CNSC confirms orders on CANDU restarts

24 September 2021

The Canadian Nuclear Safety Commission (CNSC) has confirmed or amended orders issued to Bruce Power and Ontario Power Generation (OPG) related to pressure tube fitness for service following a public hearing held on 10 September. The regulator confirmed the orders issued for certain units at the Bruce, Darlington and Pickering CANDU plants, but removed Pickering units 1 and 4 from the list. It said it will consider restart requests for the reactors concerned on a case-by-case basis.

The Bruce site in Ontario (Image: Bruce Power)

On 26 July, a CNSC designated officer (DO) issued an order to Bruce Power for the Bruce nuclear power plant, after elevated hydrogen equivalent concentrations (Heq) were reported to the CNSC. The discovery of elevated Heq at Bruce units 3 and 6 was considered by the DO to put into question the predictive capability of the model for the Heq concentration levels in operating reactors with pressure tubes in extended operation. The DO subsequently issued orders to OPG for the Darlington and Pickering plants on 27 July.

The orders applied to the following reactors: Bruce units 3, 4, 5, 7 and 8; Pickering units 1, 4, 5, 6, 7 and 8; and Darlington units 1 and 4. The orders require Bruce Power and OPG to obtain authorisation from the CNSC prior to the restart of designated units following any outage that results in the cooldown of the heat transport system.

As required under Canada's Nuclear Safety and Control Act, the CNSC is required to review the orders and confirm, amend, revoke or replace each of them. The commission also considered the requests for restart submitted by Bruce Power and OPG pursuant to the terms of the orders, in order to determine whether to authorise the restart of designated units.

In a Summary Record of Decision, dated 22 September, CNSC confirmed the DO order issued to Bruce Power on 26 July and to OPG on 27 July for the Darlington plant. However, it amended the DO order issued to OPG for the Pickering plant by removing units 1 and 4.

For the request for authorisation from the CNSC prior to the restart of designated units, the commission said it "does not, at this time, pre-authorise the restart of any designated reactor unit pursuant to the terms of the orders." It said it will consider each request for restart on a case-by-case basis. "Any request shall contain qualitative and quantitative analysis to satisfy the conditions of the order."

The detailed reasons for the CNSC's decision will be provided in a detailed Record of Decision, to be published at a later date.

Bruce Power said it supports this decision and will "continue to provide information when available from activities outlined, consistent with the order, for staff review and commission consideration."

"Pressure tube integrity is based on a number of factors, and high levels of safety continue to be demonstrated to ensure the integrity of our pressure tubes through comprehensive inspections, verification and layers of safety," the company added.

Inside CANDU reactors, each fuel channel consists of a pressure tube, a calandria tube, end fittings and spacers. On the two opposite ends of the pressure tube are end fittings. Inside the pressure tube are the fuel bundles, which generate heat. On the outside of the pressure tube there is the calandria tube, separated from the pressure tube by multiple spacers. Within this gap there is a gas which is measured by an Annulus Gas System which measures moisture and also is a defence measure to ensure integrity of pressure tubes.

Bruce Power found elevated levels of Heq in the pressure tubes during part of ongoing planned inspection, testing, analysis and maintenance activities at Bruce units 3 and 6. Unit 3 is in a routine inspection and maintenance outage, while unit 6 is undergoing its Major Component Replacement, where all pressure tubes are being replaced.

Researched and written by World Nuclear News