Fukushima's toxic legacy: Ignorance and fear Events at the Fukushima Daiichi nuclear powerplant in Japan continue to unfold, with workers there steadily restoring redundancy and containment measures across the site. It remains highly unlikely that the workers themselves will suffer any measurable health consequences from radiation, and – continued media scaremongering …
If you are going to shut down all the nuclear reactors because (even given evidence to the contrary) they are 'unsafe' you are going to have to shut down all the coal, gas, wind and solar places too, as they present a similar if not greater risk (esp. coal with all its carcenogenic output). That leaves hydro (and how many people have drowned in those pesky lakes I ask you).
Hope you enjoy your electricity rationing.
Lets get real -
There is NO other power generation means which has even a tiny fraction of the risk that nuclear power generation has..
You talk of the dangers of coal, gas, hydro etc .. It is utterly laughable that you cannot see the difference! Even the worst of these, and the most badly designed / operated of these has NO possibility of poisoning vast areas for thousands of years.
Agreed, there are toxic and immediately harmful effects of carbon fuel based power generation.. And I CAN see an argument for nuclear power generation - we need to reduce carbon emissions or the consequences could be as disasterous as the potential consequences of nuclear accidents or waste..
BUT - There is another way! - You say "Hope you enjoy your electricity rationing".
Well, in fact, there is NO NEED for the vast energy consumption - Most is driven by the insane consumerism and quest for "economic growth" which is unsustainable.. YES! ITS BLOODY UNSUSTAINABLE!! - We live on a planet with limited resources - And we consume these resources as if they have no limit..
It is not only electricity rationing which is NEEDED, it is time us greedy indulgent arrogant western PARASITES tightened our belts and took LESS from this depleted world - I consume more than an entire African family, some western folks consume more than an entire African village.
And writing off vast areas of the planet because we pollute it with toxic waste is not going to serve anyones interests.
FredM
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So, the containment has to be strong enough to deal with any natural event (as we've just seen, it basically was in a flawed design from 40 years ago), and it must be able to withstand aircraft strike... like the reactor buildings are, indeed, designed to be.
As for criticality. That's what the automatic SCRAMs at the beginning of this whole debacle were for. The problem was maintaining cooling after power was lost to the cooling pumps - many modern designs utilise convection for cooling, negating this problem.
As for being rated to cater for any possible levels of pressure - perhaps they should be rated for higher levels. It's a cost/benefit analysis, is it not? Like, say, driving - a dangerous activity, if ever I saw one.
By and large, what we've witnessed in the media is the same phenomenon we see in any discussion of uncommon risks, most notably post-11/9 terrorism. In _Beyond Fear_, Bruce Schneier makes some points about thinking sensibly about security in an uncertain world that are equally applicable to the Fukushima situation:
* People exaggerate spectacular but rare risks and downplay common risks.
* People have trouble estimating risks for anything not exactly like their normal situation.
* Personified risks are perceived to be greater than anonymous risks.
* People underestimate risks they willingly take and overestimate risks in situations they can't control.
* People overestimate risks that are being talked about and remain an object of public scrutiny.
Unfortunately for everyone, most of the media takes advantage of this skewed perception of risk to grab attention for themselves.
1) The plants withstood a 9.0 Earthquake with apparent ease. These are 40 year old reactors, and held up well. Newer reactors like those in the USA, are built on "rollers" to help them withstand even MORE severe of an earthquke as this was.
2) The reactors were shut-down in an orderly manner and the nuclear reaction was stopped.
3) A while later the Tsunami occurred, and we see where the major flaw was, having the diesel generators susceptible to the tsunami, not with a flaw in the reactor design.
4) The storage of the spent fuel pools at the top of the reactor was a big mistake. Although the nuclear hysteria is causing problems with spent fuel storage and probably has some blame.
5) The officials where slow to react and call in external assets(fire truck pumps) to help, which is probably a cultural thing.
If they would have put some more thought into the location of their generators and their spent fuel storage units, we would have had a zero incident.
