Economic Feasibility of Electrochemical Caustic Recycling at the Hanford Site

Abstract

This report contains a review of potential cost benefits of NaSICON Ceramic membranes for the separation of sodium from Hanford tank waste. The primary application is for caustic recycle to the Waste Treatment and Immobilization Plant (WTP) pretreatment leaching operation. The report includes a description of the waste, the benefits and costs for a caustic-recycle facility, and Monte Carlo results obtained from a model of these costs and benefits. The use of existing cost information has been limited to publicly available sources. This study is intended to be an initial evaluation of the economic feasibility of a caustic recycle facility based on NaSICON technology. The current pretreatment flowsheet indicates that approximately 6,500 metric tons (MT) of Na will be added to the tank waste, primarily for removing Al from the high-level waste (HLW) sludge (Kirkbride et al. 2007). An assessment (Alexander et al. 2004) of the pretreatment flowsheet, equilibrium chemistry, and laboratory results indicates that the quantity of Na required for sludge leaching will increase by 6,000 to 12,000 MT in order to dissolve sufficient Al from the tank-waste sludge material to maintain the number of HLW canisters produced at 9,400 canisters as defined in the Office of River Protection (ORP) System Plan (Certa 2003). This additional Na will significantly increase the volume of LAW glass and extend the processing time of the Waste Treatment and Immobilization Plant (WTP). Future estimates on sodium requirements for caustic leaching are expected to significantly exceed the 12,000-MT value and approach 40,000-MT of total sodium addition for leaching (Gilbert, 2007). The cost benefit for caustic recycling is assumed to consist of four major contributions: 1) the cost savings realized by not producing additional immobilized low-activity waste (ILAW) glass, 2) caustic recycle capital investment, 3) caustic recycle operating and maintenance costs, and 4) research and technology costs needed to deploy the technology. In estimating costs for each of these components, several parameters are used as inputs. Due to uncertainty in assuming a singular value for each of these parameters, a range of possible values is assumed. A Monte Carlo simulation is then performed where the range of these parameters is exercised, and the resulting range of cost benefits is determined.