The president of TEPCO is in the hospital, suffering from dizziness and hypertension, perhaps because the Japanese government is saying that all of the Fukishima Daiichi plants should be scrapped. Scrapping 1-4 is pretty much a foregone conclusion, since they’re a contaminated mess:
One major problem, said Murray E. Jennex, an associate professor at San Diego State University with 20 years of experience in examining nuclear containment structures, was that all the water the Japanese were spraying had soaked important machinery like generators and pumps, further hampering efforts to restore the reactors’ electricity supply. The use of helicopters in the first week to drop water on the rectors from above was especially ineffective in hitting the target and may have done more harm than good, he said.
“They dumped water all over the place,” he said. “They keep on generating more contamination. That’s the consequence of doing it. They got water on things that shouldn’t be wet.”
The current strategy of “feed and bleed” will just continue to produce contaminated water, since it takes 200 tons of water per day to cool the cores of those plants. And, to top it all off, they’re running out of workers to do the work.
cathyx
I had no idea there was even a possibility of saving those reactors.
Zifnab
Hurray for safe, clean, reliable nuclear power! :-p
Seriously, though. I wonder how many wind turbines and solar panels we’re going to see off the coast of Japan in the next twenty years.
lonesomerobot
Don’t know if you saw it yesterday, but one of the GE engineers originally working on these BWR reactors believes that #2 has already melted through its containment-
http://www.guardian.co.uk/world/2011/mar/29/japan-lost-race-save-nuclear-reactor
“The indications we have, from the reactor to radiation readings and the materials they are seeing, suggest that the core has melted through the bottom of the pressure vessel in unit two, and at least some of it is down on the floor of the drywell,” Lahey said. “I hope I am wrong, but that is certainly what the evidence is pointing towards.”
Robertdsc-iPhone
Where could the Japanese have found sand and lead to throw instead as was done in Chernobyl? Water was all they had.
cathyx
@lonesomerobot: So for people who know nothing about nuclear reactors, what does that mean?
Fucen Pneumatic Fuck Wrench Tarmal
shimizu just wants his life back.
ok, that was unfair, probably.
Cermet
As I posted in another thread – current methods will take years before they can get people near enough to “fix” the reactor problems. That said, I do not believe this because surely, somehow, they will either find a way to shut down the delayed fission (boron packing with water?) or remove the fuel elements, at least from the ones that haven’t melted. If there are any good trolls, this is a good thread to provide ideas to help make this terrible event look better – right now, it looks like it will continue for many weeks, if not months before they start to get things under control.
lonesomerobot
Well, as the engineer claims, “It’s not going to be anything like Chernobyl” but he goes on to say, “it’s not going to be good news for the environment.”
It won’t be like Chernobyl because the drywell was already full of water and this reactor, at least, isn’t likely to explode. Also the fuel probably melted out of the containment like lava, easier to cool.
But the radiation is going to be enormously complicating to the efforts to cool down the other reactors and clean up the mess.
New Yorker
Or perhaps because he comes from a culture where he will be expected to commit suicide.
I sometimes wish we had a code of bushido here. We might have seen the bodies of various AIG execs splattered on the sidewalk by 70 Pine St. instead of hearing them whining about being unfairly maligned by the public.
Scott P.
As has been the case since the start of this, there is so much ambiguous information out there.
My question is this: Once the control rods were dropped into the core, just before the earthquake, the chain reaction in the reactor cores stopped. At that point, the danger was from intermediate reaction products, whose decay continues to create heat even though the reaction was stopped. However, those reaction products have fairly short half-lives; the amount of heat produced declines exponentially from that moment. By now, days after the reactors were shut down, there shouldn’t be huge amounts of residual heat. Where is all of the heat coming from? Why is it so hard to keep the cores underwater?
Similarly, the spent fuel pools should be stable when they are underwater. So why do they need tons and tons of water each day to keep these things cool?
