Synroc

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Synroc, a portmanteau of "synthetic rock", is a means of safely storing radioactive waste. It was pioneered in 1978 by a team led by Professor Ted Ringwood at the Australian National University, with further research undertaken in collaboration with ANSTO at research laboratories in Lucas Heights.

Contents

Manufacture

Synroc is composed of three titanate 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 (1,380 °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 1,150–1,200 °C (2,100–2,190 °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, 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 crystalline structure and use to store radioactive waste. Synroc-based glass composite materials (GCM) combine the process and chemical flexibility of glass with the superior chemical durability of ceramics and can achieve higher waste loadings. [1] [2]

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. Only zirconolite and perovskite can accommodate actinides. The exact proportions of the main phases vary depending on the HLW composition. For example, Synroc-C is designed to contain about 20% by weight of calcined HLW and it consists of approximately (% by weight): 30 – hollandite; 30 – zirconolite; 20 – perovskite and 20 – Ti-oxides and other phases. Immobilising weapons-grade plutonium or transuranium wastes instead of bulk HLW may essentially change the Synroc phase composition to primarily zirconolite-based or a pyrochlore-based ceramic. The starting precursor for Synroc-C fabrication contains ~57% by weight TiO2 and 2% by weight metallic Ti. The metallic titanium provides reducing conditions during ceramic synthesis and helps decrease volatilisation of radioactive cesium. [3]

Synroc is not a disposal method. [4] Synroc still has to be stored. 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. [5]

Production use

In 1997 Synroc was tested with real HLW using technology developed jointly by ANSTO and the US DoE's Argonne National Laboratory. [1] In January 2010, the United States Department of Energy selected hot isostatic pressing (HIP) for processing waste at the Idaho National Laboratory. [6]

In April 2008, the Battelle 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. [7]

Synroc was chosen in April 2005 for a multimillion-dollar "demonstration" contract to eliminate 5 t (5.5 short tons) of plutonium-contaminated waste at British Nuclear Fuel's Sellafield plant, on the northwest coast of England.

Related Research Articles

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<span class="mw-page-title-main">Radioactive waste</span> Unusable radioactive materials

Radioactive waste is a type of hazardous waste that contains radioactive material. It is a result of many activities, including nuclear medicine, nuclear research, nuclear power generation, nuclear decommissioning, rare-earth mining, and nuclear weapons reprocessing. The storage and disposal of radioactive waste is regulated by government agencies in order to protect human health and the environment.

<span class="mw-page-title-main">Nuclear fuel cycle</span> Process of manufacturing and using nuclear fuel

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<span class="mw-page-title-main">Nuclear reprocessing</span> Chemical operations that separate fissile material from spent fuel to be recycled as new fuel

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<span class="mw-page-title-main">Hot isostatic pressing</span> Manufacturing process

Hot isostatic pressing (HIP) is a manufacturing process, used to reduce the porosity of metals and increase the density of many ceramic materials. This improves the material's mechanical properties and workability.

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<span class="mw-page-title-main">PUREX</span> Spent fuel reprocessing process for plutonium and uranium recovery

PUREX is a chemical method used to purify fuel for nuclear reactors or nuclear weapons. PUREX is the de facto standard aqueous nuclear reprocessing method for the recovery of uranium and plutonium from used nuclear fuel. It is based on liquid–liquid extraction ion-exchange.

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<span class="mw-page-title-main">La Hague site</span> Nuclear fuel reprocessing plant at La Hague, France

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<span class="mw-page-title-main">High-level waste</span> Highly radioactive waste material

High-level waste (HLW) is a type of nuclear waste created by the reprocessing of spent nuclear fuel. It exists in two main forms:

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<span class="mw-page-title-main">Spent nuclear fuel</span> Nuclear fuel thats been irradiated in a nuclear reactor

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<span class="mw-page-title-main">Actinides in the environment</span>

The actinide series is a group of chemical elements with atomic numbers ranging from 89 to 102, including notable elements such as uranium and plutonium. The nuclides thorium-232, uranium-235, and uranium-238 occur primordially, while trace quantities of actinium, protactinium, neptunium, and plutonium exist as a result of radioactive decay and neutron capture of uranium. These elements are far more radioactive than the naturally occurring thorium and uranium, and thus have much shorter half-lives. Elements with atomic numbers greater than 94 do not exist naturally on Earth, and must be produced in a nuclear reactor. However, certain isotopes of elements up to californium still have practical applications which take advantage of their radioactive properties.

<span class="mw-page-title-main">High-level radioactive waste management</span> Management and disposal of highly radioactive materials

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<span class="mw-page-title-main">Nuclear transmutation</span> Conversion of an atom from one element to another

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The advanced reprocessing of spent nuclear fuel is a potential key to achieve a sustainable nuclear fuel cycle and to tackle the heavy burden of nuclear waste management. In particular, the development of such advanced reprocessing systems may save natural resources, reduce waste inventory and enhance the public acceptance of nuclear energy. This strategy relies on the recycling of major actinides and the transmutation of minor actinides in appropriate reactors. In order to fulfill this objective, selective extracting agents need to be designed and developed by investigating their complexation mechanism.

References

  1. 1 2 "Synroc – World Nuclear Association". www.world-nuclear.org.
  2. ↑ W. E. Lee, M.I. Ojovan, C.M. Jantzen. Radioactive waste management and contaminated site clean-up: Processes, technologies and international experience, Woodhead, Cambridge, 924 p. (2013). www.woodheadpublishing.com/9780857094353
  3. ↑ B.E. Burakov, M.I Ojovan, W.E. Lee. Crystalline Materials for Actinide Immobilisation, Imperial College Press, London, 198 pp. (2010). "Crystalline Materials for Actinide Immobilisation". Archived from the original on 2012-03-09. Retrieved 2010-10-16.
  4. ↑ Ron Cameron, Chief of Operations, ANSTO. The (half)-life of waste. "Ask and Expert, Nuclear Power". Australian Broadcasting Corporation . 27 October 2005.
  5. ↑ E.R Vance, D.J Gregg and D.T Chavara, ANSTO. "Past and present Applications of Synroc" (PDF).
  6. ↑ US Department of Energy (January 4, 2010), Federal Register (excerpt) (PDF), vol. 75/1, pp. 137–140, retrieved May 5, 2010
  7. ↑ "ANSTO Inc HIP demonstration contract award" (PDF) (Press release). ANSTO. April 1, 2008. Retrieved May 5, 2010.
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