Plan for waste package environment for NNWSI [Nevada Nuclear Waste Storage Investigations]

The purpose and objective of the Waste Package Environment task is to establish and characterize the environmental processes affecting the near-field repository host rock after waste package emplacement. These processes, which reflect the perturbation induces in the environment by engineering effects and by the waste package decay heat and radiation, will influence chemical, mineralogical and hydrological features of the environment. The thermal and radiation output of the waste packages will change with time, resulting in an environment in which the chemical, mineralogical and physical attributes may also change through time. To assure that waste package design considerations reflect the characteristics of this evolving environment, it is necessary to determine the range of conditions that may develop in the pre- and post-emplacement waste package environment. To assure that the emplacement configurations do not compromise the lifetime of the repository or the waste packages, the design of the emplacement configuration must also consider the environmental features. Recognition of these requirements resulted in the development of the issue an information needs. 20 refs

Chemical modeling of backfill composed of quartz sand, lime and an Fe-phase

The area adjacent to the waste package is an important component of the engineered barrier system in a high level radioactive waste repository. The combination of lime, quartz sand, and a phase containing reduced iron is investigated whether it can achieve reduction of oxygen in the waste emplacement drift (thereby reducin corrosion rates) and increase the pH. The simulations conducted to date have examined the following backfill options: Fe metal only, Fe metal and lime, and iron metal/lime/quartz sand in equal volume ratios. Each option was simulated under two environments: limited and unlimited air exchange with the atmosphere. Results suggest that the most important variable during the process of chemical conditioning is the amount of air exchange that occurs in the emplacement drift. The desired chemical conditioing (both oxidation potential and pH) will be far less effective in an emplacement that experiences an unlimited exchange of air with the atmosphere

Plan for waste package environment for NNWSI [Nevada Nuclear Waste Storage Investigations]

The purpose and objective of the Waste Package Environment task is to establish and characterize the environmental processes affecting the near-field repository host rock after waste package emplacement. These processes, which reflect the perturbation induces in the environment by engineering effects and by the waste package decay heat and radiation, will influence chemical, mineralogical and hydrological features of the environment. The thermal and radiation output of the waste packages will change with time, resulting in an environment in which the chemical, mineralogical and physical attributes may also change through time. To assure that waste package design considerations reflect the characteristics of this evolving environment, it is necessary to determine the range of conditions that may develop in the pre- and post-emplacement waste package environment. To assure that the emplacement configurations do not compromise the lifetime of the repository or the waste packages, the design of the emplacement configuration must also consider the environmental features. Recognition of these requirements resulted in the development of the issue an information needs. 20 refs

Reference waste package environment report

One of three candidate repository sites for high-level radioactive waste packages is located at Yucca Mountain, Nevada, in rhyolitic tuff 700 to 1400 ft above the static water table. Calculations indicate that the package environment will experience a maximum temperature of {similar_to}230{sup 0}C at 9 years after emplacement. For the next 300 years the rock within 1 m of the waste packages will remain dehydrated. Preliminary results suggest that the waste package radiation field will have very little effect on the mechanical properties of the rock. Radiolysis products will have a negligible effect on the rock even after rehydration. Unfractured specimens of repository rock show no change in hydrologic characteristics during repeated dehydration-rehydration cycles. Fractured samples with initially high permeabilities show a striking permeability decrease during dehydration-rehydration cycling, which may be due to fracture healing via deposition of silica. Rock-water interaction studies demonstrate low and benign levels of anions and most cations. The development of sorptive secondary phases such as zeolites and clays suggests that anticipated rock-water interaction may produce beneficial changes in the package environment