CANDU Flawed

CANDU Flawed

In the belly of the nuclear beast, the massive domes of the reactors rise ominously to a height of more than 45 m, their radioactive interiors visible only through the thick windows of airlocks. One level up at Ontario Hydro's sprawling Pickering station, 40 km east of Toronto, steam-driven turbines crouch under an array of blue, green and yellow pipes. Nearby, many of the 25 years' worth of spent nuclear fuel rods stored at Pickering lie beneath 3.5 m of water in an eerily shimmering pool. Inside the plant, it is hot, noisy and hectic as members of the 2,800-strong workforce go about their business. And on a typical day earlier this year, all seemed well. Two of Pickering's eight CANDU reactors were shut down for routine maintenance, while the remaining six sent about 3,000 megawatts of electricity surging into the provincial grid - enough, in normal circumstances, to supply every home, office and factory in Metropolitan Toronto.

But beneath the surface, there were festering, potentially deadly problems at Pickering and elsewhere among Hydro's 19 working reactors - as last week's report on the corporation's nuclear division scathingly demonstrated. The flaws go beyond the poor safety training and sloppy operating practices highlighted in the report. Ontario's CANDUs are growing old - and the four venerable A units at Pickering and three more at the Bruce generating station on the shores of Lake Huron, all of which Ontario Hydro has decided to mothball, may never resume operation. Reason: the reactors, which went into service between 1971 and 1979 - and were designed to last 40 years - are plagued by troubles that include worn pressure tubes, which will soon be in need of replacement, faulty steam generators, and safety features that fall short of the standards set by the Atomic Energy Control Board (AECB), the federal body that regulates the nuclear industry. "For years, Ontario Hydro has been living in a dream world," says Gordon Edwards, spokesman for the Montreal-based Canadian Coalition for Nuclear Responsibility. "Now, they're experiencing a shock of recognition and admitting that everything is not OK."

Hardware failings have also emerged at the two Canadian-operated CANDUs outside of Ontario - at Gentilly, Que., and Point Lepreau, N.B. At both reactors, corrosion has thinned some feeder pipes that carry radioactive heavy water from the reactor core to steam-generating boilers. Atomic Energy of Canada Ltd. officials say the corrosion has been arrested, but Julie Dingwell, of the Saint John, N.B.-based group People Against Lepreau, worries that the deficiencies in Ontario's nuclear network may afflict all CANDU operations. "The safety margins have not been good," says Dingwell. "It's really frightening." Nuclear officials maintain that many of the equipment problems are normal and acceptable. "You have to look at the broad context," says Gary Kugler, a vice-president at Mississauga, Ont.-based Atomic Energy of Canada Ltd., the Crown corporation that designed and exports the CANDU. "All machinery, including nuclear reactors, shows wear and tear after a length of time." But David Martin, spokesman for the Pickering-area anti-nuclear organization Durham Nuclear Awareness, insists that Ontario Hydro and other reactor operators in Canada face a "fundamental technology problem. Ontario Hydro is shutting down its oldest reactors because they have too many defects - and I predict that they will never be restarted."

When the CANDU (for Canadian deuterium uranium reactor) was designed back in the 1950s, its basic features were supposed to make it more versatile, cheaper to operate and safer than its competitors. At the heart of the CANDU are pellets of radioactive uranium dioxide fuel assembled into pencil-shaped sheaths that, in turn, are grouped inside six-metre-long pressure tubes. Hundreds of tubes are installed in each reactor, where heavy water - also known as deuterium oxide, a molecule containing an extra-large hydrogen atom - slows the movement of free neutrons generated by the uranium. This increases the chances that the neutrons will split uranium atoms and release their pent-up energy in a controlled chain reaction. When that happens, energy is transferred to the heavy water, which heats ordinary water to create steam that drives turbines to produce electricity.

As with many reactors, flaws were inadvertently built into the CANDU from the start. One problem stems from a decision to fabricate pressure tubes for two of Pickering A's four reactors from a tin-and-zirconium blend called zircaloy. But zircaloy tubes were prone to corrosion and blistering. As well, Pickering A's two other reactors experienced a medley of setbacks, including unexpected pressure tube vibrations that gradually weakened their structure. The extent of the flaws became dramatically apparent in August, 1983, when a metre-long gash appeared in a pressure tube in Pickering A's No. 2 reactor, spewing heavy water into the plant and shutting down part of the station. Over the next nine years, all four Pickering A reactors were refitted with new tubes at a cost of about $1 billion.

Many of the same inherent design problems have affected the four Bruce A reactors. But that plant's worst disaster was set in train when maintenance workers in 1986 left a protective lead blanket in the boiler of Bruce A's No. 2 reactor - a slipup that was not discovered until six years later. By then, the blanket had melted, injecting vaporized lead into the steam and severely damaging the boiler. "That was not a good time," recalls Ken Talbot, the Ontario Hydro official who was running Bruce at the time. By 1995, with the damaged reactor also in need of new pressure tubes and facing a total repair cost of about $500 million, Hydro took the unit out of service.

Now, the other three Bruce A reactors and Pickering A's four are going into retirement as well - the Bruce reactors because of boiler troubles, and all three will need retubing within the next decade at a cost of well over $1 billion. The Pickering A units, with their relatively new pressure tubes, still require costly upgrades to bring their safety features in line with current AECB requirements. The older Pickering units have a single emergency shutdown procedure: in an emergency, neutron-absorbing rods drop into the reactor core, halting the nuclear process within seconds. But they lack the newer reactors' backup system that stops the reactor by injecting a nitrate "poison" into the core - a feature that would cost millions of dollars.

In another telling admission of defeat, Ontario Hydro now plans to spend about $400 million - not to repair the mothballed reactors, but to upgrade equipment at the eight newer B units at Pickering and Bruce and four at eight-year-old Darlington station 75 km east of Toronto. "After years of failure," says Norm Rubin, director of nuclear research for the Toronto-based environmental organization Energy Probe, "Hydro is asking Ontario's taxpayers to pay the bill again for one last attempt to make nuclear technology work." In the end, Ontario Hydro's stunning confession of past failures could point to a more profound error half a century ago, when Ottawa and Ontario may have bet on the wrong technology.

Maclean's August 25, 1997