Plutonium hydrous oxide /Solubility /Hanford high-level waste / NaOH (aq) SummaryThe solubility of Pu(IV) hydrous oxide, PuO, · χ Η, Ο, in airequilibrated synthetic Hanford high-level waste solutions was determined as a function of NaOH, NaAl(OH)", NaN0 3 , NaNO,, and Na, C0 3 concentrations. The solubility was found to increase with the square of the NaOH chemical activity. The components NaN0 3 and NaNO, increased Pu0 2 · χ Η, Ο solubility by increasing NaOH activity. Aluminate increased solubility by the apparent formation of a 1: 1 complex with the dissolved plutonium species while carbonate increased solubility by forming a 1 : 2 plutonium-carbonate complex. Spectral, electrochemical, and solubility evidence points to the existence of hydroxidecomplexed Pu (V) dissolved species.

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This report examines the chemical disposition of plutonium (Pu) in Hanford Site tank wastes, by itself and in its observed and potential interactions with the neutron absorbers aluminum (Al), cadmium (Cd), chromium (Cr), iron (Fe), manganese (Mn), nickel (Ni), and sodium (Na). Consideration also is given to the interactions of plutonium with uranium (U). No consideration of the disposition of uranium itself as an element with fissile isotopes is considered except tangentially with respect to its interaction as an absorber for plutonium. into plutonium and absorber element behavior under alkaline and plant process conditions. Three external reviewers, Scott Barney, independent consultant, and David Hobbs and Tracy Rudisill of the Savannah River National Laboratory examined the near-complete document and provided insightful, germane, and complementary comments. We thank Reid Peterson (PNNL) for project oversight and Lisa Staudinger (PNNL) for her attention and care in formatting and technically editing this manuscript. Finally, we gratefully acknowledge the fundamental and applied research into the chemistry of plutonium and other transuranic elements in alkaline media conducted by scientists and technicians of the Institute of Physical Chemistry of the Russian Academy of Sciences. In particular we note the scientific leadership of Professors

RHO-REST -1 P WER Effects of H anford High-Level ft W aste Com ponents on Sorption o f Cobalt, S tro ntium , N eptunium , Plutonium , and A m ericium on H anford Sedim ents

Test Materials and Description The sludge used for the gas generation testing was taken from the KE Basin floor and fuel canisters in March and April 1999 by Duke Engineering & Services Hanford. A consolidated sampling technique was employed for collecting the material (i.e., sludge from several locations was combined to form "consolidated samples"). Three sludge samples were used: fuel canister sludge (KC-2/3); floor sludge collected from between slotted fuel canisters containing highly damaged fuel (KC-4); and floor sludge collected away from fuel canisters and away from areas known to contain high concentrations of organic ion exchange resin (KC-5). The canister sludge used in this testing (KC-2/3) was prepared by combining two consolidated sludge samples (i.e., KC-2, collected from canisters containing highly damaged fuel, and KC-3, collected from canisters containing moderately damaged fuel). Portions of these samples were sieved to separate particles greater than or "plus" 250 µm (P250) from particles less than or "minus" 250 µm (M250). This separation was made to mimic the separation operations that are planned for the retrieval of certain K Basin sludge types and to gain a better understanding of how uranium metal is distributed in the sludge. [The separation point for certain K Basin sludge types was subsequently changed from 250 µm to 500 µm (Pearce and Klimper 2000).] Fine uranium metal particles have a high surface area and will react rapidly. Larger uranium metal particles will react at a slower rate, since their surface area per unit mass of sludge is lower. For the testing described here, sludge samples were placed into four large-scale vessels (850 ml) and eight small-scale reaction vessels (30 ml). The gas pressure in the vessels was monitored continuously, and gas samples were collected intermittently and analyzed via mass spectrometry. The large-scale testing was initiated in August 1999, and three tests continued through June 2000. One large-scale test is still underway, and will continue into FY2001. These test vessels contained 70 to 440 grams of settled sludge held at ambient hot cell temperature (~32ºC). The large-scale-test conditions are expected to be prototypical of those that will be experienced during long-term storage of the sludge at T Plant (i.e., largescale tests serve as a mock-up for prolonged T Plant storage). The small-scale tests, which were conducted with about 15 grams settled sludge each, were initiated on October 6, 1999, and completed in June 2000. The small-scale tests were conducted at elevated temperatures (six tests at 80ºC, one at 60ºC, and one at 40ºC) to accelerate the reactions and provide conclusive gas generation data within a reasonable testing period. The temperature in all of the small-scale test vessels was increased to 95°C for a period at the end of the tests to force completion of the reactions. The table below shows the test matrix. Experimental Matrix for Large-and Small-Scale Gas Generation Tests KC-2/3 KC-4 KC-5 Temperature and Test Scale M250 µm P2...