[cdn-nucl-l] Ontario keeps reactors on longer for more power

Ontario keeps reactors on longer for more power

By Scott DiSavinoFri Sep 8, 8:50 AM ET

Ontario nuclear operators are generating more electricity by keeping their power reactors operating longer between maintenance outages, according to spokesmen at Ontario Power Generation and Bruce Power.

While improvements in maintenance and inspections have allowed the operators to reduce the number of outages, it is the unique design of the Canadian reactors themselves which allows refueling during operation that makes it possible for the units to continue operating for 30 or 36 months.

That is unheard of for a nuclear reactor in the United States, which must shut for refueling every 18 to 24 months.

OPG, the province-owned generating company, has extended the length between major maintenance outages at the 3,524-megawatt Darlington nuclear power station from 24 months to 36 months. One MW powers about 800 homes.

Unit 1 at Darlington, for example, has operated continuously since the spring of 2004 except for a couple of short outages. It is expected to continue to operate until the spring 2007.

OPG is also looking to extend the time between outages at the 3,090 MW Pickering station on the shores of Lake Erie in Pickering, about 30 miles east of Toronto, near the Darlington station.

Bruce Power, which operates the giant Bruce nuclear station, is also seeking to extend the time between outages at its power plant in Tiverton on the shores of Lake Huron, about 155 miles northwest of Toronto, from 24 months to 30 months. Unit 6 at Bruce has operated almost continuously since the fall of 2004.

U.S. VERSUS CANADA

The primary difference between the boiling water and pressurized water reactors in the United States and the Canadian Deuterium Uranium (CANDU) reactors in Ontario is that operators can refuel the CANDU reactors without shutting them.

In the U.S., operators stack enriched uranium fuel rods vertically into a large sealed pressure vessel. Each rod is about 12 feet long and about the diameter of a pencil.

Once the vessel is sealed, the operator cannot open it without shutting the reactor. As the uranium is "burned," the operator must shut the reactor every 18 to 24 months to replace about a third of the fuel.

In a CANDU reactor, operators load natural uranium fuel bundles horizontally into pressure tubes -- each of which can be isolated and acts like a small pressure vessel. There are about 360 pressure tubes at each unit at Darlington.

The operators can manually load the cylindrical fuel bundles on one side of a pressure tube and remove the used fuel from the other side. Each tube holds about 12 or 13 bundles. Each bundle, which produces the same amount of heat as 400 tonnes of coal, is about 5 inches in diameter and 15 to 16 inches long.

The used CANDU fuel is highly radioactive just like the fuel used in the United States, and cannot be handled.

If it were not for the need for maintenance (and unplanned outages), a CANDU reactor in theory could operate forever, as long as fuel was available.