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PostPosted: Mon Mar 28, 2011 8:41 pm 
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Skipjack wrote:
Quote:
http://jalopnik.com/#!5786275/this-is-the-scariest-tsunami-video-yet


After watching this video, I have a hole different level of appreciation for the stability of that nuclear power plant. It seems really hard to compete with forces like that...

Quote:
With a volume that "hot", would a robot work? Remember, the Space Shuttle main computer has processer equivalent to the old intel 286 generation because anything with smaller features is too subject to derangement by radiation.


Uhm, no. I dont know where you are getting these ideas from.
People constantly bring their laptops, ipods and other computers to the ISS with them.
The Space Shuttle computers were updated several times during the lifetime of the Shuttles. The last update brought a full glass cockpit. You think that you can run that on 286 CPUs? I doubt it.
I heard that until recently many systems were using 486 CPUs, because they are very robust and still onyl require passive cooling, but 286? I am sure not.
Also, there are actually robots that were specifically developed to work in nuclear power plants in case of an accident. If anything, you should be able to shield them sufficiently.


According to engineers during my recent visit to Kennedy to see Atlantis, Endeavor and Discovery one of the Engineers told me that the are running 386's after having upgraded from the Motorola 68000 series, for the stated reason of radiation flight safety.


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PostPosted: Mon Mar 28, 2011 10:33 pm 
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Quote:
Wrong fuel type and wrong geometry. Power plants use slow fuels, hence the need for moderators. Weapons use fast fuel, and have dense geometry. Two different animals.

Exactly.

Quote:
According to engineers during my recent visit to Kennedy to see Atlantis, Endeavor and Discovery one of the Engineers told me that the are running 386's after having upgraded from the Motorola 68000 series, for the stated reason of radiation flight safety.

Maybe SOME critical systems that must never fail do, but I DO KNOW for a fact that pretty much all of todays electronics work just fine in space.
The iPod is among the items that most astronauts take with them. They also use simple standard laptops on the ISS.
http://www.youtube.com/watch?v=H8rHarp1GEE
40 sec into the video.


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PostPosted: Mon Mar 28, 2011 11:49 pm 
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Educational response to my vague comments. I'm not sure why fast neutrons would be important for bombs but not fuel rods. I suppose it has something to do withe the density of the fuel. The neutrons are moderated by the poor moderating but high density uranium or plutonium in the bomb. The critical amount of a fissile material is dependant upon the mass but also, probably more importantly the purity and density (mass per unit volume). With the 5% or lower purity of U235 in fuel rods, the compression/ implosion would have to be perhaps 20 times as strong if it is a linier relation ship, when compared to weopens grade uranium.
The second concideration that would be very difficult in a reactor, is containment. In bombs, containment has to be strong enough (due mostly to inertia) for a significant portion of the fuel to fission in a time dependent fashion. In a pool of melted fuel rods, even if the fuel pellets settled to the bottom, fission would increase only to the point where the the heated fuel mix started boiling, or other lower boiling point material vaporized. This might quickly create an effective steam explosion, but wouldn't be anywhere near a nuclear bomb in it's intensity.

Two near (?) criticallity accidents that I know of was, first when two chunks of plutonium fell together on a table top. The researcher quickly pulled them apart- there was no explosion, but he died of radiation exposure and several others were injured.
The other was in Idaho, where something happened while staff was doing something with the rods. In this small reactor a burst of radiation quickly killed two of the three technicians present, the other did not have a chance to die of radiation poisoning as he was impaled with a fuel (or control) rod from the associated steam explosion. This explosion apparently did not do much damage to the building. So ended the Army's plan to use small reactors at remote bases.

[EDIT] A more accurate discussion of criticallity accidents in the US is at:

http://www.cddc.vt.edu/host/atomic/acci ... tical.html

Dan Tibbets

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PostPosted: Tue Mar 29, 2011 12:46 am 
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Dan,
You are referencing the SL-1 accident. The unit went prompt critical during a procedure where one of the operators (the navy guy) pulled the control rod out too far too fast. The resulting prompt critical burst flashed over the core, and the resulting steam explosion impaled him to the roof with a component of the vessel head. One operator died from the balst and ejection from the top of the vessel. The other operator sustained mortal injuries in the balst and fall as well, but survived long enough that the investigating team found him. He then died in the ambulance is my understanding.
I have seen the sight in Idaho, another geometric deadspot in the desert.

There was a facility at INEL called PCF, or Prompt Criticality Facility. The used to build scaled down reactor vessels and insert live scaled down cores in them. They would pop the rods, and test the reactor vessels for live accident containment. What a job that must have been.

Again, to level the terminology playing field: Sub-critical = power decreasing, neutron population not self sustainable at current level. Critical = self sustaining neutron population at current power. Super Critical = power increasing, neutron population growing. Prompt Critical = rapid "Holy shoot the chicken" neutron population burst growth which effectively instantly cooks off the fuel mass within the affected geometry. The prompt neutrons, or those produced directly from fission of fuel, have a 1.0 or greater proability of fission, due to extreme population density, and/or due to high density fuel (enriched or a fast fuel). Note that U-235 is considered a slow fuel. But at higher enrichment (density levels) it can cook off with fast neutrons, especially if saturated with them.

In a normally operating power plant, U-235 fissions an avg. of 2.34 neutrons, which in turn pin ball down to slow enough energies to create another fission event. The plant also gains some neutron population from fission products decay, and fission, but the majority come from the fuel itself.