The Dangerman
Prepping for The Ken Lay Gambit; well done, sir.
geg6
They had some asshole nuclear scientist (Dr. Robert Gale) on ABC this morning talking about how, even for the plant workers, there is absolutely no danger whatsoever regarding the radiation at Fukushima. None. That even the ones that were taken to the hospital with radiation burns will never get ill or have any issues. It’s completely safe! Maybe even good for you! (Okay, maybe that last line is an exaggeration, but not by much.)
http://abcnews.go.com/International/japan-nuclear-crisis-highest-radiation-levels-detected-seawater/story?id=13253117&page=1
Culture of Truth
A Danish company just announced the world’s largest offshore wind turbine, to compete in the surging European market.
Alwhite
There is no way they are running out of workers given the unemployment rate in Japan. They just have to do what American power companies do regularly – hire day labor to take high levels for short periods of time. This alleviates them from having to track the workers or be responsible for any future health issues. Its a win-win!
geg6
@Scott P.:
I saw some film this morning that showed that, even though they have the pumps working now, the pipes that they pump the water in through are totally FUBARed. And if there are cracks in the containment (which seems to be the concensus), the water is leaking out faster than they can pump it in with broken pipes.
Punchy
Which is why putting it next to the goddamn ocean was such a great idea because….why?
Also, OT: Republicans now continue to fuck up…..college football bowl games?
I love how the story waits until about the 1,293rd paragraph to finally say that the donations were for Republican candys.
lonesomerobot
@Scott P.: the belief is that reactors 1-3 are leaking somewhere near the base. Hence the radioactive water all over the place and the inability to keep the fuel under water. They’re basically having to continually run water through the cores to keep them cool.
If they’re not cooled, they can reheat and recriticality is possible. It’s clear that partial meltdown has occurred because of the isotopes they’re finding.
Cermet
@Scott P.: There are a lot of reasons and an engineer (which I am not) needs to address them but first and foremost, the design of these reactors is beyond terrible – look at a picture of the raised reactor with pumps in a lower section just outside the containment vessel – any leak means getting to the pumps id impossible. Only an insane person would 1) not have a massive containment building like most amerikan reactors 2) build such a time bomb in a area known for massive earthquaks (for god’s sake, just a 150 miles away (tokyo) they have planned for a level 8+. Beyond stupid.)
In answer to the issue of the control rods, these reactors are based on a stupid and deadly design – an amerikan sub reactor. The core will produce massive heat, more than enough to melt the rods long after the primary chain reaction has been reduced (control rods do NOT stop fission in any given fuel rod system!, only the really fast chain reaction caused by nearby fuel rods is stopped.) hence, some experts say it would take years to cool down to a safe level were water would not be needed.
Hopefully, a troll with good training or background will give more accurate answers than these. Still, looks like they are royally F’ed.
kdaug
@Scott P.:
Appears finding an answer to that question causes a good amount of stress.
My bet? Control rods weren’t fully inserted when the power went out. Dunno, not a nuclear engineer, but I admire the hell out of the folks going in to fix this.
Fuck U6: A More Accurate Measure of the Total Amount of Duck-Fuckery in the Economy
Scott P: See the wikipedia article on decay heat. The short of it is that the fuel rods have to be cooled for 5-10 years before they can be placed in dry cask storage.
gnomedad
@Cermet:
Are you sure about that? Holy crap, that’s insane.
Fuck U6: A More Accurate Measure of the Total Amount of Duck-Fuckery in the Economy
Cermet: US Navy subs use a PWR design and always have. These are BWR.
daveNYC
@Punchy:
Putting it that close to the ocean was pretty damn stupid (really, who would ever expect a tsunami in Japan), but reactors do need water for cooling, so there was some amount of flawed logic behind it.
Cermet
@gnomedad: Yes, the fuel is ENRICHED uranium and continues (in each fuel rod) to undergo fission at a rate that heats the rods to temps well over the melting point until enough daughter products break down allowing the rods to run cool enough that with minor cooling (forced air) the rods woun’t melt (dry storage.) Currently, all the rods are producing vast amounts of heat that needs constant water to prevent steam generated by the heat from removing all the water – which happened in one reactor and possibly, two others leading to melting of some or all the rods in one or more reactors.
If true (I hope not) then the fission reaction will run very fast and they are in deep trouble for so many reasons I don’t really want to talk about it – one, out of my range of knowledge and second, don’t want to think of what workers will be doing to themselves (radiated to the point of future death) to save the asses of the Japanese upper officals … .