Most likely we will have a few bannana's worth of radiation, a shit load of media hysteria, and 4 reactors that actually worked very well for being in a 9.0 earthquake and a massive tsunami.
And people will still be afraid of the cleanest and lowest cost energy source known to man.
for fuck's sake, it didn't work. unless your definition of "work" is "no catastrophic failure that resulted in the mass irradiation of a large number of people and a huge area of land'.
the reactor design is flawed. it relies on power to keep everything cooled even when the reactor is shut down. that is fucking stupid and dangerous. it's even worse when this applies to the cooling ponds which store the spent fuel. that sort of design is not fail safe.
bits of the reactor buildings blew up. hydrogen had to be vented from the cooling system. and we had helicopters and fire trucks dumping water to keep things from getting so warm there would have been a serious leakage of radiation from the spent fuel rods or even a meltdown in the reactors. this tends to suggest things did not work. if everything had worked properly, those sorts of last-ditch heroic efforts would not have been needed.
today, japanese officials are telling people in tokyo that babies can't drink the tapwater because it's too irradiated. food and milk from the area near the reactors is also banned for the same reason. none of this would have been necessary if the system "worked" and had been designed properly.
we're just lucky the incident hasn't been more serious. just as we were lucky that the windscale fire and three mile island incidents weren't more serious. seems to be a trend here, eh?
I agree with all but point 5.
The reason they were slow to react is that a massive tsunami and earthquake had just wiped out massive amounts of infrastructure.
No matter what MSM likes to claim the tsunami and earthquake are of MUCH great concern and as such the reactor probably took a back seat in the early days. Not a good thing, but totally understandable.
This is a minor nit pick i know.
In the French 'Territoire d'Outre-mer' of St-Pierre-et-Miquelon (a couple of flyspecks in the mouth of the St Lawrence Seaway) iodide tablets have been issued. Well, if the 'nuage radioactif' reaches across the Pacific + North America to the point where such protective measures become necessary, I guess we can kiss goodbye to Los Angeles, San Francisco, Seattle, Vancouver, ...
http://www.20minutes.fr/article/689078/planete-nuage-radioactif-risque-t-on-france
Warning: '20 minutes' is roughly equivalent to 'Metro' in the UK, so take this story with a grain of salt (or iodine, if preferred).
A bit of a challenge, that. It's been tried. Lots of times.
http://www.ncbi.nlm.nih.gov/pubmed/20798473
It's a paper following the most exposed individuals from the Windscale fire of 1956. Unusual in that it didn't need to be worked from epidemiological statistics (hard to do, because of a small contribution compared to natural variations), or where supposed death rates were back calculated from exposure and applying assumptions about low-dose mortality.
"This paper studies the mortality and cancer morbidity of the 470 male workers involved in tackling the 1957 Sellafield Windscale fire or its subsequent clean-up. Workers were followed up for 50 years to 2007, extending the follow-up of a previously published cohort study on the Windscale fire by 10 years. The size of the study population is small, but the cohort is of interest because of the involvement of the workers in the accident. Significant excesses of deaths from diseases of the circulatory system (standardised mortality ratio (SMR) = 120, 95% CI = 103-138; 194 deaths) driven by ischaemic heart disease (IHD) (SMR = 133, 95% CI = 112-157, 141 deaths) were found when compared with the population of England and Wales but not when compared with the population of Northwest England (SMR = 105, 95% CI = 90-120 and SMR = 115, 95% CI = 97-136 respectively). When compared with those workers in post at the time of the fire but not directly involved in the fire the mortality rate from IHD among those involved in tackling the fire was raised but not statistically significantly (rate ratio (RR) = 1.11, 95% CI = 0.92-1.33). A RR of 1.11 is consistent with an excess relative risk of 0.65 Sv(-1) as reported in an earlier study of non-cancer mortality in the British Nuclear Fuels plc cohort of which these workers are a small but significant part. There was a statistically significant difference in lung cancer mortality (RR = 2.18, 95% CI = 1.05-4.52) rates between workers who had received higher recorded external doses during the fire and those who had received lower external doses. Comparison of the mortality rates of workers directly involved in the accident with workers in post, but not so involved, showed no significant differences overall. On the basis of the use of a propensity score the average effect of involvement in the Windscale fire on all causes of death was - 2.13% (se = 3.64%, p = 0.56) though this difference is not statistically significant. The average effect of involvement in the Windscale fire was - 5.53% (se = 3.81, p = 0.15) for all cancers mortality and 6.60% (se = 4.03%, p = 0.10) for IHD mortality though neither figure was statistically significant. This analysis of the mortality and cancer morbidity experience of those Sellafield workers involved in the 1957 Windscale fire does not reveal any measurable effect of the fire upon their health. Although this study has low statistical power for detecting small adverse effects, due to the relatively small number of workers, it does provide reassurance that no significant health effects are associated with the 1957 Windscale fire even after 50 years of follow-up."
