The UK’s Small Modular Reactor Competition

Guest Post by Andy Dawson who is an energy sector systems consultant and former nuclear engineer.

The UK government has launched a competition to select a design of a small modular reactor (SMR) for future deployment in the UK. The idea behind SMRs is that they can be factory built and stamped out like aircraft and transported to location on the back of a truck. With thirty-three companies / designs on the shortlist, this looks like the process could take a while to complete.

In this post, nuclear engineer Andy Dawson provides an overview of SMR technology together with descriptions of the leading contenders.

A few weeks ago, Euan was kind enough to publish a piece I wrote on the possibility of an all-nuclear UK generation system, supported by pumped storage. In the responses to that, I was asked several times to comment on the virtues (or otherwise) of various reactors types either currently intended for construction in the UK, or other possibilities. Subsequent to that, it’s been announced that there have been 38, now cut down to a “shortlist” of 33 (we’ll leave aside for the moment the thought that only a Civil Servant could consider 33 a short list…)[1].

On the basis of which, it occurred to me that a short exercise to run through the “runners and riders” likely to be in the competition – I should stress that since the listing is still “commercial in confidence”, I cannot state with any certainty that any of the firms and designs I’ll go through are definitely “in play” – these are simply the expectations of what I’d like to think is a reasonably well-informed observer.

It’s worth spending a moment going through the background to the process, albeit I don’t intend here to debate the positives and negatives for the case for SMRs; I will say, however, that I have some doubts that they’ll necessarily be quite so transformational as some proponents believe; my views are close to those of Admiral Rickover, the creator of the US “nuclear navy”:

“An academic reactor or reactor plant almost always has the following basic characteristics: (1) It is simple. (2) It is small. (3) It is cheap. (4) It is light. (5) It can be built very quickly. (6) It is very flexible in purpose. (7) Very little development will be required. It will use off-the-shelf components. (8) The reactor is in the study phase. It is not being built now.

On the other hand a practical reactor can be distinguished by the following characteristics: (1) It is being built now. (2) It is behind schedule. (3) It requires an immense amount of development on apparently trivial items. (4) It is very expensive. (5) It takes a long time to build because of its engineering development problems. (6) It is large. (7) It is heavy. (8) It is complicated…”.

Although the process was announced formally by the Chancellor in last November’s Autumn Statement, it has in reality been running for some time – the National Nuclear Laboratory was instructed in 2014 to prepare a feasibility study on UK engagement in an SMR market, and to review then available designs[2], which concluded that such was viable, and that there were a number of viable designs – that viability being based on a combination of:

  • Technical maturity and viability
  • Maturity of Safety Case and certification
  • Key strengths and areas for development
  • Programmes to address development needs
  • Available resources – people, capability, facilities and funding
  • Economic viability.

I’ve seen nothing in the process subsequently to make me think that the competition assessment will be conducted on any other basis (with the possible exception of the addition of a large UK role in the supply chain being mandated). The questionnaire submitted to test the firms making Expressions of Interest is consistent with that view, placing heavy stress on the readiness to enter Generic Design Assessment, stability and technical resourcing of the consortium/company, and willingness to make an early commitment (for example, pre-siting decisions). To be clear about one thing – the intent is to select a SINGLE design.[3][4]

The broad classes of candidate designs:

Small Modular Reactors (SMRs), like larger reactors, fall into a number of major classes. A short run through these is in order, before moving onto the specifics:

Light Water Reactors (LWRs):

LWRs, for good or ill, form the background of the global fleet – and hence represent the class of which there’s by far most design and operational experience. The common characteristics are:

  • Light water acting as coolant and moderator (all LWRs use the thermal part of the neutron spectrum)
  • Steam raising – either directly as in Boiling Water Reactors (BWR), or via an indirect circuit as in Pressurised Water Reactors (PWR)
  • Using low enrichment fuel (~5%) clad with zirconium or other low-absorption alloys
  • Operate at significant pressure – c. 80 bar in the case of BWRs, c. 150 bar for PWRs.
  • Low to moderate thermal efficiency, due to temperature limits imposed by the use of water as coolant.

LWRs require a “containment” capable of bearing significant overpressure in the case of a failure in the “primary circuit” (those parts of the reactor containing pressurised coolant); containment designs vary from large volume/moderate pressure typically used for PWRs( ~2 bar), to close-fitting, low volume designs for BWRs (~5 bar), relying on steam-suppression systems.

PWR containment volume is largely determined by the need to accommodate several steam generators, which are considerably larger than the reactor vessel itself, plus other systems like coolant pumps, the pressuriser and various safety related systems. BWRs do not require steam generators, operating “direct cycle”. Ancillary systems are also somewhat simpler, and things like emergency make-up tanks are usually installed externally to the containment.

LWRs typically operate an 18-month to 2 year refuelling cycle, requiring shutdown and depressurisation, although some military versions run as “Fuelled for life” using high enrichment fuel.

Liquid Metal-cooled Reactors (LMRs)

Liquid Metal cooling is almost invariably associated with “fast” reactors – as such they need no moderator, and hence can be considerably more compact that thermal designs. The use of liquid metals brings its own challenges, however – the two main candidates are Sodium and Lead. Both have many remarkably benign characteristics as a coolant – extremely good heat transport characteristics, and very high boiling points (and in the case of lead, heat capacity). The challenge with them has historically been chemical – Sodium reacts, of course, with water, and the behaviour of any oxygen in lead coolant is surprisingly complex and corrosive of many engineering materials. Both allow reactors to operate at high (600C+) temperatures, hence with high thermal efficiency; Lead in particular offers opportunities for extremely high temperature operation (800C+), potentially usable for process heat applications.

Liquid metal cooling obviates the need for pressurisation, albeit it remains necessary to isolate the coolant from atmospheric contact (achieved by blanketing with inert gas); Lead coolant, through its sheer mass, can pose challenges to design against seismic events. In recent years, LMRs have been very much a Russian specialism, having brought a new unit into operation (“BN800”) as recently as last year[5].   Western experience has been chequered; some systems worked well (most notably “EBR II” in the US) and others less well (PFR at Dounreay, Superphenix at Creys-Malville, France).

