Nuclear technology is “the technology that involves the reactions of atomic nuclei”. It has found applications from smoke detectors to nuclear reactors and from gun sights to nuclear weapons.
• In 1896, Henri Becquerel was investigating phosphorescence in uranium salts when he discovered a new phenomenon which came to be called radioactivity.
• Henri Becquerel, Pierre Curie and Marie Curie began investigating the phenomenon. They 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 kinds of radiation could pass through ordinary matter, and all of them could cause damage in large amounts. Many of the scientists working on radioactivity died of cancer as a result of their exposure.
• In the process they isolated the element radium, which is highly radioactive.
• The atom is the fundamental building block of all stuff, or what scientists like to call “matter”. An individual atom is very small. Atoms are mostly empty space, but in the center of the atom is a structure called a nucleus. The nucleus is a congregation of protons and neutrons. Neutrons are neutral, or have no electrical charge. Protons, however, carry a positive electrical charge of 1.
• Changes that occur in the structure of the nuclei of atoms are called nuclear reactions. Energy created in a nuclear reaction is called nuclear energy, or atomic energy.
• Nuclear energy is produced naturally and in man-made operations under human control. Naturally: Some nuclear energy is produced naturally. For example, the Sun and other stars make heat and light by nuclear reactions. Man-Made: Nuclear energy can be man-made too. Machines called nuclear reactors, nuclear power plants provide electricity for many cities. Man-made nuclear reactions also occur in the explosion of atomic bomb.
Splitting the Uranium Atom:
• Uranium 235U is the principle element used in nuclear reactors and in certain types of atomic bombs. When a stray neutron strikes a 235U nucleus, it is at first absorbed into it. This creates 236U. 236U is unstable and this causes the atom to fission in the process.
235U + 1 neutron = 2 neutrons + 92Kr + 142Ba + ENERGY (236 = 236)
• When the atom is split, 2 additional neutrons are released. This is how a chain reaction works. If more 235U is present, those 2 neutrons can cause 2 more atoms to split. Each of those atoms releases 1 more neutron bringing the total neutrons to 4. Those 4 neutrons can strike 4 more 235U atoms, releasing even more neutrons. The chain reaction will continue until all the 235U fuel is spent. This is roughly what happens in an atomic bomb. It is called a runaway nuclear reaction.
TYPES OF NUCLEAR REACTIONS
There are two types of nuclear reactions they are:
• In nuclear fission, the nuclei of atoms are split, causing energy to be released. The atom bomb and nuclear reactors work by fission. Uranium nuclei can be easily split by shooting neutrons at them, thus resulting in release of energy.
• In nuclear fusion, the nuclei of atoms are joined together, or fused. This happens only under very hot conditions. In the Sun, hydrogen nuclei fuse to make helium. The hydrogen bomb, humanity’s most powerful and destructive weapon, also works by fusion. The heat required to start the fusion reaction is so great that an atomic bomb is used to provide it. Hydrogen nuclei fuse to form helium and in the process release huge amounts of energy thus producing a huge explosion.
Where Does the Energy Come From?
• When the uranium atom is split, some of the energy that held it together called binding energy is released as radiation in the form of heat. Therefore, the total mass does decrease a tiny bit during the reaction. Thus the energy released can be calculated by using the mass of fuel spent by using Einstein equation E=MC2.
NUCLEAR POWER REACTORS
A nuclear reactor produces and controls the release of energy from splitting the atoms of certain elements. Ina nuclear power reactor, the energy released is used as heat to make steam to generate electricity. In a research reactor, the main purpose is to utilise the actual neutrons produced in the core. In most naval reactors, steam drives a turbine directly for propulsion.
The principles for using nuclear power to produce electricity are the same for different types of reactor. The energy released from continuous fission of the atoms of the fuel is harnessed as heat in either a gas or water, and is used to produce steam. The steam is used to drive the turbines which produce electricity (as in fossil fuel power plants).
There are several components common to all types of reactors:
• Fuel: Usually pellets of uranium oxide (UO2) arranged in tubes to form fuel rods. The rods are arranged into fuel assemblies in the reactor core
• Moderator: This is material which slows down the neutrons released from fission so that they cause more fission. It is usually water, but may be heavy water or graphite.
