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Encyclopedia > Pebble bed reactor
Graphite Pebble for Reactor
Graphite Pebble for Reactor

The pebble bed reactor (PBR) or pebble bed modular reactor (PBMR) is an advanced nuclear reactor design. Image File history File linksMetadata Download high-resolution version (2048x1536, 1703 KB) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Pebble bed reactor Metadata This file contains additional information, probably added from the digital camera or scanner used... Image File history File linksMetadata Download high-resolution version (2048x1536, 1703 KB) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Pebble bed reactor Metadata This file contains additional information, probably added from the digital camera or scanner used... Core of a small nuclear reactor used for research. ...


This technology claims a dramatically higher level of safety and efficiency. Instead of water, it uses pyrolytic graphite as the neutron moderator, and an inert or semi-inert gas such as helium, nitrogen or carbon dioxide as the coolant, at very high temperature, to drive a turbine directly. This eliminates the complex steam management system from the design and increases the transfer efficiency (ratio of electrical output to thermal output) to about 50%. Also, the gases do not dissolve contaminants or absorb neutrons as water does, so the core has less in the way of radioactive fluids and is more economical than a light water reactor. This diagram demonstrates the defense in depth quality of nuclear power plants. ... Pyrolytic carbon is a material similar to graphite, but with some covalent bonding between its graphene sheets. ... This does not adequately cite its references or sources. ... An inert gas is any gas that is not reactive under normal circumstances. ... General Name, Symbol, Number helium, He, 2 Chemical series noble gases Group, Period, Block 18, 1, s Appearance colorless Atomic mass 4. ... General Name, Symbol, Number nitrogen, N, 7 Chemical series nonmetals Group, Period, Block 15, 2, p Appearance colorless gas Atomic mass 14. ... Carbon dioxide is a chemical compound composed of one carbon and two oxygen atoms. ... A Siemens steam turbine with the case opened. ... MWe and MWt are units for measuring the output of a power plant. ... A light water reactor or LWR is a thermal nuclear reactor that uses ordinary water (as opposed to heavy water) as its neutron moderator. ...


The technology was first developed in Germany[1] but political and economic decisions were made to abandon the technology. [2] In various forms, it is currently under development by MIT, the South African company PBMR, General Atomics (U.S.), the Dutch company Romawa B.V., Adams Atomic Engines, INL, and the Chinese company Huaneng [3]. The Massachusetts Institute of Technology (MIT) is a private, coeducational research university located in Cambridge, Massachusetts. ... General Atomics is a nuclear physics and defense contractor in southern California. ... The Idaho National Laboratory (INL) is an 890 square mile (2,300 km²) complex located in the Idaho desert between the towns of Arco and Idaho Falls. ...


In June 2004, it was announced that a new PBMR would be built at Koeberg, South Africa by Eskom, the government-owned electrical utility[4]. There is considerable opposition to the PBMR from groups such as Koeberg Alert and Earthlife Africa, the latter of which has sued Eskom to stop development of the project [5]. Koeberg is located 30 km north of Cape Town, on the West coast of South Africa, next to the SA Police Training College and the suburb of Melkbosstrand. ... Koeberg Alert formed in 1983 and started out as a local campaign against South Africas nuclear programme, in particular the construction of Koeberg Nuclear Power Station. ... Earthlife Africa is a South African environmental organization founded in August 1988, in Johannesburg. ...

Contents

Pebble bed design

A pebble bed power plant combines a gas-cooled core[6] and a novel packaging of the fuel that dramatically reduces complexity while improving safety by an equal margin[7] .


The uranium, thorium or plutonium nuclear fuels are in the form of a ceramic (usually oxides or carbides) contained within spherical pebbles made of pyrolytic graphite, which acts as the primary neutron moderator. Each sphere is effectively a complete "mini-reactor", containing all of the parts that would normally be separate components of a conventional reactor. Simply piling enough of the fuel spheres together will eventually reach criticality. General Name, Symbol, Number uranium, U, 92 Chemical series actinides Group, Period, Block n/a, 7, f Appearance silvery gray metallic; corrodes to a spalling black oxide coat in air Atomic mass 238. ... General Name, Symbol, Number thorium, Th, 90 Chemical series Actinides Group, Period, Block n/a, 7, f Appearance silvery white Atomic mass 232. ... General Name, Symbol, Number plutonium, Pu, 94 Chemical series actinides Group, Period, Block n/a, 7, f Appearance silvery white Atomic mass (244) g·mol−1 Electron configuration [Rn] 5f6 7s2 Electrons per shell 2, 8, 18, 32, 24, 8, 2 Physical properties Phase solid Density (near r. ... Nuclear Fuel Process A graph compairing nucleon number against binding energy Nuclear fuel is any material that can be consumed to derive nuclear energy, by analogy to chemical fuel that is burned to derive energy. ... Fixed Partial Denture, or Bridge The word ceramic is derived from the Greek word κεραμικός (keramikos). ... An oxide is a chemical compound containing an oxygen atom and other elements. ... Calcium carbide. ... This does not adequately cite its references or sources. ... Criticality could mean critical mass in nuclear reactors; self-organized criticality; criticality matrix; Criticality accident This is a disambiguation page — a navigational aid which lists pages that might otherwise share the same title. ...


The reactor design is such that it is power-limited or inherently self controlling due to doppler broadening. Doppler broadening is a broadening of spectral lines due to thermal agitation. ...


The pebbles are held in a bin or can. An inert gas, helium, nitrogen or carbon dioxide, circulates through the spaces between the fuel pebbles to carry heat away from the reactor. Ideally, the heated gas is run directly through a turbine. However, if the gas from the primary coolant can be made radioactive by the neutrons in the reactor, it may be instead brought to a heat exchanger, where it heats another gas, or produces steam. The exhaust of the turbine is quite warm and may be used to warm buildings or chemical plants, or even run another heat engine. An inert gas is any gas that is not reactive under normal circumstances. ... General Name, Symbol, Number helium, He, 2 Chemical series noble gases Group, Period, Block 18, 1, s Appearance colorless Atomic mass 4. ... General Name, Symbol, Number nitrogen, N, 7 Chemical series nonmetals Group, Period, Block 15, 2, p Appearance colorless gas Atomic mass 14. ... Carbon dioxide is a chemical compound composed of one carbon and two oxygen atoms. ... A Siemens steam turbine with the case opened. ... A coolant, or heat transfer fluid, is a fluid which flows through a device in order to prevent its overheating, transferring the heat produced by the device to other devices that utilize or dissipate it. ... This article or section does not adequately cite its references or sources. ... A heat exchanger is a device built for efficient heat transfer from one fluid to another, whether the fluids are separated by a solid wall so that they never mix, or the fluids are directly contacted. ... In engineering and thermodynamics, a heat engine performs the conversion of heat energy to mechanical work by exploiting the temperature gradient between a hot source and a cold sink. Heat is transferred from the source, through the working body of the engine, to the sink, and in this process some...


