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

Regulatory Operations Branch

March 7, 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 Regulatory Hold Point-4, Prior To Exceeding 35 % Full Power

Dear Mr. Grace and Mr. Smyth:

The purpose of this letter is to respond to Ontario Power Generation’s (OPG) submission [1], which requested removal of Regulatory Hold Point-4 (RHP-4), allowing operation above 35 % full power for the refurbished Darlington Unit 4 reactor, and provided the associated Completion Assurance Document.

Canadian Nuclear Safety Commission (CNSC) staff’s assessment [2] of OPG’s submission [1], as well as of all supporting documentation, concluded that OPG has met all the pre-requisites established by the Commission to remove RHP-4. 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-4 and OPG may now proceed with operation above 35 % full power for the Unit 4 reactor.

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. Hazelton, 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 35% Full Power (RHP4)”, NK38-CORR-000531-26652, March 4, 2026.
2. CNSC staff document: “Request by Ontario Power Generation Inc. to Remove Regulatory Hold Point for Prior Consent Prior to Exceeding 35% Full Power (RHP4)”, March 7, 2026.