation in India. Estimates by us in the Department of Atomic Energy (DAE) and also by other agencies in the country indicate that we will have difficulties with regard to availability of coal by the middle of the present century. In addition, coal-based stations are likely to pose serious problems in the future arising out of transport of large quantities of coal across the country and environmental problems related to disposal of ash and emission of greenhouse and acid gases. Our oil and natural gas reserves are very modest and we are importing very substantial quantities of our requirements -a major part of our overall imports. Our hydro-potential is renewable and must be exploited to the maximum. But the exploitation of hydel resources is handicapped by issues like displacement of people. Non-conventional sources like solar, biomass and wind will no doubt play their useful roles. But at the present level of technology development they can only complement electricity generation by base load stations dependent on fossil, hydro or nuclear plants.
From a long-term perspective, nuclear energy and solar energy can play an important role in addressing our energy security needs. The spiralling oil import bill will put unbearable burden on the nation’s economy and all energy resources — coal, gas, oil, hydro and nuclear along with renewables — need to be developed. Energy security was of critical importance when the nation was aiming for a 10 per cent growth rate. India’s energy needs, which will increase the pace of economic development, cannot be met with oil and gas for long
These facts compel us to think of a new strategy to deal with the rising energy demand. So it calls for exploring new technology options, new financing means, identifying new sources and building bridges with new partners. There are many options of using alternative fuels and technologies. Huge traffic and vehicular movement in India is contributing to global warming. But the huge need of energy in India cannot be ignored. Coal, gas or oil alone cannot be an enduring solution. So civil nuclear energy is a clean solution. Clean coal technology was needed to tackle greenhouse issues, while nuclear power was “cleaner than clean coal” India’s conventional resources are far from being adequate to achieve the targeted mission of ‘Power for All’ by 2012
Why nuclear power? First- an alternative to future fossil fuel, second- cost-effective option, third- environmentally sustainable and reliable energy source, fourth- it provides secure fuel supply or a fair amount of stability; and finally- is inevitable for long term energy security with new technological developments and substantial improvement in safety performance.
The country plans to increase its nuclear power capacity to 20,000 MW by 2020 from the current 5,000 MW, at which level it meets just 1.2 per cent of the country’s energy needs.
Though nuclear energy will come at a huge cost, it is imperative that this mode be adopted with an eye on the future needs.
NUCLEAR PROCESSES
Ø NUCLEAR FISSION
Nuclear fission is the process of breaking a heavier nucleus into two (or more rarely three) lighter nuclei which results in the release of the neutrons. It is accompanied by the release of energy in the form of gamma radiations and the kinetic energy of the particles. Fission is a form of nuclear transmutation because the resulting fragments are not the same element as the original atom.
Nuclear fission provides energy for nuclear power as well as for producing nuclear bomb. Fission reaction differs from other forms of radioactive decay by the harnessing technology available through a controllable chain reaction. Chain reaction happens when the free neutrons released by each fission event can trigger yet more events, which in turn release more neutrons and cause more fissions. For sustaining a chain reaction, nuclear fuel which is fissionable (fissile material) is required . The most common nuclear fuels are Uranium-235(with 92 protons and 143 neutrons has an unstable nucleus, uneasily held together and of use in nuclear reactors) ,Uranium-238 (natural uranium)and 239Pu (the isotope of plutonium with an atomic mass of 239).As Uranium-235 is a fissile element ,it is easily broken apart when hit by a neutron and it is converted to barium, krypton and enormous amount of heat energy.
Not all fissionable isotopes can sustain a chain reaction. For example, 238U, the most abundant form of uranium, is fissionable but not fissile: it undergoes induced fission when impacted by an energetic neutron. But too few of the neutrons produced by 238U fission are energetic enough to induce further fissions in 238U, so no chain reaction is possible with this isotope. Instead, bombarding 238U with slow neutrons causes it to absorb them (becoming 239U) and decay by beta emission to 239Np which then decays again by the same process to 239Pu; that process is used to manufacture 239Pu in breeder reactors, but does not contribute to a neutron chain reaction. Fissionable, non-fissile isotopes can be used as fission energy source even without a chain reaction. Bombarding 238U with fast neutrons induces fissions, releasing energy as long as the external neutron source is present.
