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Below is edited material sent to me in confidence from some colleagues in the professional nuclear engineering and research community. It provides some further insight into what is going on at Fukushima, and what is still unknown.
The main document was written by one nuclear engineer; the quotes are the response from another engineer.
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1. Likely timeline of incident is:
a. Reactors 1, 2 and 3 were in operation at Fukushima Daiichi nuclear power plant when the earthquake struck.
b. all three reactors were shut down and control rods were inserted when earthquake struck.
c. Cooling was maintained to remove decay heat
d. decay heat drops rapidly on reactor shut down (e.g a 3GW reactor will reduce to 200MW decay heat after 1s and 50MW after 1 hour… But takes long time (3-6months!) to reduce to negligible levels)
e. sometime (≈1hr) later tsunami struck and mains power was lost to coolant circuit on Unit 1
f. Diesel generators also failed when tsunami hit so cooling was run by backup batteries for 7-8 hours
g. Other emergency diesel generators brought in but insufficient to run pumps
h. loss of coolant leads to fuel rods no longer being cooled by two phase flow (it is a Boiing water Reactor) and eventually get hot enough to recat with steam to produce Hydrogen.
{While this is plausible it would suggest massive loss of Pressure Vessel (PV) generated steam beyond the containment boundary (since the explosion did not disrupt the containment). In my view a far more plausible explanation is that hydrogen routinely injected in the Make Up Water System to control the corrosives (mainly O2) produced by radiolysis was released suddenly and catastrophically from outside the containment and within the reactor building. In reacting with oxygen from the atmosphere within the building at the correct concentration of hydrogen (4-74%) only a spark is required to detonate a hydrogen oxygen explosion.
By contrast the spontaneous splitting of water to hydrogen and oxygen requires a temperature of greater than 2000 C in the absence of a catalyst. The normal radiolytic environment of a BWR core produces an excess of oxygen, not hydrogen. Given that the explosion reduced the source term, by all accounts, the reaction with hydrogen for Make UP water injection is a likely scenario and potentially the most plausible explanation for such an explosion at present. This could be even more plausible and verifiable if the Daiichi plants were not retrofitted with Noble metal corrosivity reduction systems (Pt) which have been implemented in many BWRs to reduce site hydrogen inventory. Even with noble metal systems there is still a significant hydrogen inventory external to the containment in BWRs to manage the corrosivity of PV water}
i. Gas pressure in steel reactor pressure vessel rises when coolant systems are not active and is vented to reactor building by engineers. {In my view there is not yet plausible evidence that the temperature of the PV water was sufficiently high to spontaneously split water}
j. The hydrogen in the reactor building is ignited in an explosion which blows out the walls but is not likely to have damaged Steel pressure vessel or concrete containment.
{this is true of both scenarios –but the source of the hydrogen is also external to the PV and containment in my explanation, overcoming the problem of why there was not a hydrogen explosion within the containment and outside the PV!}
k. Operators are now flooding reactor with borated sea water. Would only do this of they had run out of demineralised water – and were sure that water was not spontaneously being split in the PV.
2. Other relevant observations
a. These reactors are old generation I GE BWR’s nearing the end of their useful life so economic loss would not be large: but decommissioning and decontamination costs may be significant.
b. Some reports say 50-100cm of fuel was above coolant. Not necessarily serious in BWR but hydrogen explosion suggests some of the core got very hot
{wrong explanation in my view}!
c. No evidence of catastrophic loss of fuel element integrity yet. BWR fuel often gets small leaks and fission fragments enter water! Only relatively low levels of Cs and I reported so far suggesting fuel integrity still OK.
d. Increase in Cs and I would accompany fuel element breakdown and eventual meltdown.
e. A parallel series of event may now be happening in Unit 3.
f. MOX fuel may have been in one of these reactors
g. to a first approximation there is no difference on the present context between conventional and MOX fuel
h. If anything, the MOX should be marginally more benign for a radiological point of view than UO2 based fuel. It may have a higher toxicological risk however.
3. It is expected that enough coolant and power will be found to avoid meltdown. In which case it could be argued that this is a reasonable result for 50 year old Gen I Reactors exposed to the worst earthquake and tsunami for 100+ years!
4. If meltdown does occur fuel should melt through to concrete basement spread and eventually cool. Not a good result but hopefully, predictable.
5. These events would not happen in modern reactors which are designed to be cooled on shutdown by natural convection.
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Response: H2 (production due to oxidation of Zircalloy by high temp steam has to be seriously considered in all full or partial LOCA (loss of coolant accident) scenarios, so I remain conservatively suspicious.
Reply: You then still have to explain why the primary event chain for PV generated H2 and O2 which is 1) PV to containment, then 2) containment (no explosion in the containment) prior to 3) venting to atmosphere!!! (which would in any event be to the stack via filters not via the reactor building)!!! The video footage of the explosion was clearly a fast H2/O2 (shockwave evident) and asymmetrical event– blast leaves to screen left – which implies a concentrated source of H2 mixing with oxygen (Make Up water inventory) rather than a diluting source into atmosphere via the stack which would have taken out the filters at least and increased rather than deceased the site boundary source term.
But I agree very hot Zircalloy in steam is a plausible low temperature route to H2/O2, but remember that the temperature is decay heat not fission generated so radiolysis to produce extra O2 will be many orders of magnitude below that of an operating BWR. I’ll regard a PV chain as more plausible if you can explain how hydrogen (very light stuff) got from containment to reactor building – possible with certain piping configurations…I guess.
Unit 1 was the GE BWR design. These references might assist:
Radiochemistry in Nuclear Power Reactors (1996) Commission on Physical Sciences, Mathematics, and Applications
BWR water chemistry – a delicate balance (2000) British Nuclear Society
Meaty stuff! Internet is absoultely THE best way for information to be circulated and reviewed during fast-developing situations.
Keep it up.
BTW, there will also be large quantities of H2 on site for generator cooling, but remote from the blast locations. I have witnessed the results of two H2 explosions, one of which I was on site for. Exciting stuff, perhaps, but not adequate justification for spreading FUD around the globe about supposed nuclear risks.
Just thought you should know that “daichi” means “first” so that refers to first plant and it went critical in October of 1970 and started commercial operation March 1971 and was originally scheduled to be shut down March 2011. Exactly 30 years which means now basically.
