CHARACTERIZATION, COMMINUTION, LEACHING AND ENCAPSULATION METHODS OF SURROGATE CEMENTED RADIOACTIVE WASTES
3rd Canadian Nuclear Waste Management Decommissioning and Environmental Restoration - 2016 Sept. 11-14


Presented at:
3rd Canadian Nuclear Waste Management Decommissioning and Environmental Restoration
2016 Sept. 11-14
Location:
Ottawa, Canada
Session Title:
Session W3: Waste Characterization

Authors:
J.F. Fiset (CanmetMINING, Natural Resources Canada)
N. Reynier (CanmetMINING, Natural Resources Canada)
A. Bilodeau (CanmetMINING, Natural Resources Canada)
M. Bilodeau (CanmetMINING, Natural Resources Canada)
F. Kassimi (CanmetMINING, Natural Resources Canada)
R. Lastra (CanmetMINING, Natural Resources Canada)
M. Chapman (Canadian Nuclear Laboratories)
  

Abstract

The medical isotope production at Chalk River Laboratory involves the dissolution of irradiated targets prior to extraction of Mo-99. This process generates a liquid that is cemented in a container and transferred to an outdoor waste-management facility for intermediate storage. Over the past decades, AECL has produced a large number of containers of cemented radioactive waste that are in storage, and must develop a process to convert this material to a form suitable for permanent storage. Two methods were investigated: recovery of element of interests (Hg, Cs and U) and further cement encapsulation.

First, a proper comminution strategy was developed. Among the numerous technologies that were evaluated for unmolding, crushing and grinding the surrogate cemented waste, the high pressure water jet was selected for unmolding and coarse crushing; whereas the attrition mill was selected for fine grinding.

The composition of the surrogated cemented radioactive waste poses significant impediments to the extraction and recovery of uranium using conventional technology. Characterization of the surrogate cemented radioactive waste revealed that the uranium is precipitated as calcium uranate. Mercury exists as a combination of mercury oxide, elementary mercury, and with ageing, mercury sulphide is produced.

This research proved that the use of sulfuric acid with salts allows the complete dissolution of U, Cs and Hg by a combination of acidification, complexation and oxidation. Mercury and cesium were recovered selectively with removal efficiencies reaching 99% respectively. A recovery of 98% for the U in sulfuric liquor was achieved using the chelating resin and high purity yellow cake was obtained by precipitation.

Macro and micro encapsulation formulations were also successfully developed for long term storage. The element recovery process offers the possibility of various waste management options whereas encapsulation methods offer a long term alternative to manage this type of waste.

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