@Fuck U6: A More Accurate Measure of the Total Amount of Duck-Fuckery in the Economy: didn’t say they were exact but the fact remains, the basic design IS based on US sub reactors – these are far larger – the fact that the civil reactor boils at high presure and navy reactors don’t boil (sound issues matter for a sub, I wonder why?) does not change the basic design, nor layout. The issue is fuel type and power density and those are far to similar and what leads to disaster when coolant flow is stop in either a sub or civilian reactor.
Fuck U6: A More Accurate Measure of the Total Amount of Duck-Fuckery in the Economy
gnomedad: Control rods tend to absorb prompt neutrons and do inhibit the general fission chain reaction (i.e. render the pile sub-critical). This does not end the entire process, especially where heat generation is concerned.
Then it gets complicated. The truth lies somewhere between Cermet’s panic and pro-nukers’ reassurances.
Sentient Puddle
Not entirely on topic, but this sort of thing has been sticking out to me this entire crisis…
@New Yorker:
This strikes me as potentially wrong in the context of modern Japan, and I can’t find any information that suggests that this is the case. Is there any reason why we keep ascribing samurai culture to Japan beyond just sort of assuming that it’s the case?
Fuck U6: A More Accurate Measure of the Total Amount of Duck-Fuckery in the Economy
Cermet: If that’s what you meant then you are taking unconcionable shortcuts in describing the systems to laymen. While the fuel type and power density considerations are similar, many basic systems are entirely different, and describing the designs as based on Navy reactor designs is confusing at best.
Roger Moore
@Scott P.:
I think this is the underlying misconception. “Dropping” the control rods* doesn’t stop the chain reaction like switching off a light switch. Instead, it moves the chain reaction to just below the level where it can sustain itself, after which it can take a long time to die down completely. IIRC, there was also some suspicion that the control rods or their operating mechanism failed, resulting in the rods not making it all the way into position.
The decay heat is another question. Some of the decay isotopes are relatively short lived, like the iodine everyone has been getting KI tablets to protect against. That means they generate a lot of heat over the few days after the plant has been shut down. Others, like cesium have a longer half life that requires keeping the rods under cooling water for more than a year to keep them from degrading.
One of the safety flaws of the BWR design at Fukushima is that the cooling water doesn’t have enough heat capacity to absorb all the residual heat from a reactor shutdown. Part of this is that the reactor is already hot from operation. The water in the reactor is already hot enough to produce something like 35 atmospheres of steam. That’s why they have the torus everyone has been talking about; it provides a reservoir of cold water to help absorb residual heat. But they can still have a problem where the residual heat in the reactor can boil off all the coolant. After that, there’s still enough residual heat to melt some of the fuel and cause a really serious accident.
*IIRC one of the safety deficiencies of these reactors’ design is that the rods have to be actively raised into position, not passively dropped.
patrick II
@kdaug:
1. The spent fuel rods aren’t in the core, but in cooling pools on a floor above the core. I don’t believe they insert/remove cooling rods in the pool.
2. Evaporation. The pool water warms up and evaporates more quickly than a pool without spent rods under normal conditions, and water has to be replenished daily. When the replenishment water was shut off after the earthquake, the water warmed up more quickly, evaporated more quickly, causing an increasing cycle of heat and evaporation and eventually exposing the spent rods.
3. cracks in the pools. It has been asserted by various news sources that the hydrogen explosions the first week caused cracks in at least one of the pools, causing the water to leak out and frustrating attempts to refill the pool.
Jude
@Cermet: I’ve liked your comments, man, but you really don’t know what you’re talking about vis-a-vis navy reactors.
You still have to boil water to make steam to turn turbines to generate electricity and turn the propeller. There’s just a secondary system for that. The reactor still heats water, but it transfers that heat to non-irradiated water in a steam generator. It requires more piping, but it’s a safer system.
The enrichment for civilian plants is not nearly to the same level as for navy reactors, but the civilian plants do tend to run at much higher reactor power ratings for long periods of time. That leads to a buildup of a lot more fission products in the fuel rods, and necessitates more frequent refuelings (that is, the higher power output AND the less-heavily enriched fuel requires these refuelings).