The other plant is 11 km south. Fukushima Daini. “Daini” means “second”
Rather than the other diesel generators being insufficient to run cooling pumps I suspect there was damage to the demin water makeup tank or associated pipework outside containment. Otherwise they would have been able to use the Reactor Core Isolation Cooling (RCIC) system as used to cool unit 2.
Following.
[…] Further technical information on Fukushima reactors « BraveNewClimate […]
The hydrogen that is injected into the coolant to scavenge the oxygen… are we talking about actual gaseous hydrogen here? I was familiar with the use of reducing agents like hydrazine, but not hydrogen gas.
Does anyone know for a 4th gen reactors like LFTRs or IFRs how fast would the decay heat decay to negligible levels?
Here’s a portion of the Scientific American article
http://www.scientificamerican.com/article.cfm?id=fukushima-core&page=2
“…So there’s some advantages to the BWR in terms of severe accidents. But one of the disadvantages is that the containment structure is a lightbulb-shaped steel shell that’s only about 30 or 40 feet across—thick steel, but relatively small compared to large, dry containments like TMI. And it doesn’t provide as much of an extra layer of defense from reactor accidents as containments like TMI. So there is a great deal of concern that, if the core does melt, the containment will not be able to survive. And if the containment doesn’t survive, we have a worst-case situation.”
And just what is that worst-case scenario? “They’re venting in order to keep the containment vessel from failing. But if a core melts, it will slump to the bottom of the reactor vessel, probably melt through the reactor vessel onto the containment floor. It’s likely to spread as a molten pool—like lava—to the edge of the steel shell, and melt through. That would result in a containment failure in a matter of less than a day. It’s good that it’s got a better containment system than Chernobyl, but it’s not as strong as most of the reactors in this country.”
Finally, Bergeron summed up the events so far: “Based on what we understand, the reactor has been shut down, in the sense that all of the control rods have been inserted. Which means there’s no longer a nuclear reaction. But what you have to worry about is the decay heat that’s still in the core, that will last for many days.
“And to keep that decay heat of the uranium from melting the core, you have to keep water on it. And the conventional sources of water, the electricity that provides the power for pumps, have failed. So they are using some very unusual methods of getting water into the core, they’re using steam-driven turbines—they’re operating off of the steam generated by the reactor itself.
“But even that system requires electricity in the form of batteries. And the batteries aren’t designed to last this long, so they have failed by now. So we don’t know exactly how they’re getting water to the core, or if they’re getting enough water to the core. We believe, because of the release of cesium, that the core has been exposed above the water level, at least for a portion of time, and has overheated. What we really need to know is how long can they keep that water flowing. And it needs to be days to keep the core from melting.
“The containment, I believe, is still intact. But if the core does melt, that insult will probably not be sustained, and the containment vessel will fail. All this, if it were to occur, would take a matter of days. What’s crucial is restoring AC power. They’ve got to get AC power back to the plant to be able to control it. And I’m sure they’re working on it…”
“Does anyone know for a 4th gen reactors like LFTRs or IFRs how fast would the decay heat decay to negligible levels?”
Basically the same sort of time frame.
Basically, fission products are fission products, and they’re pretty much the same, whether you’re talking about LWRs or IFRs or LFTRs. Fission heavy element, get fission products.
But IFR, LFTR, etc, will dissipate the decay heat passively without active operation of cooling systems.
If you look at the explosion then you’ll notice that there was no excess burnoff of hydrogen after the explosion as would undoubtedly have happened if this had been a reaction with atmospheric O2. Also, the shock wave was way too strong for that.
If you have ever seen an explosion of H2 with atmospheric O2 (have a look at launches of H2 powered rockets) you know that this is not what happened here.
_IF_ this was an H2/O2 explosion (and not a steam explosion, which would fit the cloud even better) it was clearly an explosion of split water.
What? We are talking neither about thermolytically splitting water, nor radiolytic splitting; we’re talking about a redox reaction between water and zirconium: Zr + 2H2O -> ZrO2 + 2H2 (not sure if valence is correct).
BTW, that _second_ explosion looked much more like a “normal” hydrogen explosion although it’s still much too strong to be explained by a reaction with atmospheric oxygen.
To elaborate: significant hydrogen generation starts at around 1000-1200 K (800-1000 C), according to this technical reference I googled:
http://www.oecd-nea.org/nsd/reports/2009/nea6846_LOCA.pdf
(page 211, table 6.7)
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Thank you Mr. Brook, and all the others, who have provide this excellent discussion of the risks. I live in Tokyo and am faced with the real decision of evacuating with my family (with young children) or not. Thus please address the specific circumstances as have evolved in Units 2 and 3 over the past day. PLEASE respect the difficult decision I and other must make and keep the anti/pro nuclear religious rhetoric out of this discussion. The core of both units have been partially or completely exposed for some period hours. This seems to imply that a complete core “melt down” is probable (yes or no?). If such happens what is the risk that the outer containment will breach? If there is a breach what is the transport mechanism and time for the radiation to reach a 200km radius?
Putting this in some perspective, it is now believed that over 10,000 lost their lives to the main event.
How many dead from these reactors was it?
You won’t be able to say but the evacuations alone will cost lives under these conditions. Plus the resources missing in other areas due to that.
And I don’t believe they are doing the evacuations just for the fun of it.
From the photograph of aftermath of explosion at FD#3, the damage looks potentially much more serious than at #1 – the relative power of the blast is indicated by the fact that most of the structural steel in the crane-shed is gone or totally mangled and it also seems to have ruptured at least some of the outer concrete walls at lower levels – which I suppose bodes ill for the integrity of cooling pools and/or secondary containment structure.
What I do not understand is, if this was so predictable that the PM forecast it yesterday, why did they not take emergency measures to dilute or divert H2 from all enclosed spaces?
Could the reactor venting not go straight to atmosphere? [seems like it probably does now anyhow :(]
It just seems like somebody was betting rather long odds that “we will be lucky a second time, with minimal effective blast damage” – either that or things are really beyond control and there was nothing they could do to prevent it.
In any case am keeping fingers crossed that major contamination can still be prevented.
Rick Maltese, on 14 March 2011 at 6:19 PM said:
“started commercial operation March 1971 and was originally scheduled to be shut down March 2011. Exactly 30 years which means now basically”.
