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Darlington New Nuclear Project public summary

The Darlington New Nuclear Project (DNNP) involves the site preparation, construction, operation, decommissioning and abandonment of up to 4 new nuclear reactors at the existing Darlington site, owned by Ontario Power Generation (OPG). In December 2021, OPG announced its selection of the General Electric Hitachi BWRX‑300 reactor for deployment at the DNNP site. The BWRX‑300 is a 300 MWe water-cooled, natural circulation small modular reactor. In October 2022, OPG applied for a licence to construct a single BWRX‑300 reactor. CNSC staff have reviewed OPG’s submissions relating to the new technology and have assessed whether this technology fits within the bounds of the environmental assessment and plant parameter envelope.

Overview and background

1.1 Darlington New Nuclear Project

The scope of the DNNP encompasses the operational lifecycle Footnote 1 of up to 4 new nuclear reactors that can generate enough electricity to power about 1.2 million homes. The proposed site is located within the existing Darlington nuclear site on the north shore of Lake Ontario, within the Municipality of Clarington (figure 1). OPG owns the site and currently holds a CNSC licence to prepare the site for the DNNP. The CNSC acknowledges that the DNNP is on the traditional territory of the Michi Saagiig Anishinaabe people. These lands are covered by the Williams Treaties between Canada and the Mississauga and Chippewa Nations.

Aerial view of the Darlington New Nuclear Project site on the north shore of Lake Ontario. The adjacent, existing Darlington Nuclear Generating Station is visible in the top right corner.
Figure 1: Aerial view of the DNNP site on the north shore of Lake Ontario. The adjacent, existing Darlington Nuclear Generating Station is visible in the top right corner. Source: OPG

1.2 Brief history of the DNNP environmental assessment

OPG submitted an application for a site preparation licence to the CNSC in 2006, followed by an environmental impact statement (EIS). An environmental assessment (EA) was initiated under the 1992 Canadian Environmental Assessment Act (CEAA 1992), the legislation then in force. At the time, no nuclear reactor technology had been selected. The EA was conducted based on a range of design parameters and variables from different technologies under consideration by OPG. This is referred to as a plant parameter envelope (PPE) approach. The EA proceeded with the understanding that the reactor technology selected by OPG in the future would need to be within the bounds, or range of values, of the defined PPE.

A joint review panel reviewed the EA under CEAA 1992 and the licence application under the Nuclear Safety and Control Act. The panel conducted a public hearing from March 21 to April 8, 2011, and heard from Indigenous Nations and communities, federal and provincial governments, environmental groups, individuals and others interested in the project. The panel concluded that the project could proceed and made a number of recommendations on its safe implementation, as outlined in the Joint Review Panel Environmental Assessment Report (PDF, 3 MB). In 2012, the Government of Canada issued its response report, agreeing with all recommendations directed to federal departments and determining that the DNNP is not likely to adversely affect the environment. The CNSC issued a 10‑year site preparation licence to OPG.

1.3 Rationale for environmental impact statement review

The EA completed under CEAA 1992 will still apply if the scope of the project remains within the boundaries of the EA. Therefore, the panel recommended that the Commission determine, prior to construction activities, whether the original EA is applicable to OPG’s selected reactor technology (see info box).

In 2021, OPG selected the General Electric Hitachi Boiling Water (BWRX‑300) small modular reactor technology (figure 2). Since this reactor technology was not considered in the initial assessment, it was not obvious whether the technology was bounded by the PPE. The CNSC required OPG to review the BWRX‑300 design against the original EA. OPG submitted its EIS review (PDF, 2 MB), PPE review (PDF, 3 MB) and supporting documentation in 2022.

Joint Review Panel Recommendation #1

The Joint Review Panel (PDF, 3 MB) understands that prior to construction, the Canadian Nuclear Safety Commission will determine whether this environmental assessment is applicable to the reactor technology selected by the Government of Ontario for the Project. Nevertheless, if the selected reactor technology is fundamentally different from the specific reactor technologies bounded by the plant parameter envelope, the Panel recommends that a new environmental.

Conceptual view of the proposed nuclear facility for the Darlington New Nuclear Project.
Figure 2: Conceptual view of the BWRX-300 SMR at the DNNP site. Source: OPG

1.4 Scope of the Commission’s determination

The purpose of the public hearing in January 2024 is for the Commission to determine whether the original EA can be applied to OPG’s selected BWRX-300 technology.

The scope of the hearing will not include a decision on whether OPG can construct a reactor at the DNNP site. If the Commission decides that the existing EA applies, a separate public hearing on OPG’s licence to construct application will be required at a future date.