High Temperature Reactors (HTRs)

HTRs are usually – but not exclusively – thermal in spectrum. They’re designed to operate at 800C+, using helium coolant. In many ways they can be regarded as a descendant of the Magnox-AGR design concepts, using graphite moderator and gas coolant. However, the fuel concept is very different – it’s based on a concept called “TRISO” (TRIstructural iSOtropic), which a ceramic form – typically pellets of Uranium Carbide, embedded in a matrix of pyrolitic Carbon, and the whole element enrobed in a layer of Silicon Carbide. It’s EXTREMELY tough and tolerant of very high temperatures. It basically integrates fuel and moderator into either a single prismatic block, or into “pebbles”.

HTRs do operate at some pressure, albeit not overly high – 40bar would be typical. Although a number of prototypes were built in the 1960s and 1970s, the field have been pretty much moribund

in recent years. However, it’s been reopened by China’s construction of a pair of 250MW modular prototypes at Shiadowan[6]

Probably the biggest downside to HTRs (beyond immaturity) is that the fuel is just about completely un-reprocessable. That can be argued as a virtue, for proliferation reasons, but it may hurt plant economics in the long run.

Molten Salt Reactors (MSRs)

I enter this topic with trepidation… within the pro-nuclear community, there’s no topic so polarising between enthusiasts and doubters. I’ll declare my hand up-front – I suspect that the concept may have virtues (but perhaps no more than LMRs), and I can see significant issues ahead, not least because most designs are “academic” in the Rickover sense. That confusion is not helped by the sheer proliferation of MSR concepts – ranging from this with discrete fuel and molten salt coolant (which, contrary to popular belief, is the nature of the ongoing Chinese work), to those operating with fuel dissolved in coolant, to breeder concepts based on either Uranium or Thorium. On that latter note, let’s be clear – there are no Thorium fuelled designs. The Thorium is “bred” into U233 in order to be fissionable.

Whatever your views on MSRs, one thing should be common; the designs that are out there at the moment are immature at best (most are best described as conceptual), and many of the companies proposing them are under-resourced and lack nuclear sector experience. On that ground alone, I anticipate that most will struggle with processes like GDA and in particular Probabilistic Safety Analysis.

Assuming a design can be brought to maturity, MSR can have design advantages – lack of pressurisation, high temperatures, etc. On the downside, there are needs to demonstrate the durability of structural materials, radiolytic problems with moderators (or the need to validate assumptions about core-replacement options), handling of fission products that are outgassed or extracted from fuel salt, and so on.

“Nuclear Batteries”

In more than one sense, “Nuclear Batteries” do not represent a distinctive technology – in fact, the various designs that have been announced cover a range of technologies, fast and thermal, various coolants, unusual control mechanisms and so on. However, I think it’s worth separating them out – not least because they have potential applications beyond power generation. Some designs have potential to form the basis for propulsion power units for shipping, for example.

They’re typically small – the largest design that I think legitimately falls into the category is would have about a 10MWe capacity; They’re designed to be “sealed for life”, installed into remote sites or as local power sources and swapped out when the fuel is exhausted. They’re designed for zero operator intervention in normal operation, and extremely high levels of inherent safety.

Runners and Riders

Having run over the basics of the various technologies, let’s now start to look at who’s definitely in the competition, or is suspected to be there. One note I should add is that if 30+ designs remain in, there are obviously some very under-developed designs in there, or vendors who’ve not broken cover yet.

The leading pack

Both from looking at the NNL report, and seeing who’s being mentioned in the press from leaks, we can pick out a small group of designs that are either recognised as “in”, or are so unlikely not to be there that I’m willing to risk embarrassment by publically assuming that they are:

The Westinghouse SMR –

Probably one of the most mature designs in the market, this is what I suspect to be the most probable winner. The design makes heavy use of technology derived from the AP1000 full sized PWR, which is currently nearing the end of its GDA process and is planned for the Moorside site. At 225MWe, it’s one of the larger designs (the upper limit is approx. 300MWe), which is a good match for “off the shelf” steam turbines used in the back-end of CCGT units.

Westinghouse (owned by Toshiba), have moved early to establish a strong potential UK supply chain – they’ve aligned with the Nuclear Advanced Manufacturing Research Centre (NAMRC) of Sheffield University, and through that are already working in collaboration with firms like Sheffield Forgemasters, Weirs and so on. The design utilises the same fuel as the AP1000, which will be manufactured at Springfields, near Preston.

It’s what’s called an “Integral” PWR – that is, all the major components are incorporated into a single vessel, factory manufactured and assembled on site. In broad terms, the upper half of the vessel (which bolts off for refuelling) contains pressuriser and heat exchanger, the lower half the core, pumps and control rods and actuators (it uses the same submerged actuation system as the AP1000, which has great virtues in terms of things like vessel integrity).

It’s a relatively conventional design (albeit integral reactors are a new concept), heavily based on proven or near-proven technologies, and of all the probable vendors, Westinghouse has most recent experience of the GDA process.  Physically, the Reactor Vessel is approximately 25 metres tall by 3.5 in diameter. The Containment is close fitting, but still about 27 metres tall by almost 10m in diameter – which makes me think it’ll have to be constructed on-site from factory-supplied modules. It’s designed to be installed below-ground level, and with the containment submerged in a water tank, acting as a heat sink in the case of accident.

If we’ll allow divergence into personal opinion, rather than fact, the rating of this is close to a “sweet spot” – not so large that it represents a massive addition to a grid, with the associated cost and risk, but not so small that it would struggle with scale economies, numbers in deployment and so on.


NuScale is another integral PWR, but of notably smaller capacity – 50MWe/unit. Conceptually, that aside, there’s little major difference from the Westinghouse unit. Surprisingly, the Reactor Vessel is little difference in size from Westinghouse’s – quoted as 20 metres tall and 2.75 metres in diameter.

The containment is 23.4 metres tall and 4.6 in diameter. I understand the plan is to ship a combined Reactor/Containment unit as a single assembly.

Perhaps the main delta between the two designs is the NuScale’s use of an entirely natural circulation model – the design has no coolant pumps. The Westinghouse unit uses such passive flow in an accident situation, but is actively pumped in normal operation. Again, the containment is submerged and below ground. The intent is for units to be deployed in cluster of up to about a dozen, feeding one or two turbines. Unusually, for refuelling an entire unit would be lifted out of place and craned to a separate refuelling pond, which the remainder of the plant continued operation.

