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How our nuclear reactors failed us

Ottawa Citizen - August 20, 2003
by Paul McKay


It took nine seconds to knock out Ontario's high-priced fleet of Candu nuclear reactors last Thursday, but it may take nine days to bring them all back to full power -- leaving the province acutely dependent on imported electricity and vulnerable to rolling blackouts.

The big test will likely come tomorrow afternoon. Sweltering summer weather and business power demands typically drive demand into the 23,000-25,000 megawatt range. Tomorrow, temperatures are expected to exceed 30 degrees.

Provincial utility managers will be in a race against time to bring the hobbled nuclear units back online, because Ontario can import a maximum of only 4,000 megawatts to meet any power deficit -- and power is in high demand in all areas recovering from the biggest blackout in North American history.

When the blackout hit last Thursday, most of Ontario's nuclear units tripped into full shutdown mode -- despite technology designed to de-couple them from the grid, but leave them in standby mode at 60 per cent of power output. Instead, three of the four 500-megawatt units at the Pickering B nuclear station automatically slammed into total shutdown mode, along with one 750-megawatt unit at the Bruce B complex. The station operators have declined to disclose why this occurred.

Nuclear station operators, erring on the side of safety, also put three 850-megawatt units at Darlington into full shutdown mode, as well as one 500-megawatt unit at Pickering B. That left only one 850-megawatt Darlington unit, and one 750-megawatt unit at Bruce B, operating at standby power levels. Both were feeding power back into the grid by Friday.

Another four 500-megawatt units at Pickering A, and four 750-megawatt units at Bruce A, have been out of commission since 1997 because of poor performance, costly repairs and safety upgrades. After repair and safely upgrade costs estimated at $2.5 billion, the Pickering A reactors are scheduled to return to service during the next year. For cost and safety reasons, the four Bruce A reactors will likely never be restored to service.

The combination of blackout-triggered shutdowns and out-of-commission nuclear units has put Ontario in a razor-thin power-supply deficit. It has prompted pleas from Premier Ernie Eves for large industrial users to suspend operations, a sharp cutback in civil services, and a request for citizens to minimize power consumption, especially air conditioning.

The problem has been magnified by a unique feature on Candu reactors. One of their split-second shutdown systems sends high-pressure jets of an exotic element called gadolinium into the heavy water that both cools and controls the chain reactions inside the atomic plants. The gadolinium "poisons" the reaction process by absorbing the neutrons that split uranium atoms. As a safety feature, this automatic shutdown system appears to have performed well as the blackout hit last Thursday. But once the Candu reactor moderator is "poisoned," it takes up to three days for the element to naturally dissipate so that the reactor can be restarted. That means extra power has to be found -- and paid for -- to replace that lost during downtime.

When station managers at Darlington and Pickering B also chose to put units there into total shutdown mode for safety reasons, the gadolinium "poison" process also kicked in. Once a reactor goes into cold mode, it can take days to power the unit back up because thousands of complex performance and safety circuits have to be checked. During that downtime, replacement power has to be found and purchased.

By contrast, the reactor design used in the U.S. does not use a Candu-type moderator/coolant, so they can be shut down without "poisoning" the reaction process. Consequently, the U.S. reactors affected by the blackout have returned to service much more quickly than those in Ontario.

A final hurdle in bringing Ontario's nuclear fleet back into full service is that provincial utility managers must carefully match the power output to demand from Ontario industries, commercial businesses and 12 million consumers. A sudden excess of power sent into the grid, or a surge in demand that is not met instantaneously by power-plant output, could trigger new domino-effect blackouts. So literally, hour by hour, the nuclear units must be brought back online and adjusted as provincewide power demands fluctuate. It is a balancing act that has never been executed in Ontario because the massive 1965 blackout occurred before any commercial-scale Candus were operating in Ontario. The task is complicated by the fact that each of the nuclear units represents a huge single block of power, so the reactors are not as agile to operate as a hydro station like those on the Ottawa River, or a coal plant. (For example, two Darlington units could supply all of Ottawa's power.) When Candu units come onto the grid, they provide huge jolts that must be absorbed within seconds. Also, because they are located a long way from Ontario's major load centres, fine-tuning output with demand can be a complex technical task.

The main tactic will likely be to match the returning Candu units to the demands of Ontario's large industrial power users such as steel mills, automakers, pulp and paper plants, chemical producers and mines. Currently, most have suspended production precisely because of the downed nuclear units and fragility of power imports. They use huge amounts of power around the clock, and often have designated transmission supply routes, so their return to production can be more easily matched to Candu units coming back onto the grid. It is possible, for example, to synchronize a common hour at which both the Stelco steel complex in Hamilton and specific Candu units can return to production -- but they must do so within seconds of each other. Despite lost production costs almost certainly exceeding billions of dollars, it will likely be the weekend before Ontario's largest industries and the Candu units operated by Ontario Power Generation are in balance again.

Meanwhile, Ontario's hydro and coal plants will be running flat-out, and the transmission lines bringing imported power into the province will likely be pushed to their limits. It will take another Sunday, when Ontario's power demand is lightest, for the province's largest industries and its largest power plants to complete the delicate electrical dance needed to keep the economy humming.

Even if no further blackouts occur because of Thursday's grid collapse, Ontario faces a daunting shortfall of power for years to come because of its problem-plagued nuclear fleet, and aging, smog-producing coal plants, which all three political parties have vowed to retire. They currently provide about 75 per cent of the power produced in Ontario.

Most ominously, Ontario's biggest, most costly power plant at Darlington is already overdue for a major overhaul. That has been repeatedly deferred because the province's acute power deficit has left no time or breathing space for any of the 850-megawatt units to be taken off-line. If they go down due to mechanical failure or equipment stress related to running flat out, 24 hours per day for months on end, then only a miracle would avert future blackouts.


Paul McKay is a Citizen reporter, and author of 'Electric Empire: The Inside Story of Ontario Hydro.' He is involved in a proposed green energy project in Northern Ontario.


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