On Mar 21, 2011, at 5:01 PM, Edmund Storms wrote:
On Mar 21, 2011, at 5:40 PM, Horace Heffner wrote:
On Mar 21, 2011, at 1:51 PM, Edmund Storms wrote:
[snip stuff related to metallic uranium because there is no
evidence such exists in such GE designed reactors.]
According to the authorities I have consulted, only reactor 3
contained UO2+PuO2 fuel.
That is correct and that is precisely what I said earlier, that
reactor 3 has plutonium containing MOX fuel. Ordinary boiling water
reactor (BWR) fuel is called "UOX" fuel.
Where did you get your information?
Providing information that uranium metal is used in the fuel rods is
*your* job, because you made the assertion that uranium metal was
involved there. It was I who made the assertion there is no evidence
that those GE designed reactors have metallic uranium in the fuel
rods. I said they have uranium oxide pellets, *not* also plutonium,
except in the case of reactor 3.
Here is a 2005 discussion of interest by the Union of Concerned
Scientists regarding the safety GE designed fuel rods:
http://www.unplugsalem.org/PDF/20050628_ucs_brief_ge_fuel_defects.pdf
Note it says: "A nuclear fuel bundle consists of uranium dioxide
(UO2) fuel pellets stacked inside long, cylindrical fuel rods."
There are numerous other references regarding the use of uranium
oxide pellets (UOX, without plutonium) in BWR fuel rods.
On Mar 14, 2011, at 11:12 PM, Horace Heffner wrote:
I think the primary danger from Fukushima 1 lies in the fact it uses
MOX fuel (mixed oxide fuel, the oxides being of uranium and
plutonium). Also, there is a vast amount of stored fuel outside all
the reactor containment vessels. There is at this point no telling
what the condition of the stored fuel rods is. In addition,
plutonium produces a lot of neutrons, which increases the chances for
spontaneous chain reactions if the fuel melts into a blob. These
would be small explosions or thermal excursions, but still very
dangerous, and possibly repetitive if the material is located in a
confined space, like a hole bored into the ground.
See:
http://www.washingtonpost.com/business/economy/nuclear-crisis-deepens-
as-third-reactor-loses-cooling-capacity/2011/03/14/ABk6rQV_story.html
http://tinyurl.com/67tp62y
"A commercial satellite photo of the complex showed piles of debris
on top of units 1 and 3, which raised new fears about the condition
of the pools where spent fuel is stored, especially at unit 1, where
a design by General Electric placed the pool on top of the reactor
but below the outer structure that was destroyed. The ability of
workers to assess the damage was hindered by fears that another
explosion might occur."
"In March 2010, 1,760 tons of spent fuel was stored in the six pools
— 84 percent of capacity, according to Tokyo Electric."
That is over 250,000 kg of uranium (plus possibly some plutonium in
the case of MOX) per storage pool on average. What is that going to
do if it melts into a blob and starts boring a hole into the earth?
That's a rhetorical question. For many answers google(China syndrome).
That 250,000 kg contains many times the fissionable material in an
atom bomb. This is a big problem even given it is almost all U238.
MOX fuel, used in unit 3, is a *huge* problem. Plutonium is one of
the most radiologically poisonous materials on earth. Pu242 has a
half-life of 376,000 years. The atomic bomb Little Boy, dropped on
Hiroshima, had 64 kg of uranium. Fat Man, dropped on Nagasaki,
contained 6.2 kg of plutonium. For background information on Fat Man
and Little Boy see wikipedia.
The UO2 fuel is more stable but the Zr will react with air and
water, which would release the fuel pellets and cause them to be
distributed at random over the bottom of the pond.
Yes, we are agreed on something.
This is not a good thing because clean up is made that much more
difficult and this allows the fission products to be released.
Adding water simply insures that the Zr will be converted to
oxide if it has not already been destroyed.
The Zr will also burn when merely exposed to air. Without water
the fuel can still rubblize.
So what? The point is that the fuel will release fission fragments
if the Zr or the uranium reacts with water while hot. The less
reaction the better.
This is like saying, if two guys are going to shoot you, one with a
shotgun and one with a rifle, that if you knock off the guy with the
shotgun you will be fine.
