Advances In Harnessing Nuclear Energy





Technology, 29 Jan - 2018 ,

Advances In Harnessing Nuclear Energy
Credit: pixabay.com

The price rise in oil and gas markets, realisation that these resources may not last long and warning signs of climate change have once again diverted attention towards harnessing

The price rise in oil and gas markets, realisation that these resources may not last long and warning signs of climate change have once again diverted attention towards harnessing of nuclear energy in its safest and efficient modes. There still prevail, however, proliferation fears and concerns about long-term management of radioactive wastes, including spent fuel. However, with greater progress in technology, nuclear power plants may one day be safe and that to bar them will be against progress. Nuclear energy can be one of the most potent means for long-term energy security. The changing economic and geopolitical situation in the energy sector has made it imperative to emphasize the significance of nuclear energy in the future energy landscape.  This paper discusses some advanced nuclear energy harvesting technologies with a promising future.

Nuclear energy

Nuclear energy will continue to have an important role in the production of electricity in the world. Nuclear power provides over 16% of the world's electricity. At the middle of 2007 there were a total 437 nuclear power reactors in operation around the world, around 80% of them in developed countries. The position of nuclear energy in the world is fairly stable. In Asia and Russia intensive investment in new capacity is taking place, while in the USA the focus is on life extension of existing nuclear power plants. Similarly, in Europe, new nuclear power plants are being built in many countries. One of the key reasons for extending the life of nuclear power plants and for planning new ones is the fact that it is possible to solve the problem of air pollution through increased use of nuclear energy, since this does not release greenhouse gases. Even the permanent disposal of radioactive waste is being dealt with in an ever more rational way. The majority of countries have already solved the problem of permanent disposal of low and intermediate level radioactive waste. The construction of the first permanent repositories for high-level radioactive waste is also close at hand.

Indian Nuclear Energy Programme

Electricity demand in India has been increasing rapidly, and the 534 billion kilowatt hours produced in 2002 was almost double the 1990 output, though still represented only 505 kWh per capita for the year.  In 2006, 744 billion kWh gross was produced, but with huge transmission losses this resulted in only 505 billion kWh consumption.  The per capita figure is expected to almost triple by 2020, with 6.3% annual growth.  Coal provides 68% of the electricity at present, but reserves are limited. Gas provides 8%, hydro 15%. Some 300 reactor-years of operation had been achieved by mid 2009. India's fuel situation, with shortage of fossil fuels, is driving the nuclear investment for electricity, and 25% nuclear contribution is foreseen by 2050, from one hundred times the 2002 capacity. Nuclear power supplied 15.8 billion  kWh (2.5%) of India's electricity in 2007 from 3.7 GWe (of 110 GWe total) capacity and this will increase steadily as imported uranium becomes available and new plants come on line. 

India's nuclear power program has proceeded largely without fuel or technological assistance from other countries. Its power reactors to the mid 1990s had some of the world's lowest capacity factors, reflecting the technical difficulties of the country's isolation, but rose impressively from 60% in 1995 to 85% in 2001-02. India's nuclear energy self-sufficiency extended from uranium exploration and mining through fuel fabrication, heavy water production, reactor design and construction, to reprocessing and waste management. It has a small fast breeder reactor and is building a much larger one. It is also developing technology to utilize its abundant resources of thorium as a nuclear fuel. Plans for building the first Pressurised Heavy Water Reactor (PHWR) were finalized in 1964, and this prototype - Rajasthan-1, which had Canada's Douglas Point reactor as a reference unit, was built as a collaborative venture between Atomic Energy of Canada Ltd (AECL) and The Nuclear Power Corporation of India Ltd (NPCIL). It started up in 1972 and was duplicated Subsequent indigenous PHWR development has been based on these units.

