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Dismantling a Nuclear Reactor
AmiMoJo sends in a BBC story about the hardware used to decommission a nuclear reactor:
"The device cost £20m to design and build and will operate in highly radioactive conditions inside Dounreay's landmark Dome. Its detachable tool bits cost £100,000 each and weigh between 37-93kg. They will cut and grab 977 metal rods once used to 'breed' plutonium from uranium. ... Once in place, the device will operate in highly radioactive conditions and in a nitrogen atmosphere. Nitrogen prevents any residue of the liquid metal from reacting. Exposure to water or oxygen would cause the metal to catch fire. ... Up to three tool bits will be in use at any one time and can be replaced by another three carried in a special tool box without the need to remove the tool itself from the reactor. The rest of the tool bits will be stored above the reactor and would be fitted into place during service and maintenance breaks."
After all, the japanese managed to dismantle a reactor for free.
Too soon?
"None can love freedom heartily, but good men; the rest love not freedom, but license." --John Milton
Something to rub real science in the face of the cargo cult fanboys that think reprocessing and decomissioning is easy and 1970's technology is all we need.
Small units, reuse of high grade waste with something like accelerated thorium, and actual containment of the remaining waste are the way to go instead of treating it all as a solved problem fixed by magic.
A repetitive dangerous task and, while I could say the obligatory "what could go wrong", often the robotic type of setup does better than people (simply because one doesn't have to worry about risk to self). I've seen this kind of thing before. They use them in commercial large scale breweries to clean the brew tanks (which is another dangerous and repetitive job for people).
DFR, the reactor they're talking about in this case, used a liquid sodium potassium alloy for coolant.
What do you mean "hidden"? Nobody has ever denied that nuclear reactors eventually have to be dismantled, and, at least in the U.S., afaik, the operators of nuclear plants, BY LAW, are required to set aside funds starting the first day of operation, to decommission the plant when the time comes.
I don't believe decommissioning costs are some secret government subsidy. . .
Actually, yes. According to Wikipedia, this reactor is cooled by liquid sodium-potassium metal. The BBC mentions it several times as "liquid metal", but never by name, likely because "liquid metal" is a much cooler name than "sodium-potassium." Or because the less scientific might think "Sodium and potassium? You mean salt and the stuff in bananas?" This is BBC, so I'll give them the benefit of the doubt and say the latter. Sadly, its also probably what most people would think. Never mind liquid sodium-potassium is flammable in air, and the idea of radioactive NaK burning gives me the heeblie-jeeblies, as much as I like nuclear power.
Long story short: bad nuclear reactor design, should never be done again. Also, its been being decommissioned since 1977. So, yeah, lets not do that again.
"None can love freedom heartily, but good men; the rest love not freedom, but license." --John Milton
This story is a bit misleading because the reactor being dismantled is an experimental fast neutron reactor. The materials it is made of were not really designed to be easily disassembled. This is different from a commercial light water reactor where part of the design requirements are being comparatively straightforward to dismantle.
Long story short: bad nuclear reactor design, should never be done again.
Hi! You must be new here. Let me introduce you to the Slashdot resident "sodium cooled fast breeder reactors are way cool, we should build loads more of them and solve all the world's ecological problems!" contingent.
You are not a brain: http://books.google.com/books?id=2oV61CeDx-YC
Sooo. We implement a technology (thorium breeders) that we have far less engineering experience with than the standard reactors and it will automagically instantly be better?
Uh. Who's doing cargo cult again?
(I favor thorium fueled reactors, but it will not automatically be a solution to all problems without further engineering and experience. Nothings easy.)
Oh, and are we talking about using 70s tech to clean sites up to 70s de facto standards of safe it, lock the place up and monitor it forever?
Or the massively more stringent modern ones requiring removal of all the radioactives and chemical contaminants?
Anything worth being impressed by is also worth being afraid of.
Nobody cares what the CAPTCHA for your post was.
Oh, don't get me wrong: I do still think FBRs are really cool. While I was reading about this reactor, my inner nerd was going "Holy shit, using NaK as a coolant is awesome and kinda badass!" even while it was also going "Holy shit, using a material that can spontaneously explode in air as coolant for nuclear material is a really bad idea!". Many bad ideas are also really cool. Doesn't mean they aren't still bad ideas. Can't even imagine what would happen if the public found out about it. Or if, God forbid, one of these things actually exploded.
Now, something like a Molten Salt Reactor , on the other hand, is both cool and (probably) not a bad idea. And could possibly solve most of the world's ecological problems.
"None can love freedom heartily, but good men; the rest love not freedom, but license." --John Milton
The Japanese have built and used a similar tool for removing fuel from their troubled Monju fast breeder reactor prototype. The latest glitch was that the tool fell into the reactor and got stuck. The senior engineer on the effort committed suicide after this.
The tool was retrieved last month, after much effort.
It would be a shame if the Brits ran into similar problems, so hopefully they are talking to the Japanese and getting some lessons learned.
Indeed, that thing is a giant lightening rod. And apparently without a rubber nub at the top a single lightening strike could fry the earth like a potato.
In all seriousness, newer technology is generally safer than old technology, and several proposed reactor designs reduce nuclear waste, which is the biggest issue with nuclear power.
