ONTARIOF Eil GENERATION PO. Box 4000 Bowmanville, Ontario L 1C 3Z8

December 10, 2014

CD# NK38·CORR-00531-17143

Mr. F. Rinfret Director Darlington Regulatory Program Division Canadian Nuclear Safety Commission 280 Slater Street Ottawa, Ontario K1P 5S9

Dear Mr. Ri nfret:

Brian Duncan Senior Vice President

Darlington Nuclear

Tel : 905·697·7499 Fax: 905·697·7596 brian.duncan@opg.com

OPG Proprietary

Darlington NGS - Additional Information to Support Darlington Request for Licence Amendment to Incorporate REG DOC- 2.4.2 on Probabilistic Safety Assessment

Pursuant to the OPG letter (Reference 1), requesting the amendment of the Darlington Power Reactor Operating Licence to incorporate new Regulatory Document REG DOC-2.4.2, "Probabilistic Safety Assessment (PSA) for Nuclear Power Plants", OPG is providing additional information regarding the planned PSA work to be submitted to CNSC staff and/or to the Commission prior to the 2015 Darlington licence renewal hearings.

This information is provided in Attachment 1. It outlines OPG's plans and timelines for:

• Updates to the Darlington Risk Assessment (DARA),

• Assessing the impact of the Safety Improvement Opportunities (SIOs) being implemented as part of Darlington Refurbishment, and of post-Fukushima Emergency Mitigating Equipment (EME),

• Comparison of PSA results to OPG safety goals and an action plan to reduce risk should any safety goal target not be met,

• Aggregation of PSA results ,

• Strategy related to whole-site PSA; and

• Public posting of a Darlington PSA summary report.

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Mr. F. Rinfret OPG Proprietary December 10, 2014

NK38-CORR-00531-1 7143

Per Table 1, OPG has initiated two new regulatory commitment actions to provide the CNSC staff with additional information to support the Darlington's request for licence amendment to incorporate REG DOC- 2.4.2.

If you have any questions, please contact Dr. Carlos Lorencez, Director, Nuclear Safety, at (905) 839-6746, extension 5024.

Brian Duncan Senior Vice President Darlington Nuclear Ontario Power Generation Inc.

All.

cc: Mr. A. Ling - CNSC Site Office (Darlington)

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Mr. F. Rinfret

Reference:

OPG Proprietary December 10, 2014

NK38-CORR-00531-17143

1. OPG Letter, B. Duncan to M. Leblanc, "Darlington NGS­Request for Licence Amendment to Darlington PROL 13.00/2015 to Implement New Regulatory Documents REGDOC-2.4.1 and REG DOC- 2.4.2," October 31,2014, CD# NK38-CORR-00531-17057.

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Attachment to OPG Letter, B. Duncan to F. Rinfret, "Additional Information to Support Darl ington Request for Licence Amendment to Incorporate REGDOC 2.4.2 on Probabilistic Safety Assessment", CD# NK38-CORR-00531 -17143

ATTACHMENT 1

OPG's Plan for Submission of PSA Material in Support of 2015 Darlington Licence Renewal

In view of the upcoming Darlington's licence renewal hearings, currently scheduled to be held in August (Part 1) and November of 2015 (Part 2), the following further describes Phase 1 of OPG's licensing strategy for transition from Regulatory Standard S-294 to regulatory Document REGDOC-2.4.2 as outlined in Attachment 4 of Reference [1] .

By June 19, 2015, OPG expects to have provided the CNSC staff with the majority, or all (to the extent practicable) of the updated portions of the PSA; these may include some simplifying assumptions. The updated PSA will be presented to the Commission in Part 1 of the Darlington 's relicensing hearing and will include consideration for the impact of Safety Improvement Opportunities (SIOs) and the impact of Emergency Mitigating Equipment (EME) . The PSA results will be compared to the OPG safety goals and an action plan will be developed in accordance with OPG governance should safety goal targets for any individual hazard not be met. OPG will also provide an update on the whole-site PSA work that is being conducted through an Industry joint project and currently includes a pilot application for the Pickering NGS; future work in this area will depend on the lessons learned and utility licensing commitments.

By August 12, 2015, well ahead of Part 2 of the Darlington licence renewal hearing planned for November 4 - 5, OPG will post a publ ic PSA summary report. This will allow interveners ample time to review and comment on the results .

Further detai ls on the PSA items mentioned are provided below:

OPG will provide to the CNSC by June 19, 2015, items 1 to 4.

1, Darlington NGS 2015 PSA Update

This submission will be comprised of the available S-294 compliant risk results from the 2015 DARA update with a focus on the most risk-significant elements, in time for the CNSC to prepare their Part 1 Hearing CMD.

PSA elements which were previously exempted from a detailed PSA study, such as LRF estimates for the external hazards, will be reviewed for validity of assumptions and in light of updated PSA results . They will be resubmitted if there are significant changes.

OPG will endeavor to hold regular status update meetings with CNSC staff to report on the status of the PSA update projects and any preliminary results available. Where interim deliverables have been finalized and are unlikely to change, OPG may choose to send these to the CNSC to aid in their review of the Darlington NGS 2015 PSA update.

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Attachment to OPG Letter, B. Duncan to F. Rinfret, "Additional Information to Support Darlington Request for Licence Amendment to Incorporate REGDOC 2.4.2 on Probabilistic Safety Assessment", CD# NK36-CORR-00531-17143

2, Impact from Safety Improvement Opportunities (SIOs) and EME

It is the intention of OPG to include Phase 1 EME in the baseline Darlington NGS 2015 PSA update studies. These PSA studies will include separate sensitivity analyses related to the SIOs and results without the EME (as a means of gauging the risk-benefit of EME). The sensitivity results will be communicated as part of the technical reports submitted to the CNSC.

3, Action Plan

Should the results for any individual element of the Darlington NGS 2015 PSA exceed safety goal targets, an action plan will be developed outlining physical and analytical improvements to reduce risk.

4. Update on Whole Site PSA and Risk Aggregation

There is a COG joint project on safety goals, risk aggregation , and whole site PSA, which will include as part of its deliverables, a pilot whole-site PSA for Pickering NGS by 2017. The lessons learned from this pilot project will be studied prior to tackling other whole-site PSA work, including a potential Darlington whole-site PSA. The benefit and timing of a potential Darlington whole-site PSA project will need to be carefully assessed , based on the lessons learned from the Pickering pilot, and given that Darlington NGS wil l be undergoing several configuration changes over the course of the refurbishment project.

Although risk aggregation across internal and external hazards is currently outside of RECDOC-2.4.2 (see Section 4.7) and site-wide safety goals are not in place at OPG at this time, OPG will assist the CNSC by providing a risk aggregation calculation based on the available Darlington PSA results using the CNSC's simplified aggregation method that was recently used for the Pickering NGS licensing hearings. OPG continues to work with Industry on developing a more rigorous risk aggregation methodology. Canada would be the first jurisdiction to develop and apply such a methodology to a multi-unit site.

5, Darlington NGS PSA Summary Report

A Darlington NGS PSA Summary Report will be prepared as part of the supplementary information and will be publicly posted on OPG.com by August 12, 2015.

Reference: [1] . OPG Letter, B. Duncan to M. Leblanc, "Darlington NGS -Request for Licence Amendment to Darlington PROL 13.00/2015 to Implement New Regulatory Documents REGOOC-2.4.1 and REG DOC- 2.4.2," October 31, 2014, CD# NK38-CORR-00531-17057 .

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