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China to Pioneer Melt-Down Proof Reactors
pease1 writes "FT.com reports China is poised to develop the world's first
commercially operated "pebble bed" nuclear reactor. If successfully commercialized, the pebble bed reactor would be the first radically new reactor design for several decades. It would push China to the forefront of development of a technology that researchers claim offers a new "meltdown-proof" alternative to standard water-cooled nuclear power stations." This was mentioned in September of last year but now looks as though the plan is moving forward.
Here is the better article from Wired all about these types of reactors.
m l
http://www.wired.com/wired/archive/12.09/china.ht
Actually, the design of these reactors is nothing short of ingenious.
The reactive elements are spherical pebbles, each with just a tiny amount of radioactive material inside.
Individually, they do not have enough material to go critical.
when you put them all together inside the reactor, the shape of them puts its nearest neighbour just in range to react.
If the reaction begins to cascade, the elements heat up and expand. This automatically seperates them and cools the stack back down.
You can pour new elements into the top, and extract the lowest from the bottom in a relatively safe manner.
liqbase
Are you actually basing your knowledge of the safety features of a nuclear reactor on an animated cartoon?
You do realize that Homer Simpson is a fictional character, right?
Life, the Universe, and Everything... in my image.
Umm. Candu reactors shut down when they lose coolant because the coolant is what sustains the reaction. I'd say thats meltdown proof. They can crank out a heck of a lot more power than a pebble bed reactor because a pebble bed reactor creates less heat - unless thats what they are working on fixing.
> net negative sources of fuel
:P
God, when will this myth stop propagating? They haven't been net negatives since the 1970s; and of the dozens of studies done since then by everyone from the DOE to various universities (essentially all except anti-ethanol crusader Pimental) have shown a 30-50% positive energy balance, and with current tech it may be able to scale up as high as 70%.
Furthermore, even if it were a net negative, this is completely irrelevant. Example: During WWII, the Germans made petroleum from coal. This was a costly process that used many times more energy to produce the oil than the oil contained (they burned much of the very coal that they were converting in order to power the conversion). And yet, it largely fuelled the Nazi war machine.
The issue is converting a *non-mobile* source of energy to a *mobile* source of energy that you can put into your gas tank. If an ethanol plant takes in grid power, it's eating mostly coal. If it doesn't use grid power, it's most likely burning ag waste or other local non-mobile sources of energy. It's not like they're burning ethanol to produce ethanol
Of course, this is all irrelevant: Ethanol *IS* a net positive.
Dear Lord: One of your creatures may be hurt tonight. Please let it be the other creature.
Depends on the type of breeder.
:)
I wouldn't trust a sodium-cooled breeder worth anything - look at the MONJU accident, for example. Superhot liquid sodium in a building whose protective shell is made of concrete (which sodium explodes in contact with)? Not a good plan.
On the other hand, the BREST reactor (a Russian lead-bismuth design) is just great. Can survive on just convection cooling, uses an unreactive moderator, great temperature range, easy maintainance, low waste, anti-proliferation, etc. What isn't there to like?
Dear Lord: One of your creatures may be hurt tonight. Please let it be the other creature.
Actually the NRC has recently approved new construction permits; the US for the first time in a long time will begin constructing new nuke plants.
In some ways this has turned out well for us because we are jumping straight from Generation 1 to Generation 3/4 power plants, which are safer, produce less waste, and are cheaper to run.
Natural != (nontoxic || beneficial)
The main difference is that they don't get the water as hot.
In terms of volume, this produces more "radioactive waste" since there is non-nuclear material included with the waste. In terms of radioactivity, it produces approximately equivalently the same amount of waste.
This is similiar technology, and quite a bit simpler to build. It can be basically just a big bucket with a tapered bottom to allow removal of pebbles. Cut of the water supply the temperature increases, the pebbles seperate due to heat expansion and the reaction slows down and comes to the equilibrium temperature which is set at the design time.
Calling pebble beds "meltdown proof" is really a stretch.
First off, meltdown aside, their moderator is *graphite*. Their emergency cooling scenario is that air will cool the reactor. Nice, except for the fact that even nuclear grade graphite will burn in extreme conditions quite fiercely (it was the burning graphite, more than anything else, that spread the radiation from Chernobyl). Hot graphite also produces explosive hydrogen gas in contact with water (in fact, many of these plants are going to be designed to produce hydrogen from water, so we know it will be present, even if in a different loop).