Much of the cost of a conventional, water-cooled nuclear power plant is the complexity of the cooling systems. These are part of the safety of the overall design, and thus require extensive safety systems and redundant backups. A water-cooled reactor is generally dwarfed by the cooling systems attached to it. Additionally, the core irradiates the water with neutrons. The water, and impurities dissolved in it become radioactive. Further, the high pressure piping in the primary side becomes embrittled and requires continual inspection and eventual replacement. Hydrogen embrittlement is the process by which various metals, most importantly high-strength steel, become brittle and crack following exposure to hydrogen. ...


In contrast, a pebble bed reactor is gas cooled, sometimes at low pressures. The spaces between the pebbles form the "piping" in the core. Since there's no piping in the core, and the coolant contains no hydrogen, embrittlement of the pipes from neutrons and hydrogen cannot occur. The preferred gas, Helium, does not easily absorb neutrons or impurities, and therefore is both more efficient, and less radioactive than water.


A large advantage of the pebble bed reactor over a conventional light-water reactor is that it operates at higher temperatures. The reactor can directly heat fluids for low pressure gas turbines. The high temperatures allow a turbine to extract more mechanical energy from the same amount of thermal energy; therefore, the power system uses less fuel per kilowatt-hour. A light water reactor or LWR is a thermal nuclear reactor that uses ordinary water (as opposed to heavy water) as its neutron moderator. ... This machine has a single-stage centrifugal compressor and turbine, a recuperator, and foil bearings. ...


A significant technical advantage is that some designs are throttled by temperature, not by control rods. The reactor can be simpler because it does not need to operate well with the varying neutron profiles caused by partially-withdrawn control rods. For maintenance, many designs include control rods, called "absorbers" that are inserted through tubes in a neutron reflector around the reactor core. A control rod is a rod made of a chemical element capable of absorbing many neutrons without decaying themselves. ... Nuclear weapon designs are often divided into two classes, based on the dominant source of the nuclear weapons energy. ...


If throttled by temperature, the reactor can change power quickly, just by changing the coolant flow rate. A coolant-throttled design can also change power more efficiently (say, for utility power) by changing the coolant density or heat capacity.


Another advantage is that fuel pebbles for different fuels might be used in the same basic design of reactor (though perhaps not at the same time). Proponents claim that some kinds of pebble-bed reactors should be able to use thorium, plutonium and natural unenriched uranium, as well as the customary enriched uranium. There is a project in progress to develop pebbles and reactors that use MOX fuel, that mixes uranium with the plutonium from surplus or expired nuclear weapons. General Name, Symbol, Number thorium, Th, 90 Chemical series Actinides Group, Period, Block n/a, 7, f Appearance silvery white Atomic mass 232. ... General Name, Symbol, Number plutonium, Pu, 94 Chemical series actinides Group, Period, Block n/a, 7, f Appearance silvery white Atomic mass (244) g·mol−1 Electron configuration [Rn] 5f6 7s2 Electrons per shell 2, 8, 18, 32, 24, 8, 2 Physical properties Phase solid Density (near r. ... General Name, Symbol, Number uranium, U, 92 Chemical series actinides Group, Period, Block n/a, 7, f Appearance silvery gray metallic; corrodes to a spalling black oxide coat in air Atomic mass 238. ... These pie-graphs showing the relative proportions of uranium-238 (blue) and uranium-235 (red) at different levels of enrichment. ... Mixed oxide, or MOX fuel, is a blend of plutonium and natural uranium or depleted uranium which behaves similarly (though not identically) to the enriched uranium feed for which most nuclear reactors were designed. ... General Name, Symbol, Number uranium, U, 92 Chemical series actinides Group, Period, Block n/a, 7, f Appearance silvery gray metallic; corrodes to a spalling black oxide coat in air Atomic mass 238. ... General Name, Symbol, Number plutonium, Pu, 94 Chemical series actinides Group, Period, Block n/a, 7, f Appearance silvery white Atomic mass (244) g·mol−1 Electron configuration [Rn] 5f6 7s2 Electrons per shell 2, 8, 18, 32, 24, 8, 2 Physical properties Phase solid Density (near r. ... The mushroom cloud of the atomic bombing of Nagasaki, Japan, 1945, rose some 18 km (11 mi) above the epicenter. ...


Stationary designs and history

In most stationary pebble-bed reactor designs, fuel replacement is continuous. Instead of shutting down for weeks to replace fuel rods, pebbles are placed in a bin-shaped reactor. A pebble is recycled from the bottom to the top about ten times over a few years, and tested each time it is removed. When it is expended, it is removed to the nuclear waste area, and a new pebble inserted.


The concept was invented by Professor Dr. Rudolf Schulten in the 1950s. The basic concept was to make a very simple, very safe reactor, with a commoditized nuclear fuel. The crucial breakthrough was the idea of combining fuel, structure, containment, and neutron moderator in a small, strong sphere. The concept was enabled by the realization that engineered forms of silicon carbide and pyrolytic carbon were quite strong, even at temperatures as high as 2000 °C (3600 °F). The natural geometry of close-packed spheres then provides the ducting (the spaces between the spheres) and spacing for the reactor core. To make the safety simple, the core has a low power density, about 1/30 the power density of a light water reactor. In the 1950’s, Dr. Rudolf Schulten (later Prof. ... This does not adequately cite its references or sources. ... Silicon carbide (SiC) is a ceramic compound of silicon and carbon and occurs in nature as the extremely rare mineral moissanite. ... Pyrolytic carbon is a material similar to graphite, but with some covalent bonding between its graphene sheets. ... In engineering, specific power (sometimes also power per unit mass or power density) refers to the amount of power delivered by an energy source, divided by some measure of the sources size or mass. ...


The core generates less power as its temperature rises, and therefore cannot have a criticality excursion when the machinery fails. At such low power densities, the reactor can be designed to lose more heat through its walls than it would generate. In order to generate much power it has to be cooled, and then the power is extracted from the coolant. A criticality accident (also sometimes referred to as an excursion or power excursion) occurs when a nuclear chain reaction is accidentally allowed to occur in fissile material, such as enriched uranium or plutonium. ...