I think your finger must have slipped on the keyboard:
March 1971 – March 2011 = 40 years (a good innings though, no?)
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Linked to yesterday already, this paper from 1987 says venting would end up in the reactor building:
The venting of primary containment after reaching 75 psia (0.52 MPa) is found to result in the
release of the vented steam inside the reactor building, and to result in inadequate Net Positive Suction Head (NPSH) for any
system pumping from the pressure suppression pool.
Still strange they did not vent via exhaust stack; the following article says all Mark-I have been retrofitted with the lines required. But what is and what is not still working by the book there, rather unclear.
Meanwhile, NNN reports fully exposed fuel rods in Fukushima 1 Block 2.
Edano in presser: radiation leak detected outside reactor2, possibility of damage to the fuel rods
sorry, forgot link:
Containment venting as a mitigation technique for BWR MARK I plant ATWS
http://tinyurl.com/6hlrzwj
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Rick Maltese wrote, quoting ‘Scientific American’:
And just what is that worst-case scenario? “They’re venting in order to keep the containment vessel from failing. But if a core melts, it will slump to the bottom of the reactor vessel, probably melt through the reactor vessel onto the containment floor. It’s likely to spread as a molten pool—like lava—to the edge of the steel shell, and melt through. That would result in a containment failure in a matter of less than a day. It’s good that it’s got a better containment system than Chernobyl, but it’s not as strong as most of the reactors in this country.”
I don’t see why the core should melt through the reactor vessel with just a minimum of cooling. In the case of Three Mile Island, the core that melted penetrated about 16 mm into the reactor vessel that had a total thickness of about 200 mm (if I am not mistaken).
Masashi Goto a former design engineer of nuclear containment vessels with Toshiba Corporation says: who earned his PhD by evaluating the stress that reactor container vessel can endure, quit his job with Toshiba Corporation due to his concerns over reactor safety. “I came to the conclusion that the vessels being built were not adequate enough to be the last line of defense,” he says. “They weren’t designed to withstand the kinds of problems currently being experienced in the Fukushima plants.”
http://spectrum.ieee.org/tech-talk/energy/nuclear/second-explosion-damages-japanese-nuclear-plant-third-blast-could-follow
is, I think, the source of the Masashi Goto quote posted above. More info at the IEEE link.
H2 is from zirconium water reaction. It is oxidation reaction so oxygen is used up. U2 explosion need u2,oxygen an ignition source. Only H2 in reactor—no explosion. Rx vessel must be vented to allow low pressure pumps to inject water. Venting releases hydra. And radioactive materiAl. For same reason- pressure too high-must also vent. When oxygen and hydrogen and any spark get together inrx building—explosion.
One operator killed in Unit 1. No one offside. Doses offside and onside no where near fatal or enough to injure. Death due to hydrogen explosion
I found the Scientific American article a bit ridiculous. Where do they get the idea that melted reactor core material will just breeze through a pressure vessel bottom, let alone the concrete containment beyond? They should supply references to something in the literature.
What can happen if a reactor core melts down was assessed in a peer reviewed article published in Science in 2002, i.e. “Nuclear Power Plants and Their Fuel as Terrorist Targets” available here http://www.atomicinsights.com/pdf_files/SciencePaper-9.02.pdf
After Three Mile Island cooled down, sections of the bottom of the pressure vessel were cut out and examined. 10 to 20 metric tonnes reactor core had indeed melted at TMI, but whatever reached the bottom of the pressure vessel was unable to penetrate the 0.5 cm cladding of the 13 cm thick pressure vessel bottom. The concrete containment beyond was not called on to contain this melted material.
“the China Syndrome is not a credible possibility” is one quote from this article in Science.
That reactor at TMI was 906 MWe, compared to Daiichi 1 at 460 MWe and units 2 and 3 at 784 MWe by the way….
I wonderr at those who say the reactors in Japan were old and near the end of their useful life. Although the original certifications were for 40 years, reactors in the US are routinely being re-certified for use out to 60 years and responsible highly placed individuals are saying they don’t think it is impossible that the norm will become 80 or even 100 years.
I must not be following the explanation about the hydrogen explosion correctly. It seems to me, that once you blow the roof off, then it shouldn’t be possible to build up hydrogen for a second explosion. It should be vented immediately since it is lighter than air.
Joel, there were two H explosions at two separate reactors (at the same plant).
Is it possible to cool the reactor containment vessel on the bottom, from within the containment building, somehow?
A full core meltdown seems unlikely, if they just keep pumping water into the building. They have to keep releasing radioactive steam, so that the pressure is lessened enough for the pumps to put water in. Releasing radioactive steam, potentially with fission products and uranium is bad, but that’s better than a meltdown.
Not enough information 🙁 .
Anyone know at what temperature the control rods will melt? I just wonder if it will be back to higher number of reactions if the temperature rises.
http://www.telegraph.co.uk/news/worldnews/asia/japan/8382416/Japan-crisis-third-explosion-at-Fukushima-nuclear-plant.html
12:46AM GMT 15 Mar 2011
“The operator of the Fukushima Daiichi complex said radiation levels around the site immediately after the blast, the third there, were rising fast but still far from levels that local authorities say would cause large-scale radiation sickness.
Authorities are trying to prevent meltdowns in all three of the plant’s nuclear reactors by flooding the chambers with seawater to cool them down.
Japan has asked the United States for more equipment to help cool the reactors, after a dangerous drop in cooling water levels that exposed fuel rods in the No. 2 reactor, where Tuesday’s blast took place.
“It was a hydrogen explosion. We are still assessing the cause and unsure whether the explosion was caused by damage to the suppression chamber,” an official at the nuclear safety agency told Reuters. He did not have any more details.”
With the hydrogen explosions and the possibility that some radioactive elements were condensed inside of the building before the explosions, will subsequent steam releases be more likely to expose the surrounding area to radioactive elements?
If there is a complete or partial meltdown, how does that happen – will the control rods melt first or the fuel rods? If the control rods melt first, would that mean an increase in fission?
Assuming meltdown and that the containment vessel remains intact, will the subsequent mess be able to sustain any kind of reaction?
