Long-term Stability Analysis of DGRs in Crystalline and Sedimentary Settings

Abstract

A bounding numerical analysis was performed to illustrate the stability and integrity of the rock mass enclosing a used fuel Deep Geologic Repository (DGR) during a 1Ma period. The analysis included a sequence of simulations designed to illustrate sedimentary or crystalline rock mass response to normal repository evolution and extreme events. Among others, scenarios considered include: i) repository gas pressure generation; ii) long-term rock strength degradation; iii) used fuel canister heat generation; iv) continental ice-sheet advance and retreat; and v) rare strong seismic ground motions. Results indicate that rock damage evolves with time but is primarily driven by thermally induced stresses about 1000 years after repository closure. Glacial and earthquake forcing was found not to yield significant rock damage even when combined. It is evident that the engineered backfill system provides the necessary confinement to prevent spalling and/or fracture dilation, and likely contributes to slowing the rate of time-dependent strength degradation.A bounding numerical analysis was performed to illustrate the stability and integrity of the rock mass enclosing a used fuel Deep Geologic Repository (DGR) during a 1Ma period. The analysis included a sequence of simulations designed to illustrate sedimentary and crystalline rock mass response to expected repository evolution and extreme events. Among others, scenarios considered include: i) repository gas pressure generation; ii) long-term rock strength degradation; iii) used fuel canister heat generation; iv) continental ice-sheet advance and retreat; and v) rare, strong seismic ground motions. Results indicate that rock damage evolves with time but is primarily driven by thermally-induced stresses occurring within 1000 years of repository closure. Glacial and earthquake perturbations did not yield significant rock damage even when combined. It is evident that the engineered backfill system provides sufficient confinement to prevent spalling and/or fracture dilation, and likely contributes to slowing the rate of time-dependent strength degradation. The numerical simulations also provide insight on the transient loading of a used fuel canister in response to internal and external repository perturbations.