This is a hot water boiling reactor. It boils water. Steam normally
forms on the Zr surface. The problem with steam arises if the rods
get way too hot. However, if they are hot and in air, as they are
when exposed in an empty storage pool, the Zr still will oxidize or
even catch fire.
The problem is to prevent rubblization and the risk of a critical
mass forming. If all coolant is gone then some other means must be
in place to prevent concentration of the fuel pellets in the bottom
of the storage pools. On network TV I saw a report that a sand slurry
might be used. They have a concrete pump on site, but apparently no
one there is trained to use it.
http://en.wikipedia.org/wiki/Corium_(nuclear_reactor)
"During a meltdown, the temperature of the fuel rods increases and
they begin deforming, in case of Zircaloy above 700–900°C. If the
reactor pressure is low, the pressure inside the fuel rods
ruptures their cladding."
Yes, but again so what? The point is that extra water makes things
worse. This does not prevent damage not involving water.
Again, a lack of water does not prevent the loss of Zr cladding
integrity in air. If the Zr cladding is removed and there is still
some water left in the bottom meter or so of the storage pool, then I
think criticality is feasible. I think it is key to prevent
sufficient rubblization to form a critical mass while water or any
moderator is present. If seawater keeps being pumped in and
evaporated it is possible there will be a lot of carbon in the
rubble. If very wet cement is pumped into a fully dry and fully
rubblized mass, it is possible that could moderate sufficiently to
cause a chain reaction too.
It doesn't take a lot (when you are talking tons) of uranium close
together to reach a critical mass. The requirements for storage pools
is apparently farily minimal along those lines. See:
http://library.lanl.gov/cgi-bin/getfile?00406379.pdf
"A typical arrangement should be expected to result in a maximum
neutron multipliciitlon factor not exceeding about 0.9 for all
evaluated credible contingencies. Further, it is required that no
single mishap, misoperation, or violation of procedure will lead to
nuclear criticality."
"The additional mass necessary to achieve prompt criticality with a
single unit is between 1 and 3% of its
critical mass, depending on whether the material is plutonium or
uranium. The same can be said of an array at critical. However, the
relation between the reactivity change to a unit in the array and the
array reactivity is such that the 1 to 3% change in mass must be
uniform throughout the array, i.e., to increase the array reactivity
by an amount delta k, each unit in the array must be increased by
this same delta k.
An equivalent reactivity addition to the array may be also effected
by increasing the number of storage units or by *reducing the volume*
of the storage container or of the storage cell volume in the array.
In either of these cases, there is a dependence on the neutronic
coupling between the units of the
array. At critical, low-mass units will be strongly coupled, while
large-mass units will be weakly coupled, a condition that also
subsists in the subcritical state."
"For example, to change the k_eff (for uranium units) from the
critical state to a value of 1.01 would require a unlform change in
excess of 3% in the mass of the units in the array, or a 5 to 7%
uniform reduction in the volume of the array, or a 7 to 13% increase
in the number of units in the array."
"An accident during operation in a facility, however, can be expected
to be initiated from the subcritical state. If the sequence of events
leading to delayed criticality in a storage array were to begin at a
nominal k_eff of 0.9, then the above required chanqes become a
uniform mass augmentation of 37%, a uniform array volume reduction
ranging from 44 to 53%, and an increase ranging from 262 to 377% in
the number of units."
We've certainly seen more than one mishap in this case! So Fukushima
went beyond design criteria. What is important in the above is the
reduction in array volume of 44% to 53% to go critical. I think this
requirement should be reduced if biological carbon is accumulated in
the process. It seems that an analysis is required of what volume
reduction would occur if the fuel pellets were to all accumulate in
the bottom of the tank.
This report makes a number of assumptions voided by the events at
Fukushima. It appears to downplay "E. R. Woodcock, 1966, “Potential
Magnitude of Criticality Accidents,” United Kingdom Atomic Energy
Authority Report AHSB (RP)R-14 (1966)." For something related see:
http://www.osti.gov/bridge/
purl.cover.jsp;jsessionid=6B44C46F1B6F9A12D08EDD96F60CD56E?purl=/
464472-7hCeKj/webviewable/
http://library.lanl.gov/cgi-bin/getfile?00406379.pdf
"There had been many critical experiments, and several criticality
accidents involving solid fissile systems. These solid criticality
events exhibited different reactivity feedbacks and shutdown
mechanisms than the aqueous criticality, and in general, yielded a
smaller number of fissions. It is proposed then that a data base of
fission yields for these critical experiments and known accidents
(both aqueous and solid) should be generated by using existing or new
computer codes. The success in compiling this data base would provide
useful source-terms for criticality excursions, realistic estimates
of emergency response boundary, as well as a replacement for the
“rule-of-thumb” or “bounding” method."
http://www.tpub.com/content/doe2/h3010v1/h3010v10245.htm
Yes, but no geometry that can form under these conditions will go
critical under these conditions.
