Friday, 13 April 2012

PRISM for the UK's plutonium – Pros and Cons

By guest blogger, Matthew Gill

The UK has a lot of plutonium and recently decided to look at GE-Hitachi's PRISM reactor as an alternative disposal method to the more common MOX (mixed oxide) route. It's an important issue at the moment as the UK's large stockpile of civil plutonium goes against the ideology of a proliferation-resistant fuel cycle and is widely regarded as unacceptable.


The author would like people to know that this is in no way peer reviewed, information is from the media and wider public domain and, as such, should not be judged as scientific fact. This article is a reflection of personal opinions, not necessarily the author's, and does not reflect the views or opinions of any the author's commercial or academic associates.

You can read about the plan for PRISM (Power Reactor Innovative Small Module) here (BBC), here (WNN), and in more detail here. I'm going to give a quick overview of how we could get rid of our plutonium, and why PRISM is interesting.

There are 3 potential routes for plutonium disposal.
  • Put it into a fast reactor – The PRISM route, discussed here. 
  • Turn it into MOX and use it as fuel in our new build reactors – This is what France currently does, which is using plutonium as well as uranium in reactor fuel. However, there have been issues making MOX fuel in the UK.
  • Make a suitable waste form and bury it – There is no approved waste form as yet. 
There's also a 4th, temporary route, that's store the plutonium where it is and wait. Non of these methods are cheap or without problems.

There are differing opinions on what might be the best method. PRISM is a very unusual one but has had a lot of attention recently. Below are, in my opinion, the main pros and cons that make it an interesting idea:

  • Low risk to the tax payer – The way it's funded means that there is limited financial risk to the tax payer, it's all on GE-Hitachi and their partners. Which is very good considering how much the MOX plant at Sellafield cost the tax payer.
  • Opportunity to develop expertise in the next generation of nuclear power – If nuclear continues to be a major contributor to electricity generation, uranium will run out. Current reactors only use 0.7% of natural-uranium. A PRISM type reactor has the potential to use it all, sustaining resources for thousands of years. Therefore developing expertise in this area would prove valuable in the future. 
  • Technology has other uses - As mentioned above, PRISM-type reactors can sustainably use uranium resources. They also have the potential to “burn” long-lived radioactive material. Meaning waste takes less time to decay to a safe level, making long-term disposal less of a concern.

  • The unknown – A PRISM reactor has never been built. Similar reactors have, however they have had issues with reliability. (This is probably the most significant point, read more
  • Plutonium fuel needs to be metal, UK plutonium is currently an oxide – The conversion isn't hard but, in terms of proliferation resistance, having plutonium in metallic form isn't ideal. There's also considerably less experience with metallic fuel compared to oxides.
  • PRISM is sold as being cheaper and simpler than the MOX route, which may not be true? – The main reason for saying it's cheaper is that, in general, you have to pay utilities to burn MOX fuel and MOX plants have a habit of being over budget. MOX production and use may not be simple, but its had far more experience than the PRISM equivalent. There are likely to be issues with PRISM, as with many new technologies, that could make it more expensive. However, there is limited risk to taxpayers!

I haven't covered all the points of interest here, just a few important ones. Also I'm afraid I've been been a bit "wishy washy" with some parts to keep this short. But in summary, it's understandable why there are differing views and several concerns over the proposed PRISM plan. However, I'm firmly in favour of it. For plutonium disposal it's low risk to the tax payer and has the potential to greatly benefit the future of the UK's nuclear industry. In my opinion; this far outweighs any other aspects.


  1. 2 points-

    Any UK PRISM reactors will be first of a kind plants, I believe, which always increases programme risks. OK, GE Hitachi will (probably) carry the risks rather than the taxpayer, but you'd be very brave to assume there would be no problems with first of a kind nuclear plants

    What will we do with the spent fuel? The UK is moving to an open fuel cycle, and there is little understanding of the disposability of spent PRISM fuel. One reason NDA is so keen to finish the Magnox Operating Programme (MOP) is that there is no clear alternative to reprocessing for this metallic Magnox fuel. Fast reactors have generally been thought of as part of a closed cycle, and I am not sure they make sense in an open one.