The very concerning thing is that they're so confident about them that they're not planning to build containment structures. Pebble beds are a nice design, mind you, but they're not *that* safe. A single graphite fire starts, and you've got another chernobyl that destroys a large swatch of land (it's not the casualties from nuclear events that are the problem, but the land rendered uninhabitable). Nuclear accidents have been, unfortunately, surprisingly frequent; it's the containment structures that have kept the danger that they pose limited.
Then, there's the problem with the pebbles themselves. Even in normal conditions, the German prototype experienced pebbles jamming. The safety against meltdown for the pebbles is that their expansion coefficient is designed to reduce the rate of reaction of the fuel; however, if the pellets jam against the sides as they expand, this safety won't help. This may or may not to prove to be an actual problem, of course.
I'd much rather see them go with a lead-bismuth breeder. It's a breeder (so you can utilize more fuel), it produces less waste, the waste is easier to handle, it's anti-proliferation, there's no graphite, there's no pellets to jam, etc.
Dear Lord: One of your creatures may be hurt tonight. Please let it be the other creature.
I think the CANDU reactor is inherently more meltdown-proof than this design. The CANDU reactors use heavy water as both the moderator and the coolant - if you lose the coolant, you also lose the moderator, so the reaction stops. The only bad situation would be if the coolant pumps stopped moving the coolant, but then you could dump the heavy water manually, or just wait for it to flash to steam and get sucked into the vacuum building that sits beside the containment building. Either way, the reaction stops before it gets to a "meltdown" point.
The next Cmdr Taco duplicate will be ready soon, but subscribers can beat the rush and see it early!
Still on the blood for oil game? Look at the numbers and try not to blush. 1. The US Imports roughly 70 percent of its oil 2. We get 23 percent of our imported oil from the middle east. 3. That means that 16 percent of our oil from the middle east 4. Under 5 percent of our oil comes from Iraq 5. We import roughly 11 million barrels a day 6. At 46 dollars a barrel that is $506 million a day. or $185 billion a year So your conclusion is that the US spent almost double what it costs to import its oil needs for a year to secure a minor supplier. Where can I get some of that coolaid?
Cracking open is an interesting problem. Once the pebbles aren't in a spherical packing arrangement, you don't have the spacing anymore, and the concentration goes up. However...
The reactor design (when functioning normally) is basically self-moderating. The "constant expansion and contraction" should only be a few degrees - it shouldn't be enough to cause serious thermal stress and/or fatigue on the pebbles.
I am not a nuclear engineer, so take this with a grain of salt...
The other funny thing is that coal fired reactors give off more radioactive emissions than nuclear ones.
x t/ colmain.html
There's more uranium and thorium in coal than people think...
http://www.ornl.gov/info/ornlreview/rev26-34/te
(Coal combustion: Nuclear resource or danger.)
Fortunately I just read about the term "unsinkable" as it was applied to the Titanic. The boat-maker never used the term. The dock-workers never used the term. The buyers never used the term. The only one who used it was a marketer for a travel agency booking berths aboard the Titanic. No one, the captain included, thought the ship was unsinkable. The very idea is ridiculous. Pour enough water into the ship, and it will sink.
On the other hand, pebble-bed reactors do not rely on making it difficult to meltdown, they rely on the fact that the natural state of the reactor bed is a "safe" condition. (No, that doesn't mean you can stick your head in it, just that it will not maintain a chain reaction.) So, in the case of a pebble-bed reactor, if you take away all the coolant, the reactor shuts itself down. The coolant (or more accurately the heat-transfer media, since it's used to move heat from the reactor core to the heat exchangers to make steam to turn generators) is integral to the design of the reactor.
To have a sustained reaction, there must be coolant present. If the coolant is present, then the reactor cannot melt down, because it's covered in coolant. If the coolant were to be allowed to boil off, then the reaction cannot be sustained and the reactor shuts off. So, Coolant=no meltdown, no coolant=no meltdown. Please find the way to make the reactor meltdown in the above scenario...
