Letter to Ontario Power Generation regarding Regulatory Hold Point 3 – Darlington Unit 4

Regulatory Operations Branch

February 16, 2026

Mr. Allan Grace
Senior Vice President, Nuclear
Ontario Power Generation Inc.
1 Holt Road South, P.O. Box 4000
Bowmanville, ON  L1C 3Z8

Mr. Vince Smyth
Senior Vice President, Refurbishment
Ontario Power Generation Inc.
1855 Energy Drive, 3C14
Courtice, ON  L1E 0E7

Subject: Darlington NGS – Unit 4 return to service: Request for CNSC consent to remove the regulatory hold point prior to exceeding 1% full power – New Action Item: 2026-13-39002

Dear Mr. Grace and Mr. Smyth,

The purpose of this letter is to respond to Ontario Power Generation’s (OPG) submission [1], which requests removal of the third regulatory hold point (RHP-3) so as to allow operation above 1% full power for the refurbished Darlington Unit 4 reactor, and provides the associated completion assurance document.

Canadian Nuclear Safety Commission staff’s assessment [2] of OPG’s submission, as well as all supporting documentation, concludes that OPG has met all the pre-requisites established by the Commission to remove RHP-3. Therefore, as the person authorized by the Commission and pursuant to Licence Condition 15.4 of the Darlington Nuclear Generating Station Power Reactor Operating Licence 13.00/2045, I consent to remove RHP-3. OPG may now allow operation above 1% full power for the Darlington Unit 4 reactor.

This authorization includes a special condition pertaining to the large number of items being deferred from this RHP [3, 4, 5]. CNSC staff understand, that for various reasons, the items described in the RHP-3 deferral forms could not be completed ahead of this hold point and that postponing their completion does not result in an appreciable, increased risk to operation of the plant. Nevertheless, as many of the items are being deferred to milestones beyond the last remaining Regulatory Hold Point (RHP-4), the CNSC requests that their completion be communicated to staff ahead of their newly established milestones. For items being deferred outside of refurbishment, OPG is requested to provide firm completions dates that will be used to track their completion. In addition to RHP-3 deferrals, these requests are also applicable to all other items deferred from previous and future milestones, including RHPs and OPG Restart Control Hold Points (RCHP).

To summarize, by RCHP-9 (Available Commercial Operation), or sooner (if applicable), OPG is requested to confirm that all items tied to new milestones be confirmed as closed, and for items deferred to beyond the Unit 4 refurbishment, firm dates be provided.

My consent is based on a risk informed decision, used in special circumstances, taking into account CNSC staff’s assessment [2], in which they conclude that the deferrals are acceptable but will be tracked to completion through Action Item 2026-13-39002.

Yours sincerely,

Ramzi Jammal
Executive Vice-President and Chief Regulatory Operations Officer
Regulatory Operations Branch
Canadian Nuclear Safety Commission

cc: A. Viktorov, A. Mathai, K. Lun, S. Eisan-Kouznetsova, M. Rickard, C. Loreti, E.
Delgado, A. El-Merhi, C. Brown, C. Chan, C. Badal, Darlington Site Office

References

1. OPG letter, A. Grace and V. Smyth to R. Jammal, “Darlington NGS Refurbishment: Unit 4 Return to Service – Request for CNSC Consent Prior to Exceeding 1% Full Power (RHP3)”, NK38-CORR-00531-26628, February 12, 2026.
2. CNSC staff document: “Request by Ontario Power Generation Inc. to Remove Regulatory Hold Point for Reactor Power Increases Prior to Exceeding 1% Full Power for Unit 4”, February 16, 2026.
3. OPG email, H. Innis to C. Loreti “DNRU4 - Deferral #2 - Bulk Deferral for RCHP6”, February 12, 2026.
4. OPG email, H. Innis to C. Loreti, “RHP3 Open Item #8: RCHP6 Open Item Bulk Deferral #3 for CLIV, CCW, ECI, LPSW, MOD and PHT SAFS Open Items”, February 15, 2026.
5. OPG email, H. Innis to C. Loreti, “DNRU4 RCHP6/RHP3 Deferral #4 and RHP3 Open Item #6: RM OI #7 OPS and MTCE complete GFP System start up and Operational Checks”, February 14, 2026.