INTERNATIONAL PROGRAM: SUMMARY REPORT ON THE PROPERTIES OF CEMENTITIOUS WASTE FORMS
This report provides a summary of the results on the properties of cementitious waste forms obtained as part of the International Program. In particular, this report focuses on the results of Task 4 of the Program that was initially entitled ''Improved Retention of Key Contaminants of Concern in Low Temperature Immobilized Waste Forms''. Task 4 was a joint program between Khlopin Radium Institute and the Savannah River National Laboratory. The task evolved during this period into a study of cementitious waste forms with an expanded scope that included heat of hydration and fate and transport modeling. This report provides the results for Task 4 of the International Program as of the end of FY06 at which time funding for Task 4 was discontinued due to the needs of higher priority tasks within the International Program. Consequently, some of the subtasks were only partially completed, but it was considered important to capture the results up to this point in time. Therefore, this report serves as the closeout report for Task 4. The degree of immobilization of Tc-99 within the Saltstone waste form was measured through monolithic and crushed grout leaching tests. An effective diffusion coefficient of 4.8 x 10{sup -12} (Leach Index of 11.4) was measured using the ANSI/ANS-16.1 protocol which is comparable with values obtained for tank closure grouts using a dilute salt solution. The leaching results show that, in the presence of concentrated salt solutions such as those that will be processed at the Saltstone Production Facility, blast furnace slag can effectively reduce pertechnetate to the immobile +4 oxidation state. Leaching tests were also initiated to determine the degree of immobilization of selenium in the Saltstone waste form. Results were obtained for the upper bound of projected selenium concentration ({approx}5 x 10{sup -3} M) in the salt solution that will be treated at Saltstone. The ANSI/ANS 16.1 leaching tests provided a value for the effective diffusivity of {approx}5 x 10{sup -9} cm{sup 2}/sec and a corresponding leaching index of {approx}8.2. Leaching tests at the lower bound of concentration and the leaching tests to determine the impact of redox (selenium exists in two oxidation states, selenite (SeO{sub 3}{sup -2}) and selenate (SeO{sub 4}{sup -2})) on Se-79 release were not completed due to lack of funding. The heat of hydration of a Saltstone mix limits the processing rate at the Saltstone Production Facility. Therefore, reduction in the heat of hydration of a Saltstone formulation that still complies with the remaining property requirements would provide for a greater rate of production. Initial testing for this task was completed. There was good agreement between the isothermal measurements of heat of hydration performed as part of this task with previous measurements of heat of hydration of Saltstone obtained adiabatically over the same 80 hour time period. The slightly higher heat of hydration per gram of cementitious material measured adiabatically can be explained by the higher temperatures achieved during the adiabatic measurements. The isothermal measurements reveal additional details of the heat generation process that were not evident in the adiabatic measurements. An initial heat release in the first minutes was observed isothermally. A second peak at about 5 hours was also observed isothermally that was not detected adiabatically. The major heat releases in the 10 to 30 hour period were observed by both techniques but at slightly different times and ratios of the two major peaks that comprise that region. The degree of reaction was calculated from these measurements based upon the value assigned to maximum hydration. Using the Schmidt method, the degree of reaction after 80 hours was 36% complete by isothermal calorimetry and 46% complete by adiabatic calorimetry. Using the theoretical maximum wherein the fly ash and slag are hydraulically equivalent to the portland cement, the degree of reaction after 80 hours was 20% complete by isothermal calorimetry and 25% complete by adiabatic calorimetry. This time dependence of the heat of hydration is used at SRNL as input into a model that predicts the temperature rise within the Saltstone vaults. The transport of radionuclides and oxygen within the Saltstone waste form and surrounding concrete vault were calculated using the PORFLOW{trademark} code (Performance Assessment calculations at Savannah River Site also use this commercially available code). The Tc-99 effective diffusivity, obtained through leaching tests, was used as input into the code to predict release of Tc-99 from the waste form and from the vault as a function of time (10,000 year compliance period). A sensitivity study was performed to determine the Tc-99 release as a function of changes to the hydraulic conductivity and effective diffusivity of Tc-99. These results are included in this report.
- Research Organization:
- Savannah River Site (SRS), Aiken, SC (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- DE-AC09-96SR18500
- OSTI ID:
- 902183
- Report Number(s):
- WSRC-STI-2007-00056; TRN: US0702912
- Country of Publication:
- United States
- Language:
- English
Similar Records
PRETREATMENT OF TC CONTAINING WASTE AND ITS EFFECT ON 99 TC LEACHING FROM GROUTS
HEAT OF HYDRATION OF SALTSTONE MIXES-MEASUREMENT BY ISOTHERMAL CALORIMETRY