Steam Detected at Damaged Fukushima Reactor
TOKYO — The operator of the Fukushima Daiichi nuclear power plant stood ready Thursday to inject boric acid into one of its most heavily ...
Steam Detected at Damaged Fukushima Reactor
By HIROKO TABUCHI
Published: July 18, 2013
TOKYO — The operator of the Fukushima Daiichi nuclear power plant stood
ready Thursday to inject boric acid into one of its most heavily damaged
reactors after it found steam emanating from the reactor building. The
preventive measure would stave off sustained nuclear reactions in the
reactor’s damaged core, though officials stressed that such reactions
were a remote possibility.
The Tokyo Electric Power Company, or Tepco, stressed that it continued
to safely cool the reactor core and that vital temperature and radiation
readings were stable. It said that it had not detected any signs of
criticality, or sustained nuclear reactions. But Tepco said that it had
halted all work to remove debris from the top floors of the reactor
building, also as a precaution
The incident has brought the Fukushima plant’s vulnerable state into
sharp relief, more than two years after its reactors suffered multiple
meltdowns when its cooling systems were overwhelmed by a powerful
earthquake and tsunami. A recent jump in levels of radioactive cesium
and tritium in the groundwater at the coastal plant, along with
suggestions that the groundwater is leaking into the Pacific, has also
raised alarms over the continued environmental threat posed by the
plant.
Remote camera footage Thursday showed steam escaping from the top of the
No. 3 reactor’s primary containment structure, which houses its fuel
vessel, according to the Tokyo Electric Power Company, or Tepco. A
worker who checked the footage Thursday morning noticed the steam, said
Hiroki Kawamata, a spokesman for the operator.
Mr. Kawamata said officials were unsure what was generating the steam,
and hypothesized that rainwater seeping into the containment vessel may
have turned to vapor because of elevated temperatures there. Extremely
high levels of radiation in the now roofless upper sections of the No. 3
reactor building — destroyed in a hydrogen explosion that rocked the
reactor during the early days of the 2011 disaster — make it too
dangerous for workers to approach. Remotely operated cranes are used to
remove debris from the site.
Video footage seemed to show less steam Thursday evening, and after
sundown it became too dark to accurately check for any vapor, Masayuki
Ono, acting general manager of Tepco’s nuclear power and plant siting
division, later told an emergency news conference.
Still, workers were ready to inject water containing boric acid into the
reactor from the outside at any signs of further trouble, such as a
rapid rise in temperature or radiation parameters, the company said in
an e-mailed statement.
Such spikes would raise the chilling possibility of criticality in the
reactor’s damaged fuel, most which is thought to have melted and slumped
to the bottom of its containment structure after the hydrogen
explosion, one of several at the site in 2011. Boric acid would slow
that rate of fission, preventing the worst-case scenario of uncontrolled
nuclear chain reactions in the core.
Temperature and radiation levels at the reactor appear stable so far,
Mr. Ono stressed. Tepco has also not detected any xenon gas at the
reactor, which would be produced in an event of criticality, he said.
He added that Tepco was working on a cover for the reactor building that would prevent rainwater from seeping in.
Fresh trouble at the No. 3 reactor is especially worrying because it
contains mixed uranium-plutonium oxide fuel. The upper floors of the
reactor also house its fuel pool, which stores over 500 fuel assemblies.
The reactor complex’s basement is flooded with highly radioactive
water. Studies show that an accident like a meltdown or containment
failure in a reactor that holds such fuel would result in more cancer
deaths than one in a reactor fueled only with uranium.
The No. 3 reactor’s damaged core, like the cores of two other crippled
reactors at the site, is being cooled by water that is pumped into the
reactor, filtered and recycled. But in April, the cooling system at No. 3
shut down for hours. Tepco later said a rat had somehow short-circuited
a vital switchboard, possibly by gnawing on cables.
More than 100,000 people fled their homes after the meltdowns at
Fukushima, the world’s worst nuclear crisis since the Chernobyl disaster
in 1986. While many areas are beginning to be repopulated, the
residents’ return has been overshadowed by the continued mishaps at the
plant.
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