    1. Fast reactors in an open fuel cycle is daft, but I see it as an overt segway into developing closed fuel cycle systems. In 60 years the technical expertise gained might be worth their weight in gold (or completely useless). Especially if, at a time a time when closed fuel cycle are economically worth while, we're likely to have no experience in the reprocessing field as everyone will be retired. It would be nice in 60+ years if the UK was good at something.

      If GEH think they can do it for a lower cost than the Areva-MOX route it seems like a much more fun idea.. If only to see what happens (probably not the best thing politically or financially to think, but I don't have to worry about such things).

    2. We need to think of the way UK nuclear has changed over the last decade or so. We have shifted from a closed to an open fuel cycle, and that is a Government decision. It's defensible given the fairly limited scale of proposed new build; the fact that THORP, as a middle aged plant which now has several potential single points of failure, can't support a closed fuel cycle for the next 50, 60, 70 years; and the uncertain viability of commercial recycle at the moment. Building a THORP successor now would probably be very difficult to justify and would take resource from other, higher priority areas. You also don't know if you want a new THORP- if we do build PRISM, the feedstock for any recycle process will be very different from thermal oxide fuel- so you'd struggle to specify and design the plant.

      What is important in the UK is keeping the option of recycle open, so that if we choose to follow that path in future, we can do so. The powers that be do seem to be aware of the need to do this. Also, if you think about current plans for new build spent fuel, the first stage is storage for perhaps 100 years so, if we do decide to recycle in 30 or 40 years time, the fuel will still be sitting in storage and available.

  2. Feel free to comment other Pros/Cons, or criticism of the current ones... Francis beat me to the punch.
    (Nothing too technical please.)

    1. I like the idea of Prism, but fast reactors and fuel cycle specifics are outside my current area of interest so I'm not sure how much I can add to the discussion.

      It's certainly attractive to think of GEH taking care of the UKs plutonium issue with minimal risk to the tax payer, and the experience the UK could gain in fast reactor technology could be invaluable at a time when (as Gillis rightly says) the people involved previously are coming up to retirement.

      On the other hand it seems to good to be true, so it probably is - there will certainly be problems as the first-of-a-kind plant (see the EPR development in Finland for example) which could scupper the whole project (although the MOX plant already attempted could hardly be described as a success...).

  3. "A PRISM reactor has never been built. Similar reactors have, however they have had issues with reliability."

    My understanding is that PRISM is basically a scaled-up EBR-2 which had a much better operating record than other fast reactors due to among other things the pool-type design, metal fuel and double piping for the sodium?

    1. The reliability issues are in reference to lots of examples in "Fast Breeder Reactor Programs: History and Status" on (link below). Very few fast reactors that are bigger than a few hundred MegaWatts Thermal (MWth) have fulfilled 50% of their capacity. BN-600 in Russia is the only exception, and that's due to it being able to run whilst half of it is being repaired from sodium fire damage (slight exaggeration, you can read about it here

      But still, the scaling up and changing designs is a biiiiig thing. EBR-II - 62 MWth, PRISM - 840MWth.. Scaling up something by this much is inherently difficult, and throws in a lot of engineering issues. For example, building the first EPR which is based on pretty standard technology has gone massively over budget in Finland. And the BN-800 fast reactor in Russia, a scaled up version of the BN-600 reactor has been under construction since 1987 (technically 1992 due to political issues). Proof of principle doesn't mean things easy to construct, but a company trying to sell their product wouldn't openly say that. Doesn't instil confidence.

    2. It will be no mean feat to build certainly, I just felt that the positive differences in design to a lot of the less than successful fast reactors should count for something. :) Is it 840MWth for each reactor or total for the two that's been proposed?

