Ontario Power Generation's Response to the Joint Review

Attachment 1 to OPG letter, Albert Sweetnam to Dr. Stella Swanson, “Deep Geologic Repository Project for Low and Intermediate Level Waste – Submission of
Responses to the Final Sub-set of Package #4 Information Requests”, CD#: 00216-CORR-00531-00143.
IR# EIS Guidelines
Section
EIS-04-119 � Section 13.2,
Selection of
Assessment
Scenarios
Information Request and Response
Information Request:
Provide the evidence and associated uncertainties that produce the predictions that the proposed DGR may take many
hundreds of thousands, or even millions, of years to resaturate. Evaluate and describe different saturation scenarios
(25%, 50%, 75%, 100%) with respect to the long-term performance of the proposed DGR.
Context:
The Post Closure Safety Assessment: Analysis of the Normal Evolution Scenario, section 2.1, page 22 states that “the
low permeability of the shaft seals and the host rock, plus the gas pressure in the repository and the water consumption
by corrosion reactions, all limit the resaturation of the repository. The repository might take many hundreds of
thousands or even millions of years to resaturate completely”.
OPG Response:
The saturation of the DGR excavation after closure is addressed in the postclosure safety assessment and, in
particular, the Groundwater Modelling report (GEOFIRMA 2011) and the Gas Modelling report (GEOFIRMA and
QUINTESSA 2011). In these reports, results are presented from numerical models of groundwater and gas transport in
and around the repository. These models include the effects of the shafts (including damaged zone) as pathways for
water entry, the hydraulic conditions in the surrounding rock including pressure conditions reflecting the over/under
pressures measured at the site, and gas generation from the wastes.
Specifically, the coupled gas and groundwater modelling code, T2GGM, has been used to investigate the evolution of
repository saturation (see the Gas Modelling report, GEOFIRMA and QUINTESSA 2011, for details). The model
includes waste corrosion and degradation reactions, which are dependent on the availability of water in the repository,
as well as reactions that can release water (see Chapter 4 of the T2GGM documentation, QUINTESSA and
GEOFIRMA 2011). Calculations cases have been undertaken that consider the Reference Case that best reflects our
knowledge (NE-RC), as well as various sensitivity analyses. Some cases conservatively ignore the consumption of
water by corrosion and degradation reactions, thereby allowing resaturation, as well as corrosion and degradation
reactions to proceed faster (non-water limited, NWL, cases). Other cases account of the removal of water consumed in
gas generation reactions on the repository water balance (water limited, WL, cases).
A brief description of the cases is given in Table 3.1 and Section 3.2 of the Gas Modelling report (GEOFIRMA and
QUINTESSA 2011). The results for these calculation cases are summarized in Section 8.1 of the Gas Modelling report
(GEOFIRMA and QUINTESSA 2011). The repository liquid saturation for all NWL and WL cases are presented in
Figures 8.3 and 8.4 of GEOFIRMA and QUINTESSA (2011), respectively. These figures are reproduced below.
For most cases, resaturation is limited, with correspondingly low water levels within the repository for the duration of the
simulation. Increasing the host rock vertical permeability by an order of magnitude resulted in about 10% saturation
(NE-AN3). Only the Disruptive Scenario cases with severe shaft seal failure (SF-BC and SF-ED), and the Normal
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