Give up? That's the difference between engineering and physical law. I can engineer a damn tough ship, but physical law says that if I add enough weight, it'll displace more weight than an equal volume of water, and it will sink. On the other hand, if I have a pebble and it releases X number of neutrons, nothing I can do will increase that number of neutrons or moderate them in such a way as to cause a chain-reaction, except adding a moderator, which, in-turn controls the chain-reaction. It's like claiming that I can make a light bulb that's hot get hotter and melt-down by turning off the switch.
Pebble-beds have been built and tested in the harshest ways, and no reaction can be sustained when the pebbles were "exposed" without the sustaining material. The only way to make a pebble-bed melt down is to take the pebbles, grind them down, extract the fissile material and make a regular nuclear reactor out of them.
And that's the whole point.
Life, the Universe, and Everything... in my image.
There major flaw in with your argument is that it includes nuclear with "alternative" energy sources. Most environmentalists don't, and are rigorously opposed to nuclear energy.
I say move as much energy production to nuclear as possible, and then take an incremental approach to finding better, more realistic alternatives. Electric cars, for one, powered by nuclear-benerated electricity (ya know, just plug it in overnight) could be a step in the right direction.
However I also can't deny the forces at work within our government that keep us leashed to the Middle East.
"Ask not what your country can do for you." --John F. Kennedy
Seriously, the breakdown of imports and been brought up a thousand times and shot down a thousand times. Until Arabs lose control of the liquidity of the market, they control oil prices.
The graphite is covered in silicon carbide, so it won't burn. In fact the Chinese pebble bed design IS relying on a passive system for control - the reaction can't sustain itself without the coolant present, and will quickly slow down and stop.
There is an excelent article on pebble bed reactors in wikipedia. Briefly, the idea is credited to a German physicist Rudolf Schulten. General Atomic is building one in Russia (link). Also there was a project at MIT under Andrew Kadak, but the website, gives an impression that the work did not go far.
First off in a pebble bed design the graphite is encases in a ceramic, usually SiC. For a fire of the type you are describing all the ceramic coating of all the pebbles would have to fail. And I do not mean just a few small cracks but big chunks of it would have to fail.
Second the hydrogen production is not going to be from hot graphite in contact with water. The Hydrogen production will not be in any loop of the reactor but will be at the ends of power lines coming off the generator. This is not a safety factor with the reactor.
Third as far as lead-bismuth goes I only know of one production reactor that used that. The power plant for the Alpha class sub. Guess what it was a disaster. All of them have been withdrawn from service.
Should they still use a containment dome? I would say you bet. Seems like very cheap insurance to me. If nothing else it could help to protect if from terrorist attack or even milliatry action.
All of you points though are just not issues except for maybe the lead-bismuth breeder. I would have to do more research to see what the state of the art is with those.
See my blog http://ilovecookes.blogspot.com/ for light hearted technical information.
It's kind of interesting... when they first started producing oil, natural gas was a waste product; the oil companies hated it, because they had to get rid of it. In the boomtown of New London, they had the idea to use it for heating a nearby school. So, they disconnected the old boiler and pumped natural gas into the heating system. Unfortunately, the system wasn't designed for natural gas, and it leaked. And, without the added odorants, it accumulated for a long period of time without anyone noticing - until a shop teacher created a spark, and the entire school detonated.
After that event, thankfully instead of giving up on natural gas, they added mercaptan to make it smell bad.
Dear Lord: One of your creatures may be hurt tonight. Please let it be the other creature.
pebble bed reactors have a low density, so they don't overheat , even when all cooling breaks down. The Tchernobyl reactor did overheat. Then exploded. Then the air could reach the core and start a fire.
The low density approach is actually 50 years old. The first prototype was made in the fifties. The low density track was left behind by the more evolved high density approach. High density reactors got a headstart because compact reactors were needed in submarines. Freeman Dyson describes the history in one of his books.
There's a great PBS interview with the inventor here.
A poster cites nuclear proliferation concerns as a reason for the IFR being cut by Clinton.
The real reason for the IFR being taken off-line is almost entirely political. Clinton's base is not pro-nuclear, despite the fact that it is some of the cleanest and safest energy possible.
If you read the interview, you'll see in no uncertain terms that the IFR (as designed and operated at Argonne West) is proliferation proof
------
Q: Now, what about the issue of proliferation, the issue of making plutonium available to terrorists?
