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59-520: The Pebble Bed Modular Reactor ( PBMR ) is a particular design of pebble bed reactor developed by South African company PBMR (Pty) Ltd from 1994 until 2009. PBMR facilities include gas turbine and heat transfer labs at the Potchefstroom Campus of North-West University , and at Pelindaba , a high pressure and temperature helium test rig, as well as a prototype fuel fabrication plant. A planned test reactor at Koeberg Nuclear Power Station

118-545: A 211 MW e gross unit HTR-PM , which incorporates two 250 MW t reactors. As of 2021 , four sites were being considered for a 6-reactor successor, the HTR-PM600. The reactor entered service in December 2023. In June 2004, it was announced that a new PBMR would be built at Koeberg , South Africa by Eskom , the government-owned electrical utility to operate at 940 °C (1,720 °F). The PBMR project

177-436: A design by Framatome of France. The station is located 30 km north of Cape Town. The plant is owned and operated by the country's national electricity supplier, Eskom . The Pebble bed modular reactor (PBMR) was a particular design of pebble-bed reactor under development by South African company PBMR (Pty) Ltd since 1994. The project entailed the construction of a demonstration power plant at Koeberg near Cape Town and

236-707: A dozen employees at PBMR later joined X-energy, including: Other employees joined the Ultra Safe Nuclear Corporation . A Pretoria-based South African company created a variant of the PBMR reactor. The differences in the two reactors are the Stratek HTMR-100 reactor functions at a lower temperature (from 940°C to 750°C), the HTMR-100 reactor directs the heat into water to create steam in addition to being helium-cooled. The HTMR-100 reactor

295-447: A fissile material (such as U ) surrounded by a ceramic coating of silicon carbide for structural integrity and fission product containment. Thousands of pebbles are amassed to create a reactor core . The core is cooled by a gas that does not react chemically with the fuel elements, such as helium , nitrogen or carbon dioxide . Other coolants such as FLiBe (molten Li(BeF 4 ) ) have been suggested. The pebble bed design

354-573: A fuel plant at Pelindaba near Pretoria. Government financing was withdrawn in 2010 because of missed deadlines and lack of customers. The South African Nuclear Energy Corporation (NECSA) was established as a public company by the Republic of South Africa Nuclear Energy Act in 1999 and is wholly owned by the State . NECSA replaced the country's Atomic Energy Corporation. The main functions of NECSA are to undertake and promote research and development in

413-402: A gas-cooled core and a novel fuel packaging. The uranium , thorium or plutonium nuclear fuels are in the form of a ceramic (usually oxides or carbides ) contained within spherical pebbles a little smaller than the size of a tennis ball and made of pyrolytic graphite, which acts as the primary neutron moderator . The pebble design is relatively simple, with each sphere consisting of

472-475: A human error during a blockage of pebbles in a pipe. Trying to restart the pebbles' movement by increasing gas flow stirred up dust, always present in PBRs, which was then released, unfiltered, into the environment due to an erroneously open valve. In spite of the limited amount of radioactivity released (0.1 GBq Co , Cs , Pa ), a commission of inquiry was appointed. The radioactivity in

531-484: A legal entity, preserve and optimise IP, preserve HTR license, preserve assets and solicit new investors. The strategy assumes that keeping on 9 employees in the medium term will leave sufficient funding to take PBMR to March 2013. The remaining employees will serve to end of October 2010. Some funding is foreseen for dismantling of the PBMR fuel fabrication laboratories in 2011. In Sept 2010 the SA govt announced that in future,

590-511: A long shut-down for inspections. In August, 1989, the THTR company almost went bankrupt, but was rescued by the government. The unexpected high costs of THTR operation and the accident ended interest in THTR reactors. The government decided to terminate the THTR operation at the end of September, 1989. This particular reactor was built despite criticism at the design phase. Most of those design critiques by German physicists, and by American physicists at

649-471: A loss of coolant flow. The company went out of business in December 2010. South African nuclear program As a member of the nuclear non-proliferation treaty , South Africa uses nuclear science for peaceful means. South Africa's nuclear programme includes both nuclear energy and nuclear medicine . In the past there was also a military component , and South Africa previously possessed nuclear weapons , which were subsequently dismantled. In