The big problem is decay heat. When the control rods go in (and in these kinds of reactors, they’re inserted from the bottom up), the self-sustaining chain reaction–that is, criticality–stops. Period. If you don’t provide cooling to remove the decay heat, though, the fuel rods will eventually boil off the water in the reactor vessel. Without liquid water to cool them, they heat up, the zircaloy cladding starts corroding (releasing hydrogen gas) and, if the cladding fails, you’ll get fission products and fuel material released. If they get hot enough, they melt.
Some of the fuel rods have undoubtedly melted–if, as seems possible, that slag has melted through the bottom of the reactor vessel at the #2 plant, then, well, things are very bad indeed. But that doesn’t mean that you get runaway criticality.
I am, however, curious as to where the iodine-131 is still coming from; you have to have neutrons being produced in quantity to make that stuff, and it has a half-life of just over 8 days.
Anyway, that’s enough for one comment.
Jude
Oh yeah, there are backup mechanisms to insert control rods in the case of an electric power failure (I believe this kind of BWR uses a hydraulic system to do that).
But with the crappy info coming out, we’re still not sure if those systems worked as expected. Hell, there’s a good chance that the people actually at the plants don’t yet know.
Yevgraf (fka Michael)
One word: Guilt.
The Russian guy from a couple of weeks ago had it correct – entomb it, and recognize that you’d have to mobilize what is essentially a suicide squad to dig the tunnels and lay in the concrete.
Robert Sneddon
@Cermet: Typical uranium enrichment in water-moderated reactor fuel as in the BWRs is 2 to 3%, up from the natural level of 0.6% found in uranium ore. It’s not that high, and there have been sugested designs for natural-uranium reactors but they have their own headaches.
What you probably don’t understand is that an operational reactor of these sorts creates an immense amount of heat when fission is occurring — the BWR-5 reactor cores at Fukushima each produce 3 thousand megawatts of heat for months on end (reactor 1 is a BWR-4 which only puts out about 1300 MW of heat). All of that heat energy is converted to steam and used to drive turbines and generators and produce electricity. When fission stops and the control rods are in place, which happened nine seconds after the earthquake was detected and several hours before the cooling systems stopped at Fukushima, all that was left was the decay heat from fission products which is (as I recall) about 100MW of heat immediately after shutdown. That decays quite quickly — each reactor is down to about 9-10MW now, two weeks after the earthquake and tsunami. That’s still enough concentrated heat to damage fuel rods if left uncooled but it’s not going to cause any sort of 3000 deg C Tchernobyl-style meltdown at this stage. Right now the engineers on site are putting enough water into the reactors to keep the fuel rods in the core at about 300 deg C, about what the system is designed to be at during regular operation. There’s no use adding more water than they are doing because the rods will heat up again if the amount is reduced and putting in the minimum means less contaminated water to deal with afterwards.
They won’t open up the vessel and see what the real damage is until the isotope decay drops more significantly. That part of the operation is probably some years down the line, when the reduced self-heating effect means the rods can be exposed to air without suffering (further) damage.
PeakVT
@Scott P.: According to the decay charts posted over at TOD, the fuel rods in the reactor are still producing between 5 and 10 MW of heat. They will continue to produce between 2 and 5 for the next year. Also, control rods in a BWR are pushed upwards.
@Punchy: The heat has to go somewhere, and using the ocean as a sink is cheaper than building and running cooling towers.
Robert Sneddon
@Jude: Remember that a half-life of 8 days means half, not all of the iodine-131 decays into non-radioactive xenon-86 in that period. If iodine vapour is still escaping from the site, either from leaks in reactors or from circulated cooling water then it will be “topping up” the contamination levels seen outside. There’s still a lot of I-131 inside the reactors but if the engineers can prevent more steam venting and oxyhydrogen explosions by keeping the pressures and temperatures down then that’s where it will stay, mostly.
I don’t know if the alerts about the levels of I-131 in Tokyo drinking water have been rescinded or not; the big news is usually about the dangers and when things get better that often slips down the attention queue. For example last week it was really big news that three workers exposed to contaminated water were rushed to hospital. Two of them were sent home from hospital on Monday but that detail didn’t seem to rate much press attention.
