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Nuclear reactors in the news - accurate reporting? - Page 13

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Posted by vaughn on March 28, 2011, 10:53 pm
 


Who pays for the medical costs caused by coal plane effluent?

Vaughn



Posted by Pete C. on March 22, 2011, 3:22 pm
 

Neon John wrote:

Are they really that big? I recall some years back there was a summer
power shortage in the Hartford, CT area and the utility moved in a small
group of containerized generators to pickup some of the local load. If I
recall, these were turbine sets of something like 5MW each.


My thought is that given the relative ease of running power lines, the
backup generators, or at least one redundant group of them should have
been located a mile or two further inland and feed the plant via a
hardened service tunnel.


Yep, again if the backup generators survived the tsunami, this wouldn't
have been an issue at all. The root cause of the whole incident was the
backup generators not surviving the tsunami.


It does seem that they should have had some remote robotic vehicles on
hand that could operate in the hot areas tethered by an umbilicle to a
control station a safe distance away and powered by a little Honda
generator in the parking lot if need be. Certainly similar machines
exist for bomb disposal and the like.


industry

Yep, the public just doesn't understand the level of redundancy and
fault tolerance in even the older designs.


There was some report that two of the units in trouble were scheduled
for retirement this year. Not sure if it's true.


Exactly.


The CNN poll showed solid support as well, last I looked the "expand"
category had near 50% and the "maintain" was around 25%, the "reduce"
was around 25%.


I haven't heard any reports of public panic in heavily nuclear France. I
guess they do a better job of educating their population.



Posted by daestrom on March 22, 2011, 11:52 pm
 On 3/21/2011 11:11 AM, Morris Dovey wrote:

Couple of faulty points.

1) The diesels did start and run until the Tsunami hit.  But they didn't
survive the Tsunami.  The EDGs are in a separate building along side the
Rx building and have large air intakes for combustion air and cooling
air. (although the engines are water cooled, the generator is air-cooled)

2) There was no N16 in the steam they released as it had all decayed
away within minutes of the reactor shutdown, *before* the Tsunami hit.
But even so, normal steam from a shutdown BWR is 'slightly' radioactive.
  Some of the nuclides created in the water have longer half-life than
seconds, but still rather short (O18 comes to mind).  But these really
are small amounts.  And if the vapor isn't completely 'dry', there can
be traces of other radionuclides in it even if the cladding hasn't failed.

3)There haven't been any reports of workers deliberately venting to
inside the building.  The venting of containment is supposed to go to
standby-gas treatment system.  With no power, this resulted in the
steam/gasses going into Rx building.  But no choice, have to vent
containment when pressure exceeds design.

4) The hydrogen doesn't come from super-heating the steam to the point
that it breaks down to O2 and H2.  The cladding is made from zirconium
which will 'corrode' in water.  The hotter it gets, the faster the
reaction.  This 'zirconium-water reaction' forms zirconium-oxide on the
surface of the fuel and liberates free H2.  The primary containment is
deliberately inerted with N2 to remove any O2 so that in case of an
accident, any H2 that might be formed will not be able to react with any
O2.  Unfortunately, when containment pressure rose so high, they had to
vent the torus part of the containment and that released the H2 to the
standby-gas treatment system and the reactor building where there is
normal air.

5) The power requirements for the emergency pumps is not something that
is fed from some 'plugged in' emergency generator.  Typical voltage for
the equipment is 4160V in many US designs, I expect the Japanese design
is similar, perhaps 6.9kV.  As a side note, of the many BWR plants I've
been at, many of them use a form of diesel-generator that is very
similar to a railroad locomotive in size.  Some even use a nuclear-grade
version of EMD 650 V20 engine.  It would probably fit on an oversize
flatbed truck, but it is *not* a plug in.  (besides, with a nuclear
plant's safety at stake, one would hard-wire the generator to the system
regardless of any 'plug' it came with)

6) BWR containments of that vintage don't have a 'core catcher'.
Apparently the author got this term from some other design.

