Solidification and stabilization of silver mordenite used to control radioiodine emissions from Hanford’s Waste Treatment Plant

•Hanford Waste Treatment Plant to use reduced silver mordenite to control radioiodine.•Used reduced silver mordenite will contain silver forms of chlorine and iodine.•Used silver mordenite requires treatment to satisfy silver-disposal requirements.•Simple grouting of silver mordenites does not satisfy silver disposal requirements.•Calcium iodide-modified grout is a compliant disposal form for silver mordenite.

The United States Department of Energy is building the Hanford Waste Treatment and Immobilization Plant (WTP) in south-central Washington State to immobilize a portion of the stored high-level radioactive wastes generated by decades of producing nuclear defense materials. To comply with United States Environmental Protection Agency (EPA) and Washington State air emission regulations, the WTP is planning to use reduced silver mordenite to control releases of any volatilized waste constituent radioiodine (129I t1/2 = 1.7 × 107 a). Because the EPA and Washington State have designated silver as a hazardous or dangerous waste constituent, the disposal form for the waste reduced silver mordenite must comply with their land disposal regulations. We used the mandated EPA Toxic Characteristic Leach Procedure to evaluate and qualify a disposal form for the waste reduced-silver mordenite. Our development effort resulted in a regulation-compliant disposal form which used cast American Society for Testing and Materials (ASTM) Portland Type III cement modified to include calcium iodide to solidify and stabilize the reduced-silver mordenite and control silver release to regulatory levels.