nuclear-news

New bursts of fission at the crippled Fukushima power plant

The three reactors — together with spent fuel rods stored at a fourth damaged reactor — have been leaking radioactive material since the initial disaster, and new episodes of fission would only increase their dangers.

Fears of Fission Rise at Stricken Nuclear Plant in Japan, NYT, By HIROKO TABUCHI  November 2, 2011 TOKYO — Nuclear workers at the crippled Fukushima power plant raced to inject boric acid into the plant’s No. 2 reactor early Wednesday after telltale radioactive elements were detected there, and the plant’s owner admitted for the first time that fuel deep inside three stricken plants was probably continuing to experience bursts of fission.

The unexpected bursts — something akin to flare-ups after a major fire
— are extremely unlikely to presage a large-scale nuclear reaction
with the resulting large-scale production of heat and radiation. But
they threaten to increase the amount of dangerous radioactive elements
leaking from the complex and complicate cleanup efforts, raising
startling questions about how much remains uncertain at the plant, the
site of the world’s worst nuclear disaster since Chernobyl. The
Japanese government has said that it aims to bring the reactors to a
stable state known as a “cold shutdown” by the end of the year.

On Wednesday, the plant’s operator, the Tokyo Electric Power Company,
said that measurements of gas from inside Reactor No. 2 indicated the
presence of radioactive xenon and other substances that could be the
byproduct of nuclear fission. The presence of xenon 135 in particular,
which has a half-life of just nine hours, seemed to indicate that
fission took place very recently.

Trade Minister Yukuo Edano censured Japan’s nuclear regulator, the
Nuclear and Industrial Safety Agency, for failing to report the
discovery to the prime minister’s office for hours, according to local
media reports.

The developments added to the disquiet over handling of information
related to the disaster. For almost two months after the March 11
earthquake and tsunami, disaster, both company and government
officials declared it was unlikely any meltdown had occurred at all at
the Fukushima Daichi nuclear complex, finally conceding that the fuel
had indeed slumped and had likely breached containments in three
reactors.
It is impossible to determine exactly what state the fuel is in, given
that even an intact reactor can offer only limited gauges in the form
of temperature, pressure readings and neutron flow, but not visual
observation. That lack of clarity is one of the most resonant lessons
of the Fukushima disaster, where those trying to guide the response
and assess the danger operated by what amounted to educated
guesswork…..
The three reactors — together with spent fuel rods stored at a fourth
damaged reactor — have been leaking radioactive material since the
initial disaster, and new episodes of fission would only increase
their dangers.

“Re-criticality would produce more harmful radioactive material, and
because the reactors are damaged, there would be a danger of a leak,”
said Hiroaki Koide, assistant professor at Kyoto University’s Research
Reactor Institute, whose prescient warnings about nuclear safety have
won him respect in Japan.

Mr. Koide holds that the nuclear fuel at the three reactors probably
melted through containments and into the ground, raising the
possibility of contaminated groundwater….
A former nuclear engineer said ….the  main concern was that
officials could not pinpoint the exact location of the nuclear fuel —
which would greatly complicate the cleanup.

The engineer, who has worked at all three nuclear power complexes
operated by Tokyo Electric, spoke on condition of anonymity because he
did not want to be identified by his former employers. He said that
tiny fuel pellets could have been carried to different parts of the
plant, like the spaces under the reactor during attempts to vent them
in the early days. That would explain several cases of lethally high
radiation readings found outside the reactor cores.

“If the fuel is still inside the reactor core, that’s one thing,” he
said. But if the fuel has been dispersed more widely, then we are far
from any stable shutdown.”
http://www.nytimes.com/2011/11/03/world/asia/bursts-of-fission-detected-at-fukushima-reactor-in-japan.html?_r=1&pagewanted=2

November 3, 2011 - Posted by Christina Macpherson | - Fukushima 2011, Japan, safety