Assessment of Effectiveness of Geologic Isolation Systems SYSTEMS APPROXIMATE SIMULATOR: FISCAL YEAR 1982 PROGRESS

The ISystemsl task of the Assessment of Effectiveness of Geologic Isolation Systems (AEGIS) Program is developing a Systems Approximate Simulator (SAS); a computer code of low-level technical complexity that incorporates the most significant waste-package, repository, and site processes affecting geologic nuclear waste isolation. This report discusses the AEGIS 1982 fiscal year progress toward building a SAS. A computer code, SAS(82), has been developed as the site module of the SAS development effort. The SAS(82) is an efficient and accurate simulator of one-dimensional radionuclide transport. Features of the SAS(82) are direct (Monte Carlo) simulation, linear decay and sorption models, spatially and temporally varying hydrologic and geochemical variables, general travel-time distributions (possibly non-Fickian), and multinuclide release. The SAS(82) was used to simulate radionuclide transport from a nuclear waste repository located within the Hanford basalts. A {sup 99}Tc analysis along a thermally influenced path through the Grande Ronde Formation demonstrated the complexity of modeling near-field transport. Perturbed hydrologic conditions corresponding to "Hanford Basalt Geologic Simulation Model" results (Petrie et al. 1981) were evaluated, using the SAS(82). Future work will include the development of SAS waste-package and repository modules as simplified process models become available. The SAS may eventually be used as the basis for parametric sensitivity and uncertainty studies for the entire geologic nuclear waste isolation system