Question about Fukushima in 2016

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ladajo
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Re: Question about Fukushima in 2016

Postby ladajo » Thu Mar 24, 2016 12:45 pm

"Critical" in the bad sense is a construct of Hollywood and the mass media. In the real world there is no such bad thing to it.
Even super-critical is not a bad thing in the real world. Our ability to manage reactivity and reactivity addition rates by using slow fuel and delayed (0n1)s as the primary function is what makes nuclear power a reality. It is by design, and again, why a power plant can't be a bomb.

The Soviets were never been big on safety, and this was/is(as the Russians still us Soviet based designs) especially true for nuclear engineering. Graphite moderated steam generating cores are accidents waiting to happen. In addition to slagging itself, a significant amount of fuel material became flaming projectiles that littered what was left of the building (note it was not a containment in any sense), and the surrounding grounds when the core blew. It is beyond me why anyone still operates graphite moderated, but there are still a few. They are just not safe.

Now, at the bottom of the physics of a slow core, there is a limit. This is where you produce enough primary fuel (ie not fission product) reactions that prompt (0n1)s take over the reaction, and drive the reactivity addition rate. Given the speed of production/reaction with a high enough density of prompt (0n1)s, then rate of power increase becomes uncontrollable. This is until it hits the material/mass/geometry limits of the core, and results in slag; at which point the now 'corium' mass enters a new operating regime, again self-managed for the most part. Prompt critical is really what the idiots are alluding to when they table the 'evil critical reactor' or fuel mass. Again, this is inherently how bombs work, they are fast fuel constructs with high density mass and geometry.
The development of atomic power, though it could confer unimaginable blessings on mankind, is something that is dreaded by the owners of coal mines and oil wells. (Hazlitt)
What I want to do is to look up C. . . . I call him the Forgotten Man. (Sumner)

JoeP
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Re: Question about Fukushima in 2016

Postby JoeP » Thu Mar 24, 2016 3:36 pm

So what is the likely answer for Fukushima?

If, as Chernobyl, some kind of long term containment is built, these things need regular maintenance. For thousands of years. I just do not see our current civilizations as able to maintain that kind of commitment.

It isn't even assured over a few decades.

At least the Japanese are good at robot design. Maybe an eventual cleanup is possible.

choff
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Re: Question about Fukushima in 2016

Postby choff » Thu Mar 24, 2016 5:56 pm

The last I heard they don't know where the reactor core is, and the robots can't survive the radiation long enough to find it.
CHoff

KitemanSA
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Re: Question about Fukushima in 2016

Postby KitemanSA » Thu Mar 24, 2016 6:40 pm

CharlesKramer wrote: Fukushima also plans an ice tunnel.
Not so. TEPCO plans to have an ice wall. The constrution is all done. All they have to do now is freeze it.
Which to me raises a lot of questions:

1. The cores are still "hot" enough (radioactively) to fry purpose-built robots (as of March 2016). Doesn't that imply ongoing criticality? What is the status of short-life daughter products (iodine, Xenon) that signify criticality?
Some got fried, some just got stuck and had their umbilicals cut.
No. There is no implication of recritiality. The fission products and the minor actinides are very radioactive and will be for thousands of years due to the actinides. Iodine 131, gone. much of the radoiactive xenon, gone.
2. Doesn't the plan for the ice tunnel also signify ongoing criticality?
No. The ice barrier (wall) is to divert ground water from the site so they can empty the reactor buildings of radioactive water and begin decommissioning work.
3. Is the purpose of the water cooling to draw away heat to prevent the China Syndrome? Presumably the water does not "cool" the chain reaction. Could the water even be acting as a moderator that increases the amount of fission?
The cooling water is to remove the heat of the fission product decay. There is no criticality. Boron, look it up.
4. The BBC recently ran a story claiming the abandonment of the Fukushima area did more harm than the low levels of ambient radiation would have done if people stayed. But:

-- the radiation is low because a lot of weeds and surface soil were removed. Might not hot spots remain?
No, the radiation was low before they started all that mostly needless scrapping. Look at the original radition maps from Fukushima. None of the areas except the red should have been evacuated. Indeed, most of the red should not have either. The IAEA recommnds that no one who lives where the groundshine is ≤ 25µSv/hr should be evacuated if clean food and drink can be provided. The red part of the map was marked as ≥19µSv/h except that said values were from an incorrectly converted arial Becquerel/m^2 measurement to groundshine and they appeared to have left off the divisor of 3. The red part appears to actually have been ≥~6µSv/h. THAT is plenty safe, subject to clean food and drink.
-- If no longer cooled with water couldn't the cores melt into the ground (potentially releasing radioactive steam), or generate hydrogen that might cause another radiation-spreading explosion?
At this point, almost certanly not. The heat output is VERY much smaller now than in the first days and months.
Fukushima is a classic "Cat in the Hat" problem. Try to rub out a pink stain, and you just spread it. I don't like some of the alarmist stuff written about Fukushima (like blaming it for USA West Coast starfish die-offs, which appears to be pure speculation); but the situation does seems justifiably terrifying -- and not being discussed hardly anywhere.
There are people who get paid to spread that terror. FEAR sells and they sell a lot of it. The key word in your last sentance is "seems". Study the effects of radiation on the body and you will loose your fear of those levels of radiation. Knowledge is a great antidote to fear.

Just as an example:
Fear of radiation has killed about 1700 people in Fukushima.
Radiation has killed no one yet and even the discredited Linear No Threshold (LNT) shows that no obserable number ever will. Hormesis suggests that the evacuees are doing themselves a grave disservice because they are NOT getting the free Fukushima Spa Treatment.

KitemanSA
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Re: Question about Fukushima in 2016

Postby KitemanSA » Thu Mar 24, 2016 6:56 pm

paperburn1 wrote:2. Doesn't the plan for the ice tunnel also signify ongoing criticality?

I believe you are referring to the ICE DAM the have constructed around the reactors.
Actually, I think he is refering to the ice WALL around the reactors. They tried unsuccessfully to create ice dams in the piping tunnels. There was enough volume to circulate that they just couldn't get a solid seal, so they filled the tunnels with concrete instead.

KitemanSA
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Re: Question about Fukushima in 2016

Postby KitemanSA » Thu Mar 24, 2016 7:01 pm

CharlesKramer wrote:
ladajo wrote:I beleive the crack was blamed on an H2 pop in the donut.
It was not due to the slag.

I think there were two explosions (Unit 1 and Unit 3). I don't know which one has the crack in the cement containment. I believe Gundersen speculates the Unit 3 explosion was due to criticality. Here's Gundersen in 2011 talking about it. https://vimeo.com/22865967
I wouldn't put any stock into anything that Gundersen says. He is full of sour grapes.

KitemanSA
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Re: Question about Fukushima in 2016

Postby KitemanSA » Thu Mar 24, 2016 7:10 pm

CharlesKramer wrote:More detailed explanations for me to ponder - thx! Interesting that Arne Gundersen's speculation about criticality may have been wrong.

His speculations typically are.

There is one other factor that many neglect in discussions about criticality. Is the reaction critical with prompt or delayed neutrons? When a Light Water Reactor goes critical, it is typically critical with delayed neutrons and well sub critical with prompt.

KitemanSA
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Re: Question about Fukushima in 2016

Postby KitemanSA » Thu Mar 24, 2016 7:43 pm

CharlesKramer wrote:And what makes fission scary: no off switch!
False. Fission definately DOES have an off switch. Fission product decay on the other hand does NOT. But therre is a certain, limited amount ofenergy that needs to be handled.
If I understand correctly, Chernobyl slag (the "elephant foot") is sub-critical, but still too deadly for man or machine to approach -- hence the plan to contain. Maybe Fukushima is more like that than I realized. Except Chernobyl seems stable -- no cooling water needed. What would happen at Fukushima if the water was turned off?

Chernobyl has been decaying for ~30 years. With a 1GW reactor, the decay heat after ~30 years is ~900W. Fukushima has been decaying for about 5 years. It should be evolving ~2 to 3 kW.