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708-494: A problem discovered in the Windscale fire . One reactor (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. Windscale regularly annealed the graphite to release accumulated Wigner energy. However, the effect was not anticipated, and since the reactor was cooled by ambient air in an open cycle,

767-456: A reinforced concrete containment structure. PBR waste volumes are much greater, but have similar radioactivity 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, requiring waste storage facilities. Pebble defects may complicate storage. Graphite pebbles are more difficult to reprocess due to their construction. In 2008,

826-403: A report about safety aspects of Germany's AVR reactor and general PBR features drew attention. The claims are contested. The report cited: Report author Rainer Moormann , recommended that average hot helium temperatures be limited to 800 °C (1,470 °F) minus the uncertainty of the core temperatures (about 200 °C or 360 °F). Farrington Daniels originated the concept and

885-543: A water/steam ingress accident of 30 metric tons (30 long tons; 33 short tons), which led to contamination of soil and groundwater by strontium-90 and by tritium. The leak in the steam generator leading to this accident was probably caused by high core temperatures (see criticism section). A re-examination of this accident was announced by the local government in July 2010. The AVR was originally designed to breed uranium-233 from thorium-232 . A practical thorium breeder reactor

944-435: Is passively safe . Because the reactor is designed to handle high temperatures, it can cool by natural circulation and survive accident scenarios, which may raise the temperature of the reactor to 1,600 °C (2,910 °F). Such high temperatures allow higher thermal efficiencies than possible in traditional nuclear power plants (up to 50%) while the gases do not dissolve contaminants or absorb neutrons as water does, so

1003-412: Is also smaller, with an output of 35 MWe. Pebble bed reactor The basic design features spherical fuel elements called pebbles. These tennis ball -sized elements (approx. 6.7 cm or 2.6 in in diameter) are made of pyrolytic graphite (which acts as the moderator), and contain thousands of fuel particles called tristructural-isotropic (TRISO) particles. These TRISO particles consist of

1062-691: Is based on the AVR reactor and THTR in Germany, but modified to drive a Brayton closed-cycle gas turbine . The core design is annular with a centre column as a neutron reflector . Since its establishment in 1994, Pebble Bed Modular Reactor (Pty) Ltd grew into one of the largest nuclear reactor design teams in the world. In addition to the core team of some 700 people at the PBMR head-office in Centurion near Pretoria, more than 600 people at universities, private companies and research institutes were involved with

1121-483: Is both more efficient and less likely to become radioactive. Much of the cost of a conventional, water-cooled nuclear power plant is due to cooling system complexity, which is not a factor in PBRs. Conventional plants require extensive safety systems and redundant backups. Their reactor cores are dwarfed by cooling systems. Further, the core irradiates the water with neutrons causing the water and impurities dissolved in it to become radioactive. The high-pressure piping in

1180-444: Is continuous. Pebbles are placed in a bin-shaped reactor. Pebbles travel from the bottom to the top about ten times over a period of years, and are tested after each pass. Expended pebbles are removed to the nuclear-waste area, replaced by a new pebble. When the reactor temperature rises, the atoms in the fuel move rapidly, causing Doppler broadening . The fuel then experiences a wider range of neutron speeds. Uranium-238 , which forms

1239-440: Is fuelled and moderated by graphite fuel spheres each containing TRISO coated low enriched uranium oxide fuel particles. There are 15000 fuel particles per fuel sphere the size of a billiard ball . "Each fuel pebble contains 9 g of uranium, and this holds enough generation capacity to sustain a family of four, for a year. Five tons of coal and up to 23 000 m of water will be required to generate one pebble's energy". The concept

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1298-418: Is relatively strong, inherent to the design, and does not depend on moving parts. This negative feedback creates passive control of the reaction process. Thus PBRs passively reduce to a safe power-level in an accident scenario. This is the design's main passive safety feature. The reactor is cooled by an inert, fireproof gas, which has no phase transitions—it is always in the gaseous phase. The moderator

1357-412: Is solid carbon; it does not act as a coolant, or move, or change phase. Convection of the gas, driven by the heat of the pebbles, ensures that the pebbles are passively cooled. Even in the event that all supporting machinery fails, the reactor will not crack, melt, explode or spew hazardous wastes. It heats to a designed "idle" temperature, and stays there. At idle, the reactor vessel radiates heat, but