Larry, uranium fission ceased straight away, the heat is being generated by heat decay. Even if the control rods were destroyed, it wouldn’t restart the process
[…] Japanese nuclear reactors and the 11 March 2011 earthquakeJapan Nuclear Situation – 14 March updatesFurther technical information on Fukushima reactorsTEPCO reactor by reactor status report at FukushimaAn informed public is key to acceptance of […]
We must be cautious in not assuming some of the public and/or site workers have not received significant radiation doses. One report from TEPCO ( I believe) had a site parimeter dose rate at 8200 microsv/hr. In my old fashioned units thats 82 R/hr. Another report had a site dose at 15R/hr. Another dose rate quoted (that must have been in error) was 1000R/hr. These all were most likely transients. I wonder what the dose rate history is in the control rooms?
Thanks. Another question is that if the explosions are indeed damaging the containment vessel, does it make sense to cut losses and stop trying to cool the core and allow it to meltdown?
[…] Further technical information on Fukushima reactors […]
This page has a link coming in from Next Big Future. Awesome!
///Thanks. Another question is that if the explosions are indeed damaging the containment vessel, does it make sense to cut losses and stop trying to cool the core and allow it to meltdown?///
Awesome and interesting question!
I just wanted to know if it is safe to stay in Tokyo when the worst case-scenario happens to the nuclear power plants in Fukushima (which is the core meltdown and the exposure of the radioactive substances spread in the air?). I think it’s about 155 miles (250 kilometers) from Fukushima to Tokyo. Is it far enough or should I go further?
re post by: Doug, on 15 March 2011 at 2:19 PM
Doug, if you double check your conversions, I believe you’ll find that 8200 microsv/hr is 0.82 r/hr. Still a whopping dose rate and not to be taken lightly, but nothing compared to 82 r/hr!
Most, but of course not all, of that will be from relatively short lived noble gasses (half lives from seconds to a few days) – and rapidly dispersed into the atmosphere by winds/mixing too.
In case someone hasn’t already posted these:
http://www.bousai.ne.jp/eng/ for real time rad. monitoring around Japan.
TEPCO’s press releases: http://www.tepco.co.jp/en/press/corp-com/release/index-e.html
Japan’s “Nuclear and Industrial Safety Agency” press releases: http://www.nisa.meti.go.jp/english/
Did any of you calculate how hot the fuel could get when all cooling lacked ?. It would still be cooled by thermal radiation. Suppose the Japanese managed to cool it for 8 hours, then the decay heat went down to about 0.6 % of rated reactor power. Fukushima I has an electrical power of 460 MW, thermal is about 3 times, or 1380 MW. 0.6 % of this is 8.28 MW. Assume the surface area of the core is 60 m2 (a wild guess), then that amounts to 138 kW/m2. Assuming black body radiation law (power is proportional to temperature to the power 4), I get a temperature of 1250 K or 976 degree C. Now, at this temperature the zircalloy most likely loses its mechanical properties, but this is nowhere near the melting point of the uranium oxide.
– Piet.
re post: Sat, on 16 March 2011 at 3:04 AM said:
Unfortunately I don’t think anyone can answer this (or would be willing to) nearly as definitively as you’d like. Especially now that it seems the fuel pools are also involved, and onsite radiation, at least at one point here recently and possibly still now, is making access very difficult for workers.
All I can say is personally I’d probably stay in Tokyo while keeping an eye on the situation. I’d be amazed if it were possible for there to be any significant radiation levels as far away as Tokyo. At worst I suspect it would be a matter of a breif time, a few hours, where perhaps you stay inside, or something along those lines, and that most likely far more out of an abundance of caution and peace of mind than any levels high enough to even come close to being a health concern.
For whatever it’s worth… My career has been in radiological protection/safety – but I’ve worked mainly with much larger and newer (than the Fukushimi reactors that is) PWR reactors, and a little with Nat’l labs & Dept. of Energy.
But what I’d do if I were in your shoes – and especially suggest to you – would also depend on just how easy it is or isn’t for you to go west as you suggest out of the plume path. Why do I say that? Because there really is a lot to be said for peace of mind, and this is something that clearly and understandably worries you. So if it’s easy to go and no hardship and you have a safe place to stay with electricity and water (e.g., I sure as heck wouldn’t go somewhere that’s been cut off from basics by the earthquake!)…. well, if that’s the case then why not go for a few days and see how this plays out? On the other hand, if cost or where you’d stay is an issue, or its a large inconvenience for whatever reasons, then if it were me, I’d stay put, not worry about it, but be sure to have a day or two’s worth of bottled water & food in case you decide to stay inside for a few hours (heck, I’d have that right now if possible anyhow just in case of further major earthquake after shocks!!) and keep an ear/eye out for what the radiation levels seem to be between you and the plant.
Also, for whatever this might be worth to you – while clearly you don’t want to be inhaling any significant amount of radioactive cesium or iodine – much of the radiation would be noble gasses that don’t wind up stuck inside your body – AND there are a LOT of studies, good quality double blind peer reviewed studies over several decades, that actually show that some increase in radiation exposure is actually BENEFICIAL to animal’s health [we’re animals too you know :0)]. Not joking, this is quite true although most people in the general public have no idea and would find it very hard to believe. There is no evidence of ANY long term harm until you are exposed, in a very short time period, to over 10 R – and even then we’d be talking about a small increased risk of possible cancer many years down the road. I’m not sure what the typical background radiation levels are in Japan, but here in the USA it’s roughly 350 mR per year… that’s 0.35 R/year, when it takes about 10 R in a few minutes to days before there are even any possible long term health effects….
Hopefully the blasted wind will do everyone a favor and shift eastward, so whatever radiation plume there is stops blowing down the coast and instead blows out to sea. My apologies for making this so long, but I hope perhaps this helps answer your question a little or at least make the decision a bit easier for you.
[…] Brave New Climate has a diagram of the Fukushima reactor design, with an timeline of events provided by a confidential industry source: […]
One additional note/caveat regarding my post on 16 March 2011 at 9:19 AM ….