Paul in KY
@New Yorker: Would have loved to see that. The Japanese can still feel shame. Our Galtian overlords have exised that emotion.
Nied
Those reactors were rendered useless for future power generation a few days after the quake when they started pumping boric acid and sea water into the system. All they’ve done now is make that official. I don’t know if a Chernobyl like entombment is going to be necessary since Fukushima is a very different design and has had a very different accident. At Chernobyl the reactor core itself exploded and was exposed directly to the air whereas at Fukushima the worst that may have happened is the the fuel may have melted through the first stage of the containment structure (that’s another difference Chernobyl didn’t have a containment structure! The sarcophagus was essentially a make shift one put in place after the fact).
mikej
If they run out of workers all they need to do is change the law regarding what a safe level of exposure is. It’s worked so far, of course it will work again.
WaterGirl
From the article about running out of workers:
Whichever senior official said that should be fired from that job and have to take the place of one of the workers.
Jude
@Robert Sneddon: Yeah, brother, I remember that. But it has been 18 days at this point; you’d be looking at less than a quarter of the I-131 left at this point, and it seems like they’re still finding really elevated levels of that in places. Assuming, of course, that the information we’re getting is correct.
I don’t know what’s going on over there. I really hope the rods were pushed home as planned, and things would have to be seriously, seriously fucked for that not to have happened. But, you know, magnitude 9.0 earthquakes have a way of seriously fucking things up.
There won’t and can’t be a Chernobyl-style explosion, but I sincerely hope that there’s not a spreading pool of corium underneath the #2 reactor vessel. Ugh.
Cermet
@Fuck U6:A More Accurate Measure of the Total Amount of Duck-Fuckery in the Economy: You are either a troll or just trying to make noise because you know so little. My statements was in no way over the top and please, if you think so, show it – otherwise, your statements just prove you need to learn something useful on the subject before posting.
.@Fuck U6: A More Accurate Measure of the Total Amount of Duck-Fuckery in the Economy: Really? Then give the details that show my statement is not correct – the fuel density and coolant requirements are the critical issues for any reactor and really define what it can do or not do, so stop acting like I’m wrong but you are too smart and I’m making false statements.
I really can’t believe you have so little knowledge yet post just to make noise – a sub reactor is at least a order-of-magnitude smaller than a civilian reactor so how in the world couldn’t they differ in many components? But the basic layouts are so similar because they use the same basic fuel and control/coolant systems. Like no shit and that does not change the fact that the basic design of ALL amerikan reactors are based on sub reactors so stop trying to raise bullshit just to confuse people.
@Robert Sneddon: About time someone with more detailed information is posting – thanks.
As I correctly pointed out, the fuel is enriched and I DID say the majority of the fission process shuts down but the slow fission rate (and yes, esp. latent heat) remains after the control rods are inserted.
I will most certainly take your word on the issue of not overheating as long as they add water (I did say that too) – but if it will not melt without water, why risk all the workers lives by spraying water on the reactors (Yes, the used fuel elements makes sense since these can burn if left without water.)
The fission never stops in those fuel elements completely (but yes, a world of difference, as I too posted, once the daughter products decay), but the control rods do reduce the rate to well under critical – don’t confuse people on that issue.
PeakVT
@Robert Sneddon: Reactor 1 is a BWR3/MarkI, 2-5 are BWR4/MarkI, and 6 is a BWR5/MarkII.
Cermet
Does any one know the magitude of the earthquake at the plant site? (it was no where near 9 but what was it?) Surely the most instrumented nation on earth for earth quakes has measured what occured at the site but I can’t find any posting.
Fuck U6: A More Accurate Measure of the Total Amount of Duck-Fuckery in the Economy
Cermet: A troll isn’t just someone who disagrees with you, and ‘American’ is both spelled witha ‘c’ and is a proper noun.
jheartney
In Chernobyl, the Soviets used masses of reservists to do the worst jobs, sending them in with various sorts of half-assed improvised shielding that didn’t protect them much. The ones that didn’t die outright have had their lives ruined by the effects of massive radiation exposure. Other workers (the firemen who put out the initial fires, the air crews that dumped sand and boron into the belching reactor core) died right away for the most part. Even with all that, the current setup (a hastily built containment building) is near collapse and needs a bigger, much more expensive containment building to be put up around it.
