No aging problem has been more vexing or dangerous in nuclear power plants
than the tendency of reactors to grow brittle.

This stubborn problem threatens the main radiation barrier at the plants:
the garage-size steel vessels that cradle tons of radioactive fuel.

In certain emergencies, these vessels would flood with cooling water. If
the vessel walls are too brittle, they could shatter and spew their
radioactive contents into the environment.

This kind of accident is most likely to occur at pressurized water
reactors, the superheated, high-pressure cookers that make up two-thirds
of the U.S. commercial nuclear industry.

In the early days, scientists knew that these vessels could grow brittle
from years of exposure to the neutrons darting from the core. But they had
only vague ideas about how long that would take.

The U.S. Nuclear Regulatory Commission decided to set a 200-degree
Fahrenheit benchmark known as "reference temperature" a calculated
measurement that predicts the threshold at which the vessel could break
apart. The higher the reference temperature, the more likely the coolant
will crack the vessel.

By 1982, 14 nuclear plants had violated the standard. An NRC staff report
offered the faint reassurance that no shutdowns would be needed "in the
next few years."

The agency went to work not figuring out how to fix vessels, but
justifying a higher standard.

In 1985, the NRC raised reference temperatures limits to 270 degrees for
vessel plates and up to 300 degrees for some welds.

This still wasn't enough. In 1994, the staff again issued a warning:
Vessel welds with high copper content were turning brittle faster than
expected. Nine plants might need to close early.

Plants set about rearranging fuel rods to minimize radiation damage to the
vessel walls. But reactors kept creeping toward violating the standards.

So regulations again needed to be loosened. In 2007, a top NRC official
declared outright that the old safety margins were "overly conservative."
Within two years, the NRC proposed even looser standards for reference
temperatures: up to 356 degrees.

These limits were adopted last year, again helping a handful of reactors
stay within the rules.

Industry and regulators say these rollbacks are safe. However defended,
though, they provide less of a margin for error.

"They do it to protect the acceptable lifetime of a plant and to squeeze
more lifetime out of it," said retired NRC engineer Demetrios Basdekas,
who tried to challenge embrittlement standards from within the agency.

The repeated relaxation of the standards might not be enough in the long
run.

Per Peterson, who studies reactor safety at the University of California,
Berkeley, predicted that the life span of some reactors will still be
limited by embrittlement.

And predicting future embrittlement may prove difficult.

When reactors were built beginning in the 1960s, officials placed metal
test samples inside the vessels to monitor brittle conditions. Industry
experts have warned that the supply of samples is dwindling.

--
Obama's black racist USAG appointee.

Eric Holder, racist black United States Attorney General drops voter
intimidation charges against the Black Panthers,  "You are about to be
ruled by the black man, cracker!"

Eric Holder, prejudiced black United States Attorney General settles the
hate crime debate, "Whites Not Protected by Hate Crime Laws."

Nancy Pelosi, Democrat criminal, accessory before and after the fact, to
former House Ways and Means Committee Chairman Charles B. Rangel of New
York's million dollar tax evasion.  On December 3, 2010, Congress voted to
censure Rangel for 11 ethics violations.  House Speaker Nancy Pelosi
fought removal of Charles B. Rangel from the House Ways and Means
Committee.

Felony President.  18 USC, Sec. 600. Promise of employment or other
benefit for political activity

Obama violated the law by trying to buy Joe Sestak off with a political
appointment in exchange for not pursuing an election bid to replace Arlen
Specter.  Obama violated the law by trying to buy former Colorado House
Speaker Andrew Romanoff off last fall to see if he'd be interested in an
administration job -- instead of running against Sen. Michael Bennet.

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