Pebble Bed Reactor

Coolant

Gas (e.g., Helium, Nitrogen, Carbon Dioxide)

Fuel Type

Uranium in small, tennis-ball-sized pebbles, each containing TRISO microsphere coated particles embedded in a graphite matrix

Moderator

Graphite

Classification

Generation IV nuclear reactor

Safety Feature

Meltdown-proof, inherent safety due to low power density and large graphite core, self-cooling capability

Core Composition

Graphite and fuel pebbles

Sub-classification

Very-High-Temperature Reactor (VHTR)

Refueling Capability

Online refueling (new fuel inserted, used fuel discharged during operation)

Fuel Content per Pebble

Approximately 9 grams of uranium

Example Power Output (X-energy Xe-100)

76 megawatts electric per unit

Operating Temperature (China's commercial reactor)

Up to 750 °C

2002

2006

2007

2010

2023-12

The pebble-bed reactor (PBR) is a design for a graphite-moderated, gas-coolednuclear reactor. It is a type of very-high-temperature reactor (VHTR), one of the six classes of nuclear reactors in the Generation IV initiative. Image 6 Graphite pebble for reactor [...] 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 is both more efficient and less likely to become radioactive. [...] 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 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

safe, use a demonstrated nuclear technology and can be competitive with fossil fuels. Pebble bed reactors are helium cooled reactors that use small tennis ball size fuel balls consisting of only 9 grams of uranium per pebble to provide a low power density reactor. The low power density and large graphite core provide inherent safety features such that the peak temperature reached even under the complete loss of coolant accident without any active emergency core cooling system is significantly [...] has been upgraded to 400 MWth and 165 MWe electric. It is in the final design stage with construction to begin in 2007 and commercial operation in 2010. A pebble bed reactor is graphically illustrated in Figure 2. The reactor core contains approximately 360,000 uranium fuelled pebbles about the size of tennis balls. Each pebble contains about 9 gm of low enriched uranium in 10,000–15,000 (depending on the design) tiny grains of sand-like microsphere coated particles each with its own a hard [...] silicon carbide shell. These microspheres are embedded in a graphite matrix material as shown in Figure 3. The unique feature of pebble bed reactors is the online refuelling capability in which the pebbles are recirculated with checks on integrity and consumption of uranium. This system allows new fuel to be inserted during operation and used fuel to be discharged and stored on site for the life of the plant. It is projected that each pebble will pass through the reactor 6–10 times before

Since December 2023, the first commercial pebble bed reactor in China has been producing electricity. This is no longer a small test reactor, but a real nuclear power plant. In contrast to conventional nuclear power plants, however, the temperatures in this pebble bed reactor are twice as high, at up to 750 °C. Nevertheless, it is said to be safer. Tests have now been carried out on this reactor with all cooling systems turned off. The reactor type should be able to cool itself down in an [...] This video was created in my editorial team. Editors responsible: Valentin Bruder, Jacob Beautemps; Editing: Aron Kamenz, Sören Rensch, Neo Sanjuan Thiele Sources: Source 1: Source 2: Source 3: Source 4: Source 5: Source 6: Source 7: Source 8: Source 9: Source 10: Source 11: Source 12: Source 13: Source 14: Source 15: [...] # Nuclear Power WITHOUT Fuel Rods: This Is How The Pebble Bed Reactor Works!

This pebble bed, high-temperature gas-cooled reactor can't melt down, according to X-energy. Office of Nuclear Energy Dozens of U.S. companies are developing advanced reactor designs that will bring enhanced safety, efficiency, and economics to the nuclear energy industry. X-energy, located just outside the nation’s capital in Rockville, Maryland, is working on a pebble bed, high-temperature gas-cooled reactor that the company says can’t melt down. [...] The reactor core is made of graphite and filled with 15.5% enriched fuel pebbles. Each pebble (roughly the size of a billiard ball) contains thousands of specially coated Tristructural Isotropic (TRISO) uranium fuel particles that are virtually indestructible. [...] The company's Xe-100 reactor and specialized uranium-based pebble fuel could be available in the market as early as the late 2020s and is one of two designs that secured more than $2.5 billion in funding through the Bipartisan Infrastructure Law to demonstrate their technology. Xe-100 pebble bed reactor. ### How it Works The Xe-100 is an advanced modular reactor with each unit designed to produce around 76 megawatts of electric power.