Fukushima thankfully doesn’t have a wide-open reactor core or melted fuel threatening to explode again. But instead they have multiple destroyed reactors plus spent fuel ponds to deal with. TEPCO won’t be able to handle it over the long term, and the Japanese government will have to eventually ask a large number of people to commit suicide to get this stabilized. Hopefully they’ll do it better than the Soviets did, but I think there’s no way this will be fixed without workers knowingly sacrificing their lives. Horrible.
Fuck U6: A More Accurate Measure of the Total Amount of Duck-Fuckery in the Economy
cermet: try USGS.gov for information on what the experienced movement at the plant were.
And stop dragging my good name through the mud!
Robert Sneddon
@Cermet: The earthquake was rated about magnitude 7 plus at Fukushima, roughly the same value as on the older Richter scale. Furthermore there was a lot of up-and-down shaking rather than most of the movements being side-to-side as usually occurs away from the epicentre.
The reactors and associated plant were designed to cope with this sort of earthquake intensity and maybe a little more. The few reports I’ve seen say that all of the buildings and plant rode out the earthquake without disruption and they continued to operate without problems, starting to shut down the reactors until the tsunami knocked out their generators and the cooling systems stopped when the battery power ran out several hours later.
The Daini nuclear power station across the bay from Daiichi suffered about the same amount of shaking and all their reactors are now in cold shutdown; three of the four reactors there have IAEA class-3 notices against them but I haven’t seen any reports about the problems they might have been ticketed for. They didn’t get swamped by the tsunami and their emergency power generators and cooling systems stayed up. Ditto for the four reactors at two other sites further down the coast (Onagawa and Tokai Daini) which scrammed safely when the earthquake hit.
Robert Sneddon
@PeakVT: Yes, that’s correct. The BWR-3 is about 1300MW thermal output whereas the later BWR-5 design puts out more than twice that amount of heat and more than twice as much electricity; I think their conversion efficiency is about the same.
Cermet
@Robert Sneddon: Thanks for posting that information and esp. the followup details – I really do appreciate knowledgeable people for change – it is refreshing and very nice that people with knowledge bother to post and help us mere second-guessers. Which seems to be the only way most of us can approach these issues since no one who is really in the know is putting out accurate information.
Robert Sneddon
@Nied: I’m not sure but it may be that they plan to decommission all of the reactors on the Fukushima Daiichi site, not just the four that were damaged. The other two reactors, 5 and 6 seem to have suffered no after-effects but bringing them back on-line while the other reactors next door are in a mess may be too difficult. I think they were planning to construct two new reactors on the same site to replace the ones which had reached end-of-life and that project will probably be abandoned too.
In contrast at Tchernobyl the Soviets actually kept the other three reactors on the same site running for about ten years or so after the fourth reactor blew because they needed the electricity. I suspect the Japanese authorities might hurry up bringing some of the Fukushima Daini, Okagawa and Tokai Daini reactors back on-line after inspections are complete as the long hot air-conditioned summer in Japan is steadily approaching.
Cermet
@Fuck U6: A More Accurate Measure of the Total Amount of Duck-Fuckery in the Economy: Sorry but your statements about my being over the top with my statements (and I am being restrained here) was totally uncalled for since I damn well wasn’t. That said, act like a mature person and I will stop my similar immature behavior towards your intellect.
Like any well read person who did not specialize in nuclear fission power, I will, form time to time, misread, not recall all the details, or come to the wrong conclusions and hence, post information that is either not correct (rare) or not as accurate as it should (happens to much of late thanks to trolls wasting our time), which could lead a reader to the wrong conclusions. In any case, I am happy to get corrections but flaming people you are doing there best is not helpful. If I am wrong, tell me (links are not needed if you provide fact based information) and I will post a correction and agree with you.
Roger Moore
@Robert Sneddon:
For those of you without STEM backgrounds, 1 MW is about enough power to boil 1 ton of room temperature water to steam per hour. So if the fuel rods are still putting out around 10 MW of heat right now, the plant needs to boil off something like 200-250 tons of water per day to keep from heating above acceptable levels.
