Ontario Power Generation's Response to the Joint Review

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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-04-158 � Section 13, Long term Safety of the DGR Information Request and Response During construction there will be various fan configurations until the underground fans are established (refer to Section 4.0 of OPG’s written submission to the July 18, 2012, JRP Technical Information Session (OPG 2012)). During this time, if there is a failure of a fresh air supply fan(s) sufficient to affect air quality, notifications will be made to stop work and have personnel egress from the area to the refuge station until such a time as the operation of the fan(s) is restored. Reference: OPG. 2012. OPG Letter from A. Sweetnam to S. Swanson, “Deep Geologic Repository Project for Low and Intermediate Level Waste – Submission for the July 18, 2012 JRP Technical Information Session”, Attachment 1 – Written Submission. CD# 00216-CORR-00531-00123, July 12, 2012. (CEAA Registry Doc# 636) Information Request: Provide justification for the Cobourg Water Model 2 as being representative of the water that will resaturate the DGR. Apply the model water, and all of its uncertainties, to the waste corrosion/degradation reactions to derive gas generation and contaminant mobilization rates, to justify the reaction rates assumed in the simulations. Context: For long term performance predictions, the quality of the water assumed to resaturate the repository is described by the Cobourg Water Model 2. The chemistry of this water is an important factor controlling the evolution of the repository (e.g. reaction with concrete) and the behavior of contaminants (e.g. sorption and solubility calculations). The characteristics of the groundwater and porewater chemistry are presented in Table 5.4 in the “Postclosure Safety Assessment: Data” report, with a statement that “the selected water compositions are the most appropriate ones reported in INTERA (2011, Sections 4.5.2 and 4.6)”. The porewater data in Table 5.4 are from a single core sample from DGR-3 (Sample ‘DGR3 680.46’) from which 4 subsamples were analyzed. The basis for adopting this particular sample to represent the Cobourg Formation porewater is not clearly stated. The outcome is that the concentrations of Ca, Mg, Sr and SO4 in the model water are inconsistent with the sample used as the basis for its development. Five boreholes intersect the Cobourg Formation, and thirty samples of drill core from those intersections were analyzed. Justification is required that the Cobourg Water Model 2 is representative of the water that will infiltrate the repository. In addition, the model water and all of its uncertainties (from the porewater estimates and subsequent derivation steps) should be applied to the waste corrosion/degradation reactions to derive gas generation and contaminant mobilization rates, to justify the reaction rates assumed in the simulations. OPG Response: This response is provided in four parts: Page 59 of 69
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 Information Request and Response a) an explanation as to why the estimated “DGR3 680.46” porewater composition was used as a starting point for the derivation of a model porewater; b) a justification as to why the Cobourg Model 2 porewater is a suitable representative porewater; c) an explanation of how the Cobourg Model 2 porewater has been used in the postclosure safety assessment; and d) a discussion of the uncertainties associated with Cobourg Model 2 porewater composition. a) Selection of Representative Cobourg Porewater Sample The selection of the porewater sample from the Cobourg Formation reflected the primary purposes of the calculations (see Section c) below), which were to: 1) calculate potential contaminant solubilities during the release and subsequent transport of contaminants in water through the shafts and the host rocks; 2) inform insight calculations presented on the evolution of chemical conditions within the DGR; and 3) evaluate the stability of shaft sealing materials, noting that shaft seals at different levels will come into contact with water of differing salinity and composition. Simplified conservative models of contaminant release were employed in the postclosure safety assessment calculations, which were not sensitive to the precise porewater composition in the Cobourg Formation (see Section c) below). The porewater chemistry is based on the Cobourg porewater data available at the time of the postclosure safety assessment. This included data from boreholes DGR2, DGR3 and DGR4. From the available data, the measured composition of sample “DGR3 680.46” was used as a starting point for the derivation of a model porewater because it was taken from a depth close to the assumed repository horizon (around 680 m). In addition, it had the minimum salinity among the Cobourg samples for which data were available. In contrast, a Guelph model porewater composition was also calculated based on an analysis of groundwater from the Guelph Formation, which represents the highest water salinity measured within the stratigraphic sequence (opportunistic groundwater sample OGW-12). Thus, by choosing these Cobourg and Guelph compositions, chemical variations across the maximum salinity gradient present in the rocks above the repository could be taken into account. b) Justification for Basis for the Cobourg Model 2 Porewater Any analysis of a groundwater or porewater will differ from the composition of the natural in-situ water due to processes that can occur during sampling and analysis, as well as measurement uncertainties. Such effects can never be entirely eliminated and are expected to be more prevalent for porewater, which must be extracted from the rock matrix prior to analysis. Cl and Br will usually behave much more conservatively during extraction procedures than more reactive constituents such as Ca, Mg, SO4 and Sr. Consequently, measured concentrations of Cl and Br may reflect the in-situ porewater composition. In contrast, measured concentrations of other elements such as Ca, Mg, SO4 and Sr may include contributions from both the porewater and from mineral dissolution reactions that occurred during extraction. Measured concentrations for these elements, therefore, are not necessarily considered to be representative of porewater Page 60 of 69
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Dr. Stella Swanson September 28, 20
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Attachment 1 to OPG letter, Albert
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Page 12 and 13: Attachment 1 to OPG letter, Albert
Page 74 and 75: Title: OPG’s Deep Geologic Reposi
Page 76 and 77: Table of Contents CLOSURE WALL CAPA
Page 78 and 79: Figure 1: Access tunnel geometry. C
Page 80 and 81: CLOSURE WALL CAPACITY and are the s
Page 82 and 83: CLOSURE WALL CAPACITY The shear str
Page 84 and 85: (H-a) = 4.25 m Figure 5: Return air
Page 86 and 87: Golder Associates Ltd. 6700 Century
Page 88 and 89: Title: Potential Inflows through Cr
Page 90 and 91: Serge Clement 1011170042-TM-G2100-0
Page 100 and 101: APPENDIX A Derivation of Conversion
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Ontario Power Generation's Response to the Joint Review

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