I have to say that I’m really used to thinking in terms of the typical reactor site here in the USA. The reactors at Fukushimi 1 are relatively small, but don’t have a containment building, instead they’ve got smaller containment vessels (makes the situation worse) – BUT, they were shut down before problems began, and now several days have passed (makes the situation better by far). Plus, now you’ve got multiple fuel pools that worst case would be involved too (one already is, and my guess which may be quite wrong, is that it’s what’s really pumping out the radiation right now). I have no idea what the fuel load is in those three, or how long they’ve been out of the reactors, or how long they’d been used in the reactor, and if water is being lost just thru evaporation (or possibly boiling, same thing effectively) or if there are any cracks in the fuel pool walls or floors allowing water to seep out, or if sump pumps are or aren’t working to return some/all of that water to the pools….
All factors that may make a large difference in the potential “worst case” releases…
In other words, there are a lot of unknown factors at this point that make it awfully difficult to feel very comfortable about guessing on any of this. Please don’t get me wrong, I’m not changing my mind on what I said in the earlier post, I just felt that I ought to mention these things because they make it so difficult to have a good feel for what the potential “worst case” you are asking about might be.
Rational Debate,
Thank you very much for answering my question.
One more question, if the worst case scenario ever happens and the core melts down, is the containment vessel strong enough to hold things inside safely?
People are so confused about things since TEPCO is not releasing enough valid information (they keep saying “maybe, I don’t know, etc”) but it seems like the situation is getting worse and worse…
[…] on the plants in question and interpreting the events associated with them. They have several posts on the technical details of the plants. Their most recent round-up tries to put even today’s […]
re post: Sat, on 16 March 2011 at 3:22 PM said:
You are certainly welcome. On your question – there’s that word ‘safely’ that is so difficult to answer – it means such different things to different people. Let’s see if I can help shed some light on at least some aspects, however. Keep in mind I’m not a Nuke Eng w/ core design experience tho, but can make some somewhat educated guesses. If anyone else reading knows better or disagrees with something I say, I very much hope they’ll jump in with details.
While here are a number of important factors influencing this, I suspect that the vessel would hold.
First, keep in mind that assuming the core completely melts down to slag on the bottom of the vessel, you do have TWO containment’s remaining. You’ve first got the reactor vessel it would have to penetrate, then you have the upside down lightbulb chaped containment vessel.
Three Mile Island was at power when it lost enough coolant for long enough to melt about 40% of the core into slag on the bottom of the reactor vessel. It was years before they could go in (remotely, IIRC), but they found that it only managed to penetrate the reactor vessel something like 5/8ths of an inch (vessel is roughly 6 inches thick, so it got nowhere). Now, they had managed to get some cooling going again, so they had that advantage over the worst case scenario of no cooling at all – BUT it was a much larger reactor, and at power when this started, whereas these cores were shutdown for several days, and that makes a large difference in your favor. Which scenario gives the better ultimate outcome in terms of vessel penetration heck if I know. Really worst case would be if there were a steam explosion inside the reactor vessel that was strong enough to breach the vessel walls and then the containment vessel also. Frankly I don’t even know if that is possible at this point, and suspect not. So, if not, then next worse would be if it really did manage to melt thru the reactor vessel – at which point, you’d still have containment with the containment vessel, which is metal reinforced by concrete. Could it then, assuming no cooling, manage to melt thru that too? Again, I don’t know, but am pretty doubtful. If it could, I’m not sure of the facility design, but suspect you’d still have the remnants of the core surrounded by concrete and ground all around, and various ceilings/concrete above – e.g., not just an open path for releases. At each of these steps, that mass is going to be spreading out, and loosing a lot of heat. You’ll still have the decay heat, but the more it’s spread out the less concentrated it is and the less it’ll be likely to continue to remain molten or be able to melt thru anything.
Now, in most plants these days they’ve got the more robust and larger containment building. Calculations are that even if containment were breached, say a big wide crack all down one side – it is thought that most of the worst isotopes would actually wind up plating out on the interior containment walls and internal structures rather than being released. With the smaller vessel, you’d still get some of that occurring, along with adhering to the inside of the reactor building walls and structures. All of this is from some of the brightest most knowledgeable people working on the scenario, but it is theoretical, thank god we’ve never tested it in real life. I hope we never do.
Don’t get me wrong – the very idea of these sorts of incidents are horrifying to anyone in the industry, and would increase the amount of radiation being released, quite possibly by a large amount. But it’s still nothing like Chernobyl, where the steam explosion was in the core, blew the sarcophagus lid completely off the reactor, had nothing but a regular sort of building and blew half of that away in that initial blast too – AND set the graphite on fire so you had not only the heat of a reactor that was operating ABOVE MAXIMUM POWER LEVELS when the explosion occurred, but you just added all this soot by vaporizing half the building, AND all the heat from a continuing large graphite fire to loft everything into a very large, high altitude plume full of vaporized core fragments and graphite too. Very VERY nasty. (continued in next post)
What actually worries me more than the reactors themselves right now is the fuel pools. I have no idea how much fuel is in there (in each reactor’s pool), how long it’s been out of a functioning reactor, how tightly packed they are in the pool – all things that would affect how serious it would be if those were uncovered,. BUT, the main point is that there is very little in the way of any containment around those pools as best I understand, and the wall in reactor 4′s pool area sounds like it’s been damaged (supposedly 2 approx 8 x 8… um, i THINK “foot” wide holes – cripes, I’m not sure of the unit! doesn’t really matter all that much). So, if those fuel bundles become uncovered, there’s a very easy & direct route for the significant amount of radiation those would be giving off to vent straight to the atmosphere. I suspect that would be a worse situation than the core melting thru reactor vessel & containment vessel, but again, I’m making some quasi-educated guesses here and don’t know for certain on a number of key design details that factor into the situation.
As to TEPCO and how much information they are releasing. Believe me, right now you do NOT want them making guesses about the condition of areas that they aren’t able to check and verify, and have that get out into the press. We learned that the hard way with Three Mile Island (TMI). When TMI occurred there was a media circus, and a ton of confusion. One prime example, some journalist was barely within earshot of a technican who was telling his boss or a coworker what level radiation reading he’d just taken, iirc, in the aux building – not sure what you folks call yours, maybe the turbine building, or something along those lines if not the auxiliary building like we tend to. Anyhow, the journalist for whatever reason ran with it, without checking first to see what he was even reporting. He reported it as if it was the level outside the main gate or off the plant site itself!! That caused a huge amount of utterly unnecessary panic in the general public. Levels were at least an order of magnitude lower where he was reporting that far higher level.