The "modular" concept of the pebble bed reactor uses several small reactors in a large power plant. This is convenient because new investment can be gradual, and tuned to the actual demand for electric power. Sites that require larger generation capacity can simply install more reactors. Depending on the design, there also can be economies of scale and better reliability when several reactors share equipment, and can switch sets of equipment when some part fails.


The modular design also allows a small reactor to be mass-produced, reducing the life-cycle costs of safety-certification and design qualification.


In modular systems, the equipment to cool the turbine's exhaust must be adapted to the site. The cooling equipment adaptable to the most sites is a cooling tower. However, near water, water cooling is far less expensive because the larger heat capacity of water permits the equipment to be much smaller. Image 1: Natural draft wet cooling towers at Didcot Power Station, UK Cooling towers are evaporative coolers used for cooling water or other working medium to near the ambient wet-bulb air temperature. ...


History

Germany

AVR

A 15 MWe demonstration reactor, Arbeitsgemeinschaft Versuchsreaktor (AVR - roughly translated to working group test reactor), was built at the Jülich Research Centre in Jülich, West Germany. The goal was to gain operational experience with a high-temperature gas-cooled reactor. The unit's first criticality was on August 26, 1966. The facility ran successfully for 21 years, and was decommissioned on December 1, 1988, in the wake of the Chernobyl disaster and operational problems. MWe and MWt are units for measuring the output of a power plant. ... Check [AVR] ... Position of Jülich Research Centre in Germany The Jülich Research Centre (German: Forschungszentrum Jülich, short FZJ) is based near Jülich, North Rhine-Westphalia, Germany. ... Jülich is a medium-size town in the district of Düren, in the federal state of Nordrhein-Westfalen, in Germany. ... Criticality could mean critical mass in nuclear reactors; self-organized criticality; criticality matrix; Criticality accident This is a disambiguation page — a navigational aid which lists pages that might otherwise share the same title. ... August 26 is the 238th day of the year in the Gregorian Calendar (239th in leap years). ... 1966 (MCMLXVI) was a common year starting on Saturday (the link is to a full 1966 calendar). ... December 1 is the 335th (in leap years the 336th) day of the year in the Gregorian calendar. ... 1988 (MCMLXXXVIII) was a leap year starting on Friday of the Gregorian calendar. ... The nuclear power plant at Chernobyl prior to the completion of the sarcophagus. ...


The AVR was originally designed to breed 233Uranium from 232Thorium. Thorium is about three times as abundant in the Earth's crust as uranium, and an effective thorium breeder reactor is therefore considered valuable technology. However, the fuel design of the AVR contained the fuel so well that the transmuted fuels were uneconomic to extract—it was cheaper to simply use natural uranium isotopes. Uranium-233 is a fissile artificial isotope of uranium, which is proposed as a nuclear fuel. ... Thorium 232 is a naturally occurring isotope of thorium. ... Earth cutaway from core to exosphere. ... A breeder reactor is a nuclear reactor that breeds fuel. ...


The AVR used helium coolant. Helium has a low neutron cross-section. Since few neutrons are absorbed, the coolant remains less radioactive. In fact, it is practical to route the primary coolant directly to power generation turbines. Even though the power generation used primary coolant, it is reported that the AVR exposed its personnel to less than 1/5 as much radiation as a typical light water reactor. General Name, Symbol, Number helium, He, 2 Chemical series noble gases Group, Period, Block 18, 1, s Appearance colorless Atomic mass 4. ... A coolant, or heat transfer fluid, is a fluid which flows through a device in order to prevent its overheating, transferring the heat produced by the device to other devices that utilize or dissipate it. ... The neutron cross section of an element is the effective cross sectional area that an atom of that element presents to a neutron. ...


THTR

To follow, See THTR-300. The THTR-300 was a thorium high-temperature nuclear reactor rated at 300 MW electric (THTR-300). ...


China

China has licensed the German technology and is actively developing a pebble bed reactor for power generation [8]. The 10 megawatt prototype is called the HTR-10. It is a conventional helium-cooled, helium-turbine design. The program is at Tsinghua University in Beijing. The first 200 megawatt production plant is planned for 2007. There are firm plans for thirty such plants by 2020 (6 gigawatts). By 2050, China plans to deploy as much as 300 gigawatts of reactors of which PBMRs will be a major component. If PBMRs are successful, there may be a substantial number of reactors deployed. This may be the largest planned nuclear power deployment in history. Tsinghua University, (Simplified Chinese: , Traditional Chinese: ; pinyin: Qinghuá Dàxué) is a university in Beijing, China. ...   (Chinese:  ; Pinyin: BÄ›ijÄ«ng; IPA: ), a metropolis in northern China, is the capital of the Peoples Republic of China (PRC). ...


Tsinghua's program for Nuclear and New Energy technology also plans in 2006 to begin developing a system to use the high temperature gas of a pebble bed reactor to crack steam to produce hydrogen. The hydrogen could serve as fuel for vehicles, reducing China's dependence on imported oil. Hydrogen can also be stored, unlike electricity, and distribution by pipelines may sometimes be more efficient than conventional power lines. See hydrogen economy. A hydrogen economy is a hypothetical future economy in which energy, for mobile applications (vehicles, aircraft) and electrical grid load balancing (daily peak demand reserve), is stored as hydrogen (H2). ...


South Africa

Pebble Bed Modular Reactor Pty. Ltd. (PBMR) in South Africa may be the current technology leader. It is developing a modular pebble-bed reactor. On June 25, 2003, the South African Republic's Department of Environmental Affairs and Tourism approved a prototype 110 MW pebble-bed modular reactor for Eskom at Koeberg, South Africa. PBMR also has approval for a pebble-bed fuel production plant in Pelindaba. The uranium is produced locally as a by-product of gold mining.[citation needed] 2003 (MMIII) was a common year starting on Wednesday of the Gregorian calendar. ... Koeberg is located 30 km north of Cape Town, on the West coast of South Africa, next to the SA Police Training College and the suburb of Melkbosstrand. ... The introduction to this article provides insufficient context for those unfamiliar with the subject matter. ...


