our nuclear reactors failed us
The 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
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.
© Copyright 2003 The Ottawa Citizen
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