Schreyer Award: Bruce A Plant Restart

The Bruce A Nuclear Plant on the shores of Lake Huron near Kincardine, Ontario, is a 4 x 750 MW CANDU nuclear plant commissioned in the 1970s and shut down in late 1990s. Bruce Power leased the plant in 2001 and decided to restart Units 3 and 4 to sell energy to Ontario.

The Bruce A plant was a mature facility that needed to be refurbished and refitted to bring it up to current operating standards as laid out by the Canadian Nuclear Safety Commission. This was a special challenge because of the strict protocol that has to be addressed with nuclear power facilities, such as the need for special clearances when working in restricted zones. Also, field verification was needed in many cases to establish the existing condition of the plant.

In 2001, the Acres-Sargent & Lundy-Fox Joint Venture (ASLF) was contracted as the lead engineering-procurement-construction company for the restart project. The lead member of the joint venture is Acres International of Oakville, Ontario. Sargent & Lundy of Chicago has extensive experience in nuclear generation, while E.S. Fox of Niagara Falls, Ontario is a qualified nuclear construction contractor.

The $700-million project involved 45 different modification projects, ranging in size from $41 million to $28 million. Individual assignments ranged from the maintenance and overhaul of existing equipment to the provision of two key safety components — a Secondary Control Area (SCA) and a Qualified Power Supply (QPA).

Quality assurance and efficiency

In order to ensure that the design was safe and had no adverse environmental or other impacts, a team of experts from ASLF and Bruce Power developed a system of third party reviews on all aspects of the project, from the design of critical control systems, to routine building services calculations.

Since no laid-up nuclear plants in Canada had been restarted to date, and since plants operated by other owners were experiencing large cost overruns and delays, the cost and schedule targets for the Bruce A Restart were monitored carefully as the work progressed. The ASLF joint venture met regularly with Bruce Power to redefine the scope of work. They determined that a more realistic start date would be the fall rather than the spring of 2003.

ASLF’s approach to design and construction allowed the installation to be expedited by relying on thorough documentation of each field change during construction. The alternate method is to revise work packages and drawings each time a change — along with its associated quality assurance reviews — is required. Because ASLF was also the constructor, the design and construction forces worked in integrated teams, helping to expedite communications and quality assurance reviews. ASLF produced over 2,500 drawings, of which approximately 1,000 are for the SCA and QPS projects. Other nuclear restart projects in Canada have used separate design and construction forces, resulting in fewer field changes but a longer design period and delays due to the required quality assurance review and approval process.

In the event, Bruce Power’s 750-MW Unit 4 was restarted in October 2003 and Unit 3 followed a few months later. This was the first time any company has started two CANDU units back-to-back. With 1,400 MW of extra electricity feeding into the Ontario power grid, coal-fired generation and resulting greenhouse gas emissions have been displaced.

The Secondary Control Area and Qualified Power Supply were two of the most complex of the concurrent projects. The design and construction cost for these two safety related components was $51 million, of which engineering accounted for approximately 40%. This ratio is higher than industry norms for industry retrofits due to the extensive quality assurance required for nuclear projects.

Although there were numerous scope changes, which resulted in the final cost being over the original budget estimate, the priority goals of installing these safety related systems concurrent with the restart of Units 3 and 4 were met in line with the client’s schedule and quality assurance requirements.

One of the project’s lasting legacies is that it provides a successful template for the provision of qualified power supply and back-up systems for the safe shutdown of CANDU power plants.

Secondary Control Area

The Secondary Control Area provides a completely independent system from the main control room for safe shutdown of the critical reactor systems. It is required specifically for situations where fire, smoke or radiation make the main control room unsafe for human occupation. It also functions as the Emergency Operations Centre if the main control room is declared unusable.

The start of the SCA project came after some of the other restart work had begun and needed an aggressive schedule to be completed on time. Extensive engineering and construction effort was spent locating the SCA within the plant. There were few suitable locations and each entailed expensive renovations to the existing plant. The other concern was ensuring the SCA’s response time was fast enough. The cabling had to be sized so that electronic signals provided shutdown responses with minimal delay.

In the event, the SCA is located a distance away from the main control room.

It incorporates the following features:

Shutdown. The reactor can be shut down from high power by tripping the secondary shutdown system from the SCA. It includes: reactor power monitoring; boiler level monitoring.

Cool down. Heat transport temperature monitoring; heat transport pressure monitoring; heat transport pump unit; maintenance cooling monitoring; boiler pressure monitoring; boiler BSRV cool down; high pressure emergency coolant injection (HPECI).

Maintaining containment. Vacuum building and containment pressure monitoring; emergency filtered air discharge system (EFADS) operation, EFADS stack flow monitoring and post-accident radiation monitoring system (PARMS) operation.

Communications.

Structural requirements. The SCA is designed to seismic requirements. All instruments and controls are seismically designed. It is also steam-proofed to withstand a main steam line leak, and has a two-hour wall fireproofing rating and fire detection.

Power supplies. Power to all the distribution circuits is normally supplied by the existing 500 Vac, 48 Vdc and 120 Vac Class II and Class III circuits, all backed up by the Qualified Power Supply with two Caterpillar diesel generators.

Qualified Power System

After Bruce A was laid up, many feeds to the existing qualified power system were removed and other changes were made which meant it was not cost-effective to restore the original design concept. There was also a need to address seismic and major fire events, including fire in the main control room.

In order to re-fit the main feed to the QPS, a study was performed to evaluate the design alternatives. Given the aggressive time-line, major construction activities were ruled out.

The system is designed:

to be continuously energized and capable of providing the required power to designated loads after a Main Steam Line Break (MSLB) event;

to be connected to a reliable off-site power supply that will not be adversely impacted by a MSLB event;

to have all equipment protected from, or qualified, for the conditions present following a MSLB event;

to be capable of maintaining voltage at 2.5% of nominal steady state and not to drop below 80% during motor starting;

to be capable of providing a continuous load of 750kVA for 48 hours following the event;

as a minimum to meet the screening criteria used by the safe shutdown seismic assessment;

to supply power to a designated unit or common loads for up to 72 hours.

The resultant system provides three diverse power sources; two normal and one emergency. The normal power source for the QPS ODD bus is supplied from the on-site Unit 3 4.16 kV class III system, and the normal source for the QPS EVEN bus will be supplied from the off-site 44 kV construction power distribution station DS1, via a 44 – 8.32/4.16 kV tran
sformer and 4.16 kV class III switchgear. In the interim, a temporary diesel generator SG2 provides an alternate power source to the EVEN bus. The emergency source of power is provided by the safety related 600V QPS standby diesel generator SG1, which is completely independent of the normal Class IV, III, II and I power distribution systems.

A time delay of approximately five minutes can be tolerated to restore a de-energized QPS bus. This time delay permits power to be restored either automatically or manually either from the preferred sources or from standby and temporary generators.

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Project: Bruce “A” Restart – Units 3 & 4

Award-winning firm: Acres-Sargent & Lundy-Fox (ASLF) (Alan O’Brien, John Regan, P.E., Terry Armstrong, Ray Parson, P.E., Mike Knaszak, P.E., Dan Jory, P.Eng., Anthony Stranak, Mirza Rayman, P.Eng., Dave Cromie, P.Eng., Richard Goetzke, P.E.)

Owner: Bruce Power

Other key players: Leber Rubes (fire protection); Vipond (fire protection); ABS Consulting (seismic analysis); EPM (fire analysis)

Suppliers: Edwards (fire protection panels); Nuclear Logistics (batteries)