PBMR's primary coolant is helium. The helium directly turns low-pressure turbomachinery, without intervening losses from heat-exchangers. Helium is well-favored because it is chemically inert, and neutrons do not transmute it to a radioactive element. This means that the turbomachinery should not become radioactive, even though it operates on primary coolant. While the fuel design is robust, a fuel defect could still contaminate the power production equipment. One disadvantage is that the turbine must be somewhat larger, and therefore more expensive. General Name, Symbol, Number helium, He, 2 Chemical series noble gases Group, Period, Block 18, 1, s Appearance colorless Atomic mass 4. ...


The turbine's compressors are decoupled from the turbine, which permits the turbine's pressurization to be decoupled from the generator speed. Utility generators must be synchronized to the power grid. The prototype test of the closed-cycle helium system including compressors, turbine and recuperator has been developed in the engineering lab at the Potchefstroom Campus of the North-West University. Transmission towers Transmission lines in Lund, Sweden Electric power transmission, or more accurately Electrical energy transmission, is the second process in the delivery of electricity to consumers. ... A recuperator is a heat exchanger that helps boost the efficiency of some gas turbine engines. ... The Potchefstroom campus of the North-West University (nicknamed Pukke) was formerly known as the Potchefstroom University for Christian Higher Education (abbreviated PU for CHE). ... ÁÊã{} This page is a candidate for speedy deletion, because: theres no such thing: Northwest University is not hyphenated If you disagree with its speedy deletion, please explain why on its talk page or at Wikipedia:Speedy deletions. ...


Helium is lighter than air, so air can displace the helium if the reactor wall is breached. Pebble bed reactors need fire-prevention features to keep the graphite of the pebbles from burning in the presence of air. The expression lighter than air refers to objects, usually aircraft, that are buoyant in air because they have an average density that is less than that of air (usually because they contain gases that have a density that is lower than that of air). ... Graphite (named by Abraham Gottlob Werner in 1789, from the Greek γραφειν: to draw/write, for its use in pencils) is one of the allotropes of carbon. ...


The pebble bed reactor's design can be throttled in real time to meet peak electric power loads just like conventional reactors, where power follows steam demand in seconds. The modular design also supports the speculation that it will be useful in building peak load plants. South Africa lacks natural gas for the gas turbines that normally power peak loads, but it exports uranium and thorium. Natural gas is gaseous fossil fuel consisting primarily of methane but including significant quantities of ethane, butane, propane, carbon dioxide, nitrogen, helium and hydrogen sulfide. ...


The S. African module's capacity is 165 MWe. The reactor could be a significant export item for South Africa.


PBMR's web site has also said that the reactor was designed to desalinate seawater, to help with South Africa's continuing lack of fresh water. Shevchenko BN350 desalination unit situated on the shore of the Caspian Sea. ... Annual mean sea surface temperature for the World Ocean. ... For the village on the Isle of Wight, see Freshwater, Isle of Wight. ...


An inherently self controlling modular reactor that can provide peaking-power and fresh water would be a genuinely useful addition to the market, and a valuable export item. If the trial is successful, PBMR says it will build up to ten local plants on South Africa's coast. PBMR also wants to export up to 20 plants per year. The estimated export revenue is 8 billion rand (roughly US$ 1.2 billion) per year, and could employ about 57,000 people. The program's total cost is about US$ 1 billion, and the developers estimate that about 30 plants will need to be produced to break even.


In 2005, environmental group Earthlife Africa won a court challenge requiring further hearings on the Koeberg reactors (which were originally approved in September 2003) [1]. The Cape Town city government and other civic and environmental groups also say they oppose the plant. In July 2003, following the approval of the environmental impact assessment, there were public demonstrations against the project in both Johannesburg and Cape Town. Earthlife Africa also opposed the Pelindaba fuel plant. Earthlife Africa is a South African environmental organization founded in August 1988, in Johannesburg. ... City motto: Spes Bona (Latin: Good Hope) Location of the City of Cape Town in Western Cape Province Province Western Cape Mayor Helen Zille Area  - % water 2,499 km² N/A Population  - Total (2004)  - Density Not ranked 2,893,251 1,158/km² Established 1652 Time zone SAST (UTC+2... City motto: Unity in Development Province Gauteng Mayor Amos Masondo Area  - % water 1,644 km² 0. ...


In December 2005, South Africa's PBMR company awarded a contract for engineering, procurement and construction management to SLMR - a Canadian-South African joint venture made up of Montreal-based engineering firm SNC-Lavalin and South-African construction and engineering firm Murray & Roberts - for its demonstration Pebble Bed Modular Reactor at Koeberg. Construction is envisaged starting 2007, and a second round of environmental hearings is under way at present. Meanwhile the BNFL share in PBMR has been passed to Westinghouse Electric Company and negotiations are under way with other possible investors to enable Eskom (the South African Power Utility) to reduce its stake from 30% to 5%. Koeberg is located 30 km north of Cape Town, on the West coast of South Africa, next to the SA Police Training College and the suburb of Melkbosstrand. ... British Nuclear Fuels plc or BNFL manufactures and transports nuclear fuel (notably MOX), runs reactors, generates and sells electricity, reprocesses and manages spent fuel (mainly at Sellafield), and decommissions nuclear plants and other similar facilities. ... The Westinghouse Electric Company is a nuclear reactor technology company. ... Eskom is a South African electricity public utility company. ...


On 30 January 2007 it was reported that the South African government had approved the manufacture of PBMR fuel at Nuclear Energy Corporation of South Africa's Pelindaba Beva complex in the North West Province, and transporting of the raw materials to this site and manufactured fuel from it to Koeberg.


This followed the dismissal by Environment Minister Marthinus van Schalkwyk of appeals brought by Earthlife Africa including opposition to the de-linking of the fuel plant and the PBMR. The appeal claimed that "neither process should be viewed in isolation". The appellants also registered concern about the long-term storage of high-level radioactive waste and contaminated materials, and alleged inadequate consideration of alternatives to the fuel plant.


In dismissing the appeals, van Schalkwyk noted that the two projects would be established in different places, were of different natures and came with "vastly different" environmental risks. He added that "negative environmental impacts ... can be sufficiently mitigated, provided the conditions contained in this record of decision are implemented and adhered to."


Mobile power systems

Pebble-bed reactors can theoretically power vehicles. There is no need for a heavy pressure vessel. The pebble bed produces gas hot enough that it could directly drive a lightweight gas turbine.