If that is so then neutron absorber slabs should not be required
to decrease the assembly storage distances, increase the storage
density, in these pools. They are already too near critical.
Condensing the fuel pellets in the bottom of the storage pools
represents a large volume reduction. It seems to me an analysis is
required to determine what will happen with regard to criticality.
Yes, and the result is no critically.
There is already *some* risk of criticality if the control slabs in
the pool are lost. That is why operators are forced to put them there
in order to store the assemblies more closely than originally designed.
There is a lot of fuel involved. See:
http://tinyurl.com/67tp62y
"In March 2010, 1,760 tons of spent fuel was stored in the six pools
— 84 percent of capacity, according to Tokyo Electric."
That is over 250,000 kg of uranium (plus possibly some plutonium in
the case of MOX) per storage pool on average.
The latest results show more smoke.
Yes, the smoke is variable, as are the water levels and temperatures,
and the degree of rubblization which has occurred.
So according to you, someone who has direct experience with reactor
fuel has no more importance than someone who has no knowledge or
experience what so ever.
No. What is important is that someone who has direct experience with
reactor fuel can be wrong. Witness the large science and engineering
staff responsible for the design of the reactors in question (and
those three who resigned in protest), and the history of problems
with those BWRs.
In other words, you believe my knowledge has no merit because you,
based on your reading of the press reports, have more merit.
I believe that, despite your credentials, you have no monopoly on
suggestions, and that you should consider that you might be wrong.
It seems to me one of the biggest problems now is the involvement
of so many fuel containing components at Fukushima, any one of
which could force permanent evacuation of the plant.
What do you base this conclusion on? Do you have knowledge that is
not generally available?
This is blatantly obvious to anyone with a basic understanding of
probability. You simply multiply the probabilities of no "evacuation
causing failure" occurring for each component (storage pool, or parts
of storage pools, or reactors) together to obtain the combined
probability of no failure. The probability of a lot of numbers less
than 1 but greater than zero is a number less than any of those
individual numbers. I thought the sentence below made this clear, but
I often think my writing is clear when I discover from the postings
of others it obviously is not.
The only solution is to entomb the entire site in cement, which
will happen too late to keep most of the fission fragments out of
the ocean.
Yes, entombment is a likely long term option. Also, much of the
radioactive particulates that result, if things are not brought under
control, will likely end up in the oceans, either via water or via
wind. That is the reason I posted a ref. for Pacific ocean currents
earlier.
Cement, if used, had best have a large neutron absorption
coefficient. I would assume at minimum it would be made with boric
acid. Until *proven* otherwise, caution should be used regarding the
potential for a critical mass developing somewhere in the 1,760 tons
of uranium in the stored MOX or UOX fuel.
Surly it must be apparent that time is of the essence for action. I
think we both agree that *repeated* dumping of sea water on air
exposed hot fuel rod assemblies can not go on indefinitely without
decomposition of the assemblies. Some kind of action to stabilize
the fuel rods before something happens that prevents operator
presence for a protracted time.
I think it may be a very dangerous thing to leave the stored fuel
pools at risk of remaining dry long enough for most of the stored
fuel elements to rubblize into what could become a critical mass or
almost critical mass. If such a mass forms and it is completely dry,
it may be dangerous to put water on it because the moderation and
reflection provided by the water could make that mass go critical.
I would hope that the responsible parties have already run computer
codes to examine whether 250,000 kg or so of UOX or MOX pellets on
the floors of the holding ponds, not uniformly spread, but in
somewhat random piles, can go critical in the various conditions
existing at Fukushima.
Watson's table suggests 3x10^23 fissions for such an event, or about
a million megajules, or about 0.2 kT TNT equivalent.
Eo
Best regards,
Horace Heffner
http://www.mtaonline.net/~hheffner/