1416-438: Is warm and may be used to heat buildings or in other applications. Pebble-bed reactors are gas-cooled, sometimes at low pressures. The spaces between the pebbles replace the piping in conventional reactors. Since there is no actual piping in the core and the coolant contains no hydrogen, embrittlement is not a failure concern. The preferred gas, helium, does not easily absorb neutrons or impurities. Therefore, compared to water, it

1475-669: The South African nuclear program will concentrate on conventional light water reactors . The NGNP project will continue on HTGRs with prismatic fuel elements, not with pebbles as in PBMR, as was announced in February 2012. R 9.244 billion (US$ 1.3 billion) had been invested in the PBMR project. Over 80% came from the South African government, with smaller amounts from Eskom (8.8%), Westinghouse (4.9%), Industrial Development Corporation (4.9%) and Exelon (1.1%). About

1534-514: The NGNP project will soon be issued, to which the PBMR consortium will be responding within the next few months of 2009. In 2009 PBMR (Pty) announced that it was looking at employing the technology for process heat applications, and some pebble bed reactor contracts had been put on hold to prevent unnecessary spending In February 2010 the South Africa government announced it had stopped funding

1593-646: The National Laboratory level, went ignored until shutdown. Nearly every problem encountered by the THTR 300 reactor was predicted by the physicists who criticized it as "overly complex". In 2004 China licensed the AVR technology and developed a reactor for power generation. The 10 megawatt prototype is called the HTR-10 . It is a conventional helium-cooled, helium-turbine design. In 2021 the Chinese then built

1652-410: The PBMR project by loans. PBMR's CEO resigned on March, 8th 2010. In May 2010 Westinghouse withdrew from the PBMR consortium, which led to an end of the South African engagement in NGNP. On 25 May 2010 the company announced to staff that it intends to implement a "Care and Maintenance" Strategy. This involves the reduction of staff to 9. The stated purpose of the proposed structure is; preserve PBMR as

1711-403: The U.S. equivalents, due to that construction method. The primary criticism of pebble-bed reactors is that encasing the fuel in graphite poses a hazard. Graphite can burn in the presence of air, which could happen if the reactor vessel is compromised. Fire could vaporize the fuel, which could then be released to the surroundings. Fuel kernels are coated with a layer of silicon carbide to isolate

1770-410: The bulk of the uranium, is much more likely to absorb fast or epithermal neutrons at higher temperatures. This reduces the number of neutrons available to cause fission, and reduces power. Doppler broadening therefore creates a negative feedback: as fuel temperature increases, reactor power decreases. All reactors have reactivity feedback mechanisms. The pebble-bed reactor is designed so that this effect

1829-585: The core has less in the way of radioactive fluids . The concept was first suggested by Farrington Daniels in the 1940s, inspired by the innovative design of the Benghazi burner by British desert troops in WWII. Commercial development came in the 1960s via the West German AVR reactor designed by Rudolf Schulten . This system was plagued with problems and the technology was abandoned. The AVR design

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1888-421: The crack. During this examination it was revealed that the AVR was the world's most heavily beta-contaminated ( strontium-90 ) nuclear installation and that this contamination was present as dust (the worst form). Localized fuel temperature instabilities resulted in heavy vessel contamination by Cs-137 and Sr-90 . The reactor vessel was filled with light concrete in order to fix the radioactive dust and in 2012

1947-413: The design temperature of most reactors. It slows neutrons effectively, is strong, inexpensive, and has a long history of use in reactors and other high temperature applications. For example, pyrolytic graphite is also used, unreinforced, to construct missile reentry nose-cones and large solid rocket nozzles. Its strength and hardness come from its anisotropic crystals. Pyrolytic carbon can burn in air when

2006-496: The development of the pebble bed modular reactor, and PBMR (Pty) stated it was considering 75% cuts in staff. The decision was taken because no customer or investor for PBMR was found. Unresolved technical items, a substantial increase of costs and a 2008 report from Forschungszentrum Jülich about major problems in operation of the German pebble bed reactor AVR had discouraged potential investors. International banks refused to support

2065-472: The field of nuclear energy and related technologies; to process and store nuclear material and other restricted material; and to co-ordinate with other organisations in matters falling within these spheres. The project is currently being dismantled. The following South African universities offer courses in nuclear engineering: South Africa built six nuclear bombs in the 1980s, which were subsequently dismantled. This South African military article