• Control rods: These are made with neutron-absorbing material such as cadmium, hafnium or boron, and are inserted or withdrawn from the core to control the rate of reaction, or to halt it. (Secondary shutdown systems involve adding other neutron absorbers, usually as a fluid, to the system.)
• Coolant: A liquid or gas circulating through the core so as to transfer the heat from it. In light water reactors the moderator functions also as coolant.
• Pressure vessel or pressure tubes: Usually a robust steel vessel containing the reactor core and moderator/coolant, but it may be a series of tubes holding the fuel and conveying the coolant through the moderator.
• Steam generator: Part of the cooling system where the heat from the reactor is used to make steam for the turbine.
• Containment system: The structure around the reactor core which is designed to protect it from outside intrusion and to protect those outside from the effects of radiation in case of any malfunction inside. It is typically a metre-thick concrete and steel structure.
Main types of nuclear reactors
• Boiling Water Reactors
In a typical design concept of a commercial BWR, the following process occurs:
1. The core inside the reactor vessel creates heat.
2. A steam-water mixture is produced when very pure water (reactor coolant) moves upward through the core, absorbing heat.
3. The steam-water mixture leaves the top of the core and enters the two stages of moisture separation where water droplets are removed before the steam is allowed to enter the steamline.
4. The steamline directs the steam to the main turbine, causing it to turn the turbine generator, which produces electricity.
The unused steam is exhausted to the condenser, where it is condensed into water. The resulting water is pumped out of the condenser with a series of pumps, reheated, and pumped back to the reactor vessel. The reactor’s core contains fuel assemblies that are cooled by water circulated using electrically powered pumps. These pumps and other operating systems in the plant receive their power from the electrical grid. If offsite power is lost, emergency cooling water is supplied by other pumps, which can be powered by onsite diesel generators. Other safety systems, such as the containment cooling system, also need electric power. BWRs contain between 370-800 fuel assemblies.
• Pressurised Water Reactor
In a typical design concept of a commercial PWR, the following process occurs:
1. The core inside the reactor vessel creates heat.
2. Pressurized water in the primary coolant loop carries the heat to the steam generator.
3. Inside the steam generator, heat from the primary coolant loop vaporizes the water in a secondary loop, producing steam.
4. The steamline directs the steam to the main turbine, causing it to turn the turbine generator, which produces electricity.
The unused steam is exhausted to the condenser, where it is condensed into water. The resulting water is pumped out of the condenser with a series of pumps, reheated, and pumped back to the steam generator. The reactor’s core contains fuel assemblies that are cooled by water circulated using electrically powered pumps. These pumps and other operating systems in the plant receive their power from the electrical grid. If offsite power is lost, emergency cooling water is supplied by other pumps, which can be powered by onsite diesel generators. Other safety systems, such as the containment cooling system, also need electric power. PWRs contain between 150-200 fuel assemblies.
• Fast Breeder Reactor
The nuclear chain reaction in the uranium fuel in a thermal reactor is sustained by slowing down the neutrons by a moderator. The chain reaction in FBTR is sustained by fast neutrons. The number of neutrons released per fission is more compared to that of thermal reactor. The extra neutrons are available for absorption in uranium-238 to transform it to fissile plutonium-239.
In a thermal reactor typically only about 1-2 per cent of the natural uranium is utilized whereas in FBTRs, the utilization is increased 60 to 70 times.
Considering the nuclear and heat transfer properties of various possible coolants, Sodium has been universally accepted as the coolant for FBTRs. In Thermal reactors water is used as a coolant.
The radioactivity released to the atmosphere and the radiation dose received by the operating personnel in FBTRs has been much less compared to the water control reactors.
FBTR is based on the design of the Rhapsodic reactor, France.
The fuel used to FBTR is mixed carbide of plutonium and natural uranium. The carbide fuel has higher breeding ratio due to its higher density and thermal conductivity.
Why India Prefers Fast Breeders:
• A fast breeder reactor (FBR) breeds more fuel than it consumes that is it produces more plutonium than it consumes while generating power. For a uranium scarce country like India, it is an attractive technology. Plutonium produced in the thermal reactors as spent fuel is ideally suitable as the fuel material for use in the FBR due to its high fission neutron yield.