Romawa

Romawa B.V., the Netherlands, promotes a design called Nereus. This is a 24 MWth reactor designed to fit in a container, and provide either a ship's power plant, isolated utilities, backup or peaking power. It is basically a replacement for large diesel generators and gas turbines, but without fuel transportation expenses or air pollution. Because it requires external air, Romawa's design limits itself only to environments in which diesel engines can already be used. MWe and MWt are units for measuring the output of a power plant. ... A small transportable diesel-generator A diesel generator is the combination of a diesel engine with an electrical generator to generate electric energy. ... This machine has a single-stage centrifugal compressor and turbine, a recuperator, and foil bearings. ... Before flue gas desulfurization was installed, the emissions from this power plant in New Mexico contained excessive amounts of sulfur dioxide. ...


Romawa's reactor heats helium, which in turn heats air that drives a conventional gas turbine. The Romawa design cleverly reduces the size and expense of heat exchangers. The main heat exchangers, the reactor and air-heater, operate at very high temperatures, and should therefore be small, inexpensive and efficient. The design exhausts the air from the turbine, cleverly avoiding the large, inefficient, expensive low-temperature heat exchanger that would otherwise be necessary to cool the turbine's exhaust. On a conventional light water reactor the analogous item is the steam condenser, the largest part of a light water reactor—the big cooling tower. The exhausted air is not radioactive because it never passed through the reactor's core. A heat exchanger is a device built for efficient heat transfer from one fluid to another, whether the fluids are separated by a solid wall so that they never mix, or the fluids are directly contacted. ... Condenser refers here to the shell and tube heat exchanger installed at the outlet of every steam turbine in Thermal power stations of utility companies generally. ... Image 1: Natural draft wet cooling towers at Didcot Power Station, UK Cooling towers are evaporative coolers used for cooling water or other working medium to near the ambient wet-bulb air temperature. ...


Additionally, gas turbines designed for air are well-developed for the aircraft and stationary power industries.


Romawa proposes two types of throttling. For vehicular power, they advocate a reliable, quick-acting, inexpensive valve between the turbine and reactor. For efficient utility-style throttling, they advocate a system that reduces the pressure of helium in the coolant loop that connects the reactor to the turbine.


The basic design is at least as safe as a light water reactor, because only the helium passes through the reactor. The design attempts to reproduce the very safe operational experience of the AVR by using helium as the primary coolant. A light water reactor or LWR is a thermal nuclear reactor that uses ordinary water (as opposed to heavy water) as its neutron moderator. ...


The air passing through the turbine never passes through the reactor, and is therefore never exposed to neutron flux, and therefore particles and gasses cannot become radioactive. The turbine is likewise not part of the primary loop, and uses air as its working fluid. The technology is therefore very standard. Most moving parts do not touch the primary loop, and therefore service should be relatively easy and safe. neutron flux n : the rate of flow of neutrons; the number of neutrons passing through a unit area in unit time via dictionary. ...


Romawa also proposes a clever refueling and maintenance plan, based on "pool service." Users of large gas turbines customarily pool their repair resources to minimize expensive equipment, spares and training. By shipping entire reactors, Romawa plans to eliminate on-site service, and provide all service in one or a few centralized, specialized workshops.


Romawa has neither produced nor is licensed to produce a nuclear reactor at this time.


Romawa has a business agreement with Adams Atomic Engines in the U.S., which promotes a similar reactor system.


Adams atomic engines

AAE's engine is completely self-contained, and therefore adapts to dusty, space, polar and underwater environments. The primary coolant loop uses nitrogen, and passes it directly though a conventional low-pressure gas turbine. Nitrogen and air are almost identical, so a turbine designed for air should work well almost without changes. Though AAE's design seems to require a larger secondary heat exchanger to cool the turbine's output gas, a sea-water-cooled heat exchanger might be small enough to be inexpensive, or a stationary installation might afford a small cooling tower. General Name, Symbol, Number nitrogen, N, 7 Chemical series nonmetals Group, Period, Block 15, 2, p Appearance colorless gas Atomic mass 14. ... Image 1: Natural draft wet cooling towers at Didcot Power Station, UK Cooling towers are evaporative coolers used for cooling water or other working medium to near the ambient wet-bulb air temperature. ...


AAE holds the U.S. patent on direct throttling of a turbine heated by a pebble-bed reactor. Adams Atomic Engines has neither produced nor is licensed to produce a nuclear reactor at this time.


Other issues

Both Romawa and AAE plan to use neutron reflectors (graphite) and radiation shields (heavy metals) that are bins of balls. This means that the shielding need not have complex ducting to cool it. Nuclear weapon designs are often divided into two classes, based on the dominant source of the nuclear weapons energy. ... Radiation protection, sometimes known as radiological protection, is the science of protecting people and the environment from the harmful effects of radiation. ... A heavy metal is any of a number of higher atomic weight elements, which has the properties of a metallic substance at room temperature. ...


One proposed design of nuclear thermal rocket uses pebble-like fuel containers in a fluidized-bed to achieve extremely high temperatures. In a nuclear thermal rocket a working fluid, usually hydrogen, is heated in a high temperature nuclear reactor, and then expands through a rocket nozzle to create thrust. ...


Safety features

When a pebble-bed reactor gets hotter, the more rapid motion of the atoms in the fuel decreases the probability of neutron-induced fissions by 235U atoms due to an effect known as Doppler Broadening. When the uranium is heated, its nuclei move more rapidly in random directions, and therefore see a wider range of relative neutron speeds. 238U, which forms the bulk of the uranium in the reactor, is much more likely to absorb fast or epithermal neutrons.[2] This reduces the number of thermalized neutrons available to cause 235U fission, reducing the power output by the reactor. Doppler broadening is a broadening of spectral lines due to thermal agitation. ...


When the fuel heats, the 238U reacts with a broader spectrum of neutron speeds, thereby lowering the number of available neutrons for fission with 235U. A slower fission rate generally lowers the temperature of the fuel. 238U tends to absorb instead of fission, thus contributing a negligible amount of energy. This places a natural limit on the power produced by the reactor. The reactor vessel is designed so that without mechanical aids it loses more heat than the reactor can generate in this idle state. The design adapts well to safety features (see below). In particular, most of the fuel containment resides in the pebbles, and the pebbles are designed so that a containment failure releases at most a 0.5 mm sphere of radioactive material. In a nuclear power plant, the reactor vessel is a pressure vessel containing the coolant and reactor core. ...


The reactor is cooled by an inert, fireproof gas, so it cannot have a steam explosion as a light-water reactor can.


The coolant has no phase transitions—it starts as a gas and remains a gas.