It has 15 small and two mid-sized nuclear power reactors in commercial operation, six under construction - including two large ones and a fast breeder reactor, and more planned. The two Tarapur 150 MWe Boiling Water Reactors (BWRs) built by GE on a turnkey contract before the advent of the Nuclear Non-Proliferation Treaty were originally 200 MWe. They were down-rated due to recurrent problems but have run well since. They have been using imported enriched uranium and are under International Atomic Energy Agency (IAEA) safeguards. The two small Canadian (Candu) PHWRs at Rajasthan nuclear power plant started up in 1972 & 1980, and are also under safeguards. Rajasthan-1 was down-rated early in its life and has operated very little since 2002 due to ongoing problems and has been shut down since 2004 as the government considers its future. The 220 MWe PHWRs (202 MWe net) were indigenously designed and constructed by NPCIL, based on a Canadian design. The Kalpakkam (MAPS) reactors were refurbished in 2002-03 and 2004-05 and their capacity restored to 220 MWe gross (from 170). Much of the core of each reactor was replaced, and the lifespans extended to 2033/36.

The new PHWR model nuclear reactors of large capacities are being developed indigenously. Future indigenous PHWR reactors will be 700 MWe gross (640 MWe net). A 500 MWe prototype fast breeder reactor (FBR) is under construction and is expected to start up in 2010 and produce power in 2011.  Four further oxide-fuel fast reactors are envisaged but slightly redesigned to reduce capital cost.  At the world level, more and more advanced reactor designs are in various stages of development out of which some are evolutionary from the PWR, BWR and PHWR designs above, some are more radical departures. Some to name are: Advanced Boiling Water Reactor (ABWR), Integral Fast Reactor, The Pebble Bed Reactor, a High Temperature Gas Cooled Reactor (HTGCR), Small, Sealed, Transportable, Autonomous Reactor (SSTAR), Clean And Environmentally Safe Advanced Reactor (CAESAR), Subcritical reactors and Advanced Heavy Water Reactor etc.

Generation IV reactors

Current reactors in operation around the world are generally considered second- or third-generation systems, with the first-generation systems having been retired some time ago. Generation IV reactors are a set of theoretical nuclear reactor designs currently being researched. These designs are generally not expected to be available for commercial construction before 2030. Research into these reactor types was officially started by the Generation IV International Forum (GIF) based on eight technology goals. The primary goals being to improve nuclear safety, improve proliferation resistance, minimize waste and natural resource utilization, and to decrease the cost to build and run such plants like:

·         Gas cooled fast reactor

·         Lead cooled fast reactor

·         Molten salt reactor

·         Sodium-cooled fast reactor

·         Supercritical water reactor

·         Very high temperature reactor

 

Generation V+ reactors

Designs which are theoretically possible, but which are not being actively considered or researched at present. Though such reactors could be built with current or near term technology, they trigger little interest for reasons of economics, practicality, or safety.

· Liquid Core reactor: a closed loop liquid core nuclear reactor, where the fissile material is molten uranium cooled by a working gas pumped in through holes in the base of the containment vessel.

· Gas core reactor: a closed loop version of the nuclear lightbulb rocket, where the fissile material is gaseous uranium-hexafluoride contained in a fused silica vessel. A working gas (such as hydrogen) would flow around this vessel and absorb the UV light produced by the reaction. In theory, using UF6 as a working fuel directly (rather than as a stage to one, as is done now) would mean lower processing costs, and very small reactors. In practice, running a reactor at such high power densities would probably produce unmanageable neutron flux.

· Gas core EM reactor : as in the Gas Core reactor, but with photovoltaic arrays converting the UV light directly to electricity.

·  Fission fragment reactor

Fusion reactors

Controlled nuclear fusion could in principle be used in fusion power plants to produce power without the complexities of handling actinides, but significant scientific and technical obstacles remain. Several fusion reactors have been built, but as yet none has 'produced' more thermal energy than electrical energy consumed. Despite research having started in the 1950s, no commercial fusion reactor is expected before 2050. The ITER project is currently leading the effort to commercialize fusion power.


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