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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.
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
> 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.
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!
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.
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.
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.
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
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."
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.
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