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why PBMR?
Safe, clean, cost-competitive, versatile and adaptable.  These, in a nutshell, are the features of South Africa's Pebble Bed Modular Reactor (PBMR).
Locally, the PBMR technology has the potential to provide South Africa with competitive power generation in coastal areas.  Internationally it will be competitive with virtually all other forms of energy generation.
Most of South Africa's coal-fired electricity is generated by large-scale plants built near the pit-heads of two extensive coal-producing areas, both of them far inland on the eastern side of the country.  This requires long power lines from the coal-rich areas to load centres away from the pit-heads, which in turn implies high capital costs and transmission losses.
New power stations have to be built to ensure that the country's capacity keeps up with demand.  In addition, Eskom's older power stations reach the end of their design life after 2025.  South Africa will, therefore, need to access and use all natural resources to meet the additional demand that will be needed by 2025 (over and above the currently installed 39 000 MW).
A typical coal-fired power station requires a construction lead time of four to six years, and could result in the installation of surplus capacity if economic growth is not as expected.  Shorter lead times would enable power utilities to drastically shorten their decision-making horizon for the addition of new capacity, and to add capacity in smaller increments.
Eskom, like most utilities worldwide, also experiences short, sharp demand peaks in winter that are difficult to accommodate with the slow ramping characteristics of the existing large power stations.
These factors prompted Eskom to investigate small electricity generation plants that can be placed near to the points of demand.  The PBMR concept, which has a short construction time, low operating cost and fast load-following characteristics, is such an option.
While open-cycle gas turbines, coal-fired plants and conventional nuclear reactors are all good options in the short and medium term, the PBMR could play a crucial role to help meet the countries' energy requirements from the next decade onwards.  Its inherent safe characteristics and positive attributes from an environmental point of view, add immensely to the attractiveness of this technology.
It was therefore envisaged that - should the technology be successfully demonstrated - at least 20 percent of Eskom's potential new nuclear build programme of about 20 000 MW will consist of PBMRs (24 modules generating 165 MV each).
Since the technology has not previously been commercialised, the intention was to build and operate a single module at Koeberg near Cape Town, and a fuel plant at Pelindaba near Johannesburg.  Successful demonstration was to be followed by commercialisation.
Process Heat Applications
While PBMR's design and development efforts were initially focused mainly on electricity generation, it has become increasingly apparent that the high-temperature gas-cooled reactor technology will also enable access to markets that call for process heat applications.
Heat from the PBMR can be used for a variety of industrial process applications, including process team for cogeneration applications, in-situ oil sands recovery, ethanol applications, refinery and petrochemical applications.  The high temperature heat can also be used to reform methane to produce syngas (where the syngas can be used as feedstock to produce hydrogen, ammonia and methanol);  and to produce hydrogen and oxygen by decomposing water thermochemically.  The waste heat of the PBMR can furthermore be applied to produce water via desalination.
In South Africa, there is interest in the possible use of PBMR technology in petro-chemical complexes, notably for the South African synthetic fuels giant Sasol, to either produce process steam and/or hydrogen to upgrade coal products.  In Canada, there is interest from oil sands producers to use the PBMR to produce the temperature and associated pressure needed to extract bitumen from oil sands instead of gas-fired plants.
In the USA, PBMR was a partner in the Westinghouse-led consortium which has been awarded a contract by the US Department of energy to consider the PBMR technology as heat source for producing non-carbon derived hydrogen.
Small and Adaptable
The PBMR is based on the philosophy that the new generation of nuclear reactors should be small.  Each module would be sized to produce 400 MWth (165 MWe nominal), which is about 18 percent of the output of conventional reactors such as the ones at Koeberg near Cape Town.
The main building and generator of a module will cover an area of about 4 320 m2 (108m x 40m), which means that two modules would fit on a soccer field.  The height of the building will be 66m, more than a third (23m) of which will be below ground level.
In addition, the PBMR can be used both as a base-load or load-following station and can be configured to the size required by the community it serves.
Safety Features
The PBMR has a simple design basis, with inherent safety features that require no human intervention, and which cannot be bypassed or rendered ineffective in any way.   If a fault occurs during reactor operations, the system, at worst, will shut down and merely dissipate heat on a decreasing curve without any core failure or release of radioactivity to the environment.
Green House Gas Reductions
The PBMR can provide an economic mitigation strategy for greenhouse gas reductions, since nuclear power generation produces no carbon dioxide emissions, smoke or any other gases.  France's carbon dioxide emissions from electricity generation fell by 80 percent between 1980 and 1987 as its nuclear capacity increased, and Germany's nuclear power programme has saved the emission of over two billion tons of carbon dioxide from fossil fuels since it began in 1961.
Waste Management
Compared with the huge atmospheric emissions from fossil-fuel energy, nuclear wastes exist in small, highly manageable amounts that can be stored without harm to people or the environment.
One kilogram of uranium in the PBMR fuel has a greater energy output than 430 tons of the best coal with an ash content (waste) of up to 40 percent.  A large coal-fired power station uses about 2 200 trainloads of coal per year (six a day), while only 2 truckloads of fuel per week will be required for 24 PBMR nuclear power stations of equivalent capacity.  For the PBMR demonstration unit at Koeberg, 10 truckloads would have been needed for the initial load, and only 4 truckloads per year for the replacement of spent fuel.
A 165 MWe PBMR module will generate about 32 tons of spent fuel pebbles per annum, about 1 ton of which is uranium.  The storage of PBMR spent fuel should be easier than for fuel elements or rods from conventional nuclear reactors, as no safety graded cooling systems are needed to prevent fuel failure.
The PBMR system has been designed to deal with nuclear waste efficiently and safely.  There will be enough room for the spent fuel to be stored at the PBMR plant for the power station's expected 40-year operational life, during which time no spent fuel will have to be removed from the site.  After the plant has been shut down, the spent fuel can be safely stored on site for another 40 years before being set to a final repository.
Last Updated: 6 February 2017
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