NuScale looks likely to build a demonstration plant at the US DoE’s Ohio site, and has won Federal support funds.

Again, at the level of personal opinion, I have some issues – 50MWe is probably just too small, and it’s hard to see why a 50MWe NuScale module would be built at ¼- 1/5th the price of a Westinghouse module. It’s inherent safety is good – but that applies to all the “leading pack” designs I’ll be discussing.


What Rolls are proposing is, at the moment, something of a mystery. All that’s emerged is the capacity – 220MWe; and approximate dimensions. The “Economist” quoted 16 metres tall and 4 in diameter. If those are correct this is almost certainly NOT an integral design – it’s simply too short to accommodate a heat exchanger/pressuriser above the core.

That would be consistent with Rolls’ submarine experience (integral designs are hard to fit in the space constraints of a submarine).

Non-integral designs will struggle somewhat in that they cannot be fully factory assembled – the installation of separate steam generators entails more site-works, and mitigates against a compact containment; however, I gather that Rolls do have some experience with passive designs (PWR3, destined for the Trident replacement boats is reputedly completely natural-circulation based).

So, given the uncertainty, why have I rated Rolls as a leading contender? Simple – it’s almost certainly the only credible bid led by a UK company.

Dark Horses…

There are several designs which look likely to make it into the latter stages of the contest, but are so far “below the radar”.


Few observers of the nuclear scene have failed to be impressed by Korea’s delivery of the Barakh project in the UAE on time and at a VERY competitive cost (under half the cost/MW of Hinkley C). Similarly, anyone who’s had cause to look at the APR-1400 PWR used in that project will have concluded that it’s anything other than an extremely competent design.

KAERI stands for the ”Korea Atomic Energy Research Institute”. In addition to supporting their industry on LWR development, and being probably the world leaders in electrolytic/pyrolitic reprocessing, they’re in the midst of designing their own mid-sized modular fast reactor.

Somehow, they’ve found the time, while doing all that, to produce the first SMR design that’s passed a national regulatory accreditation (their own, in 2012), at a spend well north of $300m. It’s a 100MWe design, again integral, and fully passive post-shutdown (for 20 days). There’s an AP1000 style vessel submergence system for passive heat removal.

The downside is a conventional, large volume containment, which is above-ground.

As you’d expect from having passed accreditation, this is probably the most thoroughly worked up design likely to be in play. Having said that, KAERI in particular and the Korean sector in general has never taken a design through a Western accreditation process, so it would probably need a local partner. It has, however, been confirmed a that a Korean design has been entered, and I’d be staggered if it were anything else (having said which, there’s a rather clever Nuclear Battery design – discussed in that section).

Mitsubishi IMR

I’ll start by declaring I’ve no confirmation at all that this design has been put forward – notwithstanding that, this is a design with major technical virtues, and has the backing of an experienced and competent vendor. Mitsubishi HAS taken a reactor design through US certification, which is similarly onerous to GDA, but it’s unclear how far the design has advanced into detailed design.

Once more, it’s an integral design. Where it’s unusual is that it’s a BWR-PWR hybrid – that is, it permits boiling in the core and what’s described as a “bubbly” flow upward to the steam generator. That generator is somewhat unusually sited, in a flared section of the upper Pressure vessel. The steam-water column rises, and descends through the steam generator before returning to the core. As such, it needs no pumping in either normal operation or post-accident. It uses in-vessel control rod drives, thus has minimal vessel penetrations, and is designed for 100MWe in normal operation.

It’s claimed that a conventional Emergency Core cooling system can be done away with, as a result of the vessel design, the natural circulation cooling and external vessel cooling (presumably flooding) – although I think there’d be some resistance to that concept from UK regulators.


Inevitably, it seems there’s a Chinese design in play (see the link provided under the KAERI SMART section above).

CPR100 is a scaled down equivalent to the Hualong design that’s undergoing preliminary processes for the UK GDA at the moment. It’s undergoing a preliminary IAEA review which should complete sometime soon:

I believe, although I can’t confirm that it’s the same design that’s mooted for the “floating power plants” intended for deployment in the South China Sea; capacity is about 100MWe. Overall, there seems little to separate it from other designs (Integral, semi-passive, above-ground large volume containment), except for one thing.

CNNC has already committed to building a demonstration plant.

Where I suspect this will suffer is finding space for a significant UK share in the supply chain work (perhaps an RR control and instrumentation system?)


This is the design of which China is currently building prototypes – a pair of 250MWe modules of a pebble-bed High Temperature Reactor. It’s design that has much to commend it (although it should be noted they’re intended as demonstrators for a 600MWe commercial design, rather than being the end destination in themselves). The design has received quite a lot of interest worldwide – for example, collaboration agreements between China and Saudi Arabia, presumably as a potential process heat source.

It’s another design that, no matter how promising, will probably not make the final cut on grounds of lack of ability to drive through a GDA process, and lack of UK involvement in a supply chain. I’d also have some questions about the modularity of the design; our past experience with gas-cooled designs hasn’t suggested that it’s a technology suited to factory build.

GE-Hitachi PRISM

This is truly the “left field” offer, but offers the chance of a leap ahead in terms of technology.

PRISM is a derivative of the US “Integrated Fast Reactor” design, closely based on the highly successful EBR-II; it’s a metal-fuelled fast reactor, utilizing a “pool” design with a secondary sodium circuit to steam generators. In capacity terms, it’s at the upper end of SMR designs – 300MWe, intended to be deployed in pairs driving a single shared 600WMW turbine.

The design extremely safe – it has intrinsic self-stabilising features demonstrated on EBR-II; there, it was demonstrated that control rods could be withdrawn, and coolant pumps turned off witihout damage. The reactor shuts down when overheated, as a result of a phenomenon called “Doppler broadening”. Readers can feel free to think the operators had the proverbial “balls of steel”, and it’d not be for me to contradict them…

The design is already in one competition for UK build – it’s been proposed as the solution to the “plutonium burner” requirement for disposing of the stocks held at Sellafield; to many accounts, the late David McKay was a great proponent within DECC, and GE-H have offered to fully fund the build on the basis is a “per kg” disposal charge for the plutonium burned.

