Understanding Potential Release Mechanisms of Volatile Ruthenium During the Vitrification of High Level Waste

Abstract

In the U.K., High Level Waste from reprocessing operations is vitrified at the Sellafield Waste Vitrification Plant (WVP). A small number of the nuclides present in the waste have the potential to volatilize during vitrification. In order to prevent release of any radionuclides to the environment it is important to understand the mechanisms by which volatilization may occur and to have suitable controls in place. One element of particular concern is ruthenium, formed during the fission of nuclear fuel, which has the potential to form gaseous species such as RuO4 during the vitrification process and whose behavior must therefore be understood in order to underpin the safe operation of WVP.

Behaviour of ruthenium in nitric media (HLLW) in reprocessing plants: a review and some perspectives

“…According to Wilson [21], RuÜ4(g) would be observed only when the distillation of nitric acid solution is carried out in the absence of air (N2 atmosphere) whereas in air atmosphere, he claimed that other species would be present without being able to identify them, consistently with Fletcher's experiments [20] performed with a 15M HNÜ3 solution exposed to air. It is possible that the presence of NÜx in the gas phase can also contribute to the conversion of RuÜ4(g) [22] [29] [53] [54]. In fact, under the tested conditions (393 K), it is possible to observe volatile nitrosyl ruthenium-based compounds, in addition to recombined ruthenium in the condensates, in the presence of HNÜ3, H2Ü and NÜx [55].…”

Radioactive Semivolatiles in Nuclear Fuel Reprocessing

“…Ruthenium forms volatile oxides at vitrification temperatures (Anderson et al 1994, Bancroft et al 1961, Cobb and Hrma 1991, Demin et al 1995, Gong et al 2009, Gosse et al 2010, Gruenewald et al 2008, Jouan 1969, Kelley 1975, Krause and Luckschieter 1991, Ortins De Bettencourt 1969a, 1969b, Weisenburger and Weiss 1980, Wilds 1979 and are readily treated (Lawson et al 2010, Oh et al 1997, Shin and Park 2003.…”