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Thursday, 31 July 2008

The future of nukes

Something I have never discussed until now, because there was no need to. But these week I found few very interesting articles on the future of nuclear reactors and nuclear weapons.
I have to say I'm very pro- nuclear plants, because I think this is one of the cleanest possible sources of energy. Still, i want to emphasize that the safety of those reactors still is my greatest preoccupation. And after I read an article in NY Times about some leakages in nuclear plants in USA , I have some doubts on the regulations there. Anyway, here are the articles, enjoy them and my comments will be below. As usual :) I recommend you the second article which is dealing with a new type of enriched Uranium that may cause major troubles to plants around the world.

Next generation of nukes may not happen

The US House of Representatives last week voted to deny any further funding for a programme to design the next-generation nuclear warhead. Money will instead go towards "sustaining and modernising" the nation's existing stockpile of more than 4000 warheads.

The US National Nuclear Security Administration (NNSA) had argued that the Reliable Replacement Warhead was needed because it would be safer to stockpile and harder for terrorists to acquire and use. Electronic security features would render it useless in the wrong hands, and it would feature a new breed of explosives for triggering fission, making accidental detonation less of a risk. It would also need less fissile material, making it safer to stockpile.

Nevertheless, when the House Armed Services Committee revealed its 2009 Defense Authorization Bill on 15 May, it did not include the $33 million the NNSA had requested for next year.

My comment: I don't know whether I should be happy or sad. I mean, from one side, everyone would be happier to see warheads that cannot be used by terrorists, from another-how many warheads got in the hands of terrorists. Fortunately. But from the other side-I'd rather see the world decreasing the numbers of the warheads, instead of increasing it.

Nuclear super-fuel gets too hot to handle

from New Scientist, 09 April 2008

BluereactorcoreIf you make uranium burn stronger, hotter and longer in nuclear reactors, and you'll need less fuel, and there'll be less waste to deal with when it has been exhausted.

For decades, nuclear operators have done just that, but emerging safety and waste-disposal issues are raising questions about this approach. The latest high-efficiency fuel may prove to be unstable in an emergency, and so poses a greater risk of leakage of radioactive material into the environment. What's more, the waste fuel is more radioactive, meaning it could prove even more difficult than existing waste to store in underground repositories.

To boost the efficiency of their reactors, operators have progressively enriched the uranium they use as fuel to increase its "burn-up" rate. This is a measure of the amount of electricity extracted from a given amount of fuel, and is expressed in gigawatt-days per tonne of uranium (GWd/tU). The higher the burn-up, the longer the fuel rods can remain in the reactor. This has proved particularly successful in the pressurised water and boiling water reactors commonly used in the US and elsewhere. Since 1970, the average burn-up of these reactors worldwide has almost doubled, to more than 40 GWd/tU.

The next generation of nuclear plants will bring a further step-change. Applications for the construction of 30 reactors in the US and 10 in the UK are expected over the next few years, and plans for the two designs most likely to be built - Westinghouse's AP1000 and Areva's European Pressurised Reactor - envisage burn-up rates of 60 GWd/tU or more. At these rates, uranium fuel rods should burn for around a year longer than today's best burn-up fuel.

Such gains may come at a price. Last month, at conferences in Washington DC and Rockville, Maryland, organised by the US Nuclear Regulatory Commission (NRC), a team led by Michael Billone at Argonne National Laboratory in Illinois presented findings (1.8MB pdf) on the behaviour of high burn-up fuel. They say that fuels with a burn-up above 45 GWd/tU cause previously unforeseen safety problems, and would break existing NRC safety rules (120kb pdf) unless changes are made to the way fuel elements are packaged.

The danger would come if there were a sudden loss of cooling water - as in the accident that led to the partial meltdown of a reactor core at Three Mile Island, Pennsylvania, in 1979. To contain the radioactivity in such an event, it is crucial that the fuel rods and their zirconium alloy cladding maintain their integrity as they are doused with cold water from the emergency cooling system. If the cladding has become brittle, the rods may split open and leak plutonium and other radioactive material into the reactor building.