We can but hope…albeit non-UK sales of something like the Westinghouse unit are more probable.

Also Rans

There are a number of other designs mooted – however, I suspect unlikely to progress, mostly because they offer little differentiation, and seem to be further back in the design process, or because of political/economic considerations.

Terrestrial IMSR / MSRs

Probably the furthest advanced of any of the MSR designs, Canada’s Terrestrial Energy have this design currently in process with their own national regulatory bodies, with the construction of a large-scale electrically heated mock up in mind. In reality, it’s probable that the design is 5-10 years away from being ready for submission to an accreditation process.

Other MSRs are even further behind, and in most cases the organisations proposing them are “mom and pop” shops with insufficient capacity to convince DECC that they have a high probability of progressing through GDA.

Bechtel/BWXT mPower

This is yet another integral PWR, of 180MWe capacity. It’s had a somewhat troubled gestation – BWXT is the nuclear operating unit of the former Babcock and Wilcox, post their Chapter 11 restructuring. BWXT has cut back work on the design to just $10m/year, until Bechtel partnered with them.

The most notable difference to the Westinghouse and NuScale designs is that it doesn’t use steel containment – it uses a more conventional pre-stressed/reinforced concrete design, of large volume relative to the Reactor vessel size.

It’s dimensionally similar to the Westinghouse and NuScale designs; the core Reactor module would be rail-shippable, but would require in-situ build of the containment.

Unless Bechtel were to be able to pull a rabbit out of the hat re a UK supply chain, it’s hard to see why this would succeed over-and above the front-runners. Bechtel is, however, part of the consortium named to build Wylfa Newydd, so it’s fair to assume it has some exposure to UK GDA process.

Russian Designs

There are a considerable number of Russian SMR designs, mostly but not exclusively LWRs. It’s most unlikely, given current relations that any of these will proceed to the later stages of the competition.

Nuclear Batteries

Only one Nuclear Battery design seems to have advanced beyond the conceptual design stage – the Toshiba “4S”. That is a radical design, a sealed fast reactor with sodium coolant, of about 10MWe output. As with other designs, that small scale almost certainly weighs against it.

There are obviously acceptance issues with the idea of a “neighbourhood nuclear reactor”, worthy as some designs are – given this, and the fact that many hundreds of such units would have to be constructed to make a significant dent in the UK’s electricity supply gap, it seems unlikely that there’s an attractive international market or a strong domestic case. As things stand, I expect these designs to be more acceptable in future attempts to decarbonise large-scale shipping.


At least one DECC advisor has already commented that this is not going to be a quick process – and in that context, the failure to apply a more aggressive cull at this early stage is probably a missed opportunity. DECC will also have to decide whether it’s going to continue with its current stance that the objective is a near term deployment (for example, GDA entry in 2018/19), and whether this is in parallel with, independent of, or one and the same as the Sellafield Plutonium Burner proposal. Alternatively, if this is to be an exercise of support for “blue-sky” technologies, then we won’t see a UK supply chain for a couple of decades.

Having said that, the leading players look extremely credible, and near “shovel ready”. Were DECC to get things right – a first, if it happened – I think a construction start on a first unit could be as soon as 2020-21, assuming that the Westinghouse unit is chosen, and GDA can be accelerated on the grounds of commonalities with AP1000.








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43 Responses to The UK’s Small Modular Reactor Competition

  1. Alex Cannara says:

    Very good summary. But, most designs for prompt introduction are solid-fuelled, water reactors, with lowish efficiency (~33%) and no better waste than present LWRs running steam cycles

    And, because they are low in power output, many more must be deployed to sever] actual grid needs. This means that each SMR’s safety profile (failure probability) must be higher than that for a standard LWR — 1GW/100MW safer, for example.

    Then, there’;s the used-fuel issue, which is why MSR, IFR, MSFR, etc. are both more thermally efficient and lower in waste production.

    We’ve had small reactors for a long time, but changes in fueling and operating temperature are important goals to design for, not just smaller, present, solid-fuel, water working-fluid reactors.

    The Chinese are busy doing what needs doing. So should we all.

    • Andy Dawson says:

      You seem to have missed the discussion on MSR and PRISM in the piece…

      And re China and Molten Salt:

      “ranging from this with discrete fuel and molten salt coolant (which, contrary to popular belief, is the nature of the ongoing Chinese work), ”

      The Chinese experimental rig isn’t an MSR in the context that most use the term; it’s a TRISO fuelled (it’ll actually the same fuel design as HTR PM) with a molten salt coolant. That’s got even less reprocessing potential than metal-clad fuel!

    • Alex says:

      The SMRs are safer. Being smaller, they are much easier to cool passively (assuming good design), so the consequences of a failure are much smaller.

      In terms of reliability, 12 250MW units will give better reliability than two 1.5GW units. Even things like refuelling mean you still have 2,750MW of power.

      It’s what SpaceX call “engine out” capability.

  2. Serphin says:

    Hi, wondered if you saw this ( Encouraging that some people are still working on solutions to the hard problems, even though society has thrown up its arms and declared nuclear ‘impossible’…

    • climanrecon says:

      Only a vocal minority has declared nuclear “impossible”, somewhat hard to justify when it was certainly possible 65 years ago, and there are many impossible electrons playing a vital role in many grids.

  3. Alex says:

    Good article Andy. I must say your scepticism of MSRs shows somewhat. I should probably add a bit on this subject. Feel free to disagree 🙂

    MSRs suffer a little bit from the fact that the Gen IV forum ( is focusing on the long term holy grail of MSRs, namely a Fast Spectrum, Thorium breeder reactor with a long life span and inline processing of hot, radioactive fuel. Such a design is decades away, and that sets much of the perception within the nuclear industry.

    Also, as some semi-knowledgeable keep pointing out, the material challenges – maintaining barriers under neutron bombardment in a corrosive salt, at 700C, over a time frame of decades, is not easy.

    Then there is the problem of graphite swelling under neutron bombardment. This can be solved by having a low density core – but a big core costs more money.