A: The object in the IFR demonstration was to invent, if you like, a process that did not allow separations of pure plutonium that would be necessary for weapons. In order to recycle, you need some kind of a chemical process. And the chemical process that was invented here at Argonne used quite different principles than present processes do. It allows the separation of that group of things that are useful, but not one from the other, so that you cannot separate plutonium purely from uranium and the other things. You can separate uranium, plutonium, and the other useful things from the fission products. So it does exactly what you want it to do. It gives you the new fuel, and it separates off the waste product, but it doesn't allow careful distinguishing between the materials that are useful, such that you could use one or another of those materials for weapons.
Q: So it would be very difficult to handle for weapons, would it?
A: It's impossible to handle for weapons, as it stands.
--------
The problem with nuclear power isn't the big scary scenarios that the mainstream anti-nuclear community put about. The problem is that economics suck, and probably always will. "Successful" national nuclear power programmes are propped up by artificial means--either direct government investment, or special-needs laws like the insurance liability cap, or both.
Sure, coal plants pump out a lot more garbage into the environment than nuclear plants, but coal plants have two big advantages: relatively small events don't wind up writing-off the whole plant; and you can take the damn things apart and fix them relatively cheaply because they aren't radioactive.
It isn't just "unreasonable regulatory burden" that makes nuclear plants expensive--it is the fact that the available energy density is extremely high, and any departure from equilibrium can result in sufficiently high energy density to result in plastic deformation of components of the core. Once that happens they're hellishly expensive to fix. Even relatively routine maintenance is extremely expensive due to the real safety requirements of doing engineering work in a radioactive environment.
"Inherently safe" design for fission reactors is an interesting area of research, and much progress has been made, but it isn't clear that any of them are really as safe as their designers would like to believe. And again, it isn't the possibility of catastrophic, world-ending melt-down that you need to prevent, but relatively minor excursions that will leave the containment intact but make a mess of the core.
Older designs, such as the CANDU (which has a negative temperature coefficient of reactivity, if memory serves, meaning a temperture spike will damp the reaction down) are already more-or-less "melt-down-proof". But they have also proven to be bloody expensive to maintain--far moreso than coal-fired plants run by the same utility.
These are all reasons I got out of the nuclear engineering business many years ago--the core physics of fission power is such that it is very hard to create reactors that are going to be economic to operate over the lifecycle of the plant.
--Tom
Blasphemy is a human right. Blasphemophobia kills.
The MN state legislator for starters. The nuclear power plant near my house has been in danger of being shutdown more than once because they couldn't stand the idea of clean power.
Meanwhile there are several coal power plants in the state that are polluting the air, making eating fish dangerous.
Unfortunately, however, they still don't follow the meltdown-proof pebble bed design. They may be safer than Three Mile Island and Chernobyl, but as fas as I know they can still theoretically melt down.
A pebble bed reactor cannot melt down. The hotter it gets the less energy it produces. If it overheats the fission reaction fails.
This is where the Chinese are making what I believe to be a great decision. Why bolt 8 zillion safety mechanisms to prevent a meltdown when you can forego all that cost by building a reactor that can melt down? Cheaper AND safer.
Life is short: void the warranty.
Where are these mythical people who automatically engage in "endless ranting and raving" protests against anything involved with nuclear energy?
I believe these are the people you're looking for (scroll down a bit).
"Ignorance more frequently begets confidence than does knowledge"
- Charles Darwin
Coal contains radioactive material such as uranium.4 02.HTM
http://www.newton.dep.anl.gov/askasci/gen99/gen99
Nuclear Waste can be recylced and refined. Among other ways, we can use a breeder reactor to re-enrich the spent fuel and reuse it in power plants. This would greatly decrease the amount of waste left over and the leftover would be much less radioactive. For some reason, no one seems to talk about this. Partly the reason we haven't done this is that Carter put a ban on them in the US. Overturn the ban, get much safer nuclear power.
Fly me to the moon Let me sing among those stars Let me see what spring is like On jupiter and mars
Many of those people live near me, here in Boulder, Colorado.
