PNNL

Abstract

The U. S. Department of Energy is tasked with the disposition of high-level radioactive wastes stored at the Hanford Site. The liquid waste fraction, currently stored in underground storage tanks, is to be vitrified following specific pretreatment processing, separating the waste into a relatively small-volume high-activity waste fraction (Cs-rich), and a large-volume low-activity waste (LAW) fraction (Cs-depleted). Cesium removal will be conducted using ion exchange technology at the River Protection Project-Waste Treatment Plant (RPP-WTP). The current pretreatment flowsheet includes the use of SuperLigâ 644 (SL-644) for Cs removal, which is a cesium-selective, elutable, organic ion exchange resin developed by IBC Advanced Technologies, Inc., American Fork, UT. Eight process test cycles were conducted on a small-scale dual-column ion exchange system containing the SL-644 resin with Hanford tank waste (one cycle with simulant waste and seven cycles with actual Hanford tank waste). After testing, the SL-644 was removed from the columns and analyzed for most metals and radionuclides pertinent to land disposal requirements (LDR) designation. The spent resin contained significant quantities of Resource Conservation Recrovery Act (RCRA)-listed metals: Ag and Cr. One of the two resin beds exceeded the transuranic waste limit (100 nCi/g alpha) for LDR. The final Cs isotopic distribution in the spent resin was weighted heavily with residual stable Cs from the initial simulant processing test.