SLOWPOKE reactor
Encyclopedia
The SLOWPOKE is a low-energy, pool-type nuclear research reactor
Research reactor
Research reactors are nuclear reactors that serve primarily as a neutron source. They are also called non-power reactors, in contrast to power reactors that are used for electricity production, heat generation, or maritime propulsion.-Purpose:...

 designed by Atomic Energy of Canada Limited
Atomic Energy of Canada Limited
Atomic Energy of Canada Limited or AECL is a Canadian federal Crown corporation and Canada's largest nuclear science and technology laboratory...

 (AECL) in the late 1960s. John W. Hilborn (now retired from AECL) is the scientist most closely associated with its design. It is beryllium-reflected
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, and tungsten carbide, or other materials...

 with a very low critical mass but provides neutron flux
Neutron flux
The neutron flux is a quantity used in reactor physics corresponding to the total length travelled by all neutrons per unit time and volume . The neutron fluence is defined as the neutron flux integrated over a certain time period....

es higher than available from a small particle accelerator
Particle accelerator
A particle accelerator is a device that uses electromagnetic fields to propel charged particles to high speeds and to contain them in well-defined beams. An ordinary CRT television set is a simple form of accelerator. There are two basic types: electrostatic and oscillating field accelerators.In...

 or other radioactive sources
Neutron source
A Neutron source is a device that emits neutrons. There is a wide variety of different sources, ranging from hand-held radioactive sources to neutron research facilities operating research reactors and spallation sources...

.

Basic design

The SLOWPOKE-2 uses 93% (originally) enriched uranium
Enriched uranium
Enriched uranium is a kind of uranium in which the percent composition of uranium-235 has been increased through the process of isotope separation. Natural uranium is 99.284% 238U isotope, with 235U only constituting about 0.711% of its weight...

 in the form of 28% uranium
Uranium
Uranium is a silvery-white metallic chemical element in the actinide series of the periodic table, with atomic number 92. It is assigned the chemical symbol U. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons...

-aluminum alloy
Alloy
An alloy is a mixture or metallic solid solution composed of two or more elements. Complete solid solution alloys give single solid phase microstructure, while partial solutions give two or more phases that may or may not be homogeneous in distribution, depending on thermal history...

 with aluminum cladding. The core is an assembly of about 300 fuel pins, only 22 cm diameter and 23 cm high, surrounded by a fixed beryllium
Beryllium
Beryllium is the chemical element with the symbol Be and atomic number 4. It is a divalent element which occurs naturally only in combination with other elements in minerals. Notable gemstones which contain beryllium include beryl and chrysoberyl...

 annulus and a bottom beryllium slab. Criticality
Critical mass
A critical mass is the smallest amount of fissile material needed for a sustained nuclear chain reaction. The critical mass of a fissionable material depends upon its nuclear properties A critical mass is the smallest amount of fissile material needed for a sustained nuclear chain reaction. The...

 is maintained by adding beryllium
Beryllium
Beryllium is the chemical element with the symbol Be and atomic number 4. It is a divalent element which occurs naturally only in combination with other elements in minerals. Notable gemstones which contain beryllium include beryl and chrysoberyl...

 plates in a tray on top of the core. The reactor core
Nuclear reactor core
A nuclear reactor core is the portion of a nuclear reactor containing the nuclear fuel components where the nuclear reactions take place.- Description :...

 sits in a pool of regular light-water, 2.5 m diameter by 6 m deep, which provides cooling
Coolant
A coolant is a fluid which flows through a device to prevent its overheating, transferring the heat produced by the device to other devices that use or dissipate it. An ideal coolant has high thermal capacity, low viscosity, is low-cost, non-toxic, and chemically inert, neither causing nor...

 via natural convection. In addition to passive cooling, the reactor has a high degree of inherent safety; that is, it can regulate itself through passive, natural means, such as the chain reaction
Chain reaction
A chain reaction is a sequence of reactions where a reactive product or by-product causes additional reactions to take place. In a chain reaction, positive feedback leads to a self-amplifying chain of events....

 slowing down if the water heats up or forms bubbles
Void coefficient
In nuclear engineering, the void coefficient is a number that can be used to estimate how much the reactivity of a nuclear reactor changes as voids form in the reactor moderator or coolant...

