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Decaying concrete a problem for aging nuclear power plants

concrete degradation has surfaced in the reactor containment buildings of three U.S. nuclear power stations. The Nuclear Regulatory Commission recently warned operators there that design strengths and assumptions used in original containment building design plans “may no longer hold true,” if ASR and its telltale cracks and fissures are present.

Decaying concrete raising concerns at Canada’s aging nuclear plants, National Post Ian MacLeod, Postmedia News  Jul 8, 2012 Decaying concrete at nuclear power plants is the latest concern for nuclear safety authorities.

At Quebec’s sole atomic power station, Gentilly-2, eroding concrete has prompted federal licensing officials to suggest that any provincial attempt to refurbish and re-license the 30-year-old plant must satisfy federal concerns over the aging concrete’s ability to stand up to another two or three decades of service.

The move comes as economic pressures force nuclear utilities to consider refurbishing their nuclear plants and operating them well past their 25- to 30-year initial lives.

With Gentilly-2 at the end of its service life, the Quebec government
is under pressure to decide soon whether to order a refit or shut down
the plant permanently.

Refurbishment estimates range from $2 billion to $3 billion. A
shutdown is pegged at $1.6 billion.Of particular concern for any “life
extension” is the dome-shaped containment building that encloses the
675-megawatt CANDU 6 reactor. The metre-thick, steel-reinforced
concrete structure serves as the final physical barrier against
radioactive contamination escaping into the atmosphere around
Becancour, on the south shore of the St. Lawrence River across from
Trois-Rivieres and an hour’s drive northeast of Montreal.

“Special attention is needed for the containment structure in the
longer term since it has been identified that containment concrete
suffers from” a common type of concrete decay called alkali-silica
reaction (ASR), says a 2010 report by the Canadian Nuclear Safety
Commission (CNSC) in Ottawa.

Despite those long-term concerns, the CNSC last year renewed the
plant’s operating licence until 2016……
Meanwhile, concrete degradation has surfaced in the reactor containment buildings of three U.S. nuclear power stations. The Nuclear Regulatory Commission recently warned operators there that design strengths and assumptions used in original containment building design plans “may no longer hold true,” if ASR and its telltale cracks and fissures are present.
ASR can take years to develop and its chemistry is well understood.
But its effect on the structural behaviour of nuclear reactor
containment and other buildings is not. The issue is especially
relevant to Gentilly-2, which sits on a seismic fault line.

“The potential mechanical consequences of the chemical reaction, in
terms of ultimate resistance of structural elements and overall
structural behaviour, are unknown,” according to the CNSC.

The agency says it is in the process of commissioning an independent
research project to establish an aging-concrete regulatory standard
for Canada’s fleet of nuclear power plants in general and “in
particular for Gentilly-2 with the goal to have regulatory program in
place to assess Gentilly-2 refurbishment program and to support
licensing of Gentilly-2 life extension.”….
The Charest government, accused of dithering on the fate of
Gentilly-2, obviously has been watching developments in neighbouring
New Brunswick, where the provincial power utility is mired in the
refurbishment of the Point Lepreau nuclear generation station.

Originally scheduled to take 18 months and cost $1.4 billion, the
project is expected to finish this fall, three years late and $1
billion over budget.

And that’s without having to meet any new regulatory standard for the
life-extension of aging concrete……
http://news.nationalpost.com/2012/07/08/decaying-concrete-raising-concerns-at-canadas-aging-nuclear-plants/

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July 9, 2012 - Posted by | Canada, safety, USA

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