• Since the number of neutrons produced in plutonium fission is high, it helps to produce more plutonium from uranium (U238) used as a blanket surrounding the fuel core of the FBR.
• FBR also consumes less uranium and that too very effectively. While the thermal reactors exploit only 0.6 per cent uranium, a FBR utilizes 70-75 per cent of it. Thus, it leaves less radioactive waste to dispose of. In fact, many scientists in India prefer FBRs for the same reason.
ADVANTAGES AND DISADVANTAGES OF NUCLEAR FISSION ENERGY
Nuclear power plants have three main advantages over fossil-fuel plants.
1. Once built, a nuclear plant can be less expensive to operate than a fossil-fuel plant, mainly because a nuclear plant uses a much smaller volume of fuel.
2. Uranium, unlike fossil fuels, releases no chemical or solid pollutants into the air during use.
3. They do not emit CO2 and hence, do not contribute to global warming and climate change.
However, nuclear power plants have three major disadvantages. These disadvantages have slowed the development of nuclear energy in some countries.
1. Nuclear plants cost more to build than fossil-fuel plants.
2. Because of the need to assure that hazardous amounts of radioactive materials are not released, nuclear plants must meet certain government regulations that fossil-fuel plants do not have to meet. For example, a nuclear plant must satisfy the government that it can quickly and automatically deal with any kind of emergency.
3. Used nuclear fuel produces dangerous radiation long after it has been removed from the reactor. As a result, safe disposal of nuclear waste presents a challenge.
Many experts believe that the benefits of nuclear energy outweigh any problems involved in its production. Oil may become so scarce in a few decades that it will be too expensive to drill. Canada, Germany, Russia, the United States, and even India among other countries have enough coal to meet their energy requirements for a long time at present rates of use. However, coal releases large amounts of sulfur and other pollutants into the air when it is burned. It is also a major factor in carbon emissions. If nuclear energy were fully developed, it could completely replace oil and coal as a source of electric power.
• Tata Institute of Fundamental Research (TIFR), which came up in 1945, provided the base and structure for organizing the early efforts for India’s nuclear energy programme. Hence, it is also referred to as the cradle of Indian nuclear power programme.
• The horrors of the nuclear holocaust unleashed in Hiroshima and Nagasaki were followed by a new vista of atoms for peace, of nuclear power generation, transformations in agriculture and medical diagnostics and therapy for using atomic Science & Technology.
• It’s in this context that in April 1948, the Atomic Energy Bill was enacted with the primary objective to develop, control and use atomic energy for peaceful purposes, a clear departure from the policy followed by the nuclear powers, often forgotten or ignored by the international community.
• India under the leadership of Jawaharlal Nehru was dedicated to the peaceful uses of atomic energy but it couldn’t wish away the lurking threat posed by nuclear weapons, and so per force Indian option for nuclear weapons was kept open for both areas peaceful applications and the weapon option.
• Subsequently, India’s Atomic Energy Commission was set up on 10 August, 1948 under the Chairmanship of Dr. Bhabha with the sole objective of formulation and implementation of the governmental policy relating to the development of nuclear power in India. In fact, India was among the first eight countries of the world to have an Atomic Energy Commission.
• The next step was the establishment of the Department of Atomic Energy (DAE) with Bhabha as its Secretary in August 1954, the objectives of which, inter alia included:
– Proper use of the latest technologies for the development of nuclear power.
– To ensure nuclear power generation against global economic competition by exploiting natural resources.
– Establishment of nuclear power reactors and safe use of radioactive substances.
– Production of nuclear power for meeting the defence requirements of India.
– To understand the role of nuclear power in economic development.
– To carry out programmes on isotopes and radiation technology.
– To support basic research in nuclear energy and other frontier areas of science.
• Thus, India directed its nuclear power programme for attaining self -reliance on a broad front which comprised mineral exploration and mining, extraction of uranium and zirconium, designing and fabricating reactor control systems, production of heavy water, making radio isotopes and promoting their use in agriculture, medicine, etc., safety of nuclear power reactors and monitoring the radiation level for ensuring a safe limit.
Key milestones of Nuclear Programme:
• Tarapur units 3&4, at Tarapur in Maharashtra, are the largest in India with a capacity of 540 MW for each unit.
• Rajasthan Atomic Power Station, Rawatbhata in Rajasthan, is India’s first nuclear park.
