DRAGON Reactor Experiment (DRE) was an experimental high temperature

gas-cooled reactor A gas-cooled reactor (GCR) is a nuclear reactor that uses graphite as a neutron moderator and a gas (carbon dioxide or helium in extant designs) as coolant. Although there are many other types of reactor cooled by gas, the terms ''GCR'' and to a l ...

Winfrith Winfrith Atomic Energy Establishment, or AEE Winfrith, was a United Kingdom Atomic Energy Authority site near Winfrith Newburgh in Dorset. It covered an area on Winfrith Heath to the west of the village of Wool between the A352 road and the South ...

Dorset Dorset ( ; archaically: Dorsetshire , ) is a county in South West England on the English Channel coast. The ceremonial county comprises the unitary authority areas of Bournemouth, Christchurch and Poole and Dorset (unitary authority), Dors ...

, England, an experimental reactor of the

Organisation for Economic Co-operation and Development The Organisation for Economic Co-operation and Development (OECD; french: Organisation de coopération et de développement économiques, ''OCDE'') is an intergovernmental organization, intergovernmental organisation with 38 member countries ...

(O.E.C.D) High Temperature Reactor Project. The site extended to of heathland in rural south Dorset, and nine different experimental reactors were located there. Many designs of the 1960s and 70s were based on this general tristructural-isotropic (TRISO) fuel concept, including "prismatic" designs with fixed fuel layouts like Dragon, and the

pebble-bed reactor The pebble-bed reactor (PBR) is a design for a graphite- moderated, gas-cooled nuclear reactor. It is a type of very-high-temperature reactor (VHTR), one of the six classes of nuclear reactors in the Generation IV initiative. The basic des ...

designs being developed in

Germany Germany,, officially the Federal Republic of Germany, is a country in Central Europe. It is the second most populous country in Europe after Russia, and the most populous member state of the European Union. Germany is situated betwe ...

. , these concepts have been used in several further research reactors, including Peach Bottom, AVR, HTTR, and

HTR-10 HTR-10 is a 10 MWt prototype pebble bed reactor at Tsinghua University in China. Construction began in 1995, achieving its first criticality in December 2000, and was operated in full power condition in January 2003. Two HTR-PM reactors, scale ...

as well as for commercial reactors Fort St. Vrain and

THTR-300 The THTR-300 was a thorium cycle high-temperature nuclear reactor rated at 300 MW electric (THTR-300) in Hamm-Uentrop, Germany. It started operating in 1983, synchronized with the grid in 1985, operated at full power in February 1987 and was shut ...

. The

HTR-PM The HTR-PM (球床模块式高温气冷堆核电站) is a small modular nuclear reactor in China. It is the world’s first prototype of a high-temperature gas-cooled (HTGR) pebble-bed generation IV reactor. The reactor unit has a thermal capac ...

China China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's most populous country, with a population exceeding 1.4 billion, slightly ahead of India. China spans the equivalent of five time zones and ...

is under construction, with one unit at Shidao Bay connected to the grid as of December 2021. Of the nine experimental reactors at Winfrith, only the Dragon Reactor and the Steam Generating Heavy Water Reactor remain, and they are in the process of being decommissioned. During decommissioning, the reactor vessels will be placed in reactor safestores, other structures will be dismantled and stored, any remaining waste will be sent to allocated storage sites, and the soil will be removed as necessary to a suitable

Low Level Waste Repository The Low Level Waste Repository is the UK's central long-term store for low-level radioactive waste located on the West Cumbrian coast near Drigg village and opened in 1959. It is a subsidiary of the Nuclear Decommissioning Authority. Functi ...

. Finally, the site will be declassified as a nuclear licensed site, landscaped and returned to normal use. The contract for decommissioning the site has been awarded to Costain Nuclear, and the final decommissioning phase has been deferred for twenty years.

The reactor

The Atomic Energy Establishment at

was built for the construction and operation of experimental and research nuclear reactors. DRAGON used

helium Helium (from el, ἥλιος, helios, lit=sun) is a chemical element with the symbol He and atomic number 2. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas and the first in the noble gas group in the periodic table. ...

gas as the coolant and

graphite Graphite () is a crystalline form of the element carbon. It consists of stacked layers of graphene. Graphite occurs naturally and is the most stable form of carbon under standard conditions. Synthetic and natural graphite are consumed on large ...

as the

neutron moderator In nuclear engineering, a neutron moderator is a medium that reduces the speed of fast neutrons, ideally without capturing any, leaving them as thermal neutrons with only minimal (thermal) kinetic energy. These thermal neutrons are immensely mo ...

. Fuel was formed into tiny spherical pellets and then coated with ceramics. These were then mixed with the graphite and pressed together to form blocks of various shapes and sizes. Criticality is only possible when the blocks are placed together in certain configurations within a

neutron reflector A neutron reflector is any material that reflects neutrons. This refers to elastic scattering rather than to a specular reflection. The material may be graphite, beryllium, steel, tungsten carbide, gold, or other materials. A neutron reflector ...

, allowing additional fuel to be held in a ready area and loaded on-the-fly. Helium was used due to its low

nuclear cross section The nuclear cross section of a nucleus is used to describe the probability that a nuclear reaction will occur. The concept of a nuclear cross section can be quantified physically in terms of "characteristic area" where a larger area means a larger ...

which led to higher

neutron economy Neutron economy is defined as the ratio of an adjoint weighted average of the excess neutron production divided by an adjoint weighted average of the fission production. The distribution of neutron energies in a nuclear reactor differs from the f ...

, as well as its chemical inertness allowing it to operate at higher temperatures without fear of eroding the reactor materials. Higher temperatures also allow for more efficient

steam turbine A steam turbine is a machine that extracts thermal energy from pressurized steam and uses it to do mechanical work on a rotating output shaft. Its modern manifestation was invented by Charles Parsons in 1884. Fabrication of a modern steam turbin ...

operation and make it more suitable for direct use as

process heat Process heat refers to the application of heat during industrial processes. Some form of process heat is used during the manufacture of many common products, from concrete to glass to steel to paper. Where byproducts or wastes of the overall indust ...

. In the case of a power failure, natural

convection Convection is single or multiphase fluid flow that occurs spontaneously due to the combined effects of material property heterogeneity and body forces on a fluid, most commonly density and gravity (see buoyancy). When the cause of the convec ...

of the helium provided emergency cooling. The fuel used in the reactor was coated particles, consisting of micro-pellets of a fissile material (such as U235) surrounded by a ceramic outer layer. Initially most of the fuel was

highly enriched uranium Enriched uranium is a type of uranium in which the percent composition of uranium-235 (written 235U) has been increased through the process of isotope separation. Naturally occurring uranium is composed of three major isotopes: uranium-238 (238U ...

(about 93%

uranium-235 Uranium-235 (235U or U-235) is an isotope of uranium making up about 0.72% of natural uranium. Unlike the predominant isotope uranium-238, it is fissile, i.e., it can sustain a nuclear chain reaction. It is the only fissile isotope that exis ...

), though later more lower enrichment (about 20%) fuel was used. The reactor resembled an enormous bottle, with the larger area at the bottom containing the active fuel within the reflector, and the smaller area on top holding additional fuel elements for reloading.

References

Bibliography

* Defunct nuclear reactors Former nuclear research institutes Nuclear research institutes in the United Kingdom Nuclear research reactors Nuclear technology in the United Kingdom Science and technology in Dorset 1965 establishments in England 1976 disestablishments in England {{DEFAULTSORT:DRAGON_Reactor_DRE