    The new (commercially focused) MSR designs mostly side step these problems by having a replaceable core, and focusing on burning traditional U235, rather than breeding from Thorium. The core is designed to last and be replaced every 4 to 10 years. The rest of the plant can continue indefinitely. The core contains the primary loop, the graphite moderator, and the primary heat exchanger. Fission products are for the most part locked up within the salt, though noble gases are removed. (Xenon is by far the most important fission product to remove for a variety of operational and safety reasons). Most of the designs are passively cooled in event of loss of coolant, and claim to be “walk way safe” (a term the regulators don’t really like).

    The key to this is to have a small, simple core which can be factory built and transported to the site. Terrestrial Energy’s cores can be transported by road. ThorCon on the other hand decided to focus on ship / barge based transport – and have therefore gone for a wider core. Molten Salts can give a very high power core density – making the core small and simple, and hence – in theory, and with a nod to Admiral Rickover – cheap.

    EPD did a study on the feasibility of building a MSR in the UK. This favoured the UK’s Moltex design, even though as pointed out the design is still very conceptual. Terrestrial Energy are the strongest team, with experienced nuclear engineers, and are building a non-nuclear prototype in Canada and have engaged research in the UK. It will be interesting to see how many MSR designs are on the DECC long-list.

    What is unclear is how MSRs will be regulated. There are a host of unanswered questions. For example, regulators approve designs for 40 to 60 years – fixed. A MSR power station will last forever, with components being swapped out: say 7 years for the core, 30 years for the steam turbines ….etc. How will this be approved?

    For a technical description, the Thorcon site ( has the most detailed information.

    • Andy Dawson says:


      I thought I’d been scrupulously even-handed!

      And yes, I’m aware of the “removable core” concepts- but those beg their own questions. How do you handle, store and treat at least tens of tonnes of graphite that’s been immersed in fission product laden salt for several years? What are the worker exposure issues in emplacing the new core?

      There’s also, on your own reckoning, the issue of the fuel salt. You can’t permit an indefinite build up of fission product in it, not least because some are strong neutron absorbers – so, you’ve either a treatment requirement or a need to store “used” salt.

      That’s a huge increase in the waste handling and containment issue, or a major increase in plant complexity.

      It’s issues like this that I refer to when I describe the designs as immature- this can’t be “done on the fly” as Thorcon seen minded to do (and it’s why their plan to build prototypes then validate in a country with no nuclear regulatory experience at all scars the c**p out of me).

      • Alex says:

        I guess you’ve read the answers, but for others:

        “How do you handle, store and treat at least tens of tonnes of graphite that’s been immersed in fission product laden salt for several years? What are the worker exposure issues in emplacing the new core?”

        Mainly by waiting. The ThorCon core is drained of salt, then removed. Then stored. No one opens it for at least seven years of storage, after which it’s not hot any more.

        Worker safety is ensured by not dropping sealed units. The couplings are primarily dealing with secondary salt.

        “There’s also, on your own reckoning, the issue of the fuel salt. You can’t permit an indefinite build up of fission product in it, not least because some are strong neutron absorbers – so, you’ve either a treatment requirement or a need to store “used” salt”

        Looking at this, you get 90% of the benefit of FP removal with 10% of the effort, by just taking out noble gases and plating out noble metals. ThorCon calculate their salt will last 8 years – twice as long as their graphite.

        • Andy Dawson says:

          You’ll have to wait much more than seven years, Alex- even just thinking of 14C activation, you’re dealing with an isotope with a ten year half life (so a century for that to do the the orders of magnitude decay). Most problematic fission products have half lives in the 2-30 year range; seven years won’t make a serious debt in the activity levels.

          And 90% simply isn’t enough (recall, you’ve also got to isolate, protect and cool the martial you remove).

          It’s Thorcon’s apparent unawareness of, or casual dismal of issues like these that concern me. As things stand, I doubt they and others would even allowed to enter a GDA process, and are at face value not capable of product a rigorous PSA

          • Alex says:

            The idea is to make it cool enough to open. The salt will be flushed out and then you have 10s of tons of radioactive carbon which can be buried – or if automated processes become available the 2030s, reground down to make new cores.

            The only companies currently capable of producing a PSA are the ones doing it now. That’s an exercise that needs a ramp up of skills – so please don’t throw away your notes.

  4. Alex says:

    One point to mention on “competitions”. Since DARPA started doing these, and since the X prize, Governments have realised that the investment generated far exceeds the amounts of the “prize” (which will be substantially less than the £250 million).

    DECC’s aim will be to have a dozen or so companies investing in technology development in the UK, spending billions, so that over the next 10 years, half a dozen of these designs can go through GDA, creating an industry that can solve the energy trilemma, not just for the UK, but for Europe.

    The GDA process will also see some slight improvements with an aim of approving one reactor design per year (there at about half that now). So we could well see (illustratively), starting GDA:
    2017 Hualong
    2019 Westinghouse APR
    2020 PRISM
    2021 NuScale
    2022 Terrestial

    The real prize is not the competition money, but the GDA ticket (of which there are many).

  5. Jim Brough says:

    Nuclear submarines have been powered by small modular reactors for half a century and its time to use that technology and advances to make its benefits available to the public for the production of electricity.

    • Willem Post says:


      I agree.

      Russia and the US have about 50 years of successful experience with reactors on navy surface ships, submarines and icebreakers.

      Large aircraft carriers have multiple units.

      The development of alternative reactors, a multi-year and costly endeavor, is best done under government sponsership.

  6. James Arathoon says:

    The impression I got immediately from the phase 1 guidance doc was that the aim of the competition was to get a new SMR design entered into regulatory Generic Design Assessment as quickly and directly as possible. This underlying (political?) requirement seems to rule out everything apart from a direct SMR port from an existing LWR design portfolio. I am not even sure this stipulation is appropriate for a Light Water Reactor port design, which will surely need at least one iteration before commercialisation and production line tooling investment decisions can be finalised.

    My personal assessment is that High Temperature Molten Salt Fast Reactors will ultimately be a better fit for our future energy needs here in the UK (assuming ever diminishing use of fossil fuels to 2050 and little or no winter solar power available to replace fossil fuels). However moving in this direction will probably need 4 design iterations before full commercialisation and production line tooling costs can be justified.
    This would end up being a development programme costing £10’s of billions gross, (ignoring any offset income from electricity generation coming from the prototype reactors built). Full Generic Design Assessment will not be appropriate until this development process comes close to the commercial roll out phase, which in the case of Molten Salt Reactor designs will not be achieved for at least another 20 years, even if we start the development programme today.

