Synroc
Encyclopedia
Synroc, a portmanteau of "synthetic rock", is a means of safely storing radioactive waste
. It was pioneered in 1978 by a team led by Dr Ted Ringwood
at the Australian National University
, with further research undertaken in collaboration with ANSTO
at research laboratories in Lucas Heights.
minerals – hollandite, zirconolite
and perovskite
– plus rutile
and a small amount of metal
alloy
. These are combined into a slurry to which is added a portion of high-level liquid nuclear waste
. The mixture is dried and calcined
at 750 °C (1,382 °F) to produce a powder.
The powder is then compressed in a process known as Hot Isostatic Pressing
(HIP), where it is compressed within a bellows-like stainless steel
container at temperatures of 1150–1200 °C (2,102–2,192 F).
The result is a cylinder of hard, dense, black synthetic rock.
Unlike borosilicate glass
, which is amorphous
, Synroc is a ceramic
that incorporates the radioactive waste into its crystal structure
. Naturally occurring rocks can store radioactive materials for long periods. The aim of Synroc is to imitate this by converting liquid into a crystal
line structure and use to store radioactive waste.
Different types of Synroc waste forms (ratios of component minerals, specific HIP pressures and temperatures etc.) can be developed for the immobilisation of different types of waste.
Synroc is not a disposal method. Synroc still has to be stored, often underground. Even though the waste is held in a solid lattice and prevented from spreading, it is still radioactive and can have a negative effect on its surroundings. Synroc is a superior method of nuclear waste storage because it minimises leaching
.
selected Hot Isostatic Pressing (HIP) for processing waste at the Idaho National Laboratory
.
In April 2008, the Batelle Energy Alliance signed a contract with ANSTO
to demonstrate the benefits of Synroc in processing waste managed by Batelle as part of its contract to manage the Idaho National Laboratory
.
Synroc was chosen in April 2005 for a multi-million dollar "demonstration" contract to eliminate 5 MT (5.5 ST) of plutonium
-contaminated waste at British Nuclear Fuel's Sellafield
plant, on the northwest coast of England
.
Radioactive waste
Radioactive wastes are wastes that contain radioactive material. Radioactive wastes are usually by-products of nuclear power generation and other applications of nuclear fission or nuclear technology, such as research and medicine...
. It was pioneered in 1978 by a team led by Dr Ted Ringwood
Ted Ringwood
Alfred Edward "Ted" Ringwood FRS was an Australian experimental geophysicist and geochemist, and the 1988 recipient of the Wollaston Medal....
at the Australian National University
Australian National University
The Australian National University is a teaching and research university located in the Australian capital, Canberra.As of 2009, the ANU employs 3,945 administrative staff who teach approximately 10,000 undergraduates, and 7,500 postgraduate students...
, with further research undertaken in collaboration with ANSTO
Australian Nuclear Science and Technology Organisation
The Australian Nuclear Science and Technology Organisation is a statutory body of the Australian government, formed in 1987 to replace the Australian Atomic Energy Commission. Its head office and main facilities are in southern outskirts of Sydney at Lucas Heights, in the Sutherland Shire...
at research laboratories in Lucas Heights.
Manufacture
Synroc is composed of three titanateTitanate
In chemistry, titanate usually refers to inorganic compounds composed of titanium oxides. In some cases, the term is used more generally for any titanium-containing anion, e.g. [TiCl6]2- and [Ti7]2-. This article focuses on the oxides....
minerals – hollandite, zirconolite
Zirconolite
Zirconolite is a mineral, calcium zirconium titanate; formula CaZrTi2O7. Some examples of the mineral may also contain thorium, uranium, cerium, niobium and iron; the presence of thorium and/or uranium would make the mineral radioactive....
and perovskite
Perovskite
A perovskite structure is any material with the same type of crystal structure as calcium titanium oxide , known as the perovskite structure, or XIIA2+VIB4+X2−3 with the oxygen in the face centers. Perovskites take their name from this compound, which was first discovered in the Ural mountains of...
– plus rutile
Rutile
Rutile is a mineral composed primarily of titanium dioxide, TiO2.Rutile is the most common natural form of TiO2. Two rarer polymorphs of TiO2 are known:...
and a small amount of metal
Metal
A metal , is an element, compound, or alloy that is a good conductor of both electricity and heat. Metals are usually malleable and shiny, that is they reflect most of incident light...
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...
. These are combined into a slurry to which is added a portion of high-level liquid nuclear waste
High-level radioactive waste management
High-level radioactive waste management concerns management and disposal of highly radioactive materials created during production of nuclear power and nuclear warheads. The technical issues in accomplishing this are daunting, due to the extremely long periods radioactive wastes remain deadly to...
. The mixture is dried and calcined
Calcination
Calcination is a thermal treatment process applied to ores and other solid materials to bring about a thermal decomposition, phase transition, or removal of a volatile fraction. The calcination process normally takes place at temperatures below the melting point of the product materials...
at 750 °C (1,382 °F) to produce a powder.