• Narora Atomic Power Station is Asia’s first nuclear power plant to obtain ISO-14001 accreditation for its environment management system.
• Kakrapar Atomic Power Station was the first Indian nuclear power plant to undergo a peer review by an international team of experts from the World Association of Nuclear Operators (WANO). All other Indian nuclear power stations are also peer reviewed by WANO.
N-Power Policy of India:
• In the beginning of the Eighth Plan, it was aimed to produce 10,000 MW of power by 2000, to increase the nuclear power share in total power production. In order to achieve the above objective, the Central Government established Nuclear Power Corporation to coordinate various nuclear power organisations, in 1989.
• But, it was unlikely to achieve this objective, particularly after the disintegration of USSR, and then the target was reduced to 9000 MW. However, still it was not possible in the near future. Indian scientists have planned to achieve the above target in future through the development of three generations of nuclear reactors:
– 1st Generation Nuclear Reactors: These are the pressurized Heavy Water reactors with the capacity of 235 HW each and use natural uranium as fuel. Plutonium is the by-product.
– 2nd Generation Nuclear Reactors: These are planned to be the fast breeder reactors with the capacity of 500 HW each, and use Plutonium, a by-product of the first generation reactors, as the fuel.
– 3rd Generation Nuclear Reactors: These are also planned to be the fast breeder reactors. This generation reactors will use fuel derived from second generation reactors and convert more Thorium into Uranium-233. So, the plan is to use vast Thorium deposits found in India.
• India has established 1st generation nuclear reactors at Tarapur, Kalpakkam, Narora and Rawatbhata. Other two reactors of this grade are located at Kakrapar (Gujarat) and Kaiga (Karnataka). The first generation reactors have reached commercial stage. The generation of power from nuclear energy began in India in 1969 with the commissioning of first atomic power station at Tarapore (TAPS).
• The second generation reactor has commenced with the successful operation of the Fast Breeder Test Reactor (FBTR) named KAMINI (Kalpakkam Mini Reactor) in 1985 at the Indira Gandhi Centre for Atomic Research (IGCAR) at Kalpakkam in Tamil Nadu.
• The Kalpakkam reactor is the world’s first fast-breeder reactor. The reactor has successfully used the mixed uranium – plutonium carbide fuel, hitherto untried elsewhere. Progress has also been made in the third generation reactor with the successful development of a U-233 based fuel. Work has commenced on the design of an Advanced Heavy Water Reactor which will make the use of thorium in power generation.
Indian Research Reactors
• There are seven Research Reactors working in the country named as: Apsara, Cirus, Kamini, Purnima I, Purnima II, Purnima III and Zerlina.
• India’s first research reactor, APSARA, a 1 MWe ‘swimming pool’ type, built indigenously, became operational at Trombay in 1956, heralding a novel nuclear age in Asia.
• ZERLINA, a zero energy tank type research reactor was built indigenously in 1961. CIRUS, a tank type reactor of 40 MWe was commissioned at Tarapur in 1960 with the assistance of Canada, for engineering experimental work with facilities for materials testing and radioisotope production.
• Moreover, with the commissioning of PURNIMA-I & PURNIMA-II respectively in 1972 and 1984, India achieved an important milestone in its ‘Fast Reactor’ programme.
• DHRUVA, an indigenous tank type 100 MWe reactor went into operation in 1985 for research in advanced nuclear physics and for isotope production. PURNIMA III is also a tank type reactor of 1 MWe attained criticality on 9 November, 1990. The sole objective of this reactor is to conduct mock up studies for Kamini reactor.
• The construction of KAMINI (Kalpakkam Mini Reactor) in 1996 marks an important land mark in India’s endeavour at mastering uranium-233-based nuclear fuel. Designed on the basis of Rapsody Reactor of France, it is the only reactor in the world which uses U-233 as fuel. It will be mainly used to study the highly radioactive fuel elements which are discharged from FBTR at Kalpakkam. This will help in the development of high performance plutonium fuel elements for the proto-type FBR to be built in the next century. It is also called the ‘Zero -Power’ reactor as the amount of electricity produced (40 MWe) is consumed by the reactor itself for research purposes.
