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-04-114 � Section 13.2,
Selection of
Assessment
Scenarios
Information Request and Response
Information Request:
Provide an evaluation of uncertainties in the sorption/desorption of contaminants on seal materials and host rocks, and
mineral precipitation/dissolution reactions. Discuss the impact of these uncertainties on model predictions.
Describe how the interactions of contaminants with organic compounds in the rocks of the cap rock seal have been
addressed. These interactions would include microbiological processes.
Context:
Section 13.2 of the EIS Guidelines states: “Long-term assessment scenarios should be sufficiently comprehensive to
account for all of the potential future states of the site and the environment.”
OPG Response:
The response is provided in four parts:
(a) evaluation of uncertainties in the sorption/desorption of contaminants on seal materials and host rocks;
(b) evaluation of uncertainties in the precipitation/dissolution of contaminants
(c) discussion of the impact of these uncertainties on model predictions; and
(d) discussion of the interactions of contaminants with organic compounds in the rocks of the cap rock seal.
(a) Uncertainties in Sorption/Desorption in Seal Materials and Host Rocks
The uncertainties in sorption data are discussed in Appendix D of the Data report (QUINTESSA and GEOFIRMA
2011). Preliminary safety assessment calculations indicated that potentially important radionuclides for the long-term
safety of the DGR included C-14, Cl-36, Ni-59, Zr-93, Nb-94, I-129, Ra-226, Np-237, U-238 and Pu-239. Also, nonradioactive
Cd, Cr, Cu and Pb, were identified as potentially important hazardous elements. Appendix D provides data
with respect to sorption for these 14 elements; for all other elements, it was conservatively assumed that there was no
sorption on seal materials or rocks. Appendix D.2 comments on the most important retardation processes for each
element of interest and the associated uncertainties, and Appendix D.3 presents recommended sorption values
selected following a review of relevant literature available prior to the data freeze for the postclosure safety assessment
in summer 2010 (at that time, no site-specific sorption measurements were available).
The assessment focused on sorption in bentonite-sand seals within the shafts, and in the host rocks. The
recommended values were intended to be conservative. Sorption on concrete and asphalt was conservatively taken to
be zero. Sorption on materials within the repository itself was also assumed to be zero.
Subsequently, a separate literature review was completed by Vilks (2011) for sedimentary rock and a range of
salinities. As shown in Table 1, the sorption values recommended in Appendix D.3 of QUINTESSA and GEOFIRMA
(2011) are all lower than the minimum values recommended by Vilks (2011), apart from the values for Np and Pu in
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