The waste isn't nearly the issue that it's made out to be. The problem is that the risks are overhyped. Tens to hundreds of thousands of deaths a year are attributable to cancers and respiratory disease caused by fossil fuel burning to produce electricity. For example, most of the southwest corner of Colorado and the northwest corner of New Mexico have high levels of sulfur, cadmium, mercury, and even radioactives in the air because of coal-burning plants that sell electricity over a wide territory. Respiratory disease in those areas is climbing rapidly to be on a par with the rates in the LA basin in the late 1970s, when children were being found with lung-tissue scarring normally seen in long-time smokers.
We should not think of nuclear waste in terms of the total population risk it generates, but rather in terms of the change in population risk it entails. A few hundred deaths a year attributable to the nuclear waste chain would be miniscule compared to the tens of thousands of deaths a year they would eliminate (that are attributable to the fossil fuel waste chain).
The current crop of CANDUs are unreliable and expensive to maintain. Ask any Ontarian paying a whack of "stranded debt retirement" on their hydro bill, and they wouldn't wish CANDU on anyone.
When people talk about breeder reactors as "producing more fuel than they burn", what they mean is that the reactor is run on either U-235 or Pu-239. It produces heat energy which is converted into electricity.
At the same time, excess neutrons from the reaction are reacted with an otherwise inert blanket of U-238 around the reactor, converting the U-238 into Pu-239 which can then be used to run the same reactor, or other reactors. It turns out that Pu-239 production is faster than Pu-239 or U-235 consumption.
It is relatively easy to use chemical methods to separate the produced Pu-239 from the leftover U-238 in the blanket, certainly MUCH easier than separating U-235 from natural uranium.
So it's not a perpetual motion machine because a resource is used up, i.e. the natural U-238, but that resource is plentiful and the overall process is easier than the conventional method of getting fissile fuel.
The reason that breeder reactors aren't widely used is partly technical, because they're fairly complex things to design and operate, but mostly political because the Pu-239 produced can relatively easily be used in bombs.
"Studies have shown that people who eat peanuts live longer than those who do not eat."
> encases in a ceramic, usually SiC
Above 1250C, SiC degrades relatively easily in a reactor environment;. it has varying degrees of instability above 900C, and remember that PBMRs are definintely not low-corrosion environments. A coolant-devoid reaction in a pebble bed maxes out typically around 1600C (sometimes lower); too low for meltdown but not too low to seriously jeapordize the graphite.
> The hydrogen production will not be in any loop of the reactor but will
> be at the ends of the power lines coming off the generator
Incorrect. The reason pebble beds are desirable for hydrogen production is direct thermolysis of water in the presence of a catalyst; pebble beds can reach sufficient temperatures, unlike conventional PWRs, to do this.
> as far as lead bismuth goes I only know of one..
I don't care if you don't know about a subject. Lead or lead-bismuth reactors have been built for experimentation and/or studied in France, Japan, the US, Italy, Russia (extensive), and other countries. Lead-bismuth has gotten a lot of attention recently in the nuclear power industry.
BREST is little like an Alpha-class sub's reactor. One of the most prominant features of BREST is that it is largely convection cooled. Secondly, thanks to data from Alpha, lead compatability issues have largely been addressed. The main corrosion issues were with steel; despite having largely resolved this through oxygenation and chromium steels (yes - a coating of rust, and/or stainless steel - the first Alpha reactors didn't even use stainless steel for many corroded parts!), the lead tank on BREST is mostly concrete (which never had compatability issues). And if you want to talk about corrosion, you don't have much to point to from US reactors - look at CANDU's recent troubles with feeder pipes, for example. Even if throuh some miracle the concrete base were destroyed, the lead would just solidify and trap its contents within.
Dear Lord: One of your creatures may be hurt tonight. Please let it be the other creature.
Why don't *you* RTFA? They're not building a CANDU, they're building a PBMR. Furthermore, pebble beds run in the 900C range, not 900F. Their "loss of coolent" scenario is as high as 1600C - plenty to burn graphite. I can skip all of your comments about "covered in water", because CANDU uses water as a moderator, not pebble beds (strange that you would think that CANDU uses graphite, however...)
Dear Lord: One of your creatures may be hurt tonight. Please let it be the other creature.
There is a push develope fuel cell technology and hydrogen power for transportation, ie cars. Where do you think the electricity to extract H2 from H20 or methane will come from?