    Given this I will be very surprised if any Molten Salt Reactor developers continue much further in this competition. This does not of course imply that the reactor designs that do pass to later phases will be a good match for the UK’s likely future energy needs (including the needs of industry for high temperature process heat), as well as the wider market needs of other high latitude countries e.g. Canada, Russia and the Baltic states. because such an assessment is not currently part of the competition process.

    I would have designed this SMR competition differently. In phase one I would have talked mainly to intensive energy users and other business users; that is I would have started with demand side assessment and scenario model building to set the rules for the competition. These scenario model assessments would cover how the UK’s winter peak energy needs and the needs of industry are to met cost effectively in a future world with much less use of fossil fuels. Gas CHP will likely be one of the most cost effective technology choices for meeting winter peak energy needs in the intervening years and as part of the competition I would require that thought be given to how future nuclear power can be rolled out to either replace gas CHP and gas peaking stations or to make the synthetic methane fuel using nuclear power for gas peaking generation to continue.

    I would set the maximum time frame for commercialization at 25 years.

    • Alex says:

      “My personal assessment is that High Temperature Molten Salt Fast Reactors will ultimately be a better fit for our future energy needs here in the UK”

      High temperature reactors – able to produce hydrogen – would certainly be very, very advantageous in the long term – ie for deployment in 2050.

      However, the way to get there is to deploy MSRs as soon as, and as fast as possible. These MSRs will produce heat at 700C. It is then a matter of design iteration and some materials research to raise that to the 850C required for hydrogen production.

      • Rob says:

        Andy why does the Generic Design assessment take so long at least 5 years or longer . what can they be possible doing.

        Why is it assumed that SMR will be able to get through GDA faster

        • Alex says:

          The GDA was targeted for 3 years but is taking longer. It’s a 4 stage process and everything needs to be evaluated.

          Re-engineering the process woould be good. The main gain though would be in doing it parallel with strike price negotiations and site license, so they can pour concrete as soon as GDA is done.

          Some MSR providers think that they should go through faster because:
          1. Their designs are simpler
          2. They claim they are inherently safe. So why go through a probabilistic analysis to evaluate core damage frequency, when the consequences of core damage are purely economic, and not a safety issue?

          Of course, the ONR is highly conservative so those claims need to be proven.They are also not familiar with non PWR designs,

        • Andy Dawson says:

          It’s about four (the AP1000 process was put on ice for a couple of years), so I don’t think it’s taken longer than planned – four years was always the intent to the best of my knowledge.

          I don’t assume the GDA would be faster in any case but the Westinghouse design, and in that I’ve it’s purely a matter of design commonality with the AP1000.

  7. ristvan says:

    I understand the purpose of the competition, but question its utility. The notion that SMR benefits from being ‘factory built’ presumes sufficiently lower cost to offset the loss of obvious scale economies in large conventional ‘bespoke’ units. But ‘factory’ costs are only sufficiently low when unit volumes are sufficiently high to amortize the ‘factory’ investment in tooling and such. This is evident from military procurements. Low volume ‘factory built’ B1 and B2 bombers were extremely expensive. The point of the F35a/b/c versions is to get unit volume of several thousand produced over a decade, to lower per plane cost significantly.
    It is hard to see where annual SMR unit volumes would ever be high enough to take advantage of ‘factory’ economics. Its the B1 bomber problem writ large. CCGT may be low annual volume, but derives many economic benefits from high volume jet engine production (R&D, blade production, ancillaries) and so does not incur significant low volume cost penalties. There are no such apparent synergies for an SMR. Submarine and aircraft carrier reactors are not cheap for the same reason. Specific example:
    ‘Refueling’ the USS George Washington ( installing 2 new ‘factory’ A4W reactors, aircraft carrier fourth generation westinghouse PWR) is budgeted at $678 million. A4W is 550MWt, so about (PWR is ~33% efficiency) 180MWe. That is $1.9 million/MW.
    Voglte 3 and 4 are Westinghouse AP1000 PWR designs currently under construction in Georgia, USA. $4400 million for 2234MW for the two reactors plus all ancillaries (500 foot tall natural draft cooling towers). $1.9million/MW. No economic difference between low volume ‘factory’ and large scale ‘bespoke’.

    • benj says:

      The French looked to have benefited from a learning curve a State financing. The UK seems intent on doing the opposite. A nuclear zoo financed by private backers would want a 10% return.

      Sod wasting time/cash on this competition. Get Hitach’s ESBWR through GDA, and build twenty of them financed by Government bonds.

      That way we stand a reasonable chance of keeping energy price where they are.

    • Euan Mearns says:

      Rud, I’m on the fence / in the wilderness on this one. I really don’t see the sense in SMRs. Is the idea to have nuclear reactors everywhere? The planning objections are easy to anticipate.

      And I guess I am 100% with benj:

      Get Hitach’s ESBWR through GDA, and build twenty of them financed by Government bonds

      I dont know if the Hitachi is the best option, but I'm all for making a decision on one design and going for it (manufactured in the UK of course) and capital funded by The State. With a plan to transfer operation and ownership to the private sector with time once the risks of the enterprise are understood and managed.

      20 Hitachis sound better than 100 we don't know whats. But reading Alex's comments up thread leaves me sitting on the fence. The UK should never ever have sold Westinghouse – Gordon Brown I believe, that arch trader.

      • ristvan says:

        Euan, to the extent have knowledge, agree. Wrote my thesis onnthis long ago. Don’t know all the ins and outs of UK nuclear policy. Do know it makes no commercial sense.
        As a general observation, SMR has been around since Adm. Rickover’s 1950’s nuclear fleet. Never became commercial. There are economic reasons that I tried to explain above.

      • Alex says:

        The main issue is cost. It seems that EPRs need £90/MWh, and AP1000s and ABWRs might need £70-80 or so – better, but still too expensive to provide the 100GW or so of base load that the UK might need in 2050. (A Government financed program would indeed lower that cost further).

        Hence the strategy is to implement about 16GW of Gen III reactors by 2030, and in the 2020s, look at what is more cost effective for the 2030s. Maybe that will be more Hitachis or Hualongs, but the SMRs look like being more cost effective – though not forgetting Rickover’s comments.