The powder is then compressed in a process known as Hot Isostatic Pressing
Hot isostatic pressing
Hot isostatic pressing is a manufacturing process used to reduce the porosity of metals and influence the density of many ceramic materials. This improves the material's mechanical properties and workability....
(HIP), where it is compressed within a bellows-like stainless steel
Stainless steel
In metallurgy, stainless steel, also known as inox steel or inox from French "inoxydable", is defined as a steel alloy with a minimum of 10.5 or 11% chromium content by mass....
container at temperatures of 1150–1200 °C (2,102–2,192 F).
The result is a cylinder of hard, dense, black synthetic rock.
Comparisons
If stored in a liquid form, nuclear waste can enter the environment and the waterways, and cause widespread damage. As a solid, these risks are greatly minimised.Unlike borosilicate glass
Borosilicate glass
Borosilicate glass is a type of glass with the main glass-forming constituents silica and boron oxide. Borosilicate glasses are known for having very low coefficients of thermal expansion , making them resistant to thermal shock, more so than any other common glass...
, which is amorphous
Amorphous solid
In condensed matter physics, an amorphous or non-crystalline solid is a solid that lacks the long-range order characteristic of a crystal....
, Synroc is a ceramic
Ceramic
A ceramic is an inorganic, nonmetallic solid prepared by the action of heat and subsequent cooling. Ceramic materials may have a crystalline or partly crystalline structure, or may be amorphous...
that incorporates the radioactive waste into its crystal structure
Crystal structure
In mineralogy and crystallography, crystal structure is a unique arrangement of atoms or molecules in a crystalline liquid or solid. A crystal structure is composed of a pattern, a set of atoms arranged in a particular way, and a lattice exhibiting long-range order and symmetry...
. Naturally occurring rocks can store radioactive materials for long periods. The aim of Synroc is to imitate this by converting liquid into a crystal
Crystal
A crystal or crystalline solid is a solid material whose constituent atoms, molecules, or ions are arranged in an orderly repeating pattern extending in all three spatial dimensions. The scientific study of crystals and crystal formation is known as crystallography...
line structure and use to store radioactive waste.
Different types of Synroc waste forms (ratios of component minerals, specific HIP pressures and temperatures etc.) can be developed for the immobilisation of different types of waste.
Synroc is not a disposal method. Synroc still has to be stored, often underground. Even though the waste is held in a solid lattice and prevented from spreading, it is still radioactive and can have a negative effect on its surroundings. Synroc is a superior method of nuclear waste storage because it minimises leaching
Leaching (metallurgy)
Leaching is a widely used extractive metallurgy technique which converts metals into soluble salts in aqueous media. Compared to pyrometallurgical operations, leaching is easier to perform and much less harmful, because no gaseous pollution occurs...
.
Production Use
In January 2010, the United States Department of EnergyUnited States Department of Energy
The United States Department of Energy is a Cabinet-level department of the United States government concerned with the United States' policies regarding energy and safety in handling nuclear material...
selected Hot Isostatic Pressing (HIP) for processing waste at the Idaho National Laboratory
Idaho National Laboratory
Idaho National Laboratory is an complex located in the high desert of eastern Idaho, between the town of Arco to the west and the cities of Idaho Falls and Blackfoot to the east. It lies within Butte, Bingham, Bonneville and Jefferson counties...
.
In April 2008, the Batelle Energy Alliance signed a contract with ANSTO
Australian Nuclear Science and Technology Organisation
The Australian Nuclear Science and Technology Organisation is a statutory body of the Australian government, formed in 1987 to replace the Australian Atomic Energy Commission. Its head office and main facilities are in southern outskirts of Sydney at Lucas Heights, in the Sutherland Shire...
to demonstrate the benefits of Synroc in processing waste managed by Batelle as part of its contract to manage the Idaho National Laboratory
Idaho National Laboratory
Idaho National Laboratory is an complex located in the high desert of eastern Idaho, between the town of Arco to the west and the cities of Idaho Falls and Blackfoot to the east. It lies within Butte, Bingham, Bonneville and Jefferson counties...
.
Synroc was chosen in April 2005 for a multi-million dollar "demonstration" contract to eliminate 5 MT (5.5 ST) of plutonium
Plutonium
Plutonium is a transuranic radioactive chemical element with the chemical symbol Pu and atomic number 94. It is an actinide metal of silvery-gray appearance that tarnishes when exposed to air, forming a dull coating when oxidized. The element normally exhibits six allotropes and four oxidation...
-contaminated waste at British Nuclear Fuel's Sellafield
Sellafield
Sellafield is a nuclear reprocessing site, close to the village of Seascale on the coast of the Irish Sea in Cumbria, England. The site is served by Sellafield railway station. Sellafield is an off-shoot from the original nuclear reactor site at Windscale which is currently undergoing...
plant, on the northwest coast of England
England
England is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...
.