Water, Vapor, and Salt Dynamics in a Hot Repository

Abstract

The purpose of this paper is to report the results of a new model study critically examining the high temperature nuclear waste disposal concept at Yucca Mountain using MULTIFLUX, an integrated in-drift- and mountain-scale thermal-hydrologic model. In addition to new results the paper summarizes results of a previous study. The results show that a large amount of vapor flow into the drift is expected during the period of above-boiling temperatures in the emplacement drift. This phenomenon makes the emplacement drift a water/moisture attractor for thousands of years during the above-boiling temperature operation.

The evaporation of the percolation water into the drift gives rise to salt accumulation in the rock wall, especially in the crown of the drift for about 1500 years in the example. The deposited salts over the drift footprint, almost entirely present in the fractures, may enter the drift either by rock fall or by water drippage. During the high temperature operation mode the barometric pressure variation creates fluctuating relative humidity in the emplacement drift with a time period of approximately 10 days. Potentially wet and dry conditions and condensation on the surfaces over salt-laden drift wall sections are unfavorable to the storage environment. Corrosive salt accumulation during the above-boiling temperature operation must be sufficiently addressed to fully understand the waste package environment during the thermal period. Until the questions are resolved, a below-boiling repository design is favored where the Alloy-22 will be less susceptible to localized corrosion.