In the meantime, WHC is using the rotary mode trucks in push mode to sample tanks believed to contain soft wastes. WHC discussed progress in correlating analytical data from tank samples to historical models. WHC has found that tank wastes are systematically richer in iron, chromium, calcium, and silicon than predicted by models. WHC is working to find the sources of these materials. For example, it appears that corrosion of process equipment is the source of some of the excess iron and chromium.
Organics continue to be poorly predicted by historical models.
The Los Alamos National Laboratory is attempting to develop a method to better predict the location of organic materials in the tank farms. According to a trade study performed by WHC, acid dissolution processing achieves a 12 to 1 reduction in the HLW volume over ESW, but it presents a higher technical risk because of reliance on undemonstrated technologies. Although ESW is simpler than acid dissolution, the ESW option is not without technical uncertainties. ESW has not been demonstrated on a pilot or large scale with Hanford tank waste. While this test will provide pertinent data on mixing and settling phenomena in a large tank, it does not involve the more critical step of caustic leaching.