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KitemanSA
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Re: Question about Fukushima in 2016

Postby KitemanSA » Thu Mar 24, 2016 7:47 pm

ladajo wrote: It is beyond me why anyone still operates graphite moderated, but there are still a few. They are just not safe.
What you say may be true of some water cooled graphite moderated cores, but please don't be so general in your statement. Graphite moderated molten salt fueled reactors can be VERY safe.

ladajo
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Re: Question about Fukushima in 2016

Postby ladajo » Fri Mar 25, 2016 12:07 am

Fair enough, although in my mind the discussion centered on conventional plants. OBTW, there are no operating light water fast fission plants. Your "typically" is an always. Reactivity is controlled by designed dependence on delayed (0n1)s. You can't control a fast (0n1) reaction. It doubles power in millisecond cycles.
The development of atomic power, though it could confer unimaginable blessings on mankind, is something that is dreaded by the owners of coal mines and oil wells. (Hazlitt)

What I want to do is to look up C. . . . I call him the Forgotten Man. (Sumner)

ladajo
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Re: Question about Fukushima in 2016

Postby ladajo » Fri Mar 25, 2016 1:41 pm

Which to me raises a lot of questions:

1. The cores are still "hot" enough (radioactively) to fry purpose-built robots (as of March 2016). Doesn't that imply ongoing criticality? What is the status of short-life daughter products (iodine, Xenon) that signify criticality?

Some got fried, some just got stuck and had their umbilicals cut.
No. There is no implication of recritiality. The fission products and the minor actinides are very radioactive and will be for thousands of years due to the actinides. Iodine 131, gone. much of the radoiactive xenon, gone.


With no power level operations (sufficient (0n1) thermal flux), the production of (53I135) is nil. I-135 is proportional to flux. Note that I-135 is actually produced primarily from (52Te135), but the cycle is so fast (half-life of 19sec) it can be ignored from a reactor physics standpoint. Note also that these are Beta decays. (54Xe135) is the primary product (95%) of I-135 via thermal absorption, there is also a natural decay which takes eminence if the plant is shut down. However, I-135 has a short half life (6.5hrs) when compared to Xe-135 (9.1hrs). So what this all means in practical purposes, is that I-135 and Xe-135 are both considered sources of negative reactivity or 'poisons', where Xe has a greater influence due to a larger cross section. However, due to the preference of Xe-135 to burn via thermals during power operations, it has a practical density limit during power operations that kicks in around 10x10^15 thermal flux levels, whereas I-135 remains proportional to flux. This therefore means, that Xe-135 will reach equilibrium as a poison during constant power operations in around 2 days after a change in power. On an up power cycle, given the half life of I-135 at about 6.5 hours, Xe-135 will dip due to increased flux burn, and then at about 5 hours it will bottom out and start to build again as the production of I-135 and subsequent decays kick in sufficiently against the flux burn off of the Xe-135. It will equalize at its new higher concentration after about two days, which is dependent mostly on the Xe-135 half-life of about 9.1 hours. If you reduce power, the opposite happens, Xe-135 will rise to a peak at about 5 hours after the transient, then given the lower contribution of production from I-135, it will decay away to a new equilibrium in about two days. For a shutdown, the level of Xe-135 created is related to the power level and operating history prior to the shutdown. If the plant is equalized at high power, and then shutdown on a scram, or other rapid mode, the Xe will be significant, and after about a day can still be at levels equivalent to full power. Normally, it takes about three days for Xe-135 to decay away to insignificant values after shutdown. This can be sooner, if the plant had a low power operating history prior to shutdown, and went through a controlled slow shutdown process. An interesting point is that if you have a high enough power level operating history (based on plant design), and a rapid shutdown, you can end up in a condition known as Xenon Precluded Startup, where the negative reactivity from Xe exceeds your ability to add sufficient positive reactivity (plant design) in the startup process and prevents you from achieving self sustaining operations (criticality) until sufficient Xe decays away. Again, this dead time condition is usually in a window about 7 to 13 hours after shutdown, but can be much longer in plant design with low ability to add sufficient positive reactivity. It is impacted greatly by the pre-shutdown operating history (higher for longer is generally worse, unless you have some high power significant transient ops where you can extreme peak Xe and flip the switch).