. These characteristics are so dominant, in fact, that the SLOWPOKE-2 reactor is licensed to operate unattended overnight (but monitored remotely). Most SLOWPOKES are rated at a nominal 20 kW, although operation at higher power for shorter durations is possible.

History

The SLOWPOKE research reactor was conceived in 1967 at the Whiteshell Laboratories
Whiteshell Laboratories
The Whiteshell Nuclear Research Establishment, now Whiteshell Laboratories, was established by the Government of Canada in 1963 as an AECL research laboratory in Pinawa, Manitoba...

 of AECL. In 1970 a prototype unit was designed and built at Chalk River Laboratories
Chalk River Laboratories
The Chalk River Laboratories is a Canadian nuclear research facility located near Chalk River, about north-west of Ottawa in the province of Ontario.CRL is a site of major research and development to support and advance nuclear technology, in particular CANDU reactor...

. It was primarily intended for Canadian universities, providing a higher neutron flux than available from small commercial accelerators, while avoiding the complexity and high operating costs of existing nuclear reactors. The Chalk River prototype went critical in 1970, and was moved to the University of Toronto
University of Toronto
The University of Toronto is a public research university in Toronto, Ontario, Canada, situated on the grounds that surround Queen's Park. It was founded by royal charter in 1827 as King's College, the first institution of higher learning in Upper Canada...

 in 1971. It had one sample site in the beryllium reflector and operated at a power level of 5 kW. In 1973 the power was increased to 20 kW and the period of unattended operation was increased from 4 hours to 18 hours.

The first commercial example was started up in 1971 at AECL's Commercial Products Division in Ottawa
Ottawa
Ottawa is the capital of Canada, the second largest city in the Province of Ontario, and the fourth largest city in the country. The city is located on the south bank of the Ottawa River in the eastern portion of Southern Ontario...

; and in 1976 a commercial design, named SLOWPOKE-2, was installed at the University of Toronto, replacing the original SLOWPOKE-1 unit. The commercial model has five sample sites in the beryllium reflector and five sites stationed outside the reflector.

Between 1976 and 1984, seven SLOWPOKE-2 reactors with Highly Enriched Uranium
Enriched uranium
Enriched uranium is a kind of uranium in which the percent composition of uranium-235 has been increased through the process of isotope separation. Natural uranium is 99.284% 238U isotope, with 235U only constituting about 0.711% of its weight...

 (HEU) fuel were commissioned in six Canadian cities and in Kingston
Kingston, Jamaica
Kingston is the capital and largest city of Jamaica, located on the southeastern coast of the island. It faces a natural harbour protected by the Palisadoes, a long sand spit which connects the town of Port Royal and the Norman Manley International Airport to the rest of the island...

, Jamaica
Jamaica
Jamaica is an island nation of the Greater Antilles, in length, up to in width and 10,990 square kilometres in area. It is situated in the Caribbean Sea, about south of Cuba, and west of Hispaniola, the island harbouring the nation-states Haiti and the Dominican Republic...

. In 1985 the first Low-Enriched Uranium
Enriched uranium
Enriched uranium is a kind of uranium in which the percent composition of uranium-235 has been increased through the process of isotope separation. Natural uranium is 99.284% 238U isotope, with 235U only constituting about 0.711% of its weight...

 (LEU) fuelled SLOWPOKE-2 reactor was commissioned at the Royal Military College of Canada
Royal Military College of Canada
The Royal Military College of Canada, RMC, or RMCC , is the military academy of the Canadian Forces, and is a degree-granting university. RMC was established in 1876. RMC is the only federal institution in Canada with degree granting powers...