• The design for India’s next generation of reactors, called Advanced Heavy Water Reactors (AHWRs), which will employ thorium-based fuel, has already been prepared. BARC has developed comprehensive technology for industrial operations in fuel reprocessing and waste management.
• Reprocessing plants are operational in Trombay and Tarapur. The first fuel reprocessing plant at Trombay is based on hot – cell technology. A comprehensive waste management technology for handling and safe disposal of all types of waste, generated in nuclear industries, has been perfected by the centre. It has also undertaken the recent studies of high-energy-density systems.
Bharatiya Nabhikiya Vidyut Nigam Limited (BHAVINI):
• The Department of Atomic Energy (DAE) in its Golden Jubilee Year has set up its fifth public sector unit -Bharatiya Nabhikiya Vidyut Nigam Limited (BHAVINI).
• BHAVINI is a wholly owned Enterprise of Government of India under the administrative control of the Department of Atomic Energy (DAE) incorporated on 22nd October 2003 as Public Limited Company.
• It was incorporated under the Companies Act 1956, with an authorized share capital of Rs. 5000 crore, BHAVINI is responsible for the construction and commissioning of the country’s first 500 MWe Fast Breeder Reactor (FBR) project at Kalpakkam, Tamil Nadu and to pursue construction, commissioning, operation and maintenance of subsequent Fast Breeder Reactors for generation of electricity in pursuance of the schemes and programmes of Government of India under the provisions of the Atomic Energy Act,1962.
• It is a forerunner of commercial fast breeder power reactors in the country and in this regard, it marks a major step in the country’s efforts to ensuring energy security through the use of atomic energy.
• BHAVINI is currently constructing a 500MWe Prototype Fast Breeder Reactor (PFBR) at Kalpakkam. The PFBR is the forerunner of the future Fast Breeder Reactors and is expected toprovide energy security to the country. The PFBR is being built with the design and technology developed at the Indira Gandhi Centre for Atomic Research (IGCAR) located at Kalpakkam. The four other PSUs under the Department are Nuclear Power Corporation of India Ltd. (NPCIL), Electronics Corporation of India Ltd. (ECIL), Indian Rare Earths Ltd. (IREL) and Uranium Corporation of India Ltd. (UCIL).
• The engineering design and technical expertise for BHAVINI will be drawn from the Indira Gandhi Centre for Atomic Research (IGCAR), which has accumulated over two decades of experience in fast breeder reactor technology. NPCIL, which will take 5% of the equity in the new company, will provide the expertise for project management to enable timely construction and commissioning of the project.
• NPCIL is at present operating 20 nuclear power reactors and setting up 3 more at different locations in the country. When completed, PFBR would produce electricity through recycle of plutonium and depleted uranium recovered from the spent fuel of Pressurized Heavy Water Reactors being operated by NPCIL.
1. Atomic Energy Commission: India’s Atomic Energy Commission (AEC) was established in August 1948 within the Department of Scientific Research, which was set up in June 1948. The Department of Atomic Energy (DAE) came into existence in August 1954 through a Presidential Order. Thereafter, a Government Resolution in1958 transferred the DAE within the AEC. The Secretary to the Government of India in the DAE is the ex-officio Chairman of the AEC. The other Members of the AEC are appointed on the recommendation of the Chairman of the AEC.
2. AERB : The AERB reviews the safety and security of the country’s Operating Nuclear Power Plants, Nuclear Power Projects, Fuel Cycle Facilities, and Other Nuclear/Radiation Facilities and Radiation Facilities. The regulatory authority of AERB is derived from the rules and notifications promulgated under the Atomic Energy Act, 1962 and the Environmental (Protection) Act, 1986. The headquarters is in Mumbai. The mission of the Board is to ensure that the use of Ionising Radiation and Nuclear Power in India does not cause undue risk to health and the Environment. Currently, the Board consists of a full-time Chairman, an ex officio Member, three part-time Members and a Secretary.
3. NPCIL: Nuclear Power Corporation of India Limited (NPCIL) is a Public Sector Enterprise under the administrative control of the Department of Atomic Energy (DAE), Government of India. The Nuclear Power Corporation of India Ltd (NPCIL) is responsible for design, construction, commissioning and operation of thermal nuclear power plants.
