[A-List] Fwd: [R-G] Second Chances: Containment of a Reactor Meltdown

[Suzanne de Kuyper]

And what has happened to Julian Assange?

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From: Richard Menec <menecraj at shaw.ca>
Date: Wed, Mar 16, 2011 at 4:39 AM
Subject: [R-G] Second Chances: Containment of a Reactor Meltdown
To: Suzanne de Kuyper <suzannedk at gmail.com>
Cc: RAD TIMES <resist at comcast.net>, "Radical anti-capitalist environmental
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http://thebulletin.org/node/8616

Bulletin of the Atomic Scientists

Second Chances: Containment of a Reactor Meltdown

By Frank Von Hippel | 14 March 2011

One aspect of the drama that we have been witnessing at Japan's Fukushima
Nuclear Power Plants since the March 11 earthquake and tsunami is the
efforts of Tokyo Electric Power (TEPCO) to prevent the over- pressurization
of the containments of its boiling water reactors at plants I and II. These
reactors lost power from the grid due to the earthquake and their backup
emergency diesel generators failed, apparently due to damage from the
tsunami.

As a result, there was no power for pumping outside water through the heat
exchangers used to remove the heat generated by the residual radioactivity
in the fuel. The pressure in the reactors therefore began to rise and their
pressure- relief valves were opened to relieve this pressure. The reactor
containments did have backup pressure-suppression pools of water in their
basements and steam-powered pumps that could circulate water from the pools
to the reactors. After some time, however, the pressure suppression pools
began to boil and were no longer useable for cooling.

In three of the reactors (Fukushima-Daiichi units numbers 1, 2, and 3 -- the
units that were operating at the time of the earthquake and therefore hot)
the water levels in the reactors fell, uncovering their fuel, which
overheated and released some of its reactivity into the containment. The
steam pressure also built up in the containments to the point where they
were on the verge of bursting.

TEPCO therefore received permission from Japan's government to release some
of the gas from the containments. Because this gas contained radioactivity,
the surrounding population was evacuated out to a distance of 20 kilometers
(12 miles). Fortunately, the release was orders of magnitude smaller than
occurred at Chernobyl.  Much of the radioactivity is still trapped in the
fuel and most what was released probably dissolved in the water. Most
importantly, the wind blew the plume to sea.

As a result of the overheating of the reactor fuel, its zirconium cladding
reacted with the steam to oxidize the zirconium and release hydrogen from
the steam. The hydrogen didn't explode in the containments because they had
been "inerted" by being filled with pure nitrogen (i.e. no oxygen) but, when
the hydrogen was vented into the outer containment buildings, it mixed with
the air there and exploded, blowing the roofs off the outer buildings but
(except perhaps for unit number two) leaving the inner containments and
massive spent fuel pools intact.

In 1979, during the accident at reactor number two at Three Mile Island, the
fuel was similarly partially uncovered and its fuel cladding failed,
releasing a great deal of radioactivity to the containment atmosphere, and
there was a hydrogen explosion.  But the containment was not over- pressured
and no significant amount of radioactivity was released to the atmosphere.
The main difference was that electricity was available to power the
reactor's containment cooling systems and condense the steam within it.  If
the power had failed, the containment of reactor number two would have been
over-pressured as well.

The problem of containment over-pressurization and the potential need to
vent has been a long-term issue in the nuclear reactor safety community. In
1977, a group of nuclear engineers at the University of California suggested
that a robust filtration system be installed in reactors to remove the
radioactivity from the vented gases. Some countries picked up the idea.
Sweden installed a filtered vent system at the Barseback reactors
(subsequently shutdown) across the strait from Copenhagen and France
installed filtered vent systems at all of its reactors, which interested
both Germany and Japan.

In 1982, after the accident at Three Mile Island, Jan Beyea and I wrote an
article on filtered vents in the Bulletin of the Atomic Scientists in 1982
(page 52). As we reported in that article, the US Nuclear Regulatory
Commission (NRC) was negative about the idea. They had a number of arguments
but none of them seemed very strong to us. Those interested can read our
summary of the arguments pro and con in the 1982 article.

The unspoken argument against requiring that US nuclear power plants be
retrofitted with filtered vents was that the industry thought that they were
already safe enough and that the expense would be wasteful. And, as today,
the commission did not want to force the industry to do more than it was
willing to do.

In 2002, the NRC, despite alarming evidence that a pressure vessel had
almost corroded through, refused to force an owner to shutdown the reactor
for inspection before its regular refueling shutdown. After a review, the
NRC's own inspector general concluded:

"NRC appears to have informally established an unreasonably high burden of
requiring absolute proof of a safety problem, versus lack of a reasonable
assurance of maintaining public health and safety."

We failed after Three Mile Island in 1979 to reform the Nuclear Regulatory
Commission or force improved containment designs. The tragedy in Japan may
have given us another opportunity.


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