2003 International High-Level Radioactive Waste Management Conference Breached Drip Shield Test and Validation of a TSPA Sub-Model

The Engineered Barrier System (EBS) represents the system of human engineered barriers in the isolation of high-level radioactive waste in the proposed repository at Yucca Mountain. It is designed to complement and enhance the natural barriers to isolate and prevent the transport of radionuclides into the surrounding environment. The transport mechanism most frequently postulated for radionuclides is liquid water flux that has penetrated the EBS through corrosion breaches in the drip shield and waste packages (WP). A water flux-splitting model is used to predict flow through WP and drip shield breaches and is documented in the ''EBS Radionuclide Transport Abstraction''. A future revision of the ''EBS Radionuclide Transport Abstraction'' will be one component of the total system performance assessment--license application (TSPA-LA) for the Yucca Mountain repository. The flux-splitting model is conservative based on the following assumptions: (1) Drip impact occurs without a loss of water mass. (2) Dripping flux falls exactly at the crown of the drip shield as opposed to different locations on the curved surface, which will effect splashing and flow patterns. (3) The flux passing through a drip shield patch is proportional to the ratio of the length of the penetration in the axial direction to the total axial length of the drip shield. In this assumption all fluid that drips and flows from the drip shield crown toward a penetration will be collected if the axial locations of the source and patch coincide. (4) The potential for evaporation is ignored. Because of these conservatisms, the current version of the flux-splitting model is incapable of accounting for water that has been splashed from the impact location, the deviation of water paths (rivulets) from the axis of impact, and water loss due to evaporation. This paper will present the results of a series of breached drip shield tests used to collect empirical data for the initial validation and further development of the flux-splitting model. Additionally, this paper will present a comparison between numerical calculations used as a part of the flux-splitting model validation and calibration and a portion of the data collected from the breached drip shield test. Topics addressed in the comparison will be the potential for splashing, rivulet spread, collection of flow in breaches, and evaporation losses