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The Pebble Bed Modular Reactor (PBMR) project in South Africa is probably the most publicized of the current efforts [http://www.pbmr.co.za]. A decision is expected from the South African government by late 2002 or early 2003 whether to construct the prototype. The prototype would be approximately 150 MWe and would have online refueling capability. If built, this project would answer many questions on the feasibility of both helium turbines as well as the economics of the pebble bed reactor. In addition, the South African effort may provide impetus for other HTGR projects. In the US, a smaller scale effort is underway to design a pebble bed reactor [http://web.mit.edu/pebble-bed/]. This effort is part of the Generation IV project of the US Department of Energy.
In the Netherlands, a more unusual pebble bed reactor is being studied. Called NEREUS [http://www.romawa.nl], this design is both smaller (8 MWe) and would not have online refueling capability. Instead the fuel design would permit longer periods of operation between refuelings (three years). The main objective for the NEREUS design would be either for commercial ship propulsion or could be used for small remote villages. NEREUS has even been studied for desalination due to both its longer periods between refueling and greater portability.
Hexagonal block designs are also being considered. The main effort centers on the Gas Turbine - Modular Helium Reactor (GT-MHR). This effort is also part of the Generation IV program and is an evolution from the previous US designs [http://www.ga.com/gtmhr/]. The reactor would produce approximately 150 MWe. It would not have online refueling capability, however the hexagonal blocks would be arranged in an annular pattern, in other words a "donut" of fuel containing blocks with "empty" graphite blocks in the center and surrounding the outside. This annular configuration would serve as a further absorber of excess heat should a loss of coolant occur.
This article has presented a summary of the HTGR as an alternative to renewable energy sources when such sources are either unavailable or inadequate for the particular need. While the designs presented were not all inclusive, they represent the spectrum of efforts in progress to provide energy needed for sustainable development efforts. While no single energy technology can be a panacea for global energy needs, HTGRs represent an opportunity for nuclear energy to make a relevant contribution to a more sustainable world.
The recent World Summit on Sustainable Development (WSSD) as well as the debates on the Kyoto Treaty for the reduction of greenhouse gases (e.g., carbon dioxide, methane) has renewed discussion on energy sources that are carbon-free. Most of these discussions have concentrated on how to increase the fraction of electricity supplied by renewable sources such as solar or wind. These sources have strong advantages such as no-fuel cost, much lower greenhouse gas emission, and political and social popularity. However, questions remain as to whether such sources alone will be able to meet the diverse needs of the world’s growing population. Even now, over 2 billion people have no electricity at all. To ensure a reliable supply of electricity that does not produce greenhouse gases will likely require other technologies besides strictly renewable sources. Several technologies have been proposed that can both fill the voids left by the renewable technologies while still being relatively carbon free. Among the advanced technologies that have been proposed to fill some of the niches is that of the High Temperature Gas Cooled Reactor (HTGR). Most of this attention has centered on the recent efforts in South Africa, however other efforts are underway with HTGR technologies that offer promise as well.
This article will focus on the HTGR without any detailed discussion of nuclear energy in general. If the reader desires detailed information on the basics of nuclear energy and reactor types please see [http://www.uic.com.au/ne3.htm] and [http://www.uic.com.au/nip64.htm] respectively.
The important aspects of the HTGR design are its higher efficiency, greater safety than standard water-cooled reactors, and lesser water requirements due to the use of helium as the main coolant. The primary reason for the enhanced safety of the HTGR is the use of the TRISO fuel particles that contain the nuclear fuel inside multiple layers of special materials such as silicon carbide (used for inside coatings of high performance devices such as aircraft jet engines). A diagram of the TRISO particle can be seen at http://www.ga.com/prg/fuel.html. These particles are less than one millimeter across and are conglomerated into either small rodlets or spheres. As will be discussed later, the HTGRs that use spheres are pebble bed reactors and those that use rods are called hexagonal block reactors (i.e., the rodlets are contained within hexagonal blocks of nuclear grade graphite )
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Nuclear Waste and Graphite Flammability Robert Margolis | Sep 29th, 2002
Reviewing my article I realized that readers may have more questions regarding nuclear waste and graphite flammability. Here is some additional information links on these important subjects.
1) Attached an interesting website on the natural reactors at Oklo (contained high-level nuclear waste for two billion (two thousand million) years:
http://www.curtin.edu.au/curtin/centre/waisrc/OKLO/index.shtml
2) In addition, here is a description on graphite flammability:
http://www.ga.com/gtmhr/graphites_all.html
Feel free to post or contact me if you have any further questions.
Pebble bed reactor Robert Hargraves | Dec 28th, 2009
Nuclear power is key to global sustainable development. South Africa intended to export the PBMR (Pebble Bed Modular Reactor) within Africa (and also the US). The key criterion is "energy cheaper than coal", wich can not only stop global warming, but increase prosperity to achieve a lifestyle that includes sustainable populations.
You can visit my blog http://tigurl.org/qpt6md for a tutorial on the PBR.
I also advocate the Liquid Fluoride Thorium Reactor (LFTR), especially for the cost goal. Check the Jan 2010 Wired or visit http://tigurl.org/g60epg
Thanks Robert Margolis | Dec 28th, 2009
Glad to see that the article still sparks interest (even after seven years). :-)
I keep in contact with some colleagues in SA and they are keeping up the work. Also, China continues to work on the HTR-PM in Shidaowan. The HTGR continues to makes its way among the more common technologies.
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