Explosion, fire at Fukushima nuclear power plant

The Los Angeles Times is reporting:

A day after responding to one of the worst earthquakes on record and a
massive tsunami, the Japanese government sought to allay fears of a
radioactive disaster at a nuclear power plant on the country’s battered
northeastern coast.

The outer walls of the Fukushima power plant’s No. 1 reactor were blown
off by a hydrogen explosion Saturday, leaving only a skeletal frame.
Officials said four workers at the site received non-life-threatening

The inner container holding the reactor’s fuel rods is not believed to
be damaged, said Japan’s Chief Cabinet Secretary Yukio Edano, and
workers were cooling the facilities with seawater.

In a press conference shortly after the explosion, which left the
facility shrouded in plumes of gray smoke, Edano explained that the
reactor is contained within a steel chamber, which in turn is surrounded
by a concrete and steel building. Although the explosion destroyed the
building, it did not occur in the chamber.

“The escape of hydrogen mixed with the air between the chamber and the
concrete-and-steel building and led to the explosion,” Edano said.

“Tokyo Electric Power Co. has confirmed that the inner reactor is
undamaged,” he added. “There was no massive release of radiation.”

This is indeed a dire situation, because if the engineers at the plant have lost control of the reactor, then it is only a matter of time before it enters a meltdown state — if that hasn’t already happened.  At this point there appears to be little that engineers can do, save for continuing to pour massive amounts of water on the exterior of the reactor structure and pray that its massively thick concrete and steel shielding can keep the reactor elements contained and radiation leaks to a minimum.

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For those of you who are unfamiliar with the physics of a nuclear power plant, its primary component is a nuclear reactor, within which a low level, contained, and dampened nuclear chain reaction occurs.  The uranium fuel
is packed into long rods, which are bundled together inside the
reactor.  In order to manage the nuclear reaction and reduce it to a
continuous, low level state, a system of “control rods” is also placed
within the reactor.  These control rods absorb the neutrons that are
released during the nuclear reaction, and through adjustments that allow
them to absorb either a greater or lesser amount of neutrons, they can
either slow down or speed up the reaction inside the chamber. 

The reactor is also filled with a liquid coolant that absorbs and
dissipates the incredible amount of thermal energy that is released
during the nuclear reaction.  In a nuclear power plant, this dissipated
heat is used to heat water and produce steam that drives a system of
dynamos connected to steam turbines.  In a nuclear engine (such as a
submarine or aircraft carrier might carry) the steam is used to turn a series of steam turbines that drive the screws and operate the steering mechanism.

The cooling and dampening systems are critical to the safe operation of
the reactor.  If either system is damaged, the state of the reactor
cannot be properly controlled, resulting in either a runaway reaction (control rod malfunction) or an extreme heat situation (cooling system malfunction) that could reach levels high enough to literally melt
the reactor — a so-called “meltdown.” 
Under these extreme conditions, where control of the reactor is
impossible, its safety mechanisms will certainly experience failure,
potentially resulting in the release of large amounts of deadly radiation.

Thanks to lessons learned from over 50 years of nuclear power plant
operation (specifically the accidents at Three Mile Island and Chernobyl) and the use of very sophisticated redundant safety systems and
continuously improving construction and shielding technology, very few
nuclear meltdowns have occurred, and the probability of a major meltdown occurring — short of a natural disaster that heavily damages a reactor — is very slim.

It will be equal parts fascinating and disturbing to watch how this episode is resolved.  It is extremely unlikely that anything resembling the massive radiation release at Chernobyl will be repeated at Fukushima.  The reactor at the Chernobyl plant was unshielded, and its safety systems were outdated and in disrepair (all typical of “Soviet engineering”) while the Fukushima reactor is a textbook example of contemporary engineering and safety technology, with a sophisticated computer-driven reactor control system and a heavy, steel-reinforced concrete shield surrounding the reactor.

I am praying that the safety systems at Fukushima work the way they were designed, and keep both radiation leaks and damage to the most minimal levels possible.  I am also praying that this incident does not result in yet another decades-long chilling of public opinion over nuclear energy.  But we will simply have to wait and see what happens first.


Thanks to commenter DodoDavid for providing clarification on the operation of nuclear powered marine steam turbine engines.  The text above has been corrected.  

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