2124-456: The fuel. THTR-300 suffered technical difficulties, and owing to these and political events in Germany, was closed after four years of operation. An incident on 4 May 1986, only a few days after the Chernobyl disaster, allowed a release of part of the radioactive inventory into the environment. Although the radiological impact was small, it had a disproportionate impact. The release was caused by

2183-434: The graphite. While silicon carbide is strong in abrasion and compression applications, it has less resistance to expansion and shear forces. Some fission products such as Xe have limited absorbance in carbon, so some fuel kernels could accumulate enough gas to rupture the silicon carbide. Some designs do not include a containment building, leaving reactors more vulnerable to attack. However, most are surrounded by

2242-474: The heat into water to create steam and is helium-cooled. The HTMR-100 reactor produces output of 35 MWe. Adams Atomic Engines (AAE) design was self-contained so it could be adapted to extreme environments such as space, polar and underwater environments. Their design was for a nitrogen coolant passing directly though a conventional low-pressure gas turbine, and due to the rapid ability of the turbine to change speeds, it can be used in applications where instead of

2301-427: The name in 1947 at Oak Ridge. Rudolf Schulten advanced the idea in the 1950s. The crucial insight was to combine fuel, structure, containment, and neutron moderator in a small, strong sphere. The concept depended on the availability of engineered forms of silicon carbide and pyrolytic carbon that were strong. A 15 MW e demonstration reactor, Arbeitsgemeinschaft Versuchsreaktor ( experimental reactor consortium ),

2360-422: The nuclear fuel, fission product barrier, and moderator (which in a traditional water reactor would all be different parts). Grouping sufficient pebbles in the correct geometry creates criticality . The pebbles are held in a vessel, and an inert gas (such as helium, nitrogen or carbon dioxide) circulates through the spaces between the fuel pebbles to carry heat away from the reactor. Pebble-bed reactors must keep

2419-478: The pebbles' graphite from burning in the presence of air if the reactor wall is breached (the flammability of the pebbles is disputed ). 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, or a fuel defect could contaminate the power production equipment, it may be brought instead to a heat exchanger where it heats another gas or produces steam. The turbine exhaust

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2478-460: The post-apartheid period, South Africa agreed to cooperate closely with the Russian state nuclear power company Rosatom on the development of new nuclear power plants in South Africa. One project was to cost US$ 76 billion, but has so far not been realized. The Koeberg nuclear power station is the only nuclear power station in South Africa and contains two uranium pressurized water reactors based on

2537-513: The power generation used primary coolant, it was reported that the AVR exposed its personnel to less than 1/5 as much radiation as a typical light water reactor. It was decommissioned on December 1, 1988, in the wake of the Chernobyl disaster and operational problems. During removal of the fuel elements it became apparent that the neutron reflector under the pebble-bed core had cracked during operation. Some hundred fuel elements remained stuck in

2596-568: The primary side eventually becomes embrittled and requires inspection and replacement. Some designs are throttled by temperature rather than control rods . Such reactors do not need to operate well at the varying neutron profiles caused by partially withdrawn control rods. PBRs can use fuel pebbles made from various fuels in the same design (though perhaps not simultaneously). Proponents claim that pebble-bed reactors can use thorium, plutonium and natural unenriched uranium, as well as enriched uranium . In most stationary designs, fuel replacement

2655-456: The process could not be reliably controlled, and led to a fire. Berkeley professor Richard A. Muller described PBRs as "in every way ... safer than the present nuclear reactors". Most PBR designs include multiple reinforcing levels of containment to prevent contact between the radioactive materials and the biosphere: Pyrolytic graphite is the main structural material in pebbles. It sublimates at 4,000 °C (7,230 °F), more than double

2714-481: The project. In 2006, the US Department of Energy awarded the PBMR consortium the primary contract for the first phase of its New Generation Nuclear Plant (NGNP) project. The scope for the first phase of this contract, which has now been completed, was for the pre-conceptual engineering of a nuclear co-generation plant for the production of electricity and hydrogen. Requests for proposals for the second phase of

2773-575: The reaction is catalyzed by a hydroxyl radical (e.g., from water). Infamous examples include the accidents at Windscale and Chernobyl—both graphite-moderated reactors. However, PBRs are cooled by inert gases to prevent fire. All designs have at least one layer of silicon carbide that serves as a fire break and seal. 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 . German-produced fuel-pebbles release about 1000 times less radioactive gas than

