Black Yellow Magenta Cyan 1 2 3 4 Chapter 2 Powering the Nation – Research & Power Reactors 6 5 7 25 The Chain Reaction-Volume 02 (Part 01) #150 Dt.:28/10/2005 The Chain Reaction-Volume CyanMagentaYellowBlack Black Yellow Magenta Cyan Captions for Photo-Collage 1. Panoramic view of the DHRUVA and CIRUS reactors located at BARC, Trombay. 2. Neutron beam utilization facility at DHRUVA. These facilities are extensively used for characterization of materials using techniques like neutron scattering, neutron activation analysis and for isotope production. 3. Top view of ZERLINA reactor core. The advantage of this reactor is extreme flexibility of reconfiguring core geometries, which is crucial for optimization of reactor design. 4. View of the end-fitting and end shield of a Pressurised Heavy Water Reactor. This design has a unique feature of refueling without having to shut down the reactor. This has enabled achieving high plant capacity factors. 5. Steam generators for the 540 MWe reactors being constructed at TAPS. These reactors are the next generation high power PHWR’s and recently, one of the reactors was made operational. The capacity to manufacture very large components to exacting standards has been pioneered by DAE and has significantly benefited Indian industry. 6. Quality assurance - the highest priority of the Department. Dr. M.R. Srinivasan, former Chairman AEC, personally inspecting the turbine blades. 7. Top view of control plug of FBTR during out-of-pile tests. 26 The Chain Reaction-Volume 02 (Part 01) #150 Dt.:28/10/2005 The Chain Reaction-Volume CyanMagentaYellowBlack Black Yellow Research Reactors – The Test Beds of Nuclear Technology and structural materials. These could be mastered only by Magenta building test reactors, which use different types of fuels, structural materials, coolants etc. Towards this end, several Cyan research reactors were systematically designed and built during different stages of the programme. The first of these reactors was a swimming pool type of reactor, aptly christened “APSARA” – the celestial water nymph, by Pandit Nehru himself. The basic design for this reactor was frozen in July 1955 and Indian scientists and engineers completed the construction in just over a year. With APSARA, India became the first Asian country outside the erstwhile Soviet Union, to have designed Panoramic view of the DHRUVA and CIRUS reactors and built its own nuclear reactor . located in BARC The next crucial step involved the planning of larger reactors On December 2nd 1942, something incredible was happening having much higher neutron flux and power than what was at the squash courts of the university of Chicago. Enrico Fermi, available at APSARA. This plan materialized in 1960 with the the Italian born physicist was demonstrating, to the world, the building of CIRUS, a high power (40 MWt) research reactor. feasibility of extracting controlled energy from self-sustaining This reactor, then known as the Canada India Reactor or CIR neutron chain reaction. Shortly thereafter, as early as in 1944, for short, was built in collaboration with Canada. These early even before India attained independence, Bhabha was already gains catapulted India into an ambitious nuclear program. formulating the strategy for setting up a nuclear research CIRUS and APSARA became centres of excellence in nuclear programme in India. Right from the formative years of the education. Experiments carried out at APSARA and CIRUS programme, Bhabha wanted India to be self-reliant in this newly have provided the necessary confidence and expertise for emerging area. design and safe operation of many nuclear reactors in the country. In early 1961, a zero energy critical facility named ZERLINA “…The emphasis throughout has been on (Zero Energy Reactor for Lattice Investigations and New developing know-how indigenously and on growing Assemblies) was built, for studying various geometrical aspects people, able to tackle the tasks, which lie ahead…” (lattice parameters) of a reactor fuelled with natural uranium and moderated with heavy water. - H. J. Bhabha It may be recalled that the three-stage programme calls for building of plutonium based reactors in the second stage. Therefore, the next logical step was to build a critical facility, which used plutonium as fuel. Such a test reactor was built in In line with his vision, one of the earliest decisions he took 1972 and was named PURNIMA (Plutonium Reactor for was to build research reactors of different types. Each of these Neutron Investigations in Multiplying Assemblies). This reactor rapidly accelerated the learning process necessary for was intended for studying the behaviour of plutonium fuel in a developing an intimate understanding of the complex issues pulsed fast reactor (PFR). Following this, a critical facility called involved in the control of nuclear chain reaction. The design of PURNIMA-2 was designed, with a solution containing 400 gms reactors involves high levels of optimization of geometry, fuel of uranyl nitrate serving as the fuel for this facility. It attained design, safety, materials selection, irradiation behavior of fuel criticality in 1984. 