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Title: Drift Degradation Analysis

Degradation of underground openings as a function of time is a natural and expected occurrence for any subsurface excavation. Over time, changes occur to both the stress condition and the strength of the rock mass due to several interacting factors. Once the factors contributing to degradation are characterized, the effects of drift degradation can typically be mitigated through appropriate design and maintenance of the ground support system. However, for the emplacement drifts of the geologic repository at Yucca Mountain, it is necessary to characterize drift degradation over a 10,000-year period, which is well beyond the functional period of the ground support system. This document provides an analysis of the amount of drift degradation anticipated in repository emplacement drifts for discrete events and time increments extending throughout the 10,000-year regulatory period for postclosure performance. This revision of the drift degradation analysis was developed to support the license application and fulfill specific agreement items between the U.S. Nuclear Regulatory Commission (NRC) and the U.S. Department of Energy (DOE). The earlier versions of ''Drift Degradation Analysis'' (BSC 2001 [DIRS 156304]) relied primarily on the DRKBA numerical code, which provides for a probabilistic key-block assessment based on realistic fracture patterns determined from field mappingmore » in the Exploratory Studies Facility (ESF) at Yucca Mountain. A key block is defined as a critical block in the surrounding rock mass of an excavation, which is removable and oriented in an unsafe manner such that it is likely to move into an opening unless support is provided. However, the use of the DRKBA code to determine potential rockfall data at the repository horizon during the postclosure period has several limitations: (1) The DRKBA code cannot explicitly apply dynamic loads due to seismic ground motion. (2) The DRKBA code cannot explicitly apply loads due to thermal stress. (3) The DRKBA code, which determines structurally controlled key-block failure, is not applicable for stress-controlled failure in the lithophysal units. To address these limitations, additional numerical codes have been included that can explicitly apply seismic and thermal loads, providing significant improvements to the analysis of drift degradation and extending the validity of drift degradation models.« less
Authors:
Publication Date:
OSTI Identifier:
837516
Report Number(s):
ANL-EBS-MD-000027, REV 03
DOC.20040915.0010, DC 36086; TRN: US0502631
DOE Contract Number:
AC28-01RW12101
Resource Type:
Technical Report
Resource Relation:
Other Information: PBD: 16 Sep 2004
Research Org:
Yucca Mountain Project, Las Vegas, Nevada (US)
Sponsoring Org:
US Department of Energy (US)
Country of Publication:
United States
Language:
English
Subject:
12 MANAGEMENT OF RADIOACTIVE WASTES, AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES; DESIGN; DYNAMIC LOADS; EXCAVATION; FRACTURES; FUNCTIONALS; GROUND MOTION; LICENSE APPLICATIONS; MAINTENANCE; OPENINGS; PERFORMANCE; POSITIONING; YUCCA MOUNTAIN