Detection systems at Bruce Nuclear Plant

FIRE PROTECTION

Bruce Power nuclear station encompasses 25 square miles near Lake Huron, northwest of Toronto. The plant is owned by a consortium of Cameco Corporation, TransCanada Pipeline, BPC Generation Infrastructure Trust, the Power Workers’ Union and the Society of Energy Professionals.

In 1999, Bruce Power began a project to retrofit two reactors built in the 1970s. The project represented the largest fire protection upgrade in the nuclear industry. [The retrofitted plants are two of four in Bruce A. The station also has four active nuclear reactors, Bruce B, built in the 1980s.]

VESDA Air Sampling Smoke Detection is designed to address the specific operational areas and environmental changes in power plants, such as remote and unmanned substations and sites, diverse temperature ranges, moisture content, particle density, and increased levels of airflow.

At Bruce Power, Vesda was chosen for several reasons. The main areas of concern were a slow, electrical and electronic-based fire load. The initial stages of these types of fires are difficult to detect using standard spot detectors. Ease of installation and maintenance were also key factors.

All nuclear power plants in Canada must conform to the National Building Code of Canada, the National Fire Code of Canada, and the Canadian Standards Association (CSA) standard N293. Edwards of Canada EST located in Owen Sound, Ontario was the main contractor for the complete turnkey fire alarm and detection system.* At its factory, the company was required to mock up the entire system for inspection and testing prior to installation.

Bruce Power uses Vesda in all its control equipment rooms, cable spreading areas, and in many of its electrical safety environments. More than 50 Vesda detectors have been installed. The Vesda units are placed to provide virtually impenetrable detection screens and an inherent level of redundancy. A two-layer fire detection concept is used. The effects of smoke layer stratification are minimized by placing sampling points to monitor the two detection zones that are created by the congestion of the cable trays and the airflow patterns typically found in the spaces. High level sampling points are located four to six inches below the underside of the ceiling slab and sample the entire ceiling area above the cable trays. These sampling points are expected to respond more quickly to a fire in the cable racks. Low level sampling points are located below the cable trays, with these points expected to respond more quickly to a fire in the equipment racks. This two-layer detection technique maximizes the points of intersection of smoke travel from potential fire sources throughout the space.

Sampling at the return air grilles located in these spaces increases the speed of detection of an incipient fire due to the predominant effect of the high air exchange rates on the airflow patterns. Smoke from an incipient fire has little plume strength and its path will be primarily governed by the airflow patterns present in the room.

The units report directly in the main control room and to the fire department via the fire alarm system. They provide a localized description of the source of the fire event. In the “alert” stage, which is well below typical fire alarm thresholds, there can be rapid intervention to contain the fire in its infancy.

Due to the magnitude of the plants’ fire protection upgrades, Bruce Power worked with the U.S. National Fire Protection Association to develop solutions. At the company’s request, NFPA convened a meeting of the technical commmittee for nuclear facilities, which encompassed NFPA 805, Performance-Based Standard for Fire Protection for Light Water Reactor Electric Generating Plants. This provided an opportunity to consider how performance-based options can be effectively applied to upgrade situations.

Vesda was installed in other nuclear power plants in Ontario and helps protect similar facilities around the world.

Article supplied by Vision Fire & Security, Norwell, Massachusetts, tel. 781-749-2223, a division of Vision Systems Inc.

* Leber Rubes of Toronto was the fire code consultant.