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Damages to nuclear reactors trouble power plant officials
by H. Josef Hebert WASHINGTON – A nuclear reactor in Ohio is found to
have a large hole nobody thought possible, burned almost through its six-inch
protective steel cover. Cracks of a type never seen before are discovered
at a reactor in South Carolina, triggering widespread inspections. Both events caught industry leaders and government regulators by surprise,
and they are fueling new questions about aging nuclear-power plants and
plant-inspection programs. The cracks found last year at the Oconee plant in South Carolina and
the hole discovered in March in the steel reactor lid at the Davis Besse
plant in Ohio were in areas thought largely impervious to such problems. “It was material degradation that wasn't expected,” acknowledges Alex
Marion of the Nuclear Energy Institute, the industry's trade group. The 25-year-old Davis Besse reactor on the shore of Lake Erie is one
of four nuclear plants owned by FirstEnergy Corp. It has been shut down
since February, waiting for the hole in the reactor dome to be patched. An inspection of most of the 68 other plants with similar designs and
conditions reported no corrosion. But the regulators ordered special inspections
at 14 reactors thought to be vulnerable to nozzle cracking because of
their age. Some senior officials at the Nuclear Regulatory Commission are viewing
the Davis Besse and Oconee discoveries as the most significant safety
issue facing the nuclear industry since the Three Mile Island accident
23 years ago. The steel reactor vessel, which encloses the reactor's core, always has
been viewed as “a sacred component” that will not be breached, said Brian
Sheron, the commission's assistant director for licensing and technology
assessment. “This really challenges that assumption.” The problems at both reactors were discovered before they posed an immediate
safety risk. A break through the reactor cover would have caused thousands
of gallons of radioactive water to spew into the containment building,
raising the risks of the core overheating and a potential meltdown and
possible release of radiation into the environment. Only a thin noncorrosive stainless steel membrane kept the hole at the
Ohio reactor from bursting open. The cracks at the Oconee plant, owned
by Duke Power, were less urgent. But had the crack expanded it could have
caused the nozzle to separate, also causing a loss of cooling water inside
the reactor, nuclear experts said. Industry spokesmen said backup safety systems would have averted more
serious problems, by pumping more water into the reactor than was being
allowed to escape, keeping the nuclear fuel safe until the reactor could
be shut down. But that's true if everything worked perfectly, said David Lochbaum,
a nuclear engineer and industry watchdog for the Union of Concerned Scientists.
And that might not be the case if emergency-pumping systems became clogged
with debris, if other equipment is damaged, or a gauge is misread by plant
operators struggling to make sure the reactor core remains covered with
water, he said. At the very least, argue nuclear industry critics, the Davis Besse and
Oconee incidents reveal shortcomings in how utilities inspect older power
plants and how the NRC monitors them. The hole and cracks were found in largely inaccessible areas where there
is substantial radiation and inspections can be done only when the plant
is shut down. |