April Lindgren
CanWest News Service
May 21, 2005

Eighteen months after it began producing electricity following a refurbishment that was years behind schedule and over budget, a key Pickering nuclear unit has been shutdown until July for unanticipated repairs.

The Unit 4 reactor, which the Ontario government is counting on to supply 500 megawatts of power throughout the summer, was taken out of service unexpectedly last month after Ontario Power Generation discovered problems with feeder pipes in another unit that is being refurbished.

“Based on the preliminary finding from the Pickering Unit 1 feeders, Unit 4 was conservatively shut down on April 2, to ensure that the feeders on that unit continued to meet the prescribed thickness,” OPG said in a May 12 submission to the Canadian Nuclear Safety Commission (CNSC). “Pickering Unit 4 will remain shutdown until inspections have been completed to determine the extent of the localized thinning, and the stress analysis to demonstrate fitness for service is reassessed.”

Unit 4 went into full service in September, 2003, after a retrofit that was almost two years behind schedule and much more costly than anticipated. OPG had planned to restart four idled reactors at Pickering by the end of 2000 at a total cost of $1.3-billion, but Unit 4 cost more than $1.2-billion on its own.

Feeder pipes supply and remove coolant for the pressure tubes that hold uranium bundles in CANDU reactors. The pipes are highly radioactive and their walls thin over time because of the fast-moving water that flows through them. High-tech ultrasound instruments are used to measure the thickness of the pipe walls to guard against leaks that would interfere with the cooling of the reactor.

While concern about the feeder pipes was enough to warrant the shutdown of Unit 4, OPG officials are downplaying its impact on the reliability of Ontario’s nuclear reactors and on plans to have the 500-megawatt Unit 1 reactor back in service by late September.

The provincial government is counting on both Unit 1 and the output from Unit 4 to help compensate for the 7,500 megawatts that will disappear when all the province’s polluting coal-fired plants are closed in 2007.

“The coal plants have traditionally been backup for the nuclear plants – that’s one of their important roles,” said Tom Adams, executive director of the watchdog group Energy Probe. “What we’re likely to see [as a result of the feeder pipe problems] are more inspections, more maintenance, more forced outages, higher costs and lower outputs.”

OPG vice-president of public affairs Chuck Pautler said the thinning of feeder pipes is a well-known phenomenon and something the utility constantly monitors.

Following the inspection of 140 feeder tubes at Unit 4, OPG decided to replace two of them, including one that was already scheduled to be replaced in September, he said. “That unit will be back in time for the hot days of the summer – by July,” Mr. Pautler said.