EFRT M-12 Issue Resolution: Solids Washing

Baldwin, David L. ; Schonewill, Philip P. ; Toth, James J. ; Huckaby, James L. ; Eslinger, Paul W. ; Hanson, Brady D. ; Kurath, Dean E. ; Minette, Michael J.

Pacific Northwest National Laboratory (U.S.)

关键词: Leaching;    Radioactive Waste Processing;    Radioactive Waste Facilities;    Washing;    Performance Testing;   

DOI  :  10.2172/963840
RP-ID  :  PNNL-18499
RP-ID  :  AC05-76RL01830
RP-ID  :  963840

美国|英语

来源: UNT Digital Library

【 摘 要 】

Pacific Northwest National Laboratory (PNNL) has been tasked by Bechtel National Inc. (BNI) on the River Protection Project-Hanford Tank Waste Treatment and Immobilization Plant (RPP-WTP) project to perform research and development activities to resolve technical issues identified for the Pretreatment Facility (PTF). The Pretreatment Engineering Platform (PEP) was designed, constructed, and operated as part of a plan to respond to issue M12, “Undemonstrated Leaching Processes.” The PEP is a 1/4.5-scale test platform designed to simulate the WTP pretreatment caustic leaching, oxidative leaching, ultrafiltration solids concentration, and slurry washing processes. The PEP replicates the WTP leaching processes using prototypic equipment and control strategies. Two operating scenarios were evaluated for the ultrafiltration process (UFP) and leaching operations. The first scenario has caustic leaching performed in the UFP-VSL-T01A/B ultrafiltration feed vessels, identified as Integrated Test A. The second scenario has caustic leaching conducted in the UFP-VSL-T02A ultrafiltration feed preparation vessel, identified as Integrated Test B. Washing operations in PEP Integrated Tests A and B were conducted successfully as per the approved run sheets. However, various minor instrumental problems occurred, and some of the process conditions specified in the run sheet were not met during the wash operations, such as filter-loop flow-rate targets not being met. Five analytes were selected based on full solubility and monitored in the post-caustic-leach wash as successful indicators of washing efficiency. These were aluminum, sulfate, nitrate, nitrite, and free hydroxide. Other analytes, including sodium, oxalate, phosphate, and total dissolved solids, showed indications of changing solubility; therefore, they were unsuitable for monitoring washing efficiency. In the post-oxidative-leach wash, two analytes with full solubility were selected as suitable indicators of washing efficiency. These were chromium and oxalate. Other analytes, including sodium, manganese, nitrate, and total dissolved solids, showed indications of changing solubility; therefore, they were unsuitable for monitoring washing efficiency. An overall wash efficiency of 1.00 ± 0.01 was determined for the post-caustic-leach wash. The overall wash efficiency for the post-oxidative-leach wash was determined also to be 0.99 ± 0.01. These wash efficiencies were based on the weighted least squares fit of the full data set for each applicable analyte and are an average of several analytes traced during the washing steps in Integrated Tests A and B. Incremental wash efficiencies as a function of wash step were also given to provide an indication of the variability during the washing process. Chemical tracer tests resulted in the major conclusion that nearly complete mixing was achieved between 2 and 4 minutes after tracer injection. With inconsistent filter-loop flow rates and other mixing parameters, future process conditions should be taken into account during further interpretation of these data. A slight decrease of 8 to 10% in the tracer concentration between 4 and 60 minutes suggests that there was a relatively small unmixed region that mixed over the course of the 1-hour test. The IW batch time interval, defined as the duration between the start of the IW wash injection for a batch to the start for the IW wash injection for the subsequent batch, was often close to or less than the required 4-minute mixing time indicated by the tracer tests. Such short batch durations did not appear to have significantly impacted the washing efficiencies.