Most people these days are advocating molten salt reactors, which do not use dangerous liquid metals. Salts are much safer than anything currently used to generate power. There's no risk of the coolant or fuel igniting, for example, which is a risk even with water cooled plants. Fukushima is a practical example: the loss of coolant water allowed Zirconium fuel element cladding to become exposed to air and catch fire. That kind of thing just can't happen with a salt. Meltdown isn't a risk either in a reactor designed to operate in a molten state to begin with!
No, you see, people who deal with nuclear energy are /responsible/ humans that clean up after themselves.
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The words "something like" were in there to provide a clue to the reader as to what the sentence was about. I think we should be moving on towards the future instead of pretending that the failures of the past are good enough, and I mentioned a promising lead so that idiots would not instantly assume that I'm against the entire concept of nuclear power for the hell of it.
It's very clear to all who take things seriously that the currently running reactors are just not good enough so the "engineering experience" argument unfortunately shows ignorance in this case. So what is your "standard reactor" that currently exists and that you think is good enough? Name it. You can't use the AP1000 as an example by your suggestion, it may be good enough but there is not yet a single completed reactor of that type so it's a step into the unknown instead of just "engineering experience". Thinking that civilian nuclear power is a solved problem is a massive step backwards and an example of that "cargo cult" where you revere the idea but want a thing that looks impressive instead of something that actually works.
The frustrating thing is that almost every reactor design more complex than a boiling water reactor has had serious problems. Most high-temperature gas-cooled reactors have had major problems, although Peach Bottom continues to generate power profitably. The German AVR reactor, which was a pebble-bed design, had a pebble jam and can't be dismantled at all. About a dozen sodium-cooled reactors have been built, with few successes and several sodium fires.
That's why reactors are still BWRs and PWRs. Everything else so far is worse.
To be fair the Dounreay FBR was not a bad design, it has been a very successful prototype and operated for many years. It can survive complete external cooling failure because of natural convection and many new designs are copying this idea. Although I do agree a liquid Sodium-Potassium mix is not a nice compound, and the newer designs are using better mediums.
While it has been theoretically in the process of decommissioning since 1977, it has started and paused many times, mainly for good reasons like allowing more decay time. They are currently removing the cooling medium and this will take a couple of years, in my opinion they are working slowly and safely, which I'm sure you'll agree is the right way.
...people who are not nuclear engineers talking about why nuclear engineers are Doing It Wrong.
Next week, Bricklayers wonder about space.
You don't happen to know why alkali metals are useful in a fast breeder?
Let me see:
Alkali metals don't corrode the structural materials in the reactor, unlike superheated water, salt or lead.
The coolant doesn't need to be pressurised, greatly reducing the risk of a leak.
The heat conductivity is superior to any other coolant, making it much easier to design a passive cooling system
The coolant is compatible with metal fuel. Metal fuel has much better heat conductivity than
the helium-ceramic type of fuel bundles used in most reactors, which aids in cooling. Metal fuel
is also MUCH easier to reprocess ( necessary for a breeding cycle ).
Unlike salt and lead, sodium alloys are liquid close to room temperature, making service, repair and standby operations much simpler.
Unlike salt and water, alkali coolants don't undergo radiolysis at any temperature.
The electrical conductivity in sodium is good enough that you can make electromagnetic pumps with no moving parts ( less risk of pump failure ).
The neutron spectrum with alkali coolants is quite hard, giving such a reactor excellent breeding and actinide burning potential.
So basically while the fire hazard is an issue for these reactors, there are numerous advantages with alkali metals that actually give a lot of safety advantages. Also, while a sodium fire would be bad, it's not exactly as if rupture of a pipe carrying superheated steam would be very benign either.
The "cargo cult" was a expectation that the form of something would produce results without any of the hard work of knowing anything at all about the function (fake military infrastructure in the Pacific Islands to get supplies to turn up by magic). Get something to about the right shape and it's good enough and the rest is magic not worth bothering about. Thus I apply this label to the people that are unquestioning fans of something but get quite irate when practicalities are discussed in any way apart from mindless cheering - if you dare to suggest a problem or difficulty you become a sworn enemy. It's a behaviour that you can see here on a few topics and nuclear is one that brings such fanboys out. Just mention some way of dealing with nuclear waste (eg. synrock) and you are bound to get one or two of them that push some line of counterproductive magical bullshit such as "nuclear waste does not exist". Such idiots in government killed off some promising nuclear research designed to overcome problems that such fanboys wanted to pretend do not exist. US civilian nuclear technology would still be stuck in the 1970s due to that attitude if there had not been a purchase of technology from Toshiba in Japan where such an attitude is not as widespread.
It's yet another disturbing manifestation of something that is almost a hatred of science despite a love of technology.
Back to thorium breeders and similar designs, there's a potential there to melt down expired fuel from old reactors instead of having to do all of that difficult reprocessing. That's one of several good ideas that are a long way ahead of the 1970s technology that is currently in operation.
From the Wikipedia MSRE page ( http://en.wikipedia.org/wiki/Molten-Salt_Reactor_Experiment ):
The ensuing decontamination and decommissioning project was called "the most technically challenging" activity assigned to Bechtel Jacobs under its environmental management contract with the U.S. Department of Energy's Oak Ridge Operations organization.