Iterative Performance Assessment for the Greater Confinement Disposal Facilities: Preliminary Results of Round Two

Abstract

The Department of Energy's Nevada Operations Office has disposed of a small quantity of transuranic waste at the Greater Confinement Disposal (GCD) facility in Area 5 of the Nevada Test Site. The Environmental Protection Agency standards for disposal of transuranic waste (40 CFR 191) require that a performance assessment be conducted and an iterative approach has been adopted. This approach consists of using performance assessment results to guide the collection of site characterization data, and in turn, new site characterization data is incorporated into each successive iteration of the performance assessment. The results of the first iteration indicated that the GCD site should be able to comply with 40 CFR 191. This paper presents results of the second iteration based on results from site-specific environmental tracer studies. These studies indicate significantly lower recharge values then those used in the first performance assessment iteration. For performance assessment these results imply that the downward ground-water advection pathway may be negligible, and therefore, the upward liquid diffusion pathway becomes more significant. The models and the model parameters that were used to simulate this upward pathway have been refined. The preliminary results from these models still indicate that the GCD facility should be able to comply with the Containment Requirements in 40 CFR 191.