The moderator is solid carbon. It does not act as a coolant, move, or have phase transitions (i.e. between liquid and gas) as the light water in conventional reactors does.


A pebble-bed reactor thus can have all of its supporting machinery fail, and the reactor will not crack, melt, explode or spew hazardous wastes. It simply goes up to a designed "idle" temperature, and stays there. In that state, the reactor vessel radiates heat, but the vessel and fuel spheres remain intact and undamaged. The machinery can be repaired or the fuel can be removed.


These safety features were tested (and filmed) with the German AVR reactor.[9]. All the control rods were removed, and the coolant flow was halted. Afterward, the fuel balls were sampled and examined for damage. There was none. Later problems with the AVR reactor resulted in a small release of radiation to the public.


PBRs are intentionally operated above the 250°C annealing temperature of graphite, so that Wigner energy is not accumulated. This solves a problem discovered in a famous accident, the Windscale fire. One of the reactors at the Windscale site in England (not a PBR) caught fire because of the release of energy stored as crystalline dislocations (Wigner energy) in the graphite. The dislocations are caused by neutron passage through the graphite. At Windscale, a program of regular annealing was put in place to release accumulated Wigner energy, but since the effect was not anticipated during the construction of the reactor, the process could not be reliably controlled and led to a fire. Annealing, in metallurgy and materials science, is a heat treatment wherein the microstructure of a material is altered, causing changes in its properties such as strength and hardness. ... Wigner energy is created inside nuclear reactors that use graphite, a form of carbon, as neutron moderator. ... On October 10, 1957, the graphite core of a British nuclear reactor at Windscale, Cumbria, caught fire releasing substantial amounts of radioactive contamination into the surrounding area. ... The Sellafield facility on the Cumbrian coast, United Kingdom Sellafield is the name of a nuclear site, close to the village and railway station of Seascale, operated by the British Nuclear Group, but owned since 1 April 2005 by the Nuclear Decommissioning Authority. ...


The continuous refueling means that there is no excess reactivity in the core. Continuous refueling also permits continuous inspection of the fuel elements.


Containment

Most pebble-bed reactors contain many reinforcing levels of containment to prevent contact between the radioactive materials and the biosphere.

  1. Most reactor systems are enclosed in a containment building designed to resist aircraft crashes and earthquakes.
  2. The reactor itself is usually in a two-meter-thick-walled room with doors that can be closed, and cooling plenums that can be filled from any water source.
  3. The reactor vessel is usually sealed, as well.
  4. Each pebble, within the vessel, is a 60 mm (2.6") hollow sphere of pyrolytic graphite. The sphere is one containment layer. The design of the pebbles (called "TRISO" fuel) is crucial to the reactor's simplicity and safety, because they include no less than four of the seven containments. The pebbles are the size of tennis balls. Each weighs 210 g, and has 9 g of uranium. It takes 380,000 to fuel a reactor of 120 MWe. The pebbles are constructed of ceramics that are known not to melt at the maximum equilibrium temperature of the reactor. The ceramics also act as a renewable moderator for the reactor, and are strong containment vessels. In fact, most waste disposal plans for pebble-bed reactors plan to store the waste within the spent pebbles.

The hollow contains fifteen thousand small "seeds" with further containment layers. Each seed surrounds a sand-grain-sized (0.5 mm) kernel of fissionables. Breaking the fissionables into pebbles, and pebbles into seeds assures that the maximum release by a cascade of containment failures will be small—at most the fissionables in one seed. A containment building, in its most common usage, is a steel or concrete structure enclosing a nuclear reactor. ... Pyrolytic carbon is a material similar to graphite, but with some covalent bonding between its graphene sheets. ... A Wilson tennis ball. ...


Each seed, from the inside out, consists of:

  • the fission fuel in the form of metal oxides or carbides (a containment),
  • low density porous pyrolytic carbon, high density nonporous pyrolytic carbon (another containment),
  • a wrapping of silicon carbide (another, fireproof containment),
  • and another wrapping of pyrolytic carbon (another containment).

Pyrolytic graphite is the main structural material in these pebbles. It melts at 3000 °C, more than twice the design temperature of most reactors. It slows neutrons very effectively, is strong, inexpensive, and has a long history of use in reactors. Its strength and hardness come from anisotropic crystals of carbon. Pyrolytic graphite is also used, unreinforced, to construct missile reentry nose-cones and large solid rocket nozzles. It is nothing like the powdered mixture of flakes and waxes in pencil leads or lubricants. Pyrolytic carbon is a material similar to graphite, but with some covalent bonding between its graphene sheets. ... General Name, Symbol, Number carbon, C, 6 Chemical series nonmetals Group, Period, Block 14, 2, p Appearance black (graphite) colorless (diamond) Atomic mass 12. ...


Some authorities say that pyrolytic graphite can burn in air, and cite the famous accidents at Windscale and Chernobyl—both graphite-moderated reactors. Others insist that it cannot, and cite engineering studies of high-density pyrolytic carbon. Of course, all pebble-bed reactors are cooled by inert gases that prevent fire. However, all pebble designs also have at least one layer of silicon carbide that serves as a fire break, as well as a seal. Pathways from airborne radioactive contamination to man This article covers notable accidents involving nuclear material. ... Silicon carbide (SiC) is a ceramic compound of silicon and carbon and occurs in nature as the extremely rare mineral moissanite. ...


The fissionables are also stable oxides or carbides of uranium, plutonium or thorium which have higher melting points than the metals. The oxides cannot burn in oxygen, but have some potential to react via diffusion with graphite at sufficiently high temperatures; the carbides might burn in oxygen but cannot react with graphite. The fission materials are about the size of a sand grain, so they are too heavy to be dispersed in the smoke of a fire. General Name, Symbol, Number uranium, U, 92 Chemical series actinides Group, Period, Block n/a, 7, f Appearance silvery gray metallic; corrodes to a spalling black oxide coat in air Atomic mass 238. ... General Name, Symbol, Number plutonium, Pu, 94 Chemical series actinides Group, Period, Block n/a, 7, f Appearance silvery white Atomic mass (244) g·mol−1 Electron configuration [Rn] 5f6 7s2 Electrons per shell 2, 8, 18, 32, 24, 8, 2 Physical properties Phase solid Density (near r. ... General Name, Symbol, Number thorium, Th, 90 Chemical series Actinides Group, Period, Block n/a, 7, f Appearance silvery white Atomic mass 232. ...


