Re: [Phys-l] Japan situation : information, or lack thereof

[John Denker <jsd@av8n.com>]

Way back on 03/15/2011 08:40 AM, Edmiston, Mike wrote:
> First, I have to admit that I don't know the details of the
> containment engineering in these troubled plants.  However, I have
> worked at some boiling-water reactors in the US (research reactors,
> not power reactors) and it seems to me that at some point it would
> have been better to walk away from it and let it melt.
...
> What would happen if these desperate measure were not undertaken and
> the vessel was not vented? 

That's a good question.

After accumulating information for six weeks, I may now have 
a partial, approximate answer.

> Presumably there would be total core
> meltdown which may or may not breach the reactor vessel, but it is
> not supposed to breach the primary containment.

That's the story we have been given, year after year and
decade after decade, but it now appears that the story is
not entirely true.

We have been told there is "defense in depth" consisting of the
following layers:
 a) The zircaloy cladding of the fuel pin encloses the fuel;
 b) The reactor pressure vessel encloses the fuel pins;
 c) The primary containment encloses the pressure vessel;
 d) The secondary containment encloses the primary containment.

That all sounds great until you realize that it can contain the
material but it cannot necessarily contain the /heat/.  All that
containment works fine provided:
 1) The reactor has never been operated, or has not been operated
  recently, and/or
 2) The cooling systems continue to operate.

To say the same thing the other way, if you have a reactor that
has been operating for a while, shut it down, and don't provide
cooling, each of the layers itemized above will fail ... with
unacceptable consequences.

> at some point it would
> have been better to walk away from it and let it melt.

The problem is that it melts in such a way as to release
unacceptable amounts of radioactivity into the environment.

=====

Another part of the "defense in depth" story says that there is
  A) The primary reactor cooling system
  B) The secondary reactor cooling system
  C) The emergency reactor cooling system
  D) et cetera.

Again, there is something they aren't telling you:  Every one
of those requires electricity!  Station blackout is a single-
mode failure, predictably leading to disaster.

They seem to have thought about that a little bit, to the point
where they provide two connections to the external power grid
and provide 13 onsite diesel generators ... which sounds like
a lot of depth, until you realize that every one of those diesels 
is in a basement, so that a single event -- such as flooding --
can take them all out simultaneously.  As it happened, the
earthquake took out the grid and the tsunami flooded the diesels.  
So earthquake+tsunami is a single-mode failure predictably 
leading to station blackout, which in turn leads to disaster.

At the next level of detail:  Typically such reactors have an
RCIC system (reactor core isolation cooling).  Reference:
slide 13 of:
  https://s3.amazonaws.com/UCS_Videos/Fukushima-Tragedy.pps

The idea is that steam from the reactor provides enough energy
to run the pumps to prevent a meltdown.  This seems like a
nice self-consistency argument, in the sense that as long as
the reactor is hot enough to make steam, the steam can be 
used to keep things from getting out of hand.

But once again, there is something the diagram is not telling
you:  The RCIC depends on station power!  I don't understand
the details of this; perhaps power is needed to keep the valves 
set properly.

So if there is a station blackout, all the operators can do
is sit and watch as the fuel pins melt and burn, the reactor 
pressure vessel vents or explodes, the primary containment 
vents or explodes, and the secondary containment vents or 
explodes, and the neighborhood becomes uninhabitable for 
many years.

This strikes me as spectacularly bad engineering.  In particular,
we can compare it to the Gimli Glider.
  http://en.wikipedia.org/wiki/Gimli_Glider
An airliner is supposed to have "defense in depth" in the sense
that one engine is a backup for the other.  However, in this case
both engines of the Boeing 767 flamed out due to fuel exhaustion.
This is reeeeally not supposed to happen, but it did.

At this point, something interesting happens:  There is such a
thing as a /ram air turbine/ (RAT) that pops out of the bottom of
the airplane.  It takes energy from the flowing air and produces
hydraulic pressure sufficient to keep the primary flight controls
operational.  No engine power is required.  No electricity is
required.  No pilot action is required.  If hydraulic pressure
is lost, the RAT pops out and does its thing.

There is a self-consistency argument here:  as long as the aircraft
has enough airspeed to keep flying, the RAT will ensure that it is
controllable.

The pilots of flight 143 flew the glider to a safe landing.

Returning to the reactor story:  It would seem to me that the
RCIC turbine should be arranged to drive the emergency cooling
pump /and/ drive a generator so as to produce enough electricity
to keep the RCIC system working.  And/or the valves in question
should fail safe so that the RCIC continues to work as long as
the reactor is hot enough to need it.

Note the contrast:  The guys who designed the Boeing 767 were 
smart enough to make sure the last line of defense (the RAT) 
was robust and independent of every other subsystem.  The 
guys who designed the GE Mark I reactor were not smart enough
to make the RCIC independent of station power.

====

As another example of bad engineering, TEPCO built the plant
in a small bay, on the lowest land for miles in any direction,
such that the front door of the plant is AFAICT only a few
meters above sea level.  If they had built the plant only a
few hundred meters away in almost any direction, it would have 
been on much higher ground, and therefore much less subject 
to flooding.

And then they put all of the emergency diesel generators in
the basement!  You would think that they could have installed
at least some of the emergency equipment on higher ground.

The diesel generators are not the whole story.  Evidently
there was flood damage to other critical stuff in the basement,
including pumps and switchgear, such that even when external
power was restored to the plant, normal cooling could not be
restored.

By way of contrast, a plant at Onagawa was built and operated
by Tohoku Electric Power Co. -- *not* TEPCO. It sits on higher
ground and survived the quake and tsunami, even though it was 
considerably closer to the epicenter:
  http://www.bloomberg.com/news/2011-03-25/tsunami-risk-well-known-to-nuclear-engineers-regulators-who-failed-to-act.html

People buy insurance on the theory that it is better to make
small payments again and again and thereby avoid a huge loss 
if something bad happens.  It seems like the decision to build
the plant on the low land, not the nearby higher land, is
tantamount to anti-insurance.  TEPCO saved a tiny amount on
operating expenses, in such a way as to increase the chance
of a 4 trillion yen loss if something bad happened.

====

And then there is unit 4.

To paraphrase Oscar Wilde:  To have meltdowns at unit 1, unit 
2, and unit 3 is unfortunate, but to have a meltdown at unit
4 begins to look like carelessness, considering that it was
shut down and de-fueled at the time.

It seems to me the industry as a whole has a long record of
sweeping spent-fuel issues under the rug.  Once again, the
"defense in depth" is not nearly as deep as we've been led 
to believe.
  http://allthingsnuclear.org/post/4814761753/susquehanna-spent-fuel-pool-concerns-and-how-i-ended

=================

A source of Fukushima-related photos and reports (and lots
of other stuff)
  http://cryptome.org/

Also there is the Union of Concerned Scientists
  http://www.ucsusa.org/nuclear_power/

An interesting photo of a GE Mark I primary containment vessel
under construction:
  http://www.moonofalabama.org/images3/primary1.jpg
To get a sense of scale, note the people in the picture.

Our hero Dr. Josef Oehmen said this structure was "hermetically"
sealed.  I'm pretty sure something with that many tubes running
in and out -- and with pressure relief valves -- doesn't qualify 
as "hermetic".

================

I am not opposed in principle to nuclear power.

I am however opposed to badly-designed and badly-operated
nuclear power plants.

I also reserve the right to get really ticked off when the
stories we are told about nuclear plant safety ("defense
in depth") turn out to be not true.