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The Basalt Waste Isolation Project (Rockwell Hanford Operations) is conducting a safety assessment of nuclear waste storage in a repository on the Hanford Site. Pacific Northwest Laboratory, in support of the assessment effort, is generating radionuclide distribution coefficient data between simulated groundwaters and basalts and their secondary mineral products under the range of physicochemical conditions expected in a repository in basalt. Experimental radionuclide distribution coefficients were determined for crushed Pomona, Flow E, and Umtanum basalts at 23/sup 0/, 60/sup 0/, 150/sup 0/, and 300/sup 0/C at both normal oxygen partial pressure (approx. 0.2 atm) and lower oxygen partial pressure (approx. 10/sup -7/ atm), using a static technique. Little or no changes in distribution coefficients were noted for selenium, uranium, technetium, neptunium, or plutonium over the oxygen partial pressure range noted above. Sodium dithionite and hydrazine are now under study as system additives to lower Eh to -0.3 to -0.5 V, the conditions expected to prevail in the closed repository in basalt. Temperature change effects on most radionuclide distribution coefficient (Kd) values over the 23/sup 0/ to 300/sup 0/C range were major with the exception of iodine and technetium, neither of which were appreciably sorbed at normal to approx. 10/sup -7/more » atm oxygen partial pressure. The effect of radionuclide concentration on the Kd value was shown graphically for cesium and strontium over a range of from 1 x 10/sup -10/ or 10/sup -12/ to 1 x 10/sup -4/M. Initial work was begun on Kd values obtained under controlled Eh and pH conditions to simulate specific oxygen partial pressure and pH conditions expected to occur in the repository environment.« less |