Then you are back to burning fossil fuels to produce electricity, and then to produce H2, which will then be converted to electricty again to drive car motor.
It's easy to see that with each conversion there are inherent inefficiencies and energy is lost. If you are using fossil fuels to produce the electricity, it would be much more efficient to just burn the fuel in the cars engine to extract its energy in one step.
Then China has changed its plans since the last time this article was up here (last September) because I spent hours researching it then and was quite impressed with their reactor design. Several other people have commented on this topic that they are building a CANDU variant, with graphite coated pebbles of slightly enriched uranium bathed in a heavy water moderator.
If they have moved away from that design, then they are in danger of burning the graphite shells and a dozen other problems (Uranium can react spontaneously with air after all.)
Lo and behold, the second sidebar article says they are going for an HTGR design using the packed pebble design. So much for their "innovative new design" that they screamed all over back in September.
Of course it would still be hard to ignite the graphite in a helium atmosphere, but that also assumes a containment vessel is present, something that China, along with Russia, seems to think is a luxury.
Of course, the second sidebar also points out that they have already done "absolute failure" scenarios where they've turned off all the safety systems and watched the reactor shut down.
Life, the Universe, and Everything... in my image.
Why don't *you* RTFA? They're not building a CANDU, they're building a PBMR. Furthermore, pebble beds run in the 900C range, not 900F. Their "loss of coolent" scenario is as high as 1600C - plenty to burn graphite. I can skip all of your comments about "covered in water", because CANDU uses water as a moderator, not pebble beds (strange that you would think that CANDU uses graphite, however...)
AFAIK they are building THTR-Type Devices. That are Pebble Bed Reactors which are cooled by Helium.
This type of device is inherently safe from meltdown because
which is absolutely inert
The german THTR-300 at Hamm-Uentrop has been a demonstration reactor at commercial size (300 MW). It was shutdown after proving to work well.
The reason to cancel the further development and building was completely political because there is no chance to get public acceptance for any Nuclear Powerplants all over Germany after Tchernobyl and Three Mile Island.
The reactors themselves may be safe, but the problems of the required fuel production and handling, especially the waste disposal, are nowhere in the world sufficiently solved. Thats a truth whatever the Nuclear Industry and there political gofers may say.
CU
And having many small nuclear power plants is much more safer than having one megasized nuclear power plant to power an entire city. Why? Simple, compare what happens if one huge plant fails than if one small plant fails.
And IIRC, the material to be heated with the reactor is not water, but helium.
From the sept. wired article:
I think that everything argument against these new nuclear plants is the existing FUD caused (with all reasons) by traditional nuclear plants.
I do not know where to put this so I'll attach it to this post. Germany has experimented extensively with breeder-type reactors but we sunk nearly 7 bilion german marks (3.5 billion Euro) into those projects without going anywhere.
The concept of pebble-bed reactors was developed in the 1950s by a german scientist named Rudolf Schulten. The first prototype had been in use between 1966 and 1988 when the project was discontinued after the chernobyl incident. The protoype used helium as a coolant but other inert substances like nitrogen or carbon dioxide are also possible maybe even water but all sources I could find claim that these designs used inert gases as coolant and moderator. Pebble-bed reactors use either uranium, thorium or plutonium for the reaction and produce new fissionable material during the reaction.
There were also plans to build a commercial type reactor using this design but the reactor was never finished due to technical difficulties with the handling of the pebbles themselves and because of safety concerns following the destruction of the chernobyl plant.
There was also another type of breeder which used uranium as fuel and natrium as coolant but there were so many technical difficulties and safety concerns (mainly with the handling of the hot liquid natrium (300 C) that the reactor was never used at all.
Research into breeder technology was cancelled after 1986 mainly because of the chernobyl incident. The other main concern was that breeder type reactors produce fissionable materials. If you use uranium as fuel you will get plutonium as product. So some were concerened that this material might be used to build bombs. This was especially a concern with the natrium-cooled reactor since it didn't use fuel enclosed in pebbles like the other reactors did.
Jeff
1) The reaction rate isn't the problem; latent heat in the graphite if the core is exposed to air is the problem.
:)
2) The "safety" mode of cooling is air cooling - i.e., if the reactor is ruptured, air can come in and cool it. In such an event, though, the graphite can burn.