    3. The rating is 311MWe per reactor so I'd think that it was at least 840MWth per reactor, perhaps more.

  4. Also, a (somewhat tacky :) mini-documentary about the EBR-2:

  5. What about the safety of the S-PRISM reactor? Is it likely to be safer or less safe than current reactors?

    1. Some things are more of an issue, some things are less of an issue.. Sodium fires in heat exchangers are the main issue, but as proved with BN-600 they can be worked around.

      Loss of coolant isn't usually a problem with pool-type reactors. If they're small enough they can cool themselves without needing pumps as the sodium conducts heat very well and there's a large pool and surface area to dissipate the heat to. So if the coolant stops flowing they don't miss behave so much, where as with water reactors the water evaporates.

      Criticality issues geneerally depend on the core size. Big cores tend to have positive reactivity coefficients (bad - temperature goes up it wants to go bang), very small ones have negative reactivity coefficients (good - more leakage so the temperature goes up, it tries to turn off). PRISM is a weird middle ground and I haven't looked at it's safety in detail, but reactivity coefficeints are worked around and going critical hasn't caused issues with fast reactors (I think).

      There are lots of other small issues that are different to water reactors, such as fission gas escaping and creating a void in the sodium. But in general these sorts of things are less serious than the above. But weather they're more common or more serious than similar water reactor issues will depend.

      Sorry to be vague, I don't know much about the safety features of PRISM, or a huge amount on reactor safety in general. Also the behaviour of large sodium cooled reactors and small modular ones can be very different in accident conditions.

  6. Most of the doubts seem to be about safety of fast breeders/solid fuel/liquid metal.

    It's a pity we can't get more interest in thermal breeders/liquid fuel/molten salt, which have the same inherent safety but avoid the possibility of fuel meltdown issues and have the boon of a much smaller size, which is a big, big safety issue in selling it to the general public. See:

    1. (Personal opinion) Afraid I'm even more sceptical of Thorium based reactors than I am of Fast reactors.. I'd rather stick with technology that is proven on a more commercial scale and has less kinks to iron out.

  7. I gather that one can use Pu-239 for a start-up core for a LFTR. Or, U-235, or U-233 contaminated with highly radioactive U-23x (x=7? I haven't looked this up again) produced by someone else's LFTR.

    The two former choices would seem to be possible under a Safeguards regime only in a "weapons state". This also applies for making MOX. Pre-Fukishima Daichi I understood Japan was working toward making their own MOX.

    1. I think you're referring to U-232 and it's decay chain has strong gamma emitters.. Uranium is only of concern it it's high enrichment, which id unlikely to be used in a modern reactor.

      However, the same U-232 effect can be achieved by pre-irradiating plutonium or uranium fuel, or by spiking it with fission products.

      Sorry if this gets too technical:
      One down side of U-232 is that, due to it being highly radioactive, you need heavy shielding in all facilities and transport, and remote handling of it. This is both difficult and expensive. Most unsophisticated-nuclear non-weapons states (the ones where the threat of nuclear proliferation is of concern) do not have the infrastructure to cope with this.
      So any open fuel cycle is impossible as no U-233 exists, and would be VERY expensive if produced from another LFTR, and any closed fuel cycle is off limits due to ta state not having the technical ability.

      Also it's interesting, U-233 has a smaller critical mass than U-235 or Pu-239.. So the Significant quantity of material that is needed to be diverted to produce a bomb, and the time-scale of diversion is very small. Which, in general, causes more of a concern for sophisticated non-weapons states.

  8. It seems like a good idea for the UK to do this. (I'm an Australian, so it won't come out of my taxes.) I really don't think that wind or solar will provide the necessary reliable energy for you to survive your appalling winters. The depleted uranium you have available should allow you to supply your present electricity consumption for about 500 years using IFR's, though you'd need plutonium or highly enriched uranium to start them up. You could turn the domestic coal you waste generating electricity into oil, and avoid being gouged by the arabs. If you're really worried about global warming, you could use the nukes to produce the hydrogen and provide the external power needed for the oil synthesis. This would reduce the carbon footprint of the synthetic fuels by 50%.