Critical mass is the minimum mass of fissile material required for sustaining a chain reaction. So the uranium- 235 is arranged in such a manner to undergo a chain reaction in a controlled environment and the heat released is sourced through the steam driven generators to produce energy. If the chain reaction happens in an uncontrolled environment instantaneously we get a nuclear bomb.
But fission reactors have many problems associated with it. They become radioactive after their lifetime is finished (maybe after 30 to 40 years). So its hard to dismantle and dispose it. It should be treated like other radioactive waste or it should be covered by a concrete shield which is a very expensive and a non-foolproof method. A small disturbance in the movement of steam from the reactor to the generator may lead to bursting of the pipes lead to the melting of the reactor. Corrosion and leakage of containers, natural hazards like earthquakes may also create problem for the reactors. Three Mile island incident of USA in 1979 and Chernobyl incident in the erstwhile Soviet Union in 1986 where the dirty reminders of the nuclear accident (still the radioactive residues are found in these places which is hard to dispose).
Ø NUCLEAR FUSION
Nuclear fusion is the process by which multiple like-charged atomic nuclei join together to form a heavier nucleus. At extremely high temperatures – in the range of tens of millions of degrees – the nuclei of isotopes of hydrogen (and some other light elements) can readily combine to form heavier elements. It is accompanied by the release or absorption of energy. Iron and nickel nuclei have the largest binding energies per nucleon of all nuclei. The fusion of two nuclei with lower mass than iron generally releases energy while the fusion of nuclei heavier than iron absorbs energy. So lighter elements like isotopes of hydrogen (deutrium) are used.
Nuclear fusion occurs naturally in stars. Artificial fusion in human enterprises has also been achieved, although not yet completely controlled. For fusion to occur, the electrostatic repulsion between the atoms must be overcome. Creating these conditions is one of the major problems in triggering a fusion reaction.
Nuclear fusion has three remarkable features. Firstly its principle raw material is the isotope of hydrogen, deutrium which can be produced from water and hence renewable. Secondly the end product is helium which is environmentally safe. Thirdly it is cheap.
Isotopes: Isotopes are atoms of the same element that have the same number of protons and electrons but a different number of neutrons. Some common isotopes in fusion are:
Protium is a hydrogen isotope with one proton and no neutrons. It is the most common form of hydrogen and the most common element in the universe. ^ Deuterium is a hydrogen isotope with one proton and one neutron. It is not radioactive and can be extracted from seawater.
- Tritium is a hydrogen isotope with one proton and two neutrons. It is radioactive, with a half-life of about 10 years. Tritium does not occur naturally but can be made by bombarding lithium with neutrons.
- Helium-3 is a helium isotope with two protons and one neutron.
- Helium-4 is the most common, naturally occurring form of helium, with two protons and two neutrons.
The most promising of the hydrogen fusion reactions which make up the deuterium cycle is the fusion of deuterium and tritium. The reaction yields 17.6 MeV of energy but requires a temperature of approximately 40 million Kelvins to overcome the coulomb barrier and ignite it. The deuterium fuel is abundant, but tritium must be either bred from lithium or gotten in the operation of the deuterium cycle.
Deuterium-Tritium Fusion: But there are some problems in tapping the fusion energy. Firstly fusion requires the forcing together of hydrogen isotopes to form a helium nucleus which requires energy to overcome the repulsion but after the fusion it provides more energy.
Secondly before the nuclear fusion reaction we have to put the nuclei in a condition to fuse. This requires (i) to separate the nuclei from the surrounding electrons, so the nuclei can be brought together (ii) to slam the nuclei together to make them fuse.
The first generation fusion reactors will use deuterium and tritium for fuel because they will fuse at a lower temperature. Deuterium can be easily extracted from seawater, where 1 in 6500 hydrogen atoms is deuterium. Tritium can be bred from lithium, which is abundant in the earth’s crust. In the fusion reaction a deuterium and tritium atom combine together, or fuse, to form an atom of helium and an energetic neutron.
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