3) The pressire is quite high in PBMRs; one that I read about was 69 bars for the core (a bar is roughly 1 atm). If it's not high, it won't run a turbine very well, now will it?
4) The German reactor was shut down due to a variety of reasons, but when it was shut down it had just gotten over a problem with a pebble jamming the retrieval system and causing big complications, including a minor radiation release and a shutdown that would be unacceptable for a commercial plant.
Dear Lord: One of your creatures may be hurt tonight. Please let it be the other creature.
That figure is measured in the same economy in which all the other numbers are measured. There is merit to talking about the productivity of, say, Uruguayan mothers who produce whole people using very little fuel, but not in the scope of this discussion. Give me some other measure that demonstrates the holes in the basic model are wider than the coverage, and we can talk about energy efficiency in some other terms. Until then, it's just unsubstantiated complaining.
--
make install -not war
As I mentioned previously, meltdown is not the serious risk; it's only a risk if pebbles get jammed. The serious risk is fire from a rupture, and especially the intake of water due to a hydrogen-generation explosion for hydrogen-producing reactors.
So, if you want to claim that it has been "tested" against failure, point to where they:
* Jammed the pebbles and then shut it down
* Ruptured the containment vessel while it was operating
* Detonated hydrogen gas in the hydrogen production loop to see if any water posed a threat to the core.
> the material to be heated with the reactor is not water, but helium
Sigh, how many times do I have to go over this? Apart from a significant containment failure when it is raining (no containment structure for chinese PBMRs), water is a secondary loop for hydrogen-generating reactors. They don't make the hydrogen through electrolysis; they run the helium (via as short of a distance as possible so as to not lose much heat) up to a tank of water and a catalyst (for example graphite), which creates hydrogen through thermal decomposition of the water. A rupture of the helium lines risks getting water vapor or outright water into them, in addition to other potentially serious problems involving the hydrogen itself.
Dear Lord: One of your creatures may be hurt tonight. Please let it be the other creature.
Liquid metal is hard stuff to contain for long periods of time - it works it's way into cracks and attacks the metal at the crack tip.
So it looks like you are describing the wrong mechanism and the wrong material - so why should your assertions based on this be correct?
Face it - these are not a mature technologies. Pebble bed at least is furthur along, and is going into production for the first time after a series of prototypes.
Davis, California is "Green, Safe and Nuclear Free", according to large billboards visible as you enter town or just pass it on I-80.
--
Evan "In fact, they are repainting/rebuilding them right now"
"$30 for the One True Ring. $10 each additional ring!" -- JRR "Bob" Tolkien
> the generative capacity of the uncooled spheres is not adequate to
> exceed the cooling capacity of the old itself
That is not true. The generative capacity of spheres when hot being reduced to where the reaction rate won't increase further is dependant on the *EXPANSION* of the spheres. Objects cannot expand when they get jammed.
> will not set off any sort of significant reaction
Hot graphite + water = H2 (likely exploding because of the temperature)
Hot graphite + air = fire (not guaranteed, but a solid possibility)
> I personally witness the shutdown test
Which, as I mentioned, doesn't cover any of the *Real* safety risks. That's like me demonstrating the safety of gunpowder by disolving it in water and saying, "look, I can make it as wet as I want without it exploding!"
> (snipped out personal attack)
When you address how you expect jammed pebbles to expand to reduce the reaction rate, or why a ruptured core wouldn't be a risk for a graphite fire, let me know. Until then, go bother someone else.
Dear Lord: One of your creatures may be hurt tonight. Please let it be the other creature.
According to the oft quoted ORNL report, there is 0.00427 millicuries/ton of coal, and each ton releases 6150 kilowatt-hours(kWh)/ton. This is therefore 6.9431e-7 mCi/kWh. The DOE's Energy Information Agency gives the world total of energy production for 2002 as 4.0512e17 BTU or 1.18699e14 kWh. Since only 9.756e16 BTU or 24.08% of the world energy production is coal for 2002, we can come to a total of 19.85 MCi/yr. Some estimates for Chernobyl put the radiation released at 1.2e19 Bq or 320 MCi. It would take coal plants at the 2002 rate of production 16 years to equal the release from Chernobyl. On the 26th of April, it will be the 19th anniversary of the Chernobyl accident! Is it really that intelligent to put the noose around the neck of our nuclear industry because a near bankrupt Cold War enemy with a poorly designed reactor had an accident that almost certainly could not happen with US reactors?
