Friday, March 1, 2013
Our nuclear legacy
The UK has 112 tonnes or more of UK (and Japanese and German) plutonium (Pu) stored at Sellafield. 84 tonnes of it is ours. Germany has said they don't want theirs back, and the Japanese probably won’t need any more either; we used to convert it to Mixed Oxide (MOX) fuel for them (Pu/U239). But the MOX fabrication plant was a disaster (it rarely worked) and has now been closed.
Options for using the plutonium are:
1. Convert it to MOX and burn that in converted old conventional UK nuclear plants (the proposed new UK plants are not at present licensed to use MOX). DECC says that ‘if all our plutonium was converted to MOX fuel it would be about enough to power two reactors for about 60 years utilising a 40% MOX core’. That's just once through, no breeding. But that would mean building a new maybe £1bn MOX plant and spending a lot of money on conversion and subsequent clean up (it would generate a lot of waste, including more Pu!) See 2 below. Building a new MOX plant just for the ~100 tones of Pu would be silly, if we weren't going to make more (which would mean a new multi billion reprocessing plant to replace THORP, which is due to close soon) and then breed more Pu from spent fuel. But at present, to save money, the spent fuel from the proposed new plants is not going the be reprocessed, just stored, so, with the existing plants mostly all closing soon, there wont be any new UK Pu sources.
2. Try to find someone else who still wants to buy MOX. MOX is a dodgy thing to transport- an ideal terrorist target! And selling it would not be commercially viable. The Nuclear Decommissioning Authority says the cost of constructing a new MOX fuel plant in the UK and operating it for about 30 years ‘could be expected to be around £5-6 bn’, with the resulting MOX fuel being worth ‘in excess of £2 bn', so it’s sale would not offset the cost of its manufacture.
3. Build a new MOX-using plant: the Canadian CANDU has entered the fray as an option. That means we would have to build a new MOX fabrication plant, and maybe, unless the CANDU plant was just for interim use once through, a new reprocessing plant to keep it fed.
4.. Burn the Pu in a new-build fast reactor like PRISM, once through, without breeding more. GE say they could burn it all off in 5 years. But this is untried technology, which would also create new wastes. PRISM is quite small (600MW), but no one has yet offered a price that I know of, but we must be talking £4-5 bn. Pity in a way not to get the full value of the Pu by breeding, just a bit of expensive power for a short while But it would get rid of the Pu.
5. Burn the Pu in a fast breeder- to get the full value. And extract fresh Pu from spent fuel . But that opens up all the problems of a long-term (100s of years) plutonium economy- more and more of it circulating and more wastes being produced. And you would need a new multi £billion reprocessing plant or two (or three)! France, the UK, US all gave up on Breeders some while back. Japan too. Too expensive, risky and proliferation prone. Russia though is still keen. And China.
6. Build a Thorium fired reactor which would need Pu to make it work (Thorium is not fissile). Molten flouride salt systems look promising but are a long shot: we are maybe a decade away from knowing (e.g from China’s efforts) if that’s a viable option. Guess the cost!! Especially if you as wanted to continue into the future- you’d need fresh Pu from somewhere (i.e. new conventional reactors and reprocessing plants).
7. Just carry on storing it! Its continued long-term storage for about 110 years would cost about £8bn and then it would still need to be dealt with. Rendering it less proliferation risky e.g. by mixing it with more radioactive materials (i.e undoing reprocessing!) might cost £5-7bn - the so called 'immobilize & dispose' option, making it is hard to steal for Pu extraction.
There are no good options. 7 appeals to some nervous eco-people, 6 to nucleholics. DECC likes 2 but may try 3 or 4 or even 1. 5 seems too big for anyone to think about. We shouldn’t have produced it! It was initially done for to make bombs, then for fuel for Fast Breeders. What now? Back to Breeders and a big expansion of reprocessing?
Reprocessing has added vastly to the nuclear wastes we also have to deal with. So will the decommissioning of our old nuclear plants. And if any new ones are built, they will add to the pile. Some of the low level waste seems to be destined for landfill sites. In theory, a ‘final’ deep geological waste repository for the high level wastes will be built somewhere by 2040- or perhaps a bit earlier, if a willing community can be found to take it (and lots of cash). But that will be earmarked for the existing wastes. The wastes from the news plants will have to be stored somewhere - until 2130! Probably on site at the new reactors. Since, to cut costs, the spent fuel from these plants is not, on current plans, going to be reprocessed, it will still contain plutonium, and be classified as high kevel waste. And since, again to improve the economics, the new plants will adopt a ‘high burn up’ strategy, the spent fuel will be much more radioactive.
We’ve got a lot of problems ahead... and they will be made even worse if we build new plants. Unless, that is, you believe new Molten Salt Thorium reactors can be used at some point to burn up some of the wastes. That’s a very long shot - decades away at best with unknown costs. What we do know is that the planned clean up will cost at least £90 bn and probably a lot more. Why did we ever go down this route? And should we contemplate yet another costly round, with Thorium breeders, as a possible way out? Double or quits?! That depends of on whether you see nuclear as just a dead weight from the past, or as having bright new future, and redeeming itself.