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Small Modular Reactors - Bath 4 October 2016: Summary and Comments

The speaker, John Earp, began by saying that his talk was largely based on an IMechE policy statement on the subject published in 2014. However this was an area that was currently attracting the attention of government and industry in the UK so there had been some recent developments, not all of which had been released to the public.

 

We were told that currently there are 436 nuclear reactors being used for power generation in the world and 462 under construction. Typically these reactors have the capacity to generate around 1000 MWe each, the planned Hinckley Point C reactor, for instance being rated at 1600 MWe. The International Atomic Energy Authority (IAEA) defines a small reactor as having an output of less than 300 MWe, though some designs in this class are marginally larger.

 

Large reactors have the advantage of economy of scale, producing electricity at the lowest cost but small reactors were now being seen as a viable alternative in some scenarios. The small size meant that the reactors could designed to be modular and capable of being factory-built rather than constructed on-site. This made them potentially suitable for use in developing countries that lacked a skilled workforce. The smaller size made them more affordable, keeping the initial investment low, and, of course better suited to supplying smaller electric grid systems.

 

Many of the security and nuclear proliferation concerns that apply to large nuclear reactors should be diminished by the design of these small reactors as they use lower grade fuel, natural cooling and can be sited underground.

 

One major advantage of these small reactors is their ability to ‘flex’, i.e. to vary the output, unlike the larger designs that are intended to supply a steady base load. It is this feature that makes them attractive to authorities that had hitherto used large reactors, especially as they now had to include highly variable wind and solar sources in the generator mix. In answer to an audience question it was explained that cycling the power output of a large reactor caused the fuel rods to distort whereas the smaller designs were intrinsically stiffer.

 

The three developed technologies were briefly described; Light Water, High Temperature Gas and Liquid Metal & Gas Cooled reactors, spanning a range of power outputs from 10 – 311 MW. Special mention was made of the integrated nature of the NuScale LWR where the steam generator was incorporated in the assembly that would be delivered to site. A typical scheme would have a building large enough to house several reactor assemblies so that the station could be expanded in stages. The PRISM liquid sodium reactor was also of note as it has been considered for use in the UK at Sellafield to re-use waste fuel. Molten Salt reactors were also being developed.

 

The US has a created a lead in for US industry by opening up the DoE Savannah River site for developing Small Modular Reactors. It was suggested that Trawsfynydd might be a suitable site in the UK for something similar, being sufficiently remote to meet the UK regulator’s requirement for ‘first of type’ while providing development opportunities that are attractive to the Welsh Assembly.

 

The talk finished by outlining the requirements of the UK regulatory regime, noting in passing that the hiatus in building reactors in the UK meant that there would a shortage of qualified engineers to do the work. It was however noted that Rolls-Royce, with considerable experience of submarine reactors, was making moves to expand into this field.

 

Finally John Earp ably answered a stream of questions from the audience that showed that he had raised a lot of interest in the topic and brought out some important points such as the suitability of these reactors for Combined Heat and Power (CHP) schemes and that CHP could tip the economic balance in favour of these plants.

 

The nuclear business in the UK has been a boom-and-bust affair with the dawn of New Elizabethan Age promising publicly ‘power to cheap to measure’ while in reality perhaps being more directed at providing a nuclear warfare capability. Couple that with being a pioneer that took ‘the wrong road’ only to fall back on US technology and then to be faced with a complete lack of political commitment and it is a miracle that the UK has any nuclear capability at all.

 

Given the movement towards undependable ‘sustainable’ power sources and ‘smart’ grids, (working on the peak of efficiency, with no resilience), the careful positioning of small modular reactors with their ‘flexible’ outputs could be critical to ‘keeping the lights on’ for a developed grid such as the UK.

 

There might be an opportunity to provide these reactors as ‘aid in kind’ to developing countries to satisfy their legitimate desire for electrical power without them having to resort to burning fossil fuels.
  • James,


    ​I forwarded your write-up to the speaker John Earp, and he has returned the following comments:

    "Some of the words used below are a bit of a stretch on what I actually said and depending on where this is going might justify a correction, for example I did not say they used lower grade fuel I actually said that the PWR variants (of SMRs) used fuel of equivalent enrichment to the larger reactors whereas some of the proposed gas cooled designs use significantly higher enrichments fuel.



     



    Also the paragraph containing fuel rods “distorting” is a bit a  “stretch” on what I said I explained that one of the issues related to larger reactors being flexible is the potential for fuel damage such as fuel rod bowing.  I also said that as SMR’s generally have shorter fuel assemblies this problem is less of an issue.  I also said large reactors could flex but this often required steam dumping.   



     



    Also I did not say anything like the paragraph that begins “The Nuclear Business in the UK -------“  these are not my words at all!


    Regards

    ​John Earp"


    ​Thank you for your write-up, but since I was unable to attend the event, I am in no position to judge the veracity of either comment.


    Regards

    Stephen Pearson


  • Stephen,


    As you are aware, but John may not,
    my comments are posted as a discussion topic. My aim is partly to
    capture the main aspects of the talks that I have attended and
    partly to initiate discussion.



    While I try my best, what I write is
    just my recollection and interpretation, not a verbatim report.
    Indeed that is the point of the discussion part of the exercise,
    did I understand the speaker correctly or perhaps read too much or
    too little into any given statement? These are general comments
    that apply to all of my 'pieces.



    Turning to John's specific comments
    now. I thought that one of the selling points for SMRs was that the
    fuel wasn't as enriched and that that was one of the reasons that
    concerns over nuclear proliferation/weapon making was reduced.
    Again the ability to flex appeared to me to be a good reason for
    using SMRs; throwing away heat energy, to my mind, is hardly
    equivalent to being able to regulate output by controlling
    'nuclear' input. Doesn't a smaller geometry result in a stiffer
    structure, less likely to distort? I worry about being too verbose
    so will truncate an argument if I can.



    My usual title for these pieces is
    "Summary and Comments". The words that John doesn't recognise are
    "Comments", my take on the subject, my bit of provocation
    perhaps?



    I would like to thank John for his
    most interesting talk and for taking time out to comment on my
    summary. Indeed by doing so he has helped me achieve my second aim,
    that of triggering and enabling the discussion that doesn't
    normally take place as attendees rapidly disperse and head
    home. 



    Jim Shaw
  • I was not at John Earp' presentation but I would like to correct some inaccuracies in the comments on it. It is true that most existing large reactors do not 'flex' but the common belief that the could not, is wrong. Reactors in France, Germany and Belgium do flex, doing load following and/or automatic frequency control as required. There are engineering issues but not insurmountable. An IAEA document to be published provides plenty of detail. The proposed SMRs based on submarine reactors ought to have even better capability to flex.

    Dave Ward