1.5 Purpose of Commission member document CMD 24-H2

CMD 24-H2 (PDF, 1 MB) captures CNSC staff’s technical assessment, conclusions and recommendations to support the Commission in determining whether the BWRX‑300 technology remains within the bounds of the accepted EA. Using their professional judgment, CNSC staff conducted a detailed as sessment of OPG’s documents against applicable legislation, panel recommendations, CNSC regulatory documents, international guidance, and codes and standards. Expertise from other federal departments was incorporated on various issues, such as species at risk, fish and fish habitat, noise, and the transportation of dangerous goods.

Summary of the plant parameter envelope review

As outlined above, the purpose of the PPE approach was to allow for an assessment of potential adverse environmental effects associated with the DNNP, without specifying a reactor technology. The PPE includes 198 parameters applicable to the DNNP. In its PPE review, OPG reviewed each parameter against the selected BWRX‑300 technology. In this context, “bounded by the PPE” means that a given parameter is within the range of variables that were assessed in the envelope. OPG’s review found that:

  • 130 parameters are bounded by the PPE
  • 60 parameters are not applicable and were therefore not considered further; these include, for example, parameters related to cooling towers, which are not required for the BWRX‑300
  • 8 parameters are outside the range of variables and require further assessment

A summary of OPG’s assessment of the 8 parameters outside the range of the PPE is presented in table 1. CNSC staff concluded that these parameters have been adequately assessed and that the mitigation measures agreed to by the panel in the original EA remain satisfactory to ensure that the BWRX‑300 does not adversely affect the environment.

Table 1 : Review summary for the 8 parameters outside the range of the plant parameter envelope for the deployment of up to 4 BWRX‑300 reactors.

Change in parameter beyond the PPE Summary of OPG’s PPE review CMD section
Fire protection: Higher rate of lake water withdrawal Despite the short-term water withdrawal and storage quantity being higher than the EA, less water overall would be withdrawn from the municipal supply when considering all uses, including for potable water, sanitary waste and fire protection. Less wastewater would be discharged to the municipal system.
Fire protection: More water storage Same as above
Foundation depth: Deeper reactor placement in the ground A temporary impact on groundwater flow during construction was predicted from dewatering operations, which would end after construction. This is a lesser impact than the permanent change to groundwater flow predicted in the EA.
Airborne releases: Lower release height above ground For the BWRX‑300, the airborne releases to the environment occur at a lower release height above ground, which would slightly alter the dispersion of radionuclides compared to the EA. The BWRX‑300 releases contain the same radionuclides as assessed in the EA, but in different proportions. Airborne emissions of tritium, particulates and noble gases were estimated to be lower than the EA, whereas radioiodine and carbon-14 releases were estimated to be slightly higher. In total, BWRX‑300 emissions are only a fraction (~1.5%) of the total emissions estimated in the EA. Accordingly, the resulting dose to the public would be less than the EA bounding dose and well below the regulatory public dose limit of 1 mSv/year.
Airborne releases: Different proportions of radiological releases Same as above
Radioactive waste: Higher radioactivity per volume for solid waste Solid waste produced by the BWRX‑300 contains slightly more radioactivity compared to the EA because the proportion of radionuclides has changed. However, a lower volume of solid waste is generated per year. Therefore, despite a higher radioactivity per volume overall, less radioactivity is generated. Handling equipment for waste containers will be designed for the higher radioactivity, and heavier casks will be used to provide adequate radiation shielding. The hauling roads onsite leading to the waste storage facility will be upgraded accordingly.
Radioactive waste: Heavier spent fuel casks Same as above
Wind impact: Updated importance factor for wind loads An updated methodology was available to reassess whether the design of certain DNNP buildings is adequate for high wind-gust speeds. This analysis relies on the “importance factor” for wind loads used to calculate the wind pressure on building surfaces. The reassessment, while different than the importance factor described in the National Building Code of Canada, was consistent with PPE conclusions on building design.

Summary of the environmental impact statement review

The original EA defined the scope of the DNNP, described the existing environment, and analyzed potential environmental effects. The analysis grouped aspects of the environment into environmental components. OPG’s EIS review assessed, for each environmental component, how the conditions onsite and near the DNNP have changed since 2009, and whether the deployment of up to 4 BWRX‑300 reactors changes the conclusions of the EA.

A summary of OPG’s EIS review based on the environmental components within the defined DNNP scope is presented in table 2. CNSC staff concluded that changes to the environmental components since the original EA have been adequately assessed and do not change the conclusions of the EA. The conclusion takes into account the fact that any adverse effects will be mitigated and that the environment will be monitored for any changes, as recommended by the panel.

Table 2 : Summary of the environmental impact statement review for the deployment of up to 4 BWRX‑300 reactors.

