[en] The performance assessment of a shaft seals system in a high-level waste repository in the Gibson Dome area in southeastern Utah is presented. The analysis of the movement of the permeant in the shaft seals system under partially saturated flow conditions was based on the Green and Ampt theory of infiltration. The analysis of the transport of radionuclides leaching out of the repository was performed using two analytical solutions: a two-dimensional solution which could handle single decaying species in homogeneous soils and a one dimensional solution designed to handle a three-member decay chain in a layered stream tube. Various conservative scenarios of water intrusion into the repository were considered and the impact of these on the travel time of the wetting front in the shaft seals, as well as the potential migration of the radionuclides released from the two types of waste form, are reported. At our present knowledge of field data, the methodology has proved useful in reasonable estimations of some important aspects of the shaft seals performance, as well as in assessments of the potential radiological impact of the release of radionuclides from the repository into the underlying aquifer. The methodology described is not meant to compete with large-scale computer models; however, it is designed to assist the prospective investigator in economical analyses