We would ALL very much like to have more specifics and details, but frankly there are things that they are literally unable to verify because of either radiation levels or instrument damage/failures. There is a lot that they can calculate, make good educated guesses about and so on, all very important in helping them decide how to precede – but the actual condition of the fuel rods, what else may or may not be damaged, etc…. well, it could in reality be far better in there than they suspect, or far worse – neither of which may make a bit of difference in terms of the amount of radiation that winds up being released or where it goes. And can you imaging what would happen later when it turned out that they’d given out details that turned out to be really wrong in either direction? Especially if it generated a panic that got people unnecessarily killed, NOT because of plant conditions, but because people panicked? So all they can do is do the very best they can to only release factual accurate information as they are able to determine various aspects of what is occurring – and primarily when it comes to the general public, only those things that really might affect radiation releases, or info about where it’s going, or recommendations for evacuation or sheltering, etc. By the way – at least here, and from the sounds of it for you also, it winds up being the top dog politicians who have the final say on telling the public what to do. The utilities can only make recommendations – and typically politicians want to cover their own butts and are far more afraid of accidentally not being proactive enough, even if the chances are slim that whatever they’re calling for is really warranted… they tend in that direction and don’t worry about a few grandma’s and auties dying from being evacuated from hospitals or nursing homes, etc.. They tend to think there will be less negative political consequences if they call for what later turns out to be really unnecessary actions, and they just apologizing “oh, gee, I just wanted to be certain everyone was safe!”
So again, I don’t know that I’ve helped you much beyond perhaps helping you understand a little better what goes into some of these things… I wish that there were some clean cut simple answer, – but there just isn’t. I know there are plenty of experts out there who could either rule in or out some of the scenarios I’ve described here (and some ‘experts’ who have the credentials but are really nuts about being irrationally anti-nuke, who ARE getting media attention and confusing things all the worse with incorrect info or grossly unlikely projections/claims – right now the media is playing this huge and disgusting game of gossip, and the factual errors are rampant in the various news articles about the situation, unforatunately).
One thing we all have to really hope for is wind that will pick up whatever radiation is being released and get it UP in the air and away from the site, so rad levels are low enough that they can at least continue working the site. The fact that it’s cold at least helps in that any heated releases will be that much more likely to loft rather than dwell around the buildings. Then I just hope to god that there isn’t another large after shock to further complicate things. Those folks are working away like mad in a very nasty situation — just think, you’re worried about your own exposure, imagine what it would be like if you were there on site trying to get this under control. I have the utmost respect for those folks.
Hang in there – even if this gets worse there locally, you’ll almost certainly be fine. You are a LONG way away from the plant, and it really is amazing how much the atmosphere disperses a plume – and a lot of the noble gasses contributing to those rad levels have half lives of literally minutes to a few hours – in other words, the rad levels quickly decrease after release.
You know, it still amazes me that considering there are over 6,000 confirmed deaths from the quake & tsunami, and all the devastation, its the nuclear plants that are getting so much air time and concern… on the one hand I totally understand how/why folks would feel this way, but on the other, it really is sort of amazing and out of all proportion. Its a horrible situation, and sort of insult to injury, but for the general public, it’s unlikely that there will be even a single radiation related death or radiation related illness in the near future, and probably not even any cancer or very little of it a decade or two from now, even worst case. Compared to what may be more than 10,000 already killed by the quake & tsunami, and god knows how many injured, or who die from medical issues here in the near future because it will likely be difficult to get immediate medical attention for some people….
I’m thinking of you and everyone over there – you’ve been dealt a wicked nasty blow, and I just hope to heck that things progress and improve as rapidly and smoothly as is possible under the circumstances. The last thing you need is ‘worst’ case on any of these reactors or fuel pools, or another large quake/tsunami.
p.s. I’ll be curious to know if you wind up deciding to stay, or if you decide to head out of Tokyo. Is it just you, or do you have family there with you also?
One other key point for your thinking on this issue – check your local weather forecast and see what direction they are predicting the wind will be blowing for the next day or two. Heading west won’t do you a bit of good if predictions are for the wind to shift to the west….so be sure to check the weather forecast before making any decision.
Here’s a site that appears to have some good basic factual information, both about what is actually known at Fukushimi 1, and also about some of the basic nuclear issues & mechanics etc., involved. They ARE making some assumptions, but seem to be reasonable ones for the most part.
http://mitnse.com/ (MIT University nuclear science and engineering information hub)
and here are some more basics on the actual layout and design of the site and reactors, in the way of simplified graphics and cross sections.
http://www.washingtonpost.com/wp-srv/special/world/japan-nuclear-reactors-and-seismic-activity/
To prevent meltdown of large steel-making furnaces we had both Electric motors AND large Caterpillar Diesel Engines that were clutch-coupled to the same 20″ pumps. It sounds to me that these units can only pump if they have electricity. If that is true – it seems rather short-sighted.
Would it be possible to produce a large scale endothermic reaction within the core. Something that would react with sea water.
re post by Steel engineer, on 17 March 2011 at 4:09 AM
Steel Engineer, fortunately that is not the case – they are running primarily with generators right now. Nuclear reactors are all built with ‘defense in depth’ for all crucial/primary systems and especially for all emergency systems. The power stations there go even one step beyond what you are suggesting as needed. They not only had back up diesel generators as you mentioned, but were able by design to shift to battery power for approx. 8 hours after those back up generators failed because of the tsunami.
Then mobile generators were brought in. I don’t know why, but apparently initially they had troubles getting those portable generators hooked into the system, but eventually got that fixed and that’s what they’ve been running off of for several days now at each of the plants.
The reactors at Fukushimi 1 are a very early design – they were built in the 60′s, started up somewhere between 69 to 71, and came online iirc in 1972 (e.g., producing power for the electric grid). These are considered to be “generation II” reactors, and the Fukushimi reactors are Mark 1, e.g., the first of the gen II designs.
If you think about it, they’ve been reliably and safely producing electricity for 40 years now!! That they have survived a 9.0 earthquake – 4th largest quake EVER recorded, which moved the entire island over by 8 feet, and shifted the earth on its axis – and massive tsunami as well as they have after 40 years of reliable service is pretty blasted impressive engineering.