7) The Emergency Core Cooling System (ECCS) criteria for US plants is to
keep the fuel cladding below 2200 degF not 2200 degC.  Above 1800 degF
the zirc-water reaction becomes self-sustaining and above 2200 degF the
zirconium solid metal undergoes a change to a different form that is
much weaker and more likely to fail (but this is much cooler than the
melting point).
http://www.nrc.gov/reading-rm/doc-collections/cfr/part050/part050-0046.html

8) As reactor pressure rose, yes the operators would have either
manually activated the safety-relief valves, or they would automatically
open without any operator or power at a slightly higher, mechanical-lift
set-point.  But these do *NOT* release steam to the atmosphere as the
second author stated.  As the first author puts it, they discharge to a
release point under-water in the torus where the steam is condensed by
the cooler water of the torus.  The only problem with doing this is that
you can't keep the water in the torus cool.  As that water heats up, it
raises the overall pressure in the containment (the torus is part of the
containment boundary).

9) Once the operators began pumping sea-water into the containment, you
write that plant off.  The cost of recovering from that is just too much
for such an old plant.  Chlorides in the salt-water will attach all the
piping and reactor vessel.  The reactor-recirculating pumps, some of the
largest and most expensive pumps in the plant will need to be replaced.
  Even the reactor vessel itself may not be reusable after that.

10) Given these were written on 3/14, they do not consider the
consequences of the overheating spent-fuel pools.  The accidents have
been upgraded to level 5.  This means the accident has a wider impact on
the public.


Some bits of speculation:

I suspect the same tsunami that damaged the EDGs also put a lot of
salt-water in the emergency system electrical switchgear.  So even with
power from a portable unit, you can't just wire it into the switchgear
and expect all the electrical equipment to just start working.

Another bit is that the fuel-oil storage tank in many US plants is
outside the building (fire-hazard).  So if the tsunami destroyed that,
you wouldn't have fuel until you truck it in.

If the EDG's were running at the time and inducted water, the
pistons/cylinders would be destroyed in a single revolution of the
crankshaft.

Since the engines are water cooled, you need a service-water pump from
the seawater intake to supply it.  These are redundant and physically
separated to provide this water, but both divisions may have been
damaged in the tsunami.  So running the engines without cooling won't
work either.


daestrom

P.S.   Despite what another 'nuclear expert' may have said here, there
are some US plants built very close to earthquake faults.  Look at
Diablo Canyon, Brown's Ferry, Columbia and San Onofre.  Although Indian
Point is technically near a fault, that fault is not considered to be
'active'.

Posted by Tom P on March 23, 2011, 3:34 pm
 On 03/23/2011 12:52 AM, daestrom wrote:

That sounds like a knowledgeable analysis. What I read between the lines
is that if you shut down the plant for any reason and the entire cooling
system fails, you have a catastrophe?

Posted by daestrom on March 23, 2011, 11:35 pm
 On 3/23/2011 11:34 AM, Tom P wrote:

Define 'catastrophe'.  Lose cooling for a few hours and you may have
core damage but not any public health risk.  That's one form of
'meltdown' of the core but it isn't releasing any radioactivity to the
public so I don't consider it a 'catastrophe' (the reactor owner would
certainly consider it a 'bad thing' from a financial point of view).

If you shut off all cooling and walk away, after many days you *may*
have a 'catastrophe' on the scale of releasing significant radioactive
material to the environment.  The clad will fail and the hot fuel may
breach the reactor vessel.  But when the fuel hits the containment
floor, there is a lot of speculation about what would happen next.

In Chernobyl, when the molten fuel flowed to lower elevations, it began
to spread out and thus cool below the melting point.  This was before
actually melting through the building floor. (the so-called "elephant's
foot" under the reactor).  So there is some reason to believe the
containment floor would *not* be breached and thus the radioactive
release could be minimal.  Granted, some radioactivity would either be
vented by operators, or could be released some other way out of the
containment.

This *could* be the scenario that plays out in a BWR design but even the
experts are divided on this issue.  Some are concerned about the fuel
reacting chemically with the concrete in some unknown way and eventually
burrow down out the bottom of the containment.  Anyone who tells you
what would happen next is guessing, pure and simple.


Of course the preferred scenario is cooling the reactor.  If this can't
be done, then cooling the containment and cooling the reactor from the
outside of the reactor vessel by flooding containment is the second
level.  And of course even if the fuel does get to the floor of
containment, cooling it there is a third alternative.

One of the requirements of getting a license from the NRC for owning a
reactor in the US is to be able to demonstrate that you have enough
qualified people and that they would *not* just 'walk away' (witness the
actions of the Japanese plant operators).

But lets put this all in perspective.  I'll make a bold prediction: "The
number of people that die from radiation from this will be < 1% of the
death toll from the quake/tsunami"

daestrom

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