Note that - at the level of raw statistics cancer mortality was LOWER than that for a similar, unexposed cohort, albeit not at a level that was statistically significant.
In fact, the evidence for a relationship between cancer rates and low doses is very questionable. The "Linear Low Dose Hypothesis" is only usually justified on the precautionary principle, not because there's good evidence for it.
Agreed, the problem of establishing (or disestablishing) a link is the thankfully small numbers exposed to low doses (i.e. > 100 < 250mSv/yr perhaps even < 500mSv/yr depending on your point of view).
From the abstract this is interesting: "Significant excesses of deaths from diseases of the circulatory system were found when compared with the population of England and Wales but not when compared with the population of Northwest England" I wonder why? Higher background radiation in the NE? More coal mines, flour mills or steel smelting perhaps leading to increased incidents of respiratory disease? Maybe the indigenous population of the North East are just a bit more sickly than the rest of England & Wales.
Would have been interesting to read the full text...
>In fact, the evidence for a relationship between cancer rates and low doses is very questionable. The "Linear Low Dose Hypothesis" is only usually justified on the precautionary principle, not because there's good evidence for it.
Questionable yes, clear cut? No. Until there is good evidence one way or the other, the precautionary principle sounds eminently sensible.
"Significant excesses of deaths from diseases of the circulatory system were found when compared with the population of England and Wales but not when compared with the population of Northwest England" I wonder why? Higher background radiation in the NE?
Well, radiation isn't normally associated with heart disease. And traditionally, high-saturated fat diets and smoking levels have tended to be higher in industrial/former industrial areas like the North West, than with the UK average.
" Until there is good evidence one way or the other, the precautionary principle sounds eminently sensible"
It depends what it's used for. In terms of setting exposure limits, perhaps. In terms of evaluating probable mortality rates from an incident like Fukushima, then the case is less good. What's most problematic is when it gets used to reveiw something like Windscale, where using it leaves to claims of up to 200 deaths as a result, but without there being a statistically extractable "signal" to demonstrate increased mortality.
Part of the problem is, even on the LLDH model, the contribution is small against the general background of cancer deaths - even at highish doses. Even applyiing it to the Hiroshima and Nagasaki survivors doesn't produce a number of deaths that can reasonably be expected to be identifiable in the "normal" death rates - to quote David Spiegelhalter, Professor of the Public Understanding of Risk at Cambridge:
"The perception of the extreme risk of radiation exposure is also somewhat contradicted by the experience of 87,000 survivors of Hiroshima and Nagasaki, who have been followed up for their whole lives.
By 1992, over 40,000 had died, but it has been estimated that only 690 of those deaths were due to the radiation. Again, the psychological effects were major."
Which I make as about a 1.7% contribution to mortality - versus 20-25% of "normal" mortality being down to cancer, without a specific radiation contribution. And to get that, you need to have been exposed to an atom bomb, and the subsequent fall-out.
Let me see if I can precis this.
Workers who fought the Windscale fire have a *slightly* increased death rate relative to similar groups in the south of England.
But
Northeners are less fit than southerners and tend to die earlier.
There is no *significant* increase in the death rates between northeners working in Windscale and northeners working in any other bit of the north. In fact their was an apparently slight lowering (but this could just be noise).
