Extracts from NATTA's journal
Renew, issue 147 Jan-Feb 2004

 14. Nuclear News Deep Burn : Nuclear Transmutation

One idea that is sometimes put forward to dealing with nuclear waste is to try to ‘transmute’ it, by using particle accelerator beams to convert isotopes into new forms with shorter half lives.  That’s the idea behind the so-called ‘energy amplifier’ developed as a concept by Carlo Rubbia at the CERN Laboratory in Switzerland.  This uses a proton accelerator firing a beam of neutrons into a sub-critical assembly of thorium coupled with plutonium. The energy output is seen as a by-product- the main aim is to convert some nuclear wastes into less hazardous forms. The system is seen as fail-safe, since the chain reaction can be instantly halted by switching off the accelerator.

Waste transmutation has obvious attractions, but a 1999 report to the European Parliament on new reactor options noted that it was perhaps ‘just nice physics’ rather than an economically and technically practical option. It would be a slow process, and only some waste would be suited to transmutation. In addition to the energy amplifier transmutation plants, a complete power system designed on these principles would also require a complex and very expensive network of fuel processing and waste reprocessing plants if significant amounts of waste throughput were to be treated in this way. That would, the EP report says, only be possible, even in theory, for ‘countries with a huge nuclear industry’.

The nuclear industry itself does not seem very keen on the idea- because of the complexity and cost.  At a recent EPSRC supported seminar at the University of Surrey, Dr Samantha King from NIREX noted that the spent fuel would first have to be reprocessed to separate out the uranium, and the remainder then processed again to separate out the specific isotopes that were to be worked on. This material would then have to be shaped in to some form of target for neutron bombardment. That would only convert of proportion of the material.  To get to high percentages of conversion, the target material would have to be reprocessed again, but the transmutation process would become less efficient with each cycle.  Moreover, at each stage, new wastes would be created. So it’s hardly a magic bullet for dealing with wastes- one blast with a neutron beam and its gone.

But the nuclear scientists have  come up with yet another scheme- the so called ‘Deep Burn’ concept.  The main current worry about un-reprocessed nuclear waste is the plutonium content, since it can be used for weapons making purposes. Of course some of the other isotopes in there are also very dangerous, but most of them have shorter half lives and will eventually reduce to low levels of activity. Indeed, it has been suggested that one possibility might be that in the far future, after a thousand years or so, our descendents might be mining nuclear waste dumps to get access to the plutonium- the radioactivity of the  rest of the nuclear products having conveniently reduced to make the Plutonium easier to get at. There certainly could be plenty for them to get access to. At the University of Surrey seminar it was noted that the USA’s proposed (but still yet to be agreed) nuclear waste repository at Yucca mountain has a designated capacity of 63,000 tonnes, but at current rates of waste generation, there will be a need for new repositories of this size every 20-30 years.

So, the argument went, what we need is some way to transmute plutonium. It wouldn’t help with the bulk of the waste but it could reduce the plutonium risks. So how do we do that?  Easy- get the plutonium to do it itself. That’s the simplified rendition of the ‘Deep Burn’ concept reported to the seminar by Francesco Venneri from the US Los Alamos labs. Basically, plutonium fission produces neutrons which is why it is a fissile material. Why not design a reactor in which the plutonium is progressively used up- not a fast reactor in which the fast neutrons go on to breed more plutonium from the uranium 238 in the fuel, but a version in which the neutrons cause more plutonium transmutations. As it happens, he said, the helium moderated pebble bed modular reactor, with its graphite coated fuel balls, is well suited to this concept. The full details are of course very complex - it’s a matter of using resonance phenomena to increase the efficiency of the neutron capture process, and a lot more!  It also sounds very far-fetched.  But then who knows, something like this may be possible, eventually. Venneri however seems very bullish. He talked of a power producing system which could burn more than 95% of the Plutonium 239, and generate electricity at 3-4 US cents/kWh. And he said that a realistic R&D time scale was 10 years....

* You can access the full report from the University of Surrey Physics Department web site at: http://www.ph.surrey.ac.uk  look under research and then CNRP, or go direct to: http://www.ph.surrey.ac.uk/cnrp/news?storyid=24     Also see our Technology section.

Sellafield  emissions

Last year, tests conducted for Greenpeace by Southampton University Oceanography centre found very low levels of  Technetium-99 in fresh and smoked salmon bought from Sainsbury’s, Tesco, Asda, Safeway, Waitrose, and Marks & Spencer.  The UK Food Standards Agency (FSA) urged consumers not to be alarmed by the results which it said were well below permitted level and were not a health issue. Dr Andrew Wadge, the UK FS’s director of food safety, said: “Even at the maximum concentrations found by Greenpeace, a person would have to  eat 700 portions of salmon a day for a year to reach the annual permitted EU radiation dose”.

But there may be other problems. A subsequent study by University College Dublin, found that the pollution of the Solway Firth by plutonium from Sellafield was up to 15,000 becquerels per kilogram- 100 times higher than previously thought. It was also discovered that, instead of staying trapped in the sediment, the plutonium was breaking loose and being carried north by  currents.  This challenges the official view, long held by BNFL, that heavy particles of plutonium sink to the bottom of the Irish Sea and are not disturbed. It implies that the  quarter of a tonne of plutonium dumped in the sea by Sellafield over the past 50 years could carry on contaminating the Scottish coast for many years to come. So sadly, even if BNFL does close THORP as they have indicated they might, by 2010, then the problem could continue.

To be fair, much lower levels of plutonium were recorded by the Scottish Environment Protection Agency in 2001 as part of the annual survey.  Samples taken by SEPA showed levels of 100-150 becquerels per kg in the Solway Firth.  But these it seems were mostly from the surface of the sea bed whereas the University College researchers went down 80cm in to it and it’s debated as to which matters most.  SEPA claim that there is no significant health risk.

Wylfa et al offline

Following the unpredicted shut down of both reactors at the Wylfa nuclear power station on Anglesey, Friends of the Earth Cymru has criticised nuclear apologists for calling renewable energy ‘unreliable’. Wylfa’s second reactor was shut down last July after weld defects were found in reactor one’s new boiler tube reinforcement brackets, which had been installed during a sixteen month shutdown three years ago. FoE Cymru also noted that cracks in nuclear power plants in Japan coupled with failures to report safety violations had resulted in the shut-down of 17 reactors there.  Some US plants had also had problems. Sizewell B has also been offline with  problems. Heysham 1 also.

Given that they were so large, and prone to shut downs, FoE claimed that, nuclear plants required more back up than wind plants, especially since a problem can affect a whole series of similar reactors..