NPCIL is presently (June-2016) operating 21 nuclear power reactors with an installed capacity of 5780 MW. The reactor fleet comprises two Boiling Water Reactors (BWRs) and 18 Pressurised Heavy Water Reactors (PHWRs) including one 100 MW PHWR at Rajasthan which is owned by DAE, Government of India.
4. Atomic Minerals Directorate for Exploration and Research: It’s prime mandate is to identify and evaluate uranium resources required for the successful implementation of Atomic Energy programme of the country. For implementing this important task investigations are taken up across the length and breadth of the country from Regional Exploration & Research Centres located at New Delhi , Bengaluru, Jamshedpur, Shillong, Jaipur, Nagpur and Hyderabad (Headquarter & South Central Region).
5. DAE’s own Research & Development wings include:
• Bhabha Atomic Research Centre (BARC), Trombay: Trombay near Mumbai. A series of ‘research’ reactors and critical facilities was built here.Reprocessing of used fuel was first undertaken at Trombay in 1964.BARC is also responsible for the transition to thorium-based systems. BARC is responsible for India’s uranium enrichment projects, the pilot Rare Materials Plant (RMP) at Ratnahalli near Mysore
• Indira Gandhi Centre for Atomic Research (IGCAR): IGCAR at Kalpakkam was set up in 1971. Two civil research reactors here are preparing for stage two of the thorium cycle. BHAVINI is located here and draws upon the centre’s expertise and that of NPCIL in establishing the fast reactor program, including the Fast Reactor Fuel Cycle Facility.
• The Raja Ramanna Centre for Advanced Technology (RRCAT): Multi-purpose research reactor (MPRR) for radioisotope production, testing nuclear fuel and reactor materials, and basic research.
• Atomic Minerals Directorate: The DAE’s Atomic Minerals Directorate for Exploration and Research (AMD) is focused on mineral exploration for uranium and thorium. It was set up in 1949, and is based in Hyderabad, with over 2700 staff.
• Variable Energy Cyclotron Centre: Variable Energy Cyclotron Centre is a premier R & D unit of the Department of Atomic Energy. This Centre is dedicated to carry out frontier research and development in the fields of Accelerator Science & Technology, Nuclear Science (Theoretical and Experimental), Material Science, Computer Science & Technology and in other relevant areas.
• Global Centre for Nuclear Energy Partnership: It will be the DAE’s sixth R&D facility. It is being built near Bahadurgarh in Haryana state and designed to strengthen India’s collaboration internationally. It will house five schools to conduct research into advanced nuclear energy systems, nuclear security, radiological safety, as well as applications for radioisotopes and radiation technologies. Russia is to help set up four of the GCNEP schools.
Besides carrying out research at its own research centres, the DAE provides full support to seven aided institutions
• Tata Institute of Fundamental Research(TIFR) : The Tata Institute of Fundamental Research is a National Centre of the Government of India, under the umbrella of the Department of Atomic Energy, as well as a deemed University awarding degrees for master’s and doctoral programs. At TIFR, carry out basic research in physics, chemistry, biology, mathematics, computer science and science education. Main campus is located in Mumbai, but additional campuses are in Pune, Bangalore and Hyderabad.
• Tata Memorial Centre : The Tata Memorial Centre commissioned state of the art new operation theatres. For delivering hi-tech patient care, sophisticated facilities such as stereotactic radiosurgery and steriotactic and intensity modulated radiotherapy, were added.
• Saha Institute of Nuclear Physics : The Saha Institute of Nuclear Physics is an institution of basic research and training in physical and biophysical sciences located in Bidhannagar, Kolkata, India. The institute is named after the famous Indian physicist Meghnad Saha.
• Institute of Physics : Institute of Physics, Bhubaneswar is an autonomous research institution of the (DAE), Government of India
• Institute for Plasma Research : Research and development in fusion technology continued at the Institute for Plasma Research
• Harish Chandra Research Institute : The Harish-Chandra Research Institute is an institution dedicated to research in Mathematics and Theoretical Physics, located in Allahabad, Uttar Pradesh in India
• Institute of Mathematical Sciences : The Institute of Mathematical Sciences (IMSc), founded in 1962 and based in the verdant surroundings of the CIT campus in Chennai, is a national institution which promotes fundamental research in frontier disciplines of the mathematical and physical sciences.