[ RadSafe ] " Kashiwazaki Kariwa Damage 'Less than Expected' Says IAEA "

[Jaro]

http://www.worldnuclear.org/_news_database/rss_detail_features.cfm?objID=77E
DDCFF-6447-4B93-977DAE21424EC433
Kashiwazaki Kariwa Damage ‘Less than Expected’ Says IAEA
14 Aug (NucNet):
The Kashiwazaki Kariwa nuclear power plant in Japan, affected by a strong
earthquake on 16 July 2007, shut down safely and damage appears less than
expected, a team of nuclear safety experts has concluded.

The International Atomic Energy Agency (IAEA) team was dispatched after a
request from the Japanese authorities. The team’s report will be issued
within a few days, the IAEA said in a statement today.

The team carried out a three-day physical examination covering the complex
of seven nuclear units, as well as analysis of instrument logs and other
records from the time of the event. The team has concluded that plant safety
features performed as required during the earthquake.

The IAEA said the team’s review supports the Japanese authorities’
conclusion that the very small amount of radioactivity released was well
below authorised limits for public health and environmental safety.

Damage from the earthquake appears to be limited to sections of the plant
that would not affect the reactor or systems related to reactor safety, the
IAEA said.

Detailed inspections are being carried out by the operator and Japanese
authorities, with work such as detailed examination of the reactor vessels,
cores and fuel elements, still to be performed.

The earthquake “significantly exceeded” the level of seismic activity for
which the plant was designed, the IAEA said. However, as with most nuclear
plants, additional robustness in design had been incorporated into plant
structures, systems and components. The IAEA team said these conservative
seismic design measures probably explain why damage was less than could
otherwise have been expected. However, it was essential to conduct further
technical analysis to understand the precise design elements that resulted
in the plant performance, today’s statement said.

The team noted that the plant owner, Tokyo Electric Power Company (Tepco),
was at the time of the event already performing a seismic hazard
re-evaluation based on new guidelines for seismic design that had been
issued in September 2006 by Japan's Nuclear Safety Commission (NSC). Because
of the July earthquake, these evaluations will be expanded to account for
the potential existence of active faults underneath the site, the team said.

The earthquake led to the automatic shut-down of three units at the plant.
Units 3, 4 and 7 shut down safely. Units 1, 5 and 6 were already shut down
at the time of the quake for periodic inspections. Unit 2 was technically
undergoing a periodic inspection and start-up operations had just begun, but
the unit was also shut down safely.
==========================


http://www.physorg.com/news106327073.html
August 14, 2007
Frigid Enceladus: An unlikely harbor for life

A new model of Saturn’s icy moon Enceladus may quell hopes of finding life
there. Developed by researchers at the University of Illinois, the model
explains the most salient observations on Enceladus without requiring the
presence of liquid water.

Orbiting Saturn since June 30, 2004, the Cassini spacecraft has revealed a
south polar region of Enceladus with an elaborate arrangement of fractures
and ridges, intense heat radiation and geyser-like plumes consisting of ice
crystals and gases such as methane, nitrogen and carbon dioxide. The plumes
erupt from vents located in large fractures called “tiger stripes” that cut
across the south pole.

The plumes monitored by Cassini had a rate of discharge similar to Old
Faithful geyser in Yellowstone National Park. Dubbed “Cold Faithful,” the
first model that was proposed to explain the plumes suggested the plumes tap
into shallow pockets of liquid water in a water-ice shell.

Last year, U. of I. geology professor and planetary scientist Susan Kieffer
and colleagues proposed an alternate model, which they called “Frigid
Faithful.” In this model, the plumes originate in the dissociation of
certain stiff compounds of ice, called clathrates, which may cover Enceladus
to a depth of tens of kilometers. The researchers published their model in
the Dec. 15, 2006, issue of the journal Science.

“Frigid Faithful gives a straightforward account of the measured
composition, including the gases left unaccounted by Cold Faithful,” said
Kieffer, who holds a Charles R. Walgreen Jr. Chair at Illinois and is also a
professor in the University’s Center for Advanced Study, one of the highest
forms of campus recognition.

“Perhaps more important, the plumes of Frigid Faithful could remain active
far below the freezing point of water, under the frigid conditions that
might be surmised inside a tiny, icy moon,” Kieffer said.

Now, Kieffer, mechanical science and engineering professor Gustavo Gioia,
geology research associate Pinaki Chakraborty and geology professor and
department head Stephen Marshak have expanded the model to account for both
the tectonic features and the heat transport in the southern hemisphere.
They describe the model in a paper accepted for publication in the
Proceedings of the National Academy of Sciences and posted on the journal’s
Web site.

By examining the deformation of a clathrate-rich shell containing a mildly
warm heat source buried under the south pole, the researchers show it is
possible for a frigid, stiff Enceladus without a shifting interior (such as
plate tectonics on Earth) to develop fractures and ridges, and convey heat
at the observed rate.

“As the heat source warmed at depth, it expanded and stretched the
clathrate-rich shell above, giving rise to tensile stresses in the south
polar cap,” said Gioia, lead author of the paper. “As a result, the shell
cracked, forming the four 130 kilometer-long fractures known as tiger
stripes.”

The researchers estimate the heat source could have been only 40 degrees
warmer than the surrounding shell. “In this model, the tiger stripes are
analogous to the cracks that form in the glazing of a porcelain vessel when
the vessel is filled with hot tea,” Gioia said.

The researchers also show that, northwards of the south polar cap (in which
the stresses were tensile), the stresses turned first from tensile to
compressive - forming the ring of ridges that circles the tiger stripes -
and then back to tensile - forming the set of “starfish” fractures that
radiates northward from the ring of ridges. Thus the model explains the
formation of the entire arrangement of fractures and ridges observed by
Cassini on the southern hemisphere of Enceladus.

The Illinois researchers estimate the tiger stripes cut through the shell of
Enceladus to a depth of about 35 kilometers. After the tiger stripes formed,
the clathrates exposed on the cracked surfaces of the tiger stripes were
decompressed. Upon decompression, the exposed clathrates absorbed heat from
the source at depth and dissociated explosively, exposing more clathrates to
decompression, in a process that continues today.

The gaseous products of clathrate dissociation rush up the tiger stripes,
transporting heat to the surface where they may occasionally leak in the
form of plumes. The transport of heat by fast-moving gases is called “heat
advection.” The cracked shell of Frigid Faithful acts as a gigantic
“advection machine,” which efficiently conveys heat from the source to the
surface.

In contrast to “heat conduction”, where the transport of heat (in a bar of
steel, for example) can only occur from points at higher temperature towards
points at lower temperature, heat advection takes place at a nearly uniform
temperature.

The implication is that Frigid Faithful’s shell remains close to the surface
temperature to a depth of about 35 kilometers, Gioia said. According to the
Cassini measurements, the surface temperature might be as many as 150
degrees below the freezing point of water.

“This is indeed a frigid Enceladus,” Gioia said. “It appears that high heat
fluxes, geyser-like activity and complex tectonic features can occur even if
moons do not have hot, liquid or shifting interiors.”

While the Enceladus envisioned by the Illinois researchers is unlikely to
possess liquid water and therefore unlikely to harbor life, it is compatible
with the available evidence and is the only model that has been shown to
explain the origin of the arrangement of fractures and ridges documented by
Cassini.


















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