Phase Chemistry of Tank Sludge Residual Components

We are attempting to understand the solid phase chemistry of the high level nuclear waste (HLW) stored in tanks at Hanford. Because this waste is compositionally complex, our approach is to study experimentally the aging dynamics of simplified systems whose bulk chemistry approximates that of the tank sludges. After a basic understanding of these dynamics has been attained we plan to increase the compositional complexities one component at a time, in order to assess the influence of each component. Results will allow for reliable prediction of sludge phase chemistry over a range of sludge compositions. Iron and aluminum comprise the bulk of most HLW sludges, so we chose to begin by studying the behavior of iron-aluminum systems. Fe/Al ratios were chosen to approximate those relevant to the solutions that produced the sludge. Aluminum and iron concentrations in the various process fluids are summarized and compared to our experimental starting solutions in Table 1 (process solution data from Krumhansl, personal communication, 1998). Our low aluminum experiments serve as direct analogues to both Bismuth Phosphate and low-Fe PUREX waste. Cornell and Giovanoli (1985) found that, in a pure iron system at 70 C, a 10-fold or even 50-fold increase in suspension concentration had only very slight effects on the final aged products. Since our experiments have similar Al/Fe ratios to some high Fe-PUREX process solutions our results are probably relevant to those wastes as well. However, our results may not apply to the high-Fe and high-Al PUREX wastes, as discussed below. The high Al experiments were designed specifically to simulate REDOX waste