QED Putting out a burning nuclear reactor does *not* shorten average life expectancy in a statistically significant way.
Living in northern England does.
Elevated background levels of .5 - 1. microsieverts per hour persist and are clearly indicated around Hitachi, Ibaraki Prefecture. http://www.rdtn.org/en
Care for some Fukushima® sashimi with a side of Chisso-Minamata dipping sauce?
http://en.wikipedia.org/wiki/Four_Big_Pollution_Diseases_of_Japan
http://en.wikipedia.org/wiki/Minamata_disease#Victims
Compare the Japanese passive aggressive display of 'Denial of Responsibility' to the British 'stiff upper lip' smirk at the prospect of being caned.
Notice that similarity between the two cultures. Interesting.
"Half a league, half a league, Half a league onward, All in the valley of Death Rode the six hundred. Forward, the Light Brigade! Charge for the guns' he said: Into the valley of Death Rode the six hundred."
That's the problem with too little ignorance and too much fear. Not like good ol' days,
4.7GWe of power generation has been completely trashed and will never restart. Factories and homes are experiencing lengthy blackouts and disruptions to production. Thousands of people are temporarily homeless. Other nuclear plants are going to need repairs and probable safety improvements to ensure backup power cannot be lost ever again.
In the context of 18,000 people dead and I imagine hundreds of square miles of populated land trashed I'd say its pretty minor...
Did Japan have any non nuclear power plants in the affected areas? Are they generating anything?
I also wonders how many radio active sources from medical or industrial uses are scattered among the debris.
Poke "wind power survive japan earthquake" into your favorite search engine
I'd place my $$ on building-top solar arrays having survived as well, at least where the building did. That's harder to measure since those installations are decentralized.
On the other hand, Fukushima created a giant urgent problem right when Japan is least able to spare the resources to deal with it. Think of all the people and equipment that are tied up in diffusing that timebomb and mitigating the impacts. Think of the all the international players who got sucked in to monitoring and supporting the staff of one stupid power plant.
A good article with some real numbers about the power station shutdowns in Japan and an explanation of Japan's two separate national grids which prevents load sharing to any great extent can be found here.
http://spikejapan.wordpress.com/2011/03/21/after-the-earthquake-a-long-hot-summer/
Another 10,000 old folks could die of heatstroke due to the reduced amount of power available for air conditioning in the big cities during the summer and autumn.
The nuclear industry itself identifies any loss-of-coolant accident as a serious incident even if no radiation is released. But not Mr Page.
I expect the many industrial customers unable to ship parts into or obtain parts from Japan's sensitive just-in-time supply chain due to electricity disruption may cite a nuclear disaster to their shareholders. But not Mr Page.
TEPCO shareholders must already view the multi-billion-dollar total writeoff and cleanup costs for four destroyed reactors as a financial catastrophe. But not Mr Page.
I rather expect the still-displaced residents of Pripyat and the birth-defect victoms of Kiev view Chernobyl as a pretty frikkin' serious disaster. But not Mr Page.
So I gotta ask, "Mr Page, what level of civilian death and economic consequence would you describe as representative of a significant nuclear disaster?" What toll separates 'engineering triumph' from gross failure in your own mind? Can a nuclear reactor fail at all?
you know there was an big earthquake, right? and a tsunami? Those will have a vastly larger economic impact than 4 reactors being scrapped.
last estimates I saw put the cleanup above 100billion, 2% of Japan's GNP. 3 Mile Island in USA cost about 1 billion to clean up one reactor, so estimate 5 billion on the high end to clean up the 4 reactors at the Fukushima plant. kinda puts it in perspective. for all the media attention and fear and vitrole thats been directed at this sideshow, it is only going to be about 5% of the total cleanup bill. Thats not even going into the human cost. The Fukushima plant will foot only a tiny tiny percentage of that bill.
This is minor, in the context that nothing significant has or will happen because of the problems at this nuclear plant, thousands of people are dead due to a natural disaster. They way the news is reporting it(and many people here) you'd think that the powerplant caused the earthquake.