Environmental component Summary of OPG’s EIS review CMD section
Air quality (non-radiological) and noise Local air quality has improved since the EA. Predicted BWRX‑300 emissions of non-radiological contaminants (e.g., particulates, nitrogen oxides) during construction – when emissions would be highest – are all below the EA bounding values. The size or footprint of the BWRX‑300 requires less excavation and heavy equipment use, therefore lowering overall emissions and noise.
Aquatic habitat and biota Aquatic habitat is less impacted given the smaller footprint of the BWRX‑300 reactors. Compared to the original assessment, 3 onsite ponds can be preserved, less fish habitat will be destroyed, and the lake nearshore will be less affected as lake infilling is not required. The effect of shoreline stabilization activities remains the same as assessed in the EA. The BWRX‑300 cooling water intake and discharge structures will require less blasting during construction. Predicted fish loss from impingement and entrainment are similar to the EA; therefore, no additional stressors are anticipated to the aquatic habitat and biota from the original EA.
Surface water The BWRX‑300 design uses a cooling water system with a lower intake flowrate compared to the EA, reducing effects on lake circulation. The BWRX‑300 is designed to not release any liquid radioactive substances. Predicted effects on lake water temperature are consistent with the EA.
Soil and groundwater The BWRX‑300’s effects on soil quality, primarily due to runoff that would be mitigated by stormwater management, are consistent with the EA. Anticipated effects on groundwater quality relate to stormwater management and routine airborne radioactive releases, consistent with the EA. The BWRX‑300’s effects on groundwater flow would originate from the development of infrastructure and dewatering. In terms of the deeper excavation required for the BWRX‑300, groundwater models indicate that groundwater flow patterns may change slightly. These effects are consistent with the EA and are restricted to the DNNP site.
Terrestrial habitat and biota The smaller physical footprint of the BWRX‑300 reactors enables some terrestrial habitat, predicted to be removed in the EA, to be retained. For example, woodland habitat for endangered bats and amphibian breeding areas can be preserved. Additional species have been identified as being of conservation concern since the EA, including breeding and migrant birds, bats, and a species of turtle.
Land use The population and economy in the region continue to grow. Ongoing monitoring of land use and engagement with the Municipality of Clarington and the Region of Durham remain the same compared to the original assessment. Negative effects on the visual landscape are no longer of concern, as the BWRX‑300 design does not use cooling towers.
Traffic and transportation The smaller BWRX‑300 physical footprint is expected to reduce the number of workers onsite and require less material excavated and moved to a disposal site by road. Both aspects reduce road traffic and vehicle collisions compared to the EA. Rail and marine transportation are similar to the EA.
Radioactivity The BWRX‑300 releases less tritium, particulates and noble gases to air, but slightly more radioiodines and carbon-14 during normal operations, compared to bounding EA predictions. The resulting radiological doses to members of the public and nuclear energy workers would remain below regulatory limits.
Human health The deployment of 4 BWRX‑300 reactors is predicted to result in a radiological dose of 1.20 µSv/year (0.0012 mSv/year) to the public from normal operations. This dose is well below the bounding dose assessed in the EA and the public dose limit of 1 mSv/year. Similarly, radiological doses to nuclear energy workers are predicted to be bounded by the EA. Non-radiological releases are also below EA predictions. Therefore, releases from the reactors are not expected to have any impact on the health of the local population.
Health of non-human biota The radiological dose assessments for the BWRX‑300 reactors for aquatic and terrestrial biota are well below EA predictions.

In addition to the environmental components above, CNSC staff’s assessment of OPG’s EIS review also considered the following:

  • radiological accidents and malfunctions (CMD section
  • effects from flooding, severe weather, seismicity, biophysical environment (e.g., mussels, algae) and climate change (CMD section
  • cumulative effects (CMD section

CNSC staff concluded that deploying the BWRX‑300 would not change the conclusions of the EA on these items. Further discussion is provided in CMD 24-H2.

Consultation and engagement with Indigenous Nations and communities

CNSC staff have conducted early and ongoing consultations with identified Indigenous Nations and communities to encourage their full participation in the regulatory process. CNSC staff have actively sought feedback on OPG’s documents and have worked to ensure that concerns are heard, considered and addressed by OPG and CNSC staff in a meaningful way. CNSC staff are of the view that their ongoing consultation and engagement activities, as well as those conducted by OPG, have been thorough, responsive and flexible. These activities included consultation and engagement on the assessment and panel process, as well as the opportunity to participate in the Commission hearing process with support from the CNSC’s Participant Funding Program. CNSC staff will continue to engage with and involve Indigenous Nations and communities on this project. Further discussion is provided in CMD 24‑H2, section 3.1.

Overall conclusions and recommendations

Based on the CNSC’s and other federal authorities’ comprehensive evaluation and assessment of OPG’s documentation, CNSC staff recommend that the Commission determine that the deployment of up to 4 BWRX‑300 reactors at the DNNP remains bounded by the original EA.

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