Abstract
Problems with pipeline plugs at Hanford have occurred throughout its tank farm system. Most cross-site transfer lines at Hanford are no longer functional due to these plugs. Waste transfers frequently led to partial line plugs, resulting in substantial amounts of water being added to the tank system in an attempt to free the lines. In response to these plugs, the Hanford tank farm developed waste acceptance criteria that a waste must pass before it can be transferred (Shekarriz et al., 1997). The criteria, which include physical properties such as viscosity, specific gravity, and percent solids, are based primarily on past operational experience. Unfortunately, the chemistry of the waste solutions was not included in the criteria even though the tank farm operators are fully aware of its importance. Pipeline plugs have also occurred during relatively short waste transfers at Hanford. In FY 2000, the effort to saltwell pump 50,000 gal of filtered waste from tank U-103 to tank SY-102 was delayed for several weeks due to a plugged pipeline. Attempts to locate the plug(s) determined that it had occurred in the 02-A flex and that other plugs were possible in each of the SY-farm flexes. Modifications such as larger flex jumpers and additional heat tracing were made to the transfer system. The plug was probably attributable to a reduction in the temperature of the waste in the pipeline. The waste in tank U-103 was approximately 30 C prior to the transfer. During tests on actual waste from tank U-103 (Herting, 1999), trisodium phosphate solids were observed at temperatures as high as 20 C after a 50% dilution with water. Therefore, the following precautions (Herting, 1999) were recommended during the saltwell pumping of tank U-103. First, the tank waste should not be heated prior to the transfer. Second, the waste should not be permitted to cool during the transfer. Third, the waste should be kept moving during the transfer. A previous Tanks Focus Area (TFA) study (Hunt et al., 1999) clearly demonstrated the need to maintain the temperature of the waste in this range. Even small reductions in the temperature of simulated wastes from 35 to 30 C and from 30 to 25 C led to high-viscosity solids that could easily plug a pipeline.
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Published on 01/01/2001
Volume 2001, 2001
DOI: 10.2172/777667
Licence: CC BY-NC-SA license
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