"Mr Page, what level of civilian death and economic consequence would you describe as representative of a significant nuclear disaster?"
level of civilan death = 0 , economic consequence = harder to calculate, but in terms of the rest of the natural disaster zone, probably very minor.
so what was your point? or are you like the main media outlets, just diaspointe dthat Lewis was right and you didn't get to see a meltdown?
Flames, as thats what you clearly wanted to see.
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Actually, one thing that hasn't been mentioned in all of this is that even if there were a core meltdown did occur in Fukushima daiichi, the reactors were designed with this in mind. To wit: outside the reaction vessel, there is a containment vessel. Should a runaway reaction in the reaction vessel cause the fuel rods to melt, they will melt their way through the bottom of it and pool in the surrounding containment vessel.
The reason why the nuclear reaction in the reaction vessel was self-sustaining to begin with is mainly a matter of geometry. By having rods in such close proximity to each other, the rate of neutron capture increases to the point where a decaying Uranium atom's decay particles have an increasing chance of being absorbed by atoms in the surrounding rods, to the point where the cascade of absorption and decay events is sufficient to produce a self-sustaining nuclear reaction.
In (one of) the worst case scenario(s) the reaction not only achieves criticality (ie, probability of decay particles causing another decay = 1), but greatly exceeds it, then the core can melt down. But even if the core does melt down through the bottom of the reaction vessel, it will form a puddle at the bottom of the containment vessel. The shape/geometry of this mass of Uranium (+ reaction byproducts + other things that melted into the vessel) is such that now the probability that decay particles will spawn another decay event is much less than what's needed for the reaction to continue to be critical (ie, less than 1).
So this brings me to the reason why I responded specifically to your post... in this case, there is almost no chance that a full core meltdown would even escape the containment vessel or melt its way down "to the water table", let alone to the centre of the Earth. Because even reaching the water table would actually be very bad, obviously the people who design reactors (even 40 years ago) foresaw the risk and designed their reactors accordingly.
One last comment in general... thanks Lewis, it's nice to read your anti-hysterical articles. Ever since this crisis came to the fore, it's been writers like yourself (along with a moderate amount of background knowledge I had) that have helped me decide early on that there wasn't really anything to worry about with these particular reactors, despite all the media reports and grumblings to the contrary. Thanks as well for bringing our attention back to the much larger problems caused by the earthquake and tsunami. Thanks & well done.
Thank you for your measured answer. There are two points I would like to bring up in turn:
a) to my knowledge, the number one plant (as well as N°2?) is not hardened against the (admittedly not very probable case) of a full core meltdown, while the newer ones (N°s 2(?) to six are. Is my understanding correct?
b) when I mentioned the "China Syndrome" that was in reference to Mr. Page overdoing his antihysterics by a long shot. Please look up his first article where he dissects this colloquialism in all undue seriousness to show that anybody who is concerned by those riscs is technically naive.
I would like to stress that from late monday onwards it became apparent that the greatest danger lay not in the cores melting down but rather in the storage basins cooking dry and the stored fuel rods catching fire in the process.
I did a search this morning to see if I could find anything about some of the cores not having a protective containment vessel, but I couldn't find anything to back up that assertion. Maybe you were referring to the state of some of the reactors which were fully shut down and so only had residual heat to dissipate, and so had no risk of meltdown?
I didn't actually read Lewis's article that mentioned the China Syndrome initially, so my "nobody has mentioned" comment might have been off the mark. The best articles I've read on the events as they unfolded have been written by Dick Ahlstrom in the Irish Times, as he's done a really good job of explaining the actual problems and defusing the hysteria.
As to the risk of fire in the spent fuel ponds, that certainly is something to be concerned about, but it's an entirely different issue, and thankfully that also seems to be under control now.
