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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."
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.
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
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!
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.