Excluding Chernobyl which was a radically different design – one that was vastly inferior to even the Fukushimi reactors in terms of emergency scenarios, in more than 50 years of electrical generation and scores of nuclear powered vessels (air craft carriers, submarines, etc) NOT A SINGLE PERSON HAS BEEN KILLED BY ANY RADIATION RELATED PROBLEM. If you look at the facts, nuclear power is far safer than coal, oil, gas, and even wind power.
For decades now the US has gotten approx 20% of our electricity from nuclear power. France has gotten about 75% of their electricity that way. Japan and several other countries are in this same category, getting a significant percentage of their electricity from nuclear power for decades now.
Rational Debate,
Thank you so much for the detailed explanation.
It’s just me living in Tokyo. My parents and relatives live far from Tokyo, so they have nothing to worry about.
Lots of my foreign friends have already left Japan and some of my friends are thinking about it, but
I’m staying in Tokyo and I probably won’t leave unless we really have to (more like no choice but to leave). I have my job here and can’t just leave everything behind.
Rational Debate,
You missed my point. I know they have backup electric power (generators and batteries) designed into the system. From what I read, the master electric panels were damaged by the tsunami thus preventing switching over. With pumps (with input shafts from each side) dual driven by diesel or gasoline engines – there is no need to worry about electrical switching – just start up the engine and move the coupling clutch ! That is what steel plants do to keep vessels with 2000 degreeF hot metal in them from being destroyed during power outages. KISS
Also, why are there no cooling towers in this plant?
re post by: Sat, on 17 March 2011 at 9:53 PM said:
You’re welcome. I just wish I could do more, a lot more!
I just have a hard time imagining that it could wind up being a problem in terms of dose rate 150 miles away in Tokyo.
There is no question that it IS a serious problem for those working at the plant – and that they are risking their lives because in those situations, the dose rate can very rapidly change and is so high that even very short exposure could have serious health consequences or even be life threatening. So they have to be very careful to monitor and know exactly what the dose rate is for each area they are entering, and carefully watch how much time they are in those areas. It’s all about the total dose you wind up being exposed to over time. It’s “time, distance, and shielding” when you are talking about a fixed source (such as the reactor core), and the exposure rate drops exponentially with distance.
When you talk about an airborne release of course, then it is a moving source to consider. But the sheer volume and turbulence in the atmosphere rapidly disperses the plume, along with some of the radioactive products also rapidly decaying to non radioactive substances, so the more time that goes by between when a part of it is released, and when that part gets to where you are, the less radioactive it will be compared to when it was released. Plus, the wider the plume is dispersed, the lower the radioactivity. Then if you go inside a building, so you aren’t right out in the plume, that provides shielding and also lowers any dose you’re exposed to.
I just hope to heck they can get things under control soon, so it won’t be an issue. Right now, as bad as it is, and for that matter, even if it kept releasing radiation exactly as it is now for some time (days, maybe even weeks), it wouldn’t be an issue for Toyko, or even those quite a bit closer to the plant than you are (although that would be a problem within just a few miles of the plant).
re post by Steel engineer, on 17 March 2011 at 10:42 PM
Hi Steel Engineer,
You’re right, I missed your point. I’m not sure how the diesel’s tie in, or what the rational would have been for going one way over the other during the design process. VERY vague memory that at least some have some diesel’s tied in as you mention, but I really don’t know. As to Fukushima’s problems with them, for anything beyond the most basic information…well, the ‘factual details’ out there seems to be all over the map as to what went wrong and why, what failed or didn’t, etc. Very contradictory stuff – and it seems that the official releases are gawd awfully vague. I don’t know if this will help answer the question wrt the diesel tie in, but for what it’s worth here’s a basic overview of the various BWR systems (pdf) http://www.nrc.gov/reading-rm/basic-ref/teachers/03.pdf
I don’t know how much of it is translation problems/errors, or misunderstandings, or sheer speculation being reported as if it were factual, or what. I mean, officials handling the problem have to be very accurate and careful what they say – but this really is starting to seem as if they just aren’t willing to provide hard facts, at least not to the public.
When it comes down to it, all of the hysteria in the media over the plant guts, and just what is or isn’t happening mechanically really isn’t important to the public. What the dose rates are coming out of the plant, and then where the plume is projected to go, and what the projected dose rates are along that plume at various distances – THAT is all very pertinent information. As is measured dose rates at various specific locations along the existing path of the plume, such as at the plant perimeter, then at say 0.5 miles, 1 mile, 2.5 miles, 5 miles, 10 miles, 20 miles…. but this sort of information seems to be gawd-awfully scarce also.
Frankly, it reminds me of some of the confusion and hysteria that occurred because of poor and mangled communication at Three Mile Island. That accident, while massive and long epidemiological studies can’t find any effect on any member of the public, taught us a HUGE lesson about dealing with any sort of nuclear accident. We (the USA) made major changes wrt how communication would be handled during any sort of major incident all meant specifically to avoid the sort of media circus that we’re seeing right now.
Anyhow, I’ll get offa my soap box! Sorry about that. As to the cooling towers – there’s no need for them, because the station is right there on the ocean. Cooling towers are only needed when there is a limited water supply, and/or if the discharge water needs to be very tightly controlled in terms of temperature. For example a smaller river, where there are heat sensitive fish, so you limit the discharge temperature to maybe no more than 5 degrees warmer than the intake water, and no higher than x degrees period. Then to get enough cooling ability, you build a cooling tower to transfer some of the heat to the atmosphere rather than to the water. Transferring the heat to the atmosphere Isn’t anywhere near as efficient as using water of course.
On the other hand, the ocean is a massive body of relatively cold water, with tremendous dispersion and mixing capability between turbulence, tides, currents, etc. So there’s simply no need for a cooling tower because you’re already right there by something that is vastly better, and to protect the biota (fish, plankton, bacteria, whatever) you just adjust how you discharge it, the outlet configuration, to avoid heating up any one small area too much.
Steel Engineer, for whatever it’s worth; these reactors are designed with a system that cools the core even when there is no off site electricity, generators, or batteries – the Reactor Core Isolation Cooling System (CCIS) and part of it, the High Pressure Coolant Injection System. They run off a small turbine (separate from the main turbine used to generate electricity) that is turned by the decay heat of the reactor itself. I’m not sure why this system failed. When it did, however, that’s when by design you have to go to a low pressure system so you can pump in water, and to do that, you periodically vent steam.