Even during normal operation, cooling water corrodes the surface of the cladding by reacting with zirconium to form zirconium oxide. The NRC's rules require that the corroded layer must not amount to more than 17 per cent of the thickness of the cladding.

Billone and colleagues say that where high burn-up fuels are used, this rule is not stringent enough. When they put different types of cladding used for fuel with a burn-up above 45 GWd/tU through a series of tests designed to simulate a loss-of-coolant incident, they found they all became brittle before oxidation had reached the 17 per cent limit.

They attribute this enhanced brittleness to the increased amounts of hydrogen released by high burn-up fuels during normal reactor operation. The gas is gradually absorbed into the cladding, where it increases the solubility of oxygen. Between 650 °C and 1200 °C, this can trigger "breakaway oxidation" of zirconium, making it rapidly more brittle in an emergency. Fuels operating at 60 GWd/tU would produce around 40 per cent more hydrogen than existing high burn-up fuels.

Edwin Lyman of the Union of Concerned Scientists (UCS) in Washington DC warns that the problems need to be solved long before the new reactors are switched on.

The Electric Power Research Institute, which represents US electricity producers, insists there is no imminent safety issue, and that modern reactors are operated in a way that ensures there will never be a catastrophic loss of coolant. Reactor materials expert Arthur Motta at Pennsylvania State University in University Park says it should be possible to solve the problems raised by Billone with new alloy types. "We should be able to safely increase burn-up."

Despite these reassurances, the NRC, which commissioned the Argonne research, has launched a three-year consultation with a view to tightening up the rules.

Questions also surround how the waste created by high burn-up fuel will be disposed of. Irradiating uranium for longer in a reactor makes it much more radioactive, and decay of this extra radioactivity generates correspondingly more heat when waste fuel is stored after being removed from the reactor. According to Nirex, which until 2006 was responsible for dealing with the UK's nuclear waste, fuel with a burn-up of 55 GWd/tU irradiated in a pressurised water reactor would be around 50 per cent more radioactive than low burn-up fuel of 33 GWd/tU throughout the time it needs to be stored.

To ensure that the build-up of heat is kept within safe limits, spent elements of the higher burn-up fuel will have to be stored further apart. Failure to allow for this would lead to a build-up of heat that could cause fractures in the containers in an underground storage site or in the surrounding rock, and so increase the risk of a leak. Though the increased efficiency of high burn-up fuel means there would be less of it, more storage space will still be required overall.

In the UK, this may mean that the government will need to find two underground repositories, instead of the one now envisaged, says Hugh Richards of the Nuclear Consultation Working Group, a group of activists and academics opposed to nuclear power. source

My comment: Notice how EPRI claims there aren't safety issues with the new reactors and then it says they are sure they can handle any problems. For me this means "we agree there are problems, we hoped no one would notice and we hope we can solve them". I think that isn't serious for something as dangerous as nuclear reactors. We shouldn't get paranoid, but when something is serious, it is serious and we have to deal with it as such! I hope this research will lead to more work and more results. And hopefully to cleaner and safer new reactors.

Invention: Diamond-cooled nuclear reactor

Nuclear plants can fail when the heat from the reactor is not removed quickly enough from the core. This can happen in pressurised water nuclear reactors if the water in the cooling system boils, because steam is a much poorer conductor of heat than liquid water.

These reactors have a primary water cooling system that directly takes heat away from the reactor. It is sealed under huge pressure to prevent it boiling and conducts heat to a secondary water cooling system that is not sealed.

But this secondary system is also at risk of boiling. If that happens, heat builds up in the primary cooling system, which can lead to meltdown.

Ronald Baney and colleagues at the University of Florida in Gainesville, think they can tackle this problem by turning to diamond – one of the best heat conductors known to science.

Their idea is to add diamond nanoparticles to the water of the secondary cooling system to dramatically improve its ability to transfer heat.

Baney and colleagues say such nanoparticles are chemically inert and radiation resistant, so are unlikely to clump together in a way that could block the cooling system. However, they don't say how much a diamond-based heat transfer fluid might cost.

Read the full diamond-cooled nuclear reactor patent application. source

My comment: Lol, that's cool. I just want to see the bill :) But it goes well with the previous article :)

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