27 The Chain Reaction-Volume 02 (Part 01) #150 Dt.:28/10/2005 The Chain Reaction-Volume CyanMagentaYellowBlack Black In the early seventies, a need was felt for a research reactor 1985, with indigenous plutonium-uranium mixed carbide fuel, Yellow having even larger neutron flux and irradiation volumes than providing valuable design and operational experience. Based CIRUS, for meeting the growing requirements for radioisotopes on the successful operation of FBTR, broad based R&D and Magenta and research. This culminated in building of a totally indigenous component development , adequate experience and confidence was gained to embark on commercial phase of fast reactor Cyan 100 MWt research reactor, having the highest flux in Asia at that time. It attained criticality in August 1985 and was named DHRUVA. programme in terms of 500 MWe FBR at Kalpakkam in 2003. Apart from thermal power reactors, it was also realized in As a part of studies with 233U fuel, a 30 kW pool type research the initial stages that adequate energy security could be reactor, KAMINI (Kalpakkam MINI), was designed and built. provided only by taking recourse to fast reactors as second Prior to this, a mock up of the core of this reactor, was built and stage power programme. Towards, gaining first hand made critical in April 1992. It was given the name PURNIMA-3. experience in the fast reactor technology, it was decided to KAMINI was made operational in 1996. This reactor is being construct a Fast Breeder Test Reactor (FBTR) at Reactor extensively used as a neutron source for research applications Research Centre, Kalpakkam (later renamed as Indira Gandhi such as neutron radiography of irradiated nuclear fuel and pyro- Centre for Atomic Research). FBTR was commissioned in devices for the Indian Space programme. Fission, Chain Reaction and Criticality When neutrons strike a uranium-235 nucleus (red ball in figure) in the fuel, sometimes the nucleus splits into two smaller nuclei or undergoes fission. These nuclei called fission fragments usually have different sizes. The kinetic energy of the fission fragments is transferred to other atoms in the fuel as heat energy, which is eventually used to produce steam to drive the turbines. Every fission event results in the release of 2 to 3 energetic neutrons. For every fission event, if at least one of the emitted neutrons, on an average, causes another fission, a self-sustaining chain reaction will result. Under such a condition, when the power remains constant in time, or the chain reaction is so controlled that exactly only one neutron from every fission event contributes to the subsequent fission process, the reactor is said to have become critical. 28 The Chain Reaction-Volume 02 (Part 01) #150 Dt.:28/10/2005 The Chain Reaction-Volume CyanMagentaYellowBlack Black Yellow Moderator The chances of occurrence of a fission event are greatly enhanced if the energetic fission neutrons are slowed down to very Magenta low energies (thermal energies). This is done when the neutrons lose their energy on being elastically or inelastically scattered Cyan by light atoms or molecules. These substances made of such light atoms/ molecules are called moderators - usually light water (H2O) or heavy water (D2O). Graphite is also occasionally used for this purpose. Schematic Representation of hydrogen and deuterium Schematic of light water and Heavy water molecules A good moderator is one that rapidly slows down neutrons by taking away their kinetic energy, but does not absorb them. Light water slows down neutrons better than heavy water, but it also absorbs more neutrons. When natural uranium (containing only 0.7% of fissile nuclei with the remaining 99.3% being 238U atoms that can contribute to non-fission absorption) is used as fuel, and light water is used as moderator, not enough neutrons are available to sustain the fission chain reaction. Therefore heavy water is used in PHWR’s, which uses natural uranium oxide as fuel. In enriched fuel having more 235U or Pu, light water can, however, be used as moderator. Breeding and fuel utilization Judicious utilization of nuclear fuel is an important consideration for the long-term exploitation of nuclear energy. Therefore, an optimum use of both fissile and fertile isotopes is essential. Fertile isotopes like 238U and 232Th are converted into fissile 239Pu and 233U in a reactor. In a PHWR, some amount of 239Pu is also formed. However, the quantity of fissile 235U consumed (0.5%) is greater than the quantity of fissile Pu (~0.3%) that is produced. The ratio of fissile isotopes produced in a reactor to that which is consumed is called the breeding ratio. When this ratio is greater than one, more fissile material is produced than is consumed. Reactors for which the breeding ratio is more than one are called breeder reactors.