The layer of porous pyrolytic graphite right next to the fissionable ceramic absorbs the radioactive gases (mostly xenon) emitted when the heavy elements split. Most reaction products remain metals, and reoxidize. A secondary benefit is that the gaseous fission products remain in the reactor to contribute their energy. The low density layer of graphite is surrounded by a higher-density nonporous layer of pyrolytic graphite. This is another mechanical containment. The outer layer of each seed is surrounded by silicon carbide. The silicon carbide is nonporous, mechanically strong, very hard, and also cannot burn. General Name, Symbol, Number xenon, Xe, 54 Chemical series noble gases Group, Period, Block 18, 5, p Appearance colorless Atomic mass 131. ...


Many authorities consider that pebbled radioactive waste is stable enough that it can be safely disposed of in geological storage. Thus used fuel pebbles could just be transported to disposal.


Production of fuel

Most authorities agree (2002) that German fuel-pebbles release about 3 orders of magnitude (1000 times) less radioactive gas than the U.S. equivalents, which is not surprising in view of the Germans' longer operational experience. [10]


All kernels are precipitated from a sol-gel, then washed, dried and calcined. U.S. kernels use uranium carbide, while German (AVR) kernels use uranium dioxide. Sol gel is a colloidal suspension of silicon dioxide that is gelled to form a solid. ...


The precipitation of the pyrolytic graphite is by a mixture of argon, propylene and acetylene in a fluidized-bed coater at about 1275 °C. The fluidized bed moves gas up through the bed of particles, "floating" them against gravity. The high-density pyrolytic carbon uses less propylene than the porous gas-absorbing carbon. German particles are produced in a continuous process, from ultra-pure ingredients at higher temperatures and concentrations. U.S. coatings are produced in a batch process. Although the German carbon coatings are more porous, they are also more isotropic (same properties in all directions), and resist cracking better than the denser U.S. coatings. General Name, Symbol, Number argon, Ar, 18 Chemical series noble gases Group, Period, Block 18, 3, p Appearance colorless Atomic mass 39. ... Propylene, also known by its IUPAC name propene, is an organic compound having the chemical formula C3H6. ... Acetylene (systematic name: ethyne) is the simplest alkyne hydrocarbon, consisting of two hydrogen atoms and two carbon atoms connected by a triple bond. ...


The silicon carbide coating is precipitated from a mixture of hydrogen and methyltrichlorosilane. Again, the German process is continuous, while the U.S. process is batch-oriented. The more porous German pyrolytic carbon actually causes stronger bonding with the silicon carbide coat. The faster German coating process causes smaller, equiaxial grains in the silicon carbide. Therefore, it may be both less porous and less brittle. General Name, Symbol, Number hydrogen, H, 1 Chemical series nonmetals Group, Period, Block 1, 1, s Appearance colorless Atomic mass 1. ...


Some experimental fuels plan to replace the silicon carbide with zirconium carbide to run at higher temperatures.


Criticisms of the reactor design

The most common criticism of pebble bed reactors is that encasing the fuel in potentially combustible graphite poses a hazard. Were the graphite to burn, fuel material could potentially be carried away in smoke from the fire. Since burning graphite requires oxygen, the fuel pebbles are coated with an impermeable layer of silicon carbide, and the reaction vessel is purged of oxygen. While silicon carbide is strong in abrasion and compression applications, it does not have the same strength against expansion and shear forces. Some fission products such as xenon-133 have a limited absorbance in carbon, and some fuel pebbles could accumulate enough gas to rupture the silicon carbide layer. Even a cracked pebble will not burn without oxygen, but the fuel pebble may not be rotated out and inspected for months, leaving a window of vulnerability. Graphite (named by Abraham Gottlob Werner in 1789, from the Greek γραφειν: to draw/write, for its use in pencils) is one of the allotropes of carbon. ... Smoke from a wildfire Smoke is a suspension in air (aerosol) of small particles resulting from incomplete combustion of a fuel. ... General Name, Symbol, Number oxygen, O, 8 Chemical series nonmetals, chalcogens Group, Period, Block 16, 2, p Appearance colorless (gas) very pale blue (liquid) Atomic mass 15. ... Silicon carbide (SiC) is a ceramic compound of silicon and carbon and occurs in nature as the extremely rare mineral moissanite. ... General Name, Symbol, Number oxygen, O, 8 Chemical series nonmetals, chalcogens Group, Period, Block 16, 2, p Appearance colorless (gas) very pale blue (liquid) Atomic mass 15. ... Physical compression is the result of the subjection of a material to compressive stress, resulting in reduction of volume. ... For the generation of electrical power by fission, see Nuclear power plant An induced nuclear fission event. ... General Name, Symbol, Number carbon, C, 6 Chemical series nonmetals Group, Period, Block 14, 2, p Appearance black (graphite) colorless (diamond) Atomic mass 12. ...


Some designs for pebble bed reactors lack a containment building, potentially making such reactors more vulnerable to outside attack and allowing radioactive material to spread in the case of an explosion. However, the current emphasis on reactor safety means that any new design will likely have strong reinforced concrete containment structure [11]. Also, any explosion would most likely be caused by an external factor, as the design does not suffer from the steam-explosion vulnerability of water-cooled reactors. It has been suggested that this article be split into articles entitled steam and water vapor, accessible from a disambiguation page. ...


There is also significantly less experience with production scale Pebble Bed Reactors than Light Water Reactors. As such, claims made by proponents are more theory-based than based on practical experience.


Since the fuel is contained in graphite pebbles, the volume of radioactive waste is much greater, but contains about the same radioactivity when measured in becquerels per kilowatt-hour. The waste tends to be less hazardous and simpler to handle. Current US legislation requires all waste to be safely contained, therefore pebble bed reactors would increase existing storage problems. Defects in the production of pebbles may also cause problems. The radioactive waste must either be safely stored for many human generations, reprocessed, transmuted in a different type of reactor, or disposed of by a method yet to be devised. The graphite pebbles are more difficult to reprocess due to their construction, which is not true of the fuel from other types of reactors. Proponents point out that this is a plus, as it is difficult to re-use pebble bed reactor waste for nuclear weapons. An illustration showing the various sources of nuclear waste Radioactive waste are waste types containing radioactive chemical elements that do not have a practical purpose. ... Radioactivity may mean: Look up radioactivity in Wiktionary, the free dictionary. ... The becquerel (symbol Bq) is the SI derived unit of radioactivity, defined as the activity of a quantity of radioactive material in which one nucleus decays per second. ... Legislation (or statutory law) is law which has been promulgated (or enacted) by a legislature or other governing body. ... The mushroom cloud of the atomic bombing of Nagasaki, Japan, 1945, rose some 18 km (11 mi) above the epicenter. ...