        I would still expect SMRs to be grouped in blocks – say twelve times 250MW. (I actually have one design for an 4 to 8GW offshore plant in shallow waters in the North Sea).

        That said, the recent story about Bristol implementing a district heating scheme prompted some calculations showing it would be quite feasible to supply that with hot water from Oldbury power station, 20-30km away. That, and the need for industrial heat, might prompt a more distributed reactor deployment. However, there is no need to put them in City centres, and we’d still be talking about GW units.

        The second advantage is economic. The UK is not going to develop a Gen III PWR. It will have to import a design. It could take a lead on Gen IV designs. The UK would like to have a site manufacturing and reprocessing core modules, being shipped across Europe.

        The third advantage – which Andy may disagree with to some extent – is to get away from the concept of boiling water to make electricity. Relying on water at >150 bar pressure is always asking for trouble, limits the efficiency with which you can generate, doesn’t provide any high grade heat, and drives up costs throughout the system.

    • James Arathoon says:

      The idea is to improve repeatability, productivity and quality control, to reduce the build and commission timescale, and make more productive use of expensive highly trained staff.

      Also if you have ever worked as a on-site contractor commissioning a large industrial plant, be it chemical, petrochemical or power generation you will know that the rate of progress on-site is always much slower and less well controlled than it would be in a well organised factory environment.

      The other point I could make is that the nuclear industry will have great difficulty attracting and keeping highly trained staff if they continually require them to work on-site away from home for extended periods (over a year at a time) without rest bite. The longer a project continues the higher the chance that someone vital to the commissioning moves on to a different job or has to return home for family reasons.

      If a factory builds ten 250MWe SMR reactors per annum and one generating site consists of 8 reactors (2 GWe total), then this is almost a full years production.

      A-380’s were made at the rate of around 40 to 50 per year at full rate production. Forty 250 MW SMR’s per annum would be a rate of 10 GWe per year installed. This might seem too many at the present time, but if these sorts of production rates are eventually required post 2040, to service a growing export market, then it will be far easier to ramp production rates in a factory environment, than it would be if most of the work was carried out on site.

      Also as has been pointed out many times the learning curve rates in factory environments are usually far higher than for bespoke on-site build and commissioning environments. There is a wider pool of skilled engineering staff used to and happy working in factory environments.

      Of course I agree if we make bad technological choices then all of this is no help whatsoever.

  8. Canon Bryan says:

    Your speculation on Terrestrial Energy’s technological and commercial readiness is not based in fact and contains many errors. Terrestrial Energy’s IMSR will be ready for broad commercial deployment in the 2020s, with its first commercial plant being commissioned and operational in Canada in that timeframe. I invite the author to visit the Company’s website to learn more.

  9. Greg Kaan says:

    I fully agree with settling on a single design and deploying them across all the contracted sites, similarly to the French build in the ’80s. But why the ESBWR?

    The AP1000, as mentioned by Rud, is well along on its GDA certification and 4 are being built in the USA and another 4 in China while there is no ESBWR being built as yet. Being 33% smaller capacity (so 30 AP1000 rather than 20 ESBWR plants) is worse in terms of staffing but better in terms of system redundancy.

    • benjamin says:

      The AWBR is reported to be the cheapest out of the reactors planned to be built in the UK. The ESBWR looks to be a big improvement on that design in every respect. The best gen3.5 design at least on paper. It’s a shame we played it safe with the ABWR.

      If we were going to build 20, then we could get them to built a demonstration reactor first, if that worked to plan contract them for the other 19.

      It is best option for the UK. But political ideology won’t let it happen.

      • Andy Dawson says:

        “The AWBR is reported to be the cheapest out of the reactors planned to be built in the UK.”

        Is it?

        I’ve seen various estimates for Wylfa, ranging from £10bn (Hitachi) to £14Bn (the Welsh Assembly). That’s for 2700MWe (2x1350MWe)

        Moorside is still being quoted at £10Bn (which seems in line with the costs at Votgle, allowing for a 15% reduction for each doubling of the population, and very expensive compared to the units built in China.). That’s for 3360 MWe (3×1120).

        To match the price range being quoted for Wylfa Newydd, Moorside would be being quoted at £12.5bn to £17Bn.

    • Andy Dawson says:

      I share your puzzlement.

      AP1000 appears superior in terms of passivity (I’m rather a fan of BWRs, but they have certain weaknesses – the dependence on operation of isolation valves to close the steam circuit and take them into blow-down mode, plus as demonstrated at Fukushima, limitations on condensation capacity without heat removal from the supression space). ESBWR does have a passive method of heat removal from the steam supressor, but it requires a relatively complex engineered heat-exchange circuit, as opposed to AP1000’s simpler mechanism.

      ESBWR at least has the potential for melt-trough of the reactor vessel, which is engineered out in AP1000; however, that could be removed as a vulnerability were you to adopt the same philosophy of flooding the reactor plenum and allowing water to boil off the outside of the reactor vessel. That’d mean a major redesign of the containment, though.

      In terms of cost/complexity, there’s not that much to choose between ABWR and ESBWR; the only major system that can be lost in the latter case is the recirculation pumps. Given that they have a rather elegant secondary capability in terms of control for load following, I’m not sure losing them is a major gain. Conversely, the shorter core means worse neutron economy, and lower fuel burn-up.

      It has been occuring to me of late there’s a potential convergence of best practice in the passive designs, especially taking AP1000 concepts and applying them to a BWR.

      Were you to take the submerged control rod drives from an AP1000 and apply them to a BWR, you could radically simplify the bottom end of the Reactor Vessel. Rearrange the containment so that reactor was mounted low, and it could be submerged from in-situ tanks by gravity, with a passive decay heat removal mechanism, you’ve basically eliminated the issue of melt-through. Steal the concept from the IMSR of “bubbly flow” through a heat exchanger, you’ve eliminated issues of needing blow down and steam suppression in the containmnent, and have the potential to raise operating temperature.

      • Greg Kaan says:

        there’s a potential convergence of best practice in the passive designs, especially taking AP1000 concepts and applying them to a BWR

        A very reasonable and sensible arguement.

