PNNL

Abstract

The design contractor for Hanford’s Waste Treatment and Immobilization Plant, which the U.S. Department of Energy plans to use for immobilizing Hanford’s high-level radioactive waste, chose reduced silver mordenite as the sorbent technology for controlling gaseous radioiodine releases from the plant. Silver land disposal is regulated by the U.S. Environmental Protection Agency (EPA) and Washington State. In support of the design contractor’s need to identify and develop a regulation-compliant disposal form for the spent silver mordenite, Pacific Northwest National Laboratory evaluated grouted potential and reference waste forms for spent reduced silver mordenite using EPA’s Toxic Characteristic Leach Procedure. Solidification and solidification using Portland III cement proved effective for iodine-loaded reduced silver mordenite at a 25-wt% waste loading. To achieve success with other silver mordenites having a more soluble silver form, it was necessary to add calcium iodide, a soluble iodide chemically compatible with the Portland Type III cement used for grouting to reduce the solubility of the silver with the low solubility product of silver iodide.