Just one more comment about reports of the Japanese authorities being deceitful or reticent about reporting on the extent of the problem. This isn't something you raised, but has certainly been a line that has been trotted out by many media outlets recently. While there may be some element of this in general due to a general culture of not wanting to admit mistakes or collectively "lose face", I've actually got the opposite impression, and trust that the authorities are mostly open and honest about problems if they recognise that they are actually big problems. Two things make me think this way. Firstly, the last time there was a major nuclear incident in Japan was when workers mixed fuel by hand in buckets rather than using the equipment/tools they should have done, causing several deaths and damage to buildings, etc. I was actually living in Japan at the time, and was following events as they unfolded on TV. The initial reports might have been a bit vague, but within a day or two, there was no doubt about what had actually happened and we were getting updates about the state of the situation, readings on radiation levels, etc.
With this particular crisis, I'm no longer living in Japan, but we do have NHK broadcasts available to us on freeview satellite. Since the quake hit, the channel has been a pretty good source of information about what's currently happening, both regarding the situation with the power plant and the wider problems with dealing with the aftermath of the quake and tsunami. It mightn't have been the most technically detailed source, of course, but overall they've done a good job of explaining the situation to regular viewers who mightn't even know how a nuclear reactor works. Overall, I'd have to say that this reporting has been pretty good and impartial, which is actually more than I can say about some other major sources.
One last point about Japan's "dishonesty" in reporting is that actually they're obliged to report all kinds of accidents and events that can pose risk of radiation release or other incident to the IAEA, and nobody, I think, is suggesting that they've failed to report what they should. While the authorities there might be a bit slow in releasing information at first (due to the afforementioned cultural issues, but also not wishing to cause panic) I don't think that there's any doubt but that when they do admit to themselves that there's a real problem, there isn't any question of covering it up, and in general western reports to the contrary are as much, if not more, about sensational stories than they are about reporting the facts.
Criticality issues are only indirectly related to meltdown potential, Bandersnatch. It's an issue of the rate of heat generation and removal.
Only a limited proportion of decay events involve a neutron emission - most are alpha or beta decay, which still generates heat, but can't drive a chain reaction. Further, in the description you
"The shape/geometry of this mass of Uranium (+ reaction byproducts + other things that melted into the vessel) is such that now the probability that decay particles will spawn another decay event is much less than what's needed for the reaction to continue to be critical (ie, less than 1)."
you miss out the main issue - the lack of moderation. the probability of neutron capture varies with the speed/energy of the neutron. In uranium and plutonium, it's much, much higher at "thermal" speeds (when the speed of the neutron is of the same sort of order as atoms moving under normal thermal excitation). When they're emitted, they're "fast" - moving a couplf of orders of magnitude faster.
You can get criticality on fast neutrons alone - that's how fast reactors or bombs work. But, you need much higher levels of enrichment to achieve it - 40% or so at absolute minimum.
At commercial reactor levels of enrichment, (2-3%) you need "moderator" - something the neutrons can bounce around in, shedding energy, and slowing to a point where they can be captured by another uranium nucleus.
Pretty much by definition, within a bolus of melted fuel, it's hard to have moderation - especially in a water-cooled and moderated reactor!
So no, the possibility of a meltdown is dependent on the ongoing decay heat, and the heat energy already in the melted fuel at the point of melting. That's part of what makes it a far less likely event that the protagonists of the "China Syndrome" would have you believe.
Hi Andydaws. I had to read your post a couple of times before realising that you're effectively agreeing with what I said. I take it your main quibble is that criticality isn't necessary to cause a reactor meltdown. That's fair enough. I was aware that it's not just neutron recapture that causes the temperature of the core to increase. I did mention (or at least hint) that the decay puts out other decay particles, not just neutrons and as you mentioned, these are the main reason why the core heats up. But I also have to quibble with your explanation, as without fission events there would be no mass->energy conversion and hence no increase in core temperature. So yes, technically criticality isn't needed for the core to be hot or get hotter, the rate of neutron recapture is, I think, quite relevant in understanding thermal runaway since, if I understand it correctly, a linear increase in the rate of neutron recapture results in an exponential increase in heat output. So maybe criticality per se isn't the main issue, but the underlying idea of neutron recapture and the chain reaction definitely is.
> Pretty much by definition, within a bolus of melted fuel, it's hard to have moderation - especially in a water-cooled and moderated reactor!