        I wonder if this is a case where engineering is ruled out by commercial realities – ie patent rights at Westinghouse and GE for the various design features that you mention in the following paragraph prevent this seemingly straightforward and logical convergence.

  10. David Richardson says:

    Thanks for the article Andy and thanks Euan for giving us the chance to read it (and previous articles). It is good to read this discussion with people who have knowledge of the subject chipping in.

    I have learned a lot and like most citizens needed to.

  11. Syndroma says:

    Being a nuclear fanboy, I’d be glad to see all of the designs implemented. Each new design gives multitude of cases to study, to gain knowledge and practical experience. But most likely the first of its kind will be a disaster. Not nuclear I hope, but definitely financial. And probably technological. Also, the first SMR will have a disadvantage of having to prove the right of such reactors to exist. To be honest I’m confused why the UK would want a SMR. They’re good for remote places with low demand. Russia wants them to be deployed in the Arctic, where the big designs are overpowered. And Russian SMRs are based on the designs of reactors for submarines and icebreakers, which are produced nowdays. Check out this 170 MWt reactor vessel:
    It is being produced for this beauty, floated today:

    My conviction is that there can be no revolutions in the nuclear field. To succeed you should evolve from the proven design. And if you didn’t use a knowledge for a generation, it’s pretty much lost. You have to start with small prototypes. Trying to build a full-scale reactor is a recipe for disaster.

  12. K.Periasamy says:

    I also share the scepticism of MSRs expressed by the author. It is always better to upgrade on scale.

    Never we must succumb to the “perceived” fears of the anti-nuclear lobby.

    They will oppose the SMRs also ! After all they do not go by facts and figures !

    • Canon Bryan says:

      Please note that within the past 12 months, Bill Gates, Peter Thiel and Ray Rothrock, Southern Company and the US Department of Energy, have all invested in Molten Salt Reactors. These people and organizations are pretty smart, and I would listen to their arguments.

    • Alex says:

      The MSR developers have looked carefully at the trade-off between volume and scale. (In some respects, it’s a similar trade-off in rocket launches).

      At one extreme you have the EPR – all 1.6GW of it, which can only ever be produced on site, and in small numbers. At the other extreme you have NuScale – with 60MW units where you need at least a dozen to create a blip on the grid.

      We want it big, but we want to build it in factories, and we want to build lots of them. Probably the biggest determinant is what can you get on to the back of a truck – and there MSRs and sodium cooled reactors will have an advantage of high power density. For MSRs, the sweet spot is around 250MWe.

      The Westinghouse PWR unit – 225MWe – looks too big for transport on UK roads. However, it does look like it can be split in two units, making transport easy.

      ThorCon’s 250MWe MSR units were designed for ship transport rather than road transport (they have the primary heat exchanger on the side of the reactor). That might be good for the developing world, where you can build a harbour wherever you want, but not for the UK where every beach is a site of special scientific interest and you need everyone’s permission to put up a tent.

  13. James Arathoon says:

    Starting with small prototypes is not a guarantee of success in the nuclear industry as most designs of nuclear reactor do not scale in the way many other engineering products scale.

    Most peoples intuitive understanding of engineering scaling is formed from seeing engineering scale models being used in wind tunnels to guide the building of full scale products. This works in large part because scaling laws can be found; often involving dimensionless numbers such as the Reynold’s number for example (Reynolds number is a dimensionless number often used to predict the boundary between laminar flow and turbulent flow in moving fluids).

    Solid fuelled nuclear reactors do not scale as easily. Particularly in the case of LWR and BWR solid fuelled reactors, new important failure modes arise as the reactor power and power density is increased. Assuming passive heat removal is designed correctly most solid fuelled reactors below a certain size and power density can’t melt down due to the decay heat given out from the fission products produced. This is definitely not true for larger designs as we all know. Small solid fuelled reactors with passive cooling are not economically viable in practice, because their output would have to be less than 60MW or so.

    Most solid fuelled SMR’s listed will melt down if decay heat is not removed by an actively powered process designed specifically to remove this heat. This active heat removal generally needs a ready supply of cooling water, actively pumped to where it is needed. Thus these reactors may still spread radioactivity into the environment if active cooling fails on shutdown. The regulators still will want to see multiple redundant backup systems increasing the size, complexity and cost.

    There definitely seems to be much greater scope for using well tried engineering scaling principles in regard to liquid fuelled reactors, than for their solid fuelled cousins. On shutdown the molten salt fluid will naturally convect (in scale predictable ways) to allow decay heat to be removed passively at much higher powers and power densities than would be possible with a solid fuelled reactor. Testing small molten salt reactors in the commissioning phase by externally heating the salt without nuclear fuel added will be much easier and practical tests to make, than analogous tests on a large solid fuelled reactors. [In fact analogous test on large solid fuelled are often so costly and impractical that they are not normally undertaken in integration testing during the commissioning phase. Designing products which cannot be adequately integration tested is something that cannot happen in other regulated industries such as aerospace. In fact it seems to me like a cultural practice almost unique to the nuclear industry.]

  14. benjamin says:

    When linked to a gas turbine, a high temperature reactor can run on the air Braydon cycle. This means any extra gas/hydrogen added will ramp up power 100 times faster that a CCGT. This changes the economics considerably. This is the sort of technology the UK should be backing. Below is a link to a presentation by Dr Forsberg on the subject. Highly recommended.

    • Andy Dawson says:

      Actually, I think on this, they’ve a good argument – see my long post on the latest “blowout” thread.

  15. Geoff Sherrington says:

    Is there not value for the UK to discern, publicise and benefit from a hard-nosed cost study on why Chinese builds are so low in cost?
    Is it still the case that many UK costs arise from extreme regulatory measures that on realistic analysis can be lowered if they do not pass a rudimentary benefit:cost analysis?
    Reluctant to invoke terms like green inspired off-putting imposts that populist past politicians accommodated, but that shows one area where estimates of costs could be cut.
    Maybe this process in under way. However, it is not very visible. General public impressions do count.
    I’m from Australia which suffers from green propaganda but which will benefit from this British survey of candidates.

    • Andy Dawson says:

      I’m not sure that’s anything obvious in terms of the technology – after all, the AP1000 is being prototyed in China, and Hualong is being entered into our GDA process.
      The cost delta is easily explainable in terms of series build and local costs

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