2832-465: The reactor vessel of 2,100 metric tons (2,100 long tons; 2,300 short tons) was to be moved to intermediate storage until a permanent solution is devised. The reactor buildings were to be dismantled and soil and groundwater decontaminated. AVR dismantling costs were expected to far exceed its construction costs. In August 2010, the German government estimated costs for AVR dismantling without consideration of

2891-427: The syngas can be used as feedstock to produce hydrogen, ammonia and methanol); and to produce hydrogen and oxygen by decomposing water thermochemically. The PBMR is modular in that only small to mid-sized units will be designed. Larger power stations will be built by combining many of these modules. As of 2008, 400MWt was emerging as an optimum module size, considerably larger than the original concept size. The PBMR

2950-578: The test series and the resulting higher contamination of the containment structure. Pebble debris and graphite dust blocked some of the coolant channels in the bottom reflector, as was discovered during fuel removal after final shut-down. A failure of insulation required frequent reactor shut-downs for inspection, because the insulation could not be repaired. Metallic components in the hot gas duct failed in September 1988, probably due to thermal fatigue induced by unexpected hot gas currents. This failure led to

3009-454: The turbine's output being converted to electricity, the turbine itself could directly drive a mechanical device, for instance, a propeller aboard a ship. Like all high temperature designs, the AAE engine would have been inherently safe, as the engine naturally shuts down due to Doppler broadening , stopping heat generation if the fuel in the engine gets too hot in the event of a loss of coolant or

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3068-481: The vessel and fuel spheres remain intact and undamaged. The machinery can be repaired or the fuel can be removed. In a safety test using the German AVR reactor, all the control rods were removed, and coolant flow was halted. The fuel remained undamaged. PBRs are intentionally operated above the 250 °C (482 °F) annealing temperature of graphite, so that Wigner energy does not accumulate. This solves

3127-461: The vessel dismantling at 600 million € ( $ 750 million, which corresponded to 0.4 € ($ 0.55) per kWh of electricity generated by the AVR. A separate containment was erected for dismantling purposes, as seen in the AVR-picture. Following the experience with the AVR, Germany constructed a full scale power station (the thorium high-temperature reactor or THTR-300 rated at 300 MW), using thorium as

3186-506: The vicinity of the THTR-300 was finally found to result 25% from Chernobyl and 75% from THTR-300. The handling of this minor accident severely damaged the credibility of the German pebble-bed community, which lost support in Germany. The overly complex design of the reactor, which is contrary to the general concept of self-moderated thorium reactors designed in the U.S., also suffered from the unplanned high destruction rate of pebbles during

3245-526: 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. Construction costs of AVR were 115 million Deutschmark (1966), corresponding to a 2010 value of 180 million €. The unit's first criticality was on August 26, 1966. The facility ran successfully for 21 years. In 1978, the AVR suffered from

3304-438: Was considered valuable technology. However, the AVR's fuel design contained the fuel so well that the transmuted fuels were uneconomic to extract—it was cheaper to use mined and purified uranium. The AVR used helium coolant , has a low neutron cross-section . Since few neutrons are absorbed, the coolant remains less radioactive. It is practical to route the primary coolant directly to power generation turbines. Even though

3363-571: Was licensed to South Africa as the PBMR and China as the HTR-10 . The HTR-10 prototype was developed into China's HTR-PM demonstration plant, which connects two reactors to a single turbine producing 210 MW e , operating commercially since 2023. Other designs are under development by MIT , University of California at Berkeley , General Atomics (U.S.), Dutch company Romawa B.V., Adams Atomic Engines , Idaho National Laboratory , X-energy and Kairos Power. A pebble-bed power plant combines

3422-490: Was not built. The PBMR is characterised by inherent safety features, which mean that no human error or equipment failure can cause an accident that would harm the public. Heat from the PBMR can be used for a variety of industrial process applications, including process steam 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

3481-471: Was opposed by groups such as Koeberg Alert and Earthlife Africa , the latter of which sued Eskom. The reactor was never completed and the testing facility was decommissioned and placed in a "care and maintenance mode" to protect the IP and the assets. A Pretoria-based company, Stratek Global, created a variant of the PBMR reactor. The Stratek HTMR-100 reactor functions at 750 °C (1,380 °F). It directs

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