nuclear-news

Under the public radar, nuclear power is “uprated”, bringing safety concerns

nuclear watchdogs and the U.S. Nuclear Regulatory Commission’s own safety advisory panel have expressed concern over larger boosts — some by up to 20% — that the NRC began approving in 1998. Twenty of the nation’s 104 reactors have undergone these “extended power uprates.”

U.S. is increasing nuclear power through uprating Turning up the power is a little-publicized way of getting more electricity from existing nuclear plants. But scrutiny is likely to increase in the wake of Japan’s nuclear crisis. LA Times, April 17, 2011|By Alan Zarembo and Ben Welsh, Los Angeles Times

The U.S. nuclear industry is turning up the power on old reactors, spurring quiet debate over the safety of pushing aging equipment beyond its original specifications.

The little-publicized practice, known as uprating, has expanded the country’s nuclear capacity without the financial risks, public anxiety and political obstacles that have halted the construction of new plants for the last 15 years.
The power boosts come from more potent fuel rods in the reactor core and, sometimes, more highly enriched uranium. As a result, the nuclear reactions generate more heat, which boils more water into steam to drive the turbines that make electricity.

Tiny uprates have long been common. But nuclear watchdogs and the U.S. Nuclear Regulatory Commission’s own safety advisory panel have expressed concern over larger boosts — some by up to 20% — that the NRC began approving in 1998. Twenty of the nation’s 104 reactors have undergone these “extended power uprates.”

The safety discussions have largely escaped public attention, but they could become more prominent as the Japanese nuclear crisis focuses more scrutiny on U.S. reactors.

In an uprated reactor, more neutrons bombard the core, increasing stress on its steel shell. Core temperatures are higher, lengthening the time to cool it during a shutdown. Water and steam flow at higher pressures, increasing corrosion of pipes, valves and other parts.

“This trend is, in principle, detrimental to the stability
characteristics of the reactor, inasmuch as it increases the
probability of instability events and increases the severity of such
events, if they were to occur,” the Advisory Committee on Reactor
Safeguards, which is mandated by Congress to advise the NRC, has
warned……
“It’s beyond the wit of mankind to identify all challenges to a
nuclear plant,” said John Large, a former researcher for the British
atomic energy agency who runs a consulting company in London
specializing in nuclear safety.

A case in point involved three uprated reactors in Illinois.

In 2002, both reactors at the Quad Cities Nuclear Plant were restarted
after having their capacity boosted by 17.8%. Pipes began to shake,
and cracks formed in a steam separator, which removes moisture from
the steam before it enters the turbines. In one case, a 9-by-6-inch
metal chunk broke off and disappeared. Similar problems were
discovered at the Dresden Nuclear Power Plant, about 60 miles
southwest of Chicago, which had undergone a 17% uprate.

Broken parts were replaced, but the problem continued. Exelon Corp.,
which owns the three plants, and the NRC were mystified.

“The greatest concern is loose parts that you can’t find,” John
Sieber, a nuclear engineer on the NRC advisory committee, said during
a 2004 meeting. “Are they in the bottom of the reactor vessel? …. Is
it floating around where it can damage internal parts of the core?”

Eventually the problem was uncovered: acoustic waves caused by the
geometry of the steam pipes. The pipes were acting like a musical
instrument. Their geometry was modified to “detune” them.

Plans to boost the power by 14.3% at three reactors in Athens, Ala.,
and 12.9% at a plant in Monticello, Minn., have been held up, in part,
by NRC concerns over the steam separators….. some things do not
change, including the suppression pool, which is designed to soak up
heat from the reactor core during some kinds of accidents, and the
heat removal pumps, which deliver water from the pool into the core to
prevent the fuel from melting down.

David Lochbaum, a nuclear engineer with the environmental group Union
of Concerned Scientists, has argued that in some uprated reactors the
pool may be too small and could become so hot that its contents could
begin to vaporize, causing the pumps to lose suction.
http://articles.latimes.com/2011/apr/17/local/la-me-uprates-20110418

July 19, 2012 - Posted by Christina Macpherson | safety, USA