Yes, we're in agreement here. I deliberately glossed over the issue of fast neutrons versus neutrons slowed down by a moderator. But since you mentioned it, I'd just like to point out to other readers, if it's not clear to them, that the right moderator and the right geometry actually serve to increase the rate of neutron recapture and hence push the reaction towards become self-sustaining, or at least generating usable amounts of heat energy. For what we're talking about, namely core meltdown and what happens after, moderation is actually a bad thing because it contributes to thermal runaway. My initial point was that if the fuel rods melt down and there is nothing more than a puddle of fuel with all the moderating material boiled off, then there is nothing to slow down neutrons enough to be recaptured, and the rate of fission greatly decreases. And as you said, the main problem at that stage is just dealing with residual heat. I simplified it by saying that the puddle of fuel simply didn't have the right geometry to sustain a chain reaction (though as you point out, my simplification of saying criticality here was technically wrong), but you can also explain it in terms of the lack of a moderating medium. On the whole, though, saying the geometry isn't right is probably more to the point, so that's why I tried to explain it in those terms.
Hi,
I think there's a bit of a point of departure - reading your last, it's about the nature of decay heat production.
If I'm understanding you, you think it's primarily due to ongoing fission events, triggered by sub-critical absorbtion of neutron emissions. While that can make a small - with the stress on the small - contribution, the majority of decay heat doesn't arise that way.
It arises from alpha and beta emissions from fission products. The neutron flux in a shut-down reactor is pretty much negligible. What's going on is the various daugher products are following their own decay paths, with those events involving mass-energy conversions. If you think about it, that's why they decay - to move to a lower energy state.
And they do involve mass-energy conversions. An beta particle spits out of a nucleus with very impressive kinetic energy indeed - mostly, to be absorbed by surrounding material, alphas slightly less so. That comes from a conversion.
As an example, think about what happens to reprocessed waste. Once the uranium and plutonium - the fisionable elements - are removed, the heat production in the waste is barely affected. The uranium and plutonium can be stored uncooled. The fission product waste most certainly can't. That requires active cooling for some decades post reprocessing. There's next to no fissionable component in that waste, so pretty much by definition, the heat production can't be rising from ongling fission.
Hi again, Andrew. Thanks for elucidating more of the picture for us. I must admit that I did overlook the fact that a fission event will often create one (or more?) radioactive isotope(s) which will in turn decay, causing more energy output. I think lurking in the background of my mind at the time was the notion that a lot of the daughter atoms are considered waste products in the general sense and reduce the reactor's efficiency. I remember reading that in an explanation of the thorium fuel cycle at energyfromthorium.com, but I guess it applies to any nuclear fuel cycle. I can't remember the exact mechanism for these causing reduced reactor efficiency, but I think I had mentally filed it away as meaning that the daughter atoms were less effective in producing heat, which is the whole point of the reactor in the first place, so I naturally discounted them as the major heat producer in the reactor. Thinking about it now, perhaps efficiency in this case isn't only referring to the ability to convert fuel to heat, but includes an element of how effectively a chain reaction can be sustained or how much total energy can be extracted from a given amount of fuel before the waste products must be separated?
Your post also begs the question... with the errors and omissions in the way I described the meltdown process corrected, does this mean that my confidence in a meltdown being effectively contained without causing a further disaster is actually misplaced? I'm genuinely curious to know, even if it contradicts what I originally thought. Or do we end up with being able to say that even if the core melts down, so long as we can cool it down in time and continue to actively cool it, that we don't have much to worry about? And what of the initial topic of the China Syndrome? Is the residual heat production capability sufficient, in your view, to melt through the bottom of the containment vessel, or is a conflagration of the melted material a more practical concern? Should I upgrade my assessment from "not much to worry about" to "everybody panic again?"
The daughter products can (in quite a few cases) act as neutron absorbers - Xenon in probably the worst (but is very short lived - it can pose a significant challenge to reactor management when output levels are being adjusted, imposing a limit on how fast power can be ramped-up). That's unrelated to heat production. That cuts down the total amount of neutrons available to maintain the chain reaction (I'll come back to why that matters particularly for the proposed molten salt thorium reactors). So your comments about the chain reaction are spot on.