Critics also often point out an accident in Germany in 1986, which involved a jammed pebble damaged by the reactor operators when they were attempting to dislodge it from a feeder tube. This accident released radiation into the surrounding area, and led to a shutdown of the research program by the West German government. West Germany was the informal but almost universally used name for the Federal Republic of Germany from 1949 until 1990, during which years the Federal Republic did not yet include East Germany. ...


Also, there is no lovely blue Cherenkov radiation to look at. Cherenkov radiation glowing in the core of a TRIGA reactor Cherenkov radiation (also spelled Cerenkov or sometimes ÄŒerenkov) is electromagnetic radiation emitted when a charged particle passes through an insulator at a speed greater than the speed of light in that medium. ...


References

  1. ^ (1990) AVR - Experimental High-Temperature Reactor, 21 Years of Successful Operation for A Future Energy Technology. Association of German Engineers (VDI), The Society for Energy Technologies, pp. 9-23. ISBN 3-18-401015-5. 
  2. ^ [http://www.inl.gov/technicalpublications/Search/Results.asp?ID=INEEL/EXT-03-00870 NGNP Point Design – Results of the Initial Neutronics and Thermal-Hydraulic Assessments During FY-03] pg 20
  3. ^ http://www.chinadaily.com.cn/english/doc/2006-02/22/content_522643.htm
  4. ^ http://www.eia.doe.gov/cabs/safrenv.html
  5. ^ "Earthlife Africa Sues for Public Power Giant's Nuclear Plans", Environment News Service, 2005-07-04. Retrieved on 2006-10-18.
  6. ^ Pebble Bed Modular Reactor - What is PBMR?
  7. ^ How the PBMR Fueling System Works
  8. ^ "China leading world in next generation of nuclear plants", South China Morning Post, 2004-10-05. Retrieved on 2006-10-18.
  9. ^ http://www.fz-juelich.de/isr/2/tint-a_e.html
  10. ^ D. A. Petti, J. Buongiorno, J. T. Maki, R. R. Hobbins, G. K. Miller (2003). "Key differences in the fabrication, irradiation and high temperature accident testing of US and German TRISO-coated particle fuel, and their implications on fuel performance". Nuclear Engineering and Design 222: 281-297. DOI:10.1016/S0029-5493(03)00033-5. 
  11. ^ http://www.nrc.gov/reading-rm/doc-collections/commission/speeches/2006/s-06-027.html

For the Manfred Mann album, see 2006 (album). ... October 18 is the 291st day of the year (292nd in leap years). ... The South China Morning Post, together with its Sunday edition, the Sunday Morning Post, is the leading English-language newspaper in Hong Kong, published by the SCMP Group. ... For the Manfred Mann album, see 2006 (album). ... October 18 is the 291st day of the year (292nd in leap years). ... A digital object identifier (or DOI) is a standard for persistently identifying a piece of intellectual property on a digital network and associating it with related data, the metadata, in a structured extensible way. ...

External links

General

Spencer Reiss (born New York 1952) is a former Newsweek foreign correspondent, now a contributing editor at Wired magazine. ... Wired is a full-color monthly magazine and on-line periodical published in San Francisco, California since March 1993. ... Peter Schwartz is a writer and journalist who follows the Objectivist philosophy of Ayn Rand. ... Spencer Reiss (born New York 1952) is a former Newsweek foreign correspondent, now a contributing editor at Wired magazine. ... Wired is a full-color monthly magazine and on-line periodical published in San Francisco, California since March 1993. ... NPR logo For other meanings of NPR see NPR (disambiguation) National Public Radio (NPR) is a private, not-for-profit corporation that sells programming to member radio stations; together they are a loosely organized public radio network in the United States. ... Living on Earth is National Public Radios weekly, hour-long environmental news program. ...

Idaho National Laboratory

  • Modular Pebble Bed Reactor Project, University Research Consortium Annual Report 2000
  • A Preliminary Study of the Effect of Shifts in Packing Fraction on k-effective in Pebble-Bed Reactors 2001
  • Modular Pebble-Bed Reactor Project: Laboratory-Directed Research and Development Program FY 2002 Annual Report
  • Matrix Formulation of Pebble Circulation in the PEBBED Code 2002
  • Conceptual Design of a Very High Temperature Pebble-Bed Reactor 2003
  • NGNP Point Design - Results of the Initial Neutronics and Thermal-Hydraulic Assessments During FY-03, Rev. 1
  • New Generation Nuclear Plant (NGNP) Project, Preliminary Point Design 2003
  • The Next Generation Nuclear Plant - Insights Gained from the INEEL Point Design Studies 2004
  • Computation of Dancoff Factors for Fuel Elements Incorporating Randomly Packed TRISO Particles 2005

Companies/reactors

  • MIT page on Modular Pebble Bed Reactor
  • Criticality testing of the AVR
  • General Atomics' Gas Turbine Modular Helium Reactor
  • Romawa — Diesel replacement
  • Adam's Atomic Engines — Diesel replacement, non-airbreathing engines
  • Differences in American and German TRISO-coated fuels

South Africa

  • Eskom
  • PBMR (Pty.) Ltd.
  • Pebble Bed Modular Recator - PBMR - Home
  • Atomic Energy in South Africa
  • Earthlife Africa: Nuclear Energy Costs the Earth campaign
  • Science in South Africa, June 2003, "South Africa's nuclear programme"
  • EIA, December 2003, Nuclear Power in South Africa
  • Christian Science Monitor, 23 September 2003, "South Africa Looks to Next-Generation Nuclear Power: But last week, opponents filed papers against a new pebble-bed reactor near Cape Town"
  • Steve Thomas (2005), "The Economic Impact of the Proposed Demonstration Plant for the Pebble Bed Modular Reactor Design", PSIRU, University of Greenwich, UK
  • NPR (April 17, 2006) NPR: South Africa Invests in Nuclear Power

  Results from FactBites:
 
Pebble bed reactor - Wikipedia, the free encyclopedia (4879 words)
In contrast, a pebble bed reactor is gas cooled, sometimes at low pressures.
Each pebble, within the vessel, is a 60 mm hollow sphere of pyrolytic graphite.
The pebbles are constructed of ceramics that are known not to melt at the maximum equilibrium temperature of the reactor.
  More results at FactBites »

 
 

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