FWIW, this is also why power plants are usually located next to large bodies of water. When the plant was running at full capacity, it was generating enormous amounts of heat. The one, lowest power core was generating over 1 GW of power, which would be enough to boil 20,000 tons of water per day. Since boiling off that much water isn’t practical or safe, they take in cold water and release warmer water. 1 GW of heat is enough to heat around 4 million tons of water per day by 5 degrees C. You need a very large body of water to act as the heat sink for that kind of power generation.
PeakVT
@Robert Sneddon: The thermal efficiencies are about the same (31-32% net), if that’s what you mean.
the basic design IS based on US sub reactors – these are far larger – the fact that the civil reactor boils at high presure and navy reactors don’t boil (sound issues matter for a sub, I wonder why?) does not change the basic design, nor layout. The issue is fuel type and power density and those are far to similar and what leads to disaster when coolant flow is stop in either a sub or civilian reactor.
Lots of misinformation here. Western PWRs can be traced back to US Navy designs. Western BWRs trace back to the BORAX experiments at ANL-W. Only BWRs boil in the primary coolant loop during normal ops. PWRs don’t. US Navy reactors use 90%+ HEU; US civilian reactors use 2-3% LEU. Power density in civilian BWRs is ~60MWth/m3, for civilian PWRs it is ~100MWth/m3, and is classified for Navy PWRs.
Roger Moore
@PeakVT:
Do sub reactors really use 90+% enriched Uranium? That’s weapons grade, not just HEU.
Monty
@Cermet:
I am NO expert on this in any way shape or form but from what Ive read Reactors used for Subs and Ships are the PWR Variety namely because Rickover did not like some of the characteristics of the BWR type reactors. Namely the PWR’s were more powerful for their size and had fewer bad “habits” compared to the BWR type reactors. Most of the original Commerical Reactors were the PWR type but the BWR type came into use later because they were less expensive to build and the NRC was convinced that they were as safe as the PWR type.
PeakVT
@Roger Moore: That’s the number that I’ve seen many places, including here. Note that the UK reactors are derived from the S5W, so use similar fuel.
Robert Sneddon
@PeakVT: The planned replacements for the Royal Navy’s Vengeance-class SSBNs will have a sealed reactor system which will not require refuelling for the service life of the boats, about 20 years or more. This will simplify things as currently refuelling the reactors on the V-boats requires cracking the hull in dry-dock, a lengthy and expensive business. I’ve not seen much detail about these reactors other than they are being designed by Rolls-Royce who, I think, fabricate all of the RN’s submarine reactors including the SSN attack boats. They may be one of the fabled “travelling-wave” reactor designs (Toshiba?) that is occasionally mooted for safe modular reactor operations but which have not been seen in the wild yet.
PeakVT
@Robert Sneddon: The Astute-class ships have a RR PWR2.
Robert Sneddon
@Roger Moore: From what I understand the engineers are not actually piping steam out of the reactors but containing it at about the usual working temperature of 300 deg C and pressure (about 3-4MPa, I think), pumping cold water in and then bleeding hot water out from the base of the vessel. I think I saw a feed rate of of 7 tonnes per hour of water mentioned in one report. Right now there’s no steam leaving the vessels if they can help it and if they can keep the zirconium alloy cladding on the fuel rods below 700 deg C they shouldn’t be getting oxy/hydrogen disassociation which could cause an explosion.
They’re now trying to figure out what to do with the waste water that’s accumulating on-site from this process; it’s contaminated and unless they run out of options then dumping it into the sea is not going to be permitted. Treating it can wait a bit as long as they can hang on to it, even if it is kept in open bunds although that would allow dissolved stuff like I-131 to escape into the atmosphere again. I think they’re considering mooring coastal tankers at the breakwater offshore.
At the same time they’re also working to get at least some the coolant pumps and loops functional again, after checking there are no breaks or unfixable leaks in the system. Once that can be done then the addition of external coolant will not be needed (hopefully).
Jude
@PeakVT: That enrichment percentage is correct.
I’m a former sub nuke, and that’s the information they taught me lo these many years ago in power school. Means you don’t have to refuel very often, if at all.