From a technical standpoint, it will be very intriguing to see what actually occurred in each unit, including exactly what failed and why.
But if these cooling systems (CCIS and High Pressure Coolant injection System) do not run when the plant is down, why is there no EMERGENCY plan for having no electricity from outside or the diesel generators (other than 8 hour batteries) ?
If they get a new power feed line to the CCIS can they operate it without Level 2 or Level 3 Controls? Can they bypass the Level 2 and 3 and pump to the spent fuel cell pools?
re post by Steel engineer, on 19 March 2011 at 3:47 AM
Steel Eng., I’m also not sure just what would qualify as an emergency plan for you. None of the multiple systems we’ve been discussing operate during normal plant conditions. They are all emergency systems designed ‘defense in depth’ for all sorts of design basis accidents – loss of coolant, loss of offsite power, earthquake or other natural disasters, etc., etc. All have very specific emergency plans that are implemented by staff depending on which condition you are in and what works and what fails.
If these things aren’t emergency plans in your mind, what possibly could be?
With all those emergency systems you mention- then why aren’t they pumping water?
Level 2 is the PLC controls at typically less than 10 volts, Level 3 is the PC level supervisory controls. Often when one i/o fails or condition is not met in Level 2 it will stop the entire operation. Can they bypass a stuck valve with Level 3 or must they manually move it? Are there dual pumps in the CCIS system if one is damaged. Can they remotely operate the plant with their Level 3 system or must someone be present to push buttons or operate the touchscreens?
I hope they keep spare CCIS pumps in stock !
re post by: #Steel engineer, on 22 March 2011 at 3:57 AM said:
Please forgive me if some of this isn’t very well worded or is redundant – I’d stared it some time ago, but just got back to it, and don’t have the time to edit…
And that, of course, is the question of the year. We are talking about 50 year old design & technology – these were pretty much the first Gen II designs and arguably the weakest of the bunch. Keep in mind that the newer design, Gen III & IV’s are ‘passively” safe or ‘inherently safe’ in that no power is needed of any sort and they’ll cool themselves sufficiently out to infinity for all intents and purposes.
But we’re talking about why these failed to perform as designed, not about present day newer plants or those yet to be built.
Of course the first failure was loss of off site power. Thing is, with massive EQ & Tsunami, I can see all sorts of ways that lines could be cut or transformers damaged etc. that really have little to do with any design issue for the plant. I gather Dai-ini, ~10KM away either kept or quickly restored offsite power and so they were able to get to cold shutdown without major problems.
Anyhow, after loss of offsite power, while the emerg. diesels should have immediately come on (and they did), as best I understand the ECCS high pressure injection system & residual heat removal system one or both (not certain if they act together, or if one is failsafe for the other, or if it can work either way depending on the situation) – anyhow, they should have kicked in within seconds of the reactor scram during the earthquake – long before the earthquake even finished actually.
Initially ALL of this occurred. ECCS kicked in, diesels also kicked in. Then ~1 hr later Tsunami hit. Diesels located approx 10 to 13 meters above sea level, and the blasted thing was STILL high enough to flood them or soak them/the electrical connections so they cut out.
Ok, not good, BUT we still had the decay heat turbine driven ECCS going at that point in all three reactors. Then about an hour later in both units 1 & 3, they lost ECCS. I don’t know why. Unit 2 ECCS continued to function satisfactorily for a few more days.
So what the heck managed to knock out ECCS in both unit 1 & 3?? Don’t see how it could have been temperature – if it were, unit 2 would also have failed, not continued for a few days. I could see a damaged pump or turbine or something causing ONE to go down, but two separate units, both within roughly an hour? Maybe a common weak spot that didn’t survive the EQ??
So, I’ve been looking/keeping an eye out for any information why the high pressure emerg. core cooling systems failed – those activate in seconds after a scram, and should run even if there is no power, just off the decay heat of the reactor turning a turbine (not the main turbine for generating electricity). That system uses water from the torus & suppression pool I believe – after some time, it can get to the point where the water volume available is all too hot for effective cooling, and that’s when it drops down to the higher volume low pressure systems, where I think you’ve got to have batteries and/or diesels. But I was under the impression that you had several days before that occurred, time to get battery and/or diesel and/or offsite power restored. Unit 2 performance seems to support that.
So I’m lost – dunno if there’s some aspect to the design that I’ve misunderstood, or what the failure mode could be, tho I’m awfully curious.
Ok, I see, and yes, now that you’re talking about it, it sounds familiar. I don’t know the answers unfortunately. Any BWR reactor operator could probably tell you off the top of his head & I’m sure Sr. RO’s could along with a host of other folks. Just not my area and I’ve mainly worked with PWR rad safety, so it’s been a long time since I boned up on or covered the details of safety system controllers/electronics & that sort of thing.
If you happen to find out, I’d be curious to know. We might be able to find that sort of info (along with greater detail on ECCS activation and so on too I’m sure) with some searching over at NRC.gov
ANY of the key parts that way – amen brother & me too! Or at least that they can quickly ship over anything that’s needed from supplier or one of the other facilities like Dai-ini – tho I don’t know how many Mark I’s they’ve got vs. newer designs & how interchangable parts might be from the newer ones. I gather that even now getting thru roads in the area may be quite difficult tho.
I need to knwo if I can send my SON back to Japan he is stuying there is it safe now or not and I need full details report of nuclear incident
thx
Japan’s major steel makers are moving to provide electricity to Tokyo Electric Power Company in an effort to help ease power shortages in Tokyo and its surrounding areas.
Sumitomo Metal Industries reactivated its conventional power station on Saturday at its steel plant in Kashima, Ibaraki Prefecture. The power station had been shut down for safety checks after the March 11th earthquake and tsunami.
The company says the power generator is capable of producing 500,000 kilowatts of electricity. The steelmaker says it will provide all the electricity generated to TEPCO.
Another major steel producer, JFE Steel, is running its conventional power station around clock in its plant in Chiba city near Tokyo. The plant can produce about 400,000 kilowatts of electricity.
Nippon Steel is also supplying 500,000 kilowatts of electricity to TEPCO by operating its own power plant at full capacity. The steel company jointly runs the power facility with TEPCO in its mill near Tokyo.
Sunday, March 27, 2011 08:53 +0900 (JST)