 (RMC) in Kingston
Kingston, Ontario
Kingston, Ontario is a Canadian city located in Eastern Ontario where the St. Lawrence River flows out of Lake Ontario. Originally a First Nations settlement called "Katarowki," , growing European exploration in the 17th Century made it an important trading post...

, Ontario
Ontario
Ontario is a province of Canada, located in east-central Canada. It is Canada's most populous province and second largest in total area. It is home to the nation's most populous city, Toronto, and the nation's capital, Ottawa....

. Since then several units have been converted to LEU.

AECL also designed and built a scaled-up version (2-10 MWth) called SLOWPOKE-3 for district heating
District heating
District heating is a system for distributing heat generated in a centralized location for residential and commercial heating requirements such as space heating and water heating...

 at its Whiteshell Nuclear Research Establishment in Manitoba
Manitoba
Manitoba is a Canadian prairie province with an area of . The province has over 110,000 lakes and has a largely continental climate because of its flat topography. Agriculture, mostly concentrated in the fertile southern and western parts of the province, is vital to the province's economy; other...

. The economics of a district-heating system based on SLOWPOKE-3 technology were estimated to be competitive with that of conventional fossil fuel
Fossil fuel
Fossil fuels are fuels formed by natural processes such as anaerobic decomposition of buried dead organisms. The age of the organisms and their resulting fossil fuels is typically millions of years, and sometimes exceeds 650 million years...

s. However, the market for this technology did not materialize.

A Chinese version of the Slowpoke exists, designated the Miniature Neutron Source Reactor
Miniature neutron source reactor
The Chinese built Miniature Neutron Source reactor is a small and compact research reactor copied from a Canadian SLOWPOKE reactor design....

 (MNSR). This version is nominally rated at 27 kW with similar characteristics and performance.

Marine Power Source

During the mid-1980s Canada briefly considered converting its Oberon class submarine
Oberon class submarine
The Oberon class was a 27-boat class of British-built diesel-electric submarines based on the successful British Porpoise-class submarine....

s to nuclear power using a SLOWPOKE nuclear reactor to continuously recharge the ship's batteries during submerged operations. A good deal of work had been done on potential marine applications of the reactor at Royal Military College of Canada
Royal Military College of Canada
The Royal Military College of Canada, RMC, or RMCC , is the military academy of the Canadian Forces, and is a degree-granting university. RMC was established in 1876. RMC is the only federal institution in Canada with degree granting powers...

.

Current applications

SLOWPOKE reactors are used mainly for neutron activation analysis
Neutron activation analysis
In chemistry, neutron activation analysis is a nuclear process used for determining the concentrations of elements in a vast amount of materials. NAA allows discrete sampling of elements as it disregards the chemical form of a sample, and focuses solely on its nucleus. The method is based on...

 (NAA), in research and as a commercial service, but also for teaching, training, irradiation studies, neutron radiography
Radiography
Radiography is the use of X-rays to view a non-uniformly composed material such as the human body. By using the physical properties of the ray an image can be developed which displays areas of different density and composition....

 (at the Royal Military College of Canada
Royal Military College of Canada
The Royal Military College of Canada, RMC, or RMCC , is the military academy of the Canadian Forces, and is a degree-granting university. RMC was established in 1876. RMC is the only federal institution in Canada with degree granting powers...

) and the production of radioactive tracer
Radioactive tracer
A radioactive tracer, also called a radioactive label, is a substance containing a radioisotope that is used to measure the speed of chemical processes and to track the movement of a substance through a natural system such as a cell or tissue...

s. The main advantages are the reliability and ease of use of this design of reactor and the reproducibility of the neutron flux. Since the fuel is not modified at all for at least 20 years, the neutron spectrum in the irradiation sites does not change and the neutron flux is reproducible to about 1%.

Six of the original reactors are still in operation and one has been refuelled. Although all of the technical goals of this reactor were achieved, the lack of foreign sales was disappointing, the market being taken by the Chinese version.

External links

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