Editing Radioactive waste (section)

==== Vitrification ====
[[File:Sellafield Vitrification Plant, interior.jpg|thumb|upright=1.8|The Waste Vitrification Plant at [[Sellafield]]]]
[[File:Vitrification2.jpg|thumb|Vitrification of waste into glass for long term storage.]]
Long-term storage of radioactive waste requires the stabilization of the waste into a form that will neither react nor degrade for extended periods. It is theorized that one way to do this might be through [[vitrification]].<ref>Ojovan, M. I. and Lee, W. E. (2005) ''An Introduction to Nuclear Waste Immobilisation'', Elsevier, Amsterdam, Netherlands, p. 315.</ref> Currently at [[Sellafield]], the high-level waste (PUREX first cycle [[raffinate]]) is mixed with [[sugar]] and then calcined. [[Calcination]] involves passing the waste through a heated, rotating tube. The purposes of calcination are to evaporate the water from the waste and de-nitrate the fission products to assist the stability of the glass produced.<ref name="council">{{cite book |author=National Research Council |title=Nuclear Wastes: Technologies for Separation and Transmutation |publisher=National Academy Press |year=1996 |location=Washington, D. C. |language=en-us}}</ref>

The 'calcine' generated is fed continuously into an induction heated furnace with fragmented [[glass]].<ref>{{citation |last1=Morrey |first1=E. V. |title=Laboratory-scale vitrification and leaching of Hanford high-level waste for the purpose of simulant and glass property models validation |date=February 1993 |osti=6510132 |last2=Elliott |first2=M. L. |last3=Tingey |first3=J. M.}}.</ref> The resulting glass is a new substance in which the waste products are bonded into the glass matrix when it solidifies. As a melt, this product is poured into [[stainless steel]] cylindrical containers ("cylinders") in a batch process. When cooled, the fluid solidifies ("vitrifies") into the glass. After being formed, the glass is highly resistant to water.<ref>{{cite web |author=Ojovan |first=M. I. |display-authors=etal |year=2006 |title=Corrosion of nuclear waste glasses in non-saturated conditions: Time-Temperature behaviour |url=http://isl.group.shef.ac.uk/papers/MIOCorrosionICG2004paper.pdf |url-status=dead |archive-url=https://web.archive.org/web/20080626191553/http://isl.group.shef.ac.uk/papers/MIOCorrosionICG2004paper.pdf |archive-date=2008-06-26 |access-date=2008-06-30}}</ref>

After filling a cylinder, a seal is [[welded]] onto the cylinder head. The cylinder is then washed. After being inspected for external contamination, the steel cylinder is stored, usually in an underground repository. In this form, the waste products are expected to be immobilized for thousands of years.<ref>{{cite book |author=OECD Nuclear Energy Agency |title=The Economics of the Nuclear Fuel Cycle |publisher=OECD Nuclear Energy Agency |year=1994 |location=Paris, France}}</ref>

The glass inside a cylinder is usually a black glossy substance. All this work (in the United Kingdom) is done using [[hot cell]] systems. Sugar is added to control the [[ruthenium]] chemistry and to stop the formation of the volatile [[ruthenium tetroxide|RuO<sub>4</sub>]] containing [[Ru-106|radioactive ruthenium isotopes]]. In the West, the glass is normally a [[borosilicate glass]] (similar to [[Pyrex]]), while in the former [[Soviet Union]] it is normal to use a [[phosphate glass]].<ref>{{cite journal |doi=10.1007/s11661-010-0525-7 |title=Glassy Wasteforms for Nuclear Waste Immobilization |journal=Metallurgical and Materials Transactions A |volume=42 |issue=4 |pages=837 |year=2010 |last1=Ojovan |first1=Michael I. |last2=Lee |first2=William E. |bibcode=2011MMTA...42..837O |doi-access=free}}</ref> The amount of fission products in the glass must be limited because some ([[palladium]], the other Pt group metals, and [[tellurium]]) tend to form metallic phases which separate from the glass. Bulk vitrification uses electrodes to melt soil and wastes, which are then buried underground.<ref name="Waste">{{cite web |title=Waste Form Release Calculations for the 2005 Integrated Disposal Facility Performance Assessment |work=PNNL-15198 |publisher=Pacific Northwest National Laboratory |date=July 2005 |url=http://www.pnl.gov/main/publications/external/technical_reports/PNNL-15198.pdf |access-date=2006-11-08 |url-status=live |archive-url=https://web.archive.org/web/20061005165228/http://www.pnl.gov/main/publications/external/technical_reports/PNNL-15198.pdf |archive-date=2006-10-05}}</ref> In Germany, a vitrification plant is treating the waste from a small demonstration reprocessing plant which has since been closed.<ref name=council /><ref>{{cite book |author1=Hensing |first=I. |title=Economic Comparison of Nuclear Fuel Cycle Options |author2=Schultz |first2=W. |publisher=Energiewirtschaftlichen Instituts |year=1995 |location=Cologne, Germany |name-list-style=amp}}</ref>