Tuesday, August 26, 2008

Doubts over Robustness of Nuclear Waste Containment.

According to a report by the Environment Agency, thousands of containers intended to hold radioactive waste are unfit for purpose. In effect it harpoons Britain's plans for long-term nuclear waste disposal, just as the government is set to proliferate the nuclear industry and is making deals with the French to develop new nuclear technology for electricity generation, which it is hoped the two nations will be able to sell around the world.

Computer simulations indicate that up to 40% of the containers could be dodgy, and the U.K.'s leading expert on nuclear waste has described the report as "devastating", which I suppose it is. If just one of the containers were to fail the consequences could "prove catastrophic", so says the opposition environment minster, Peter Ainsworth. The report goes on to say that there are "tens of thousands" of containers of immensely dangerous waste, bound in concrete, stored above ground, mainly at Sellafield, while the government and the nuclear industry make up their minds what to do with them. Yes, it's a nice picture isn't it?

According to existing plans, they are likely to stay there for up to 150 years before they are placed underground in a repository (concrete bunker). It will take 50 years to fill the bunker, which will then remain open for another 300 years (by when most of the more intensely radioactive isotopes will have decayed), before being sealed and buried.

On official estimates, the containers should survive for purpose for the 500 years these operations will take to complete (i.e. 50 + 150 + 300 = 500 years): to which the report comments upon "a lack of robust arguments which demonstrate that this target is achievable in practice". It indicates that the containers are not made from stainless steel, which is the best material to resist corrosion. An interesting point, because I heard a lecture on this topic at the Geological Society a couple of years ago, during which it was said they would be made from copper, which indeed might be expected to corrode more readily than stainless steel, but there must be some reason to use it, unless it is simply the cheaper option?

The report debates whether the types of container ail be able to withstand the prevailing conditions and are "fit for purpose over an extended time period". After 300 years, the more radioactive nuclides will have decayed (around 10 half-lives worth), and the waste would then have a comparable radioactivity to natural uranium ore. Before the bunker is sealed, there is always the option of recovering the "waste" for reprocessing into nuclear fuel, should demand and the absence of alternative sources dictate this as a viable option. There are, after all, many imponderables as to the fate and supply of the nuclear industry over the next few centuries, among all other quandaries.

Apparently the internal surfaces of the containers are not treated to remove "vulnerabilities to corrosion", and some "have seals that are not expected to be durable over periods of hundreds of years".

Well, maybe they are not really intended to be left down there for that long, but the material will be fished-out for reprocessing meanwhile?

Related Reading.
"Nuclear waste containers likely to fail, warns 'devastating report'. By Geoffrey Lean.


Anonymous said...

Please don’t let them use copper, this would exacerbate the situation. Copper “work hardens”, as any plumber will confirm. It hardens when under stress (technically, something about dislocations). So we can expect copper when used long term to become brittle. In practice a work hardened copper piece, say a gasket, can be returned to usable condition by heating in a flame until red, then quenching in water, which anneals it, and it becomes soft again. But I imagine this option would not be really practicable for a container of nuclear waste (for one thing, we really don’t have big enough blowlamps).
Peter Melia

Professor Chris Rhodes said...

It was definitely copper mentioned as the container material in the lecture I heard a couple of years back. The material was to be sealed into a kind of cement and placed in the container and this put into an underground bunker. Eventually the whole thing is to be sealed with concrete!

However, it was also stated that for as long as the bunker was not sealed, the option remained to fish the "waste" out for reprocessing, if we should need it.

Someone from BNFL told me once that if we went down the fast-breeder route, by using our warheads and other holding of uranium and plutonium we could keep the lights on in Britain for 100 years!