Iterative Performance Assessment for the Greater Confinement Disposal Facilities: Preliminary Results of Round Two
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ITERATIVE PERFORMANCE ASSESSMENT FOR THE GREATER CONFINEMENT DISPOSAL FACILITIES: PRELIMINARY RESULTS OF ROUND TWO* NATALIE E. OLAGUEa, T.A. BAERb, and S.H. CONRADa
aSandia National Laboratories, Department 6331, Albuquerque, NM 87185 b GRAM Inc., 8500 Menaul Blvd., Suite B370, Albuquerque, NM 87112 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. BACKGROUND
Greater Confinement Disposal (GCD) Facility The Department of Energy's Nevada Operations Office (DOE/NV) has disposed of a small quantity of transuranic (TRU) radioactive waste at the GCD facility in Area 5 of the Nevada Test Site (NTS). The GCD site is located in Frenchmen Flat basin, in the southern part of the Basin and Range geologic province. The climate at Frenchmen Flat is very arid and vegetation is sparse. Beneath the site, the basin is filled with alluvium to a depth of 1500 feet and the water table is located at a depth of 770 feet. The GCD facility consists of several 120 foot boreholes, 10 - 12 feet in diameter, where waste is emplaced in the bottom 50 feet and the remaining 70 feet is back-filled with sifted native material. The facility is called "greater confinement" because the disposal depth is deeper than shallow trenches that are used to dispose of low-level radioactive waste at the NTS. 40 CFR 191 The Environmental Protection Agency's regulation for the management and disposal of
"This work performed for the U.S. Department of Energy under contract DE-AC0476DP00789. Mat. Res. Soc. Symp. Proc. Vol. 294. c1993 Materials Research Society
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spent nuclear fuel, high-level and TRU radioactive waste is 40 CFR 191'"*. This regulation applies to the GCD site because TRU waste is disposed of in t
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