Atomic Energy of Canada Limited National Research Universal Reactor Safety System Upgrades and the Canadian Nuclear Safety Commission's Licensing and Oversight Process

III. Implementation of NRU Reactor “Upgrades”

III. A. Early Plans

On December 7, 1992, AECL informed the Atomic Energy Control Board (AECB) [11] of its intent to upgrade NRU reactor safety with modifications needed to achieve off-site dose and safety assessment goals. The seven safety system upgrades included an independent second trip system, a qualified emergency response center, a new emergency core cooling system, a qualified emergency water system, main pump flood protection, liquid and gaseous confinement boundary, and a new emergency power system.

The safety improvements expected from the NRU safety upgrades were described in a January 1993 Concept Safety Assessment [12]. "The EPS will provide power for the NECC (See Section 7.3), other upgraded safety systems and improve the reliability of power supplies to heavy water pumps P-104 and P-105 […] In the case of failure of the NRU Class 1 supply, this 130VDC supply will be used to supply heavy water pumps P-104 and P-105." A Core Damage Frequency improvement, due to the EPS, was tabulated. "Improvement in Core Damage Frequency when Proposed Emergency Power Supply Installed" listed four sequences: (1) Loss of Class 3 for more than 2 hours with partial loss of Class 4 was 3 x 10-3 and will be 5 x 10-5 ; (2) Loss of Class 3 for more than 2 hours caused by loss of Class 4 with failure of diesels was 3 x 10-3 and will be 5 x 10-5 ; (3) Loss of Class 3 for more 2 hours with Class 4 available was 2 x 10-3 and will be 3 x 10-5 ; and (4) Loss of Class 4 with Class 1 batteries unavailable was 1 x 10-2 and will be 2 x 10-5. The revised frequency on the expectation that the core can survive for at least 30 minutes without forced cooling flow was 4 x 10-4 and will be 8 x 10-7. The safety goals were not formally incorporated into the NRU OL, either directly or indirectly - through the FA or Final Safety Analysis Report (FSAR). The proposed safety upgrades were scheduled for completion in 1995/1996, pending approval of the AECL Board of Directors.

In a 1994 Board Member Document (BMD) [13], the AECB staff informed the Board of AECL plans “to upgrade the NRU reactor with a package of seven improvements it considers important to permit the reactor to operate safely until about the turn of the century." The BMD indicated that improvements to the EPS would be installed by 1997. The AECB staff said it agreed "that these improvements are desirable", and proposed “to authorize these on a case-by-case basis". According to the document, "The upgrades would be authorized by licence amendments.” AECB staff said in the BMD that it was “not yet in a position to assess whether the proposed set of upgrades is sufficient to allow the reactor to operate safely for the remainder of the planned life-time."

In 1997, the Nuclear Safety and Control Act (NSCA) established the CNSC, replacing the AECB as the independent regulatory body with the responsibility for the regulation of Canadian nuclear facilities.

Throughout the mid 1990s, multiple communications were held between the CNSC and AECL regarding the details of, and schedules for, the safety upgrades. In a 1995 Licensing Plan [14], AECL described the package of seven proposed upgrades including EPS which “provides a hazards qualified source of Class 1 power for the main heavy-water pumps No. 4 and 5 in the event of a loss of coolant accident.”

The Talisman Team considers that these early plans clearly included the connection of a hazards-qualified EPS backup power to the MHWPs, as a part of the planned upgrades.

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