SMRs, Size matters – or does it?
Dr Janet Wilson, Senior Nuclear Consultant

If you’re a nuke like me (an engineer who’s spent the majority of their career in the nuclear industry) you’ll be bombarded with the woes of new nuclear build; a lack of investment, massive cost overruns, construction problems, quality assurance failures, etc. You’ll also have read many articles expounding the virtues of Small Modular Reactors (SMRs) which range in design from “Mini-Me” PWRs through to innovative, conceptual designs claiming to be the next generation of passively safe reactors that can be transported on the back of a truck and installed and operated with little or no nuclear expertise.  So my question is – Why do I have to choose between these two options?  Is there room for both?  I’m no economist but here are some of my thoughts when answering these questions.

S for Small, what is the right size?

Assuming that nuclear has a place in the UK’s energy mix (a debate for another time), to provide 6,000 MW you need either 6 large capacity 1,000 MW+ light water reactors or twenty 300MW SMRs.  That’s equivalent to a thousand 6MW wind turbines.

Conventional light water reactors such as PWRs or BWRs cost £billions to build, but can operate for at least 60 years.  They are evolutionary in design, i.e. incremental safety, construction and operational improvements have been made to the original concept over the years.  They are a known and understood quantity when it comes to nuclear safety, environment and security Regulators whose regulatory costs are considerable (£millions/year).

It’s true to say that the cost of building any of the SMR designs out there can only be estimated but presumably they need to be less than a third of the price of conventional ones.  How long they can operate for also varies.  Some are “plug-and-play” and are designed to operate without refuelling and/or internal maintenance for life but it’s unlikely that that life is more than 60 years.  Others are simplified smaller versions of their big brothers but may have replacement refuelling modules that make them simpler to operate and maintain.  Importantly, SMRs are new to Regulators and will require the same level of design scrutiny as the larger reactors and must meet the same exacting standards.  Therefore, it’s difficult to see how, at least initially, the costs of permissioning them will be lower.  Let’s see what happens when the first SMRs get their Generic Design Assessments.

Before I leave small versus large, what about input to the National Grid and speed of response to demand?  It’s fair to say that PWRs and BWRs are relatively inflexible in operation whereas SMRs have the potential to be more dynamic and match their power output to demand.  A good argument then for both?  What about innovations in electricity storage?  Can stored electricity be used to respond to rapid or unexpected demand?

M for the Modular advantage.

The whole idea it seems is that these small reactors can be factory built in modules and assembled on-site thereby reducing the time and cost of construction.  Great, but isn’t that the way that some PWRs are heading with prefabricated modules?  Well no, the prefabricated modules for large reactors face a number of obstacles. Production numbers are so low, each module can be effectively viewed as an expensive one off.  The sheer scale and complexity of modules creates its own set of challenges; the number of credible suppliers is reduced as is competition, quality control is difficult and transport of very large modules can be challenging.  Worse still for the supply chain, the seemingly never ending delays are savaging cash flow, so ultimately this is making big nuclear an increasingly unattractive market.

In contrast, the production of large numbers of small reactor modules appears to offer real promise on a number of fronts.  Get it right and SMRs will create the opportunity to build true production lines for hundreds of standard modules.  In turn this could deliver a much needed step change in production efficiency and the type of quality control we have historically seen in areas such as fuel rod production.

R for new thinking on Reactors

Technically it is interesting to consider what happens if the entire reactor is the module?  The burn-up of the fuel could be considerably greater than conventional fuel cores.  That means more ‘nasties’ at the end of life.  That makes the Plutonium that is generated as the fuel ‘burns’ more difficult to access and so it could be considered to have higher proliferation resistance (using it to make a nuclear weapon) but there is more of it and it’s in a neat, transportable package.  If there needs to be the same counter-terrorist armed response presence as at other nuclear sites then how is this cheaper?  Perhaps a vision of SMR farms will combat this security risk? This brings us back to the economics of whether 6 large capacity 1,000MW+ light water reactors are more or less economically viable than 20 300MW SMRs?  

A range of sizes creates new options and possibilities.

Finally, Britain has some of the best Universities and Research establishments in the world and has a long and proud history of producing world class, innovative nuclear science, but it seems to me, we do the clever inventing and developing while others make the money.  The struggle to build a new generation of large capacity nuclear reactors in the UK has revealed many risks and demonstrated that neither government nor the UK private sector have the appetite for investment in big nuclear.

SMR’s on the other hand, present a different proposition with the potential to be produced efficiently in advanced manufacturing facilities and then deployed much more quickly.  This points to the potential for SMRs to support the delivery of far better return on investment for both manufacturers and generators.

Should we therefore be supporting our nuclear scientists and engineers and maintaining our UK capabilities? Absolutely.  This brings me back to my original question on whether size matter and do we need to choose between big and small reactors?  Regardless of the recent delays and challenges, I can still see a place for conventional large capacity PWRs and BWRs and the carbon free baseload they will deliver.  However, commercially and from a manufacturing perspective, the right size does appear to be smaller, not larger.  SMRs offer the potential not only to meet the energy demands of the future, but allow for the UK to design, manufacture and export such devices, but there again I’m an engineer not an economist or a politician!

Menu