Bottom line: Below 5x10^15 thermal flux, (54Xe135) is proportional to (53I135) which is proportional to thermal flux (power). Above this until 10x10^15 thermal flux Xe-135 hits an equilibrium limit due to the dominance of its thermal flux burn off. In shutdown conditions, I-135 is done after about a day, and Xe-135 is done after about 3 days.
Last edited by ladajo on Fri Mar 25, 2016 2:11 pm, edited 1 time in total.
The development of atomic power, though it could confer unimaginable blessings on mankind, is something that is dreaded by the owners of coal mines and oil wells. (Hazlitt)

What I want to do is to look up C. . . . I call him the Forgotten Man. (Sumner)

ladajo
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Re: Question about Fukushima in 2016

Postby ladajo » Fri Mar 25, 2016 1:57 pm

By the way, not understanding this is what caused the Chernobyl excursion. The dummies forgot about how operating history impacts Xenon poisoning and set themselves up for a positive reactivity addition accident, that then lead to a prompt criticality condition, which then lit the graphite on fire and then lead to steam explosion(s) which scattered all sorts of flaming chunks of fun stuff around the landscape. For a grand finale, the remaining corium slag ate its way into the basement creating the permanent "Chernobyl Memorial Park".
It may be that the Japanese end up with some component of the three slagged units becoming the permanent "Fukushima Memorial Park", but that depends on the motivation and determination of the Japanese to get at the slag remnants. They have a much more manageable problem than the Russians given the base plant design differences.
The development of atomic power, though it could confer unimaginable blessings on mankind, is something that is dreaded by the owners of coal mines and oil wells. (Hazlitt)

What I want to do is to look up C. . . . I call him the Forgotten Man. (Sumner)

CharlesKramer
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Re: Question about Fukushima in 2016

Postby CharlesKramer » Fri Mar 25, 2016 5:18 pm

ladajo wrote:"Critical" in the bad sense is a construct of Hollywood and the mass media

I can't reconcile that -- a view of criticality as a continuum -- to the Slotin accident at Los Alamos (criticality by fleetingly and accidentally joining the two halves of the demon core) and the Cecil Kelley centrifuge accident (criticality by centrifuge).

In both those stories, criticality was a dramatic threshold (perfect for Hollywood, but based on something real).

I believe Slotin was messing with two halves of the spherical demon core -- keeping them apart with a screwdriver. Keep the halves apart, and everyone in the room is okay. Let the cores touch, and blue light, neutrons, death. Slotin knocked the halves apart almost instantly, but not before receiving a fatal dose.

So is Hollywood that far off? _Kiss Me Deadly_ arguably (argued by me -- no one has agreed so far!) depicts a criticality event -- what would have happened if Slotin had not pushed apart the cores.

I realize this has little to do with Fukushima (both the Slotin and Kelley centrifuge stories involve Pu) except to explain my focus on the fear word "critical."
================================
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Re: Question about Fukushima in 2016

Postby CharlesKramer » Fri Mar 25, 2016 5:30 pm

Wow, this discussion is great! A good antidote to the near silience about this is in the news. Thanks to you and all.

KitemanSA wrote:There is no implication of recritiality

So... no mystery why I don't see it discussed anywhere.

KitemanSA wrote:FEAR sells and they sell a lot of it

I understand that. Whenever anything dies (starfish on the West Coast) or gets sick Fukushima is implicated. Maybe it should be, but without evidence the reports are just panic-mongering. I don't mean to contribute to it, but perhaps my skepticism has not completely protected me from it.

However, the points you raise:

KitemanSA wrote: The fission products and the minor actinides are very radioactive and will be for thousands of years

and...

KitemanSA wrote:[CBK asked] "If no longer cooled with water couldn't the cores melt into the ground (potentially releasing radioactive steam)"
At this point, almost certanly not.

are plenty scary enough.

*Almost* certainly? Even if melting into the ground water does not equal my favorite word ("criticality") Fukushima is, in 1960s parlance, a bad scene, man.
================================
CBK
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CharlesKramer
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Re: Question about Fukushima in 2016

Postby CharlesKramer » Fri Mar 25, 2016 5:41 pm

KitemanSA wrote:
CharlesKramer wrote:And what makes fission scary: no off switch!

False. Fission definately DOES have an off switch

Definitely has an off switch... meaning control rods?

My point is that does not apply to tons of corium slag which will remain hot accordingly to the rules of the decay chain (at at Fukushima so hot it cannot be approached by man or machine, at least for years).
================================
CBK
Blog: http://www.provideocoalition.com/ckramer


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