INEEL Summary on Calcination

Irradiated nuclear fuel reprocessing to recover 235U and 80Kr began at the INEEL in 1953. The resulting acidic high-level liquid radioactive waste (HLW) was stored in stainless steel tanks in underground concrete vaults. A fluidized-bed calcination process was developed during the 1950s to form a granular calcine solid from the acidic HLW with a seven-fold volume reduction. An engineering-scale demonstration, the Waste Calcining Facility (WCF) was constructed and operated in 1963. After the successful demonstration of the process, the WCF was continued as a production facility through 1981, Calcining 15,000 m3 of HLW to 2,160 m3 of calcine.1 The New Waste Calcining Facility (NWCF) was designed and constructed based on the operating experience of the WCF, and began operation in 1982. With a rated capacity of 3,000 gallons/day, the NWCF continued waste processing operations through May of 2000, resulting in an additional 2,226 m3 of calcine (total current inventory of 4,386 m3).2 During waste processing at the NWCF, sodium-bearing waste (SBW) from decontamination activities was blended with HLW to minimize alkali (sodium and potassium) concentrations in the calciner feed solution. This was necessary due to the propensity of sodium and potassium nitrates to melt in the calciner, causing the bed to agglomerate and interfere with fluidization. However, near the end of HLW processing, work was initiated to modify the calcination process to treat SBW directly, blending it with chemical additives such as aluminum nitrate rather than lower alkali content HLW liquids. The result of this development effort was to increase the operating temperature of the calciner from 500 C to 600 C. The 600 C SBW flow sheet was successfully demonstrated at the NWCF during two separate trials during 1999 and 2000.3, 4 The conclusion from these demonstrations was that operating the existing NWCF at 600 C is a viable method for solidifying SBW, and this concept is currently being evaluated as one option for preparing the SBW for disposal. To restart the NWCF for SBW processing, applicable environmental waste processing and/or air permits will be required. It is anticipated that the NWCF will be regulated as an incinerator; thus, compliance with maximum achievable control technology (MACT) emission limits will be required. To meet these stringent standards, an upgrade to the off-gas treatment train will be required. Specifically, emission of CO, total hydrocarbons (THC), and mercury must be mitigated. In addition, NOx abatement is necessary to eliminate interferences with the instrumentation required for air monitoring to demonstrate compliance.