Suddenly, the hairy finger of a familiar monkey tapped me on the shoulder. It was time.--G. T.
My point was that you're attacking a strawman by pointing out that it costs the U.S. government more to get at this oil than they could profit from it. This is true, but this is not what the original poster (or anyone positing the "blood for oil" stance) is saying. They (not I) are saying that the invasion of Iraq has spent public funds with the end result of enriching private citizens. The more cynical of them claim that Bush specifically invaded Iraq so that his friends in the oil industry could get cheap access to Iraq's oil.
I'm not saying that's happened, I'm just telling you what the argument is. You were attacking a different argument as if it were the one I've just explained.
"Destroy science and religion. Science would re-emerge exactly the same; but not religion." - Penn Jillette, paraphrased
"Above 1250C, SiC degrades relatively easily in a reactor environment;. it has varying degrees of instability above 900C, and remember that PBMRs are definintely not low-corrosion environments. A coolant-devoid reaction in a pebble bed maxes out typically around 1600C (sometimes lower); too low for meltdown but not too low to seriously jeapordize the graphite."
Notice you said degrades not disintegrates. The idea is that you never let it get to 1600c. Combine it with He as the coolant the chance of a graphite fire is extremely, extremely, low.
See my blog http://ilovecookes.blogspot.com/ for light hearted technical information.
On the other hand, in the U.S. Nuclear Reactors have killed how many civilians? So far as I know, the number of civilians killed in nuclear accidents at power plants is... zero.
Define U.S. Nuclear Reactors. I'd define that as any reactor operated by the USA. Reasonable? In that case, there indeed have been deaths and rather horrible accidents.
The 1961 SL-1 BWR experimental reactor accident in Utah comes to mind. Three fatalities, one was by control rod impalement and/or irradiation, the other two were from irradiation.
Some info about it here: http://www.radiationworks.com/sl1reactor.htm
The History channel has a documentary on this accident. Truly gruesome.
Sig for hire.
A pebble bed reactor cannot melt down.
Patently false. It's just much harder to melt down with pebble beds. And pebble-bed is among the next-gen US reactors planned.
The 'impossiblity' of meltdown argument ignores entirely the problems with pebble bed reactors -- Namely that the 'pebbles' are made of, or contain high concentrations of graphite.
The reactors use noble gases (usually helium or argon) as the coolant. The reason: If the graphite pebbles are exposed to oxygen, they burst into flame; a well-known property of graphite that 'watchdog' groups pounce on when pebble-bed reactors are proposed. It's also a property that is downplayed by proponents of pebble-beds. Both sides are right: Graphite does and will burn quite easily. It's downplayable because the risk of combustion is small compared to the probability of failure in current reactors.
If the pebble-bed combustion goes on long enough (which isn't very long), the thermal expansion 'safety' feature of pebble bed reactors is lost -- the graphite has combusted to Carbon Dioxide, nixing the effect of thermal expansion, and the reactor still melts down. As a bonus, you get measurable amounts of highly-radioactive soot with sizeable levels of high-level nuclear waste in it as well.
So, like ALL fission reactors, the coolant system (which is used to provide the usable power) still must meet certain criteria to avoid meltdown. If there is a break in a coolant line (or any other situation) allowing for combustion, all bets are completely off. The primary advantage of pebble beds is this: as long as there are not conditions to invite combustion, it won't melt down, and in fact thermal expansion stops the reaction. But the caveat remains: As long as there are not conditions that invite combustion of the graphite the pebbles are made of.
There have been many (albeit small, 'experimental') pebble bed reactors being run by power companies, generating REAL power sent across consumer lines in the US for years; there have not been large pebble bed reactors in the US; they get around the 'moratorium' on new reactors because they are primarily experimental research reactors. (either Popular Mechanics or Popular Science had an extensive article on pebble beds in the past 24 months or so.)
China's distinction is they are going to be the first to make a large-scale pebble-bed. This is fairly reasonable, since most of the western world is highly allergic to building any fission power plants at all. (Thank you very much, Montgomery Burns...)
-- Sometimes you have to turn the lights off in order to see.