Fast Fuel prefers fast neutrons to fission, slow fuel prefers slow neutrons to fission. A slow fuel can burn via fast neutrons in a saturation event, ie metric butt-ton of fast neutrons in an dense geometry. Essentially, shoot enough hot neutrons at it and it will burn (prompt criticality can do this.)

Fast fuel weapons work better and are easier to pop than slow fuel weapons. The reason the pit accident did not pop was because the was no neutron moderator or reflector to drive the neutron density high enough to get the pit to go prompt. So instead of dying painlessly in a spectacular plasma ball fashion, the dude cooked himself, and went out the painful way. If he had not of had the presence of mind to pull the pit apart, odds are several more folks would have cooked too, and the building would have burnt down, leaving an ugly mess to clean up (if possible).

Edit: I suck at spelling again.


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PostPosted: Tue Mar 29, 2011 6:07 am 
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D Tibbets wrote:

The differential decay ratios mentioned above are interesting, though I'm not sure how many scenarios could result in the ratios.
Dan Tibbets


The Ba-140/LA-140/Ce-140 decay chain make those numbers interesting, the TC99m is scary. With a 1/2 life of 6.02 hrs its basically not measurable after 62 hrs.

TMI was over in 5 days, cooling resumed about 3.5 days into the event. About 10% to 25% of the top of the fuel rods crumbled or melted, some fuel fell to the floor some fuel got caught up in the assemblies.

We have seen water measurements that suggest anywhere from 1.2 meters to 2.5 meters of Fukushima fuel rods have been exposed. The presence of Cesium & Iodine are basically defacto evidence of fuel rod impact. Is it fair to guess that the top half of some fuel rods are on the floor?

I just saw the new numbers (March 27th) from #2, they have declined, though there is still more Barium-140 than La-140. I suspect some low level recriticality between March 17th and March 23rd.

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PostPosted: Tue Mar 29, 2011 1:03 pm 
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They also noted Co-60, and that can only come from steel. Specifically the Co-59 in the alloy. That can speak to core assy or control rod failures. The amount is what splits between lifetime contaminants or structural failures.


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PostPosted: Tue Mar 29, 2011 9:20 pm 
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I am impressed if this is true:

Quote:
Nuclear expert says radioactive core in one of Japan's quake-ravaged reactors appears to have melted through the bottom of its containment vessel and cannot be saved, as displaced residents continue to be tested for radiation exposure.


They think Unit 2 cooked through the vessel.


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PostPosted: Wed Mar 30, 2011 5:00 am 
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ladajo wrote:
I am impressed if this is true:

Quote:
Nuclear expert says radioactive core in one of Japan's quake-ravaged reactors appears to have melted through the bottom of its containment vessel and cannot be saved, as displaced residents continue to be tested for radiation exposure.


They think Unit 2 cooked through the vessel.



Richard Lahey is the only source I see for that quote, which is already 13 hrs old. And hes been speculating repeatedly.

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I like the p-B11 resonance peak at 50 KV acceleration. In2 years we'll know.


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PostPosted: Wed Mar 30, 2011 12:28 pm 
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As I said, I would be impressed if true.

However, I am also not counting it out. Anything is possible, even if I think it unlikely.

One thing is for sure: Information is traveling faster than reality.


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PostPosted: Wed Mar 30, 2011 8:15 pm 
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SPEEDI rad numbers are declining over 9 days, and the picture the isotopes paint are also of declining radioactivity. Though I do think 2 & 3 have half or more of the fuel rods crumbled or worse, on the floor or caught up in the fuel/control rod assembly's.

And if unit 2 did melt/slag thru the reactor vessel, it happened at least a week ago.

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I like the p-B11 resonance peak at 50 KV acceleration. In2 years we'll know.


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PostPosted: Wed Mar 30, 2011 8:47 pm 
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I think right now the only real truth is that they have no idea what the core assy's look like.
My money is with you, but I think that all three are toast. From what I recall of the TMI-2 post accident core study and its implications, they have slag in all three, and it happened fairly early on in the adventure.
Granted these things are old, but finding Co-60 outside the plant is not a good sign by any means. As we know, at a minimum escaping H2, Cs and I are also big clues that there are significant issues in fuel assy integrity.

It will be a while before they get in there and figure out exactly what has happened.


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PostPosted: Wed Mar 30, 2011 9:28 pm 
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Has anyone seen a comparison between the TOTAL radiation released from F-Diichi vs. TMI?


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PostPosted: Wed Mar 30, 2011 10:06 pm 
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No, but I am very sure that Fuki has on orders of magnitude beaten out TMI-2.
TMI-2 never had any sort of containment breach other than core slagging which stayed in the vessel.


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PostPosted: Wed Mar 30, 2011 10:20 pm 
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ladajo wrote:
No, but I am very sure that Fuki has on orders of magnitude beaten out TMI-2.
TMI-2 never had any sort of containment breach other than core slagging which stayed in the vessel.
Well, I think you'd only have to look for any indication of cobalt-60 in the environment to compare TMI versus Fuku[p]. It is not a fission product. It is an activation product. So if you find Co-60, then something solid and 'internal' has been physically ejected from the reactor equipment (unlike, e.g. iodine which will vapourise and drift out). Not necessarily a core breach, but I'd wager Co-60 is a signature for a core disintegration.


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PostPosted: Thu Mar 31, 2011 12:44 am 
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ladajo wrote:
No, but I am very sure that Fuki has on orders of magnitude beaten out TMI-2.
Yet they are both rated at level 5. Hmmm.


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