And the heat production is a matter of relative levels. To give an example, reactor 1 at Fukushima Dai-ichi would be producing about 1500MW of heat at full power - of which, about 95 MW would be from daughter product decay, so about 6 1/2 % of the total.
As to meltdown risk. No, not really, the confidence is still well placed. TIming is everything. There's a standardised formula for the rate of decay heat production in a light water reaction, and having run it for R1 at Fukushima, the broad picture is 95MW 1 second after shutdown, about 12 MW after an hour, 7 MW after 2 days, and probably now down to about 3-4MW. So, Basically, if you can hold things togeher for the first hour or two, you're into levels where it'd be hard to imagine that the heat generation from melted fuel wouldn't be of an order where it could be lost through the RPV, or to whatever coolant was still coming in.
Basically, the "s** or bust" moment would be if criticality was maintained, so that the fuel was hitting the RPV bottom within seconds or minutes of being in full power output. Even then, I doubt it'd penetrate. You'd have to do a full heat balance of the rate of production, plus the relative heat capacities of the fuel and RPV, plus the rate of loss to remaining coolant and through the RPV wall. TMI was probably as close as you're going to get to that (although there was still lots of water in the vessel), and penetration into the RPV floor was minimal.
Back to "poisons". The reason they feature so prominently in discussions of LFTR designs isn't heat production per se - it's their impact on breeding ratios. Every neutron lost to a poison is one that's not available for breeding fuel.
Before I go any further, I'll declare my hand. I think LFTR desings are well worth exploring. But equally, I think that some of the protagonists either don't understand, or are glossing over some pretty big challenges. I don't see them being "breeders" per se, in the sense of making a surplus of fuel for new reactors to start up, but I think they'll go pretty close to being self-fuelling.
To run an LFTR on a "closed cycle" - i.e making as much fuel as it connsumes - depends utterly on good neutron economy. You have to get fission products out of the salt quickly. for some, that's easy. for example, xenon can be got out of solution simply by spraying (!) the fuel at some stage through an inert atmosphere. Other stuff is harder - and would mean that you had a big inventory of stuff like Iodine on site, outside the relative safety of the main circuit. In some ways, the biggest challenge is something that's part of the actual thorium-uranium cycle, i.e. protactinium. When thorium 232 captures a neutron, it becomes protactinium 233, which then decays back to uranium 233, with a half-life of a month or so. Unfortunately, protactinium 233 rather like to absorm neutrons, so that has to be removed (so it can be taken away and allowed to decay to useful uranium), and that involves delights like bubbling the fuel through a column of liquid bismuth. you also have to do things like sparge flourine through the fuel to extract any uranium made.
So, although from some aspects they look good, they have one f**k of a big chemical process plant stuck on the side, some of it dealing with rather nasty materials like flourine. I suspect that'll be a bigger safety challenge than the reactor itself!
And I'm not entirely convinced about the proposed cooling/safety arrangements. They may not have quite the daughter product burden of conventional reactors, but even if fuel is drained and dumped into cooling tanks, there's still an awful lot of heat to get away - more than the simple air-cooling arrangements talked about would be suitable for.
Had you followed Mr. Page closely, you would have understood by now that a reactor that blows up in a nuclear fission explosion is a failed reactor.
Below that threshold there is no problem, you see.
The China Syndrome is never going to happen, because a (purely hypothetical) molten core will never reach China as it will be stopped and cooled by the ground water table. Radioctive dust that is ingested is no problem. Chernobyl was never a real problem, so there was no need to do an epidemological follow up of the "liquidators".
Everything is explained now, we can continue to pray to our cargo dropping overlords.
</sarcasm>
A level 5 nuclear hazard does not equate a minor incident. This is equivalent to Three Mile Island. The media hysteria is bad, admittedly, but your constant downplaying of the severity of the incident is even worse. The hysteria is prompted by ignorance. You seem to know enough about nuclear power to know better, which makes you either a shill for nuclear power or an ostrich with your head in the sand.
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