Gravenstone
@gnomedad: Nothing stops fission, that’s what makes these elements “radioactive”. The radionuclides simply have to expend themselves (rule of thumb is 7 half-life cycles to reach 1% of their original potency). Cermet was correct that the job of the control rods is to dampen, or stop (depending on number and deployment depth) the chain reaction. The chain reaction, depending on core configuration and composition, can provide anything from just loads of heat (and accompanying neutron flux as well as alpha, beta and gamma particles) all the way up to criticallity.
PeakVT
@Jude: Thanks. Do you know if the specific numbers on power density are classified? I’m guessing that they are, because all I have found on the topic are the words “high” and “higher”.
Robert Sneddon
@Gravenstone: Neutrons emitted by a fissioning U-235 or Pu-239/240 nucleus are usually too fast (i.e. energetic) to reliably hit another fissionable nucleus unless the mass is large and compact — this is why nuclear weapons use implosion or a cannon-type assembly system to set them off, by shaping the fuel into a compact form very quickly.
Fuel rods are long thin strings of enriched-uranium fuel pellets in zirconium-alloy tubes; these assemblies are called fuel rods. Only if a fission neutron travels along the line of the fuel pellets is it likely to hit another nucleus nearby but nearly all of the neutrons go out sideways from the fuel rods and hit a fuel rod nearby. When the reactor is running to provide power the fuel rods are surrounded by a moderator, some kind of material that slows down these neutrons by bouncing them off non-fissile nuclei and losing some of their energy. In a BWR boiling water is just such a moderator but graphite carbon will also do the job (see the Windscale and Tchernobyl fires for one reason why graphite carbon is not considered a good reactor moderating material any more). The slowed-down “moderated” neutrons stay in the core area longer and hence have more chance of hitting and fissioning another uranium or plutonium atom, causing yet more neutrons to be emitted and more energy to be released. This is where the term “chain reaction” comes from.
Take away the moderator and fewer fission events happen per second because more fast neutrons escape the core. In the case of boiling water systems increasing the temperature and pressure of the water causes less moderation to occur. This is called a “negative void coefficient” and tends to limit the power output of the reactor core semi-automatically. In the case of carbon however heating it up causes it to be a better moderator; it has a positive void coefficient which means the hotter the reactor gets the more fission events occur per second which makes the reactor hotter and so on. This is a Bad Thing as the Soviets found out.
Control rods are something else. They are made from a material that absorbs neutrons and does not fission. Boron is one of these substances. They reduce the number of neutrons flying around in the core area and are adjusted in and out of the core to control how much power the reactor produces as fuel rods gradually use up the fissile material they contain. Inserting all the control rods into the core absorbs so many neutrons that the chain reaction dies down to almost nothing. All that is left is spontaneous fission and the rare fission event caused by the few resulting neutrons that encounter another nearby nucleus instead of hitting a control rod or escaping the core. The amount of energy produced by this residual fission is so small it is swamped by the decay heat from the fission product isotopes in the rods. I don’t know the exact figures on this though.
lonesomerobot
um….
the IAEA appears to be suggesting that re-criticality may have occurred?
http://ecocentric.blogs.time.com/2011/03/30/has-fukushimas-reactor-no-1-gone-critical/
skip to the bottom, update 2
Jude
@PeakVT: Yeah, any specifics were classified. You can easily look this stuff up online, though. Wikipedia tells me it’s at least 96%. :)
Gravenstone
@Robert Sneddon: My 30 year gone quantum physics class thanks you. Yes, moderation medium and control rods are two separate things. I was limiting the response above to the control rods since that’s what the original question/freak out concerned, i.e. why they don’t stop fission. As I stated above, nothing stops fission, your post pointed out it’s how the system controls the neutrons from the fission that matters.
PeakVT
@Jude: The enrichment level is well known. I’m looking for the power density number, which is usually given in MWth/m3. I haven’t seen a specific figure, though that may be due to the weakness of my Google-fu.
Jude
@PeakVT: Ah, yes. My bad for not reading closely. Yes, those specifics are most definitely classified.
Personally, I have classified them in the “I don’t entirely remember” file. It is, so far as I can tell, an unbreachably secure system, and only gets stronger with each passing year.