UK engineers are in the vanguard of efforts to develop compact nuclear reactors, otherwise known as small modular reactors. Stuart Nathan reports
Even before the first kilogram of concrete has been poured, Hinkley Point C may be among the last of a kind. Large nuclear reactors, producing electricity on a gigawatt scale, have dominated the sector for years, but their size and complexity are now combining to put their cost beyond the means of most countries.
A new nuclear paradigm, which seems to defy the logic that has dictated increasing the size of power stations, is being tipped to take over. Small modular reactors (SMRs), with generating capacities of up to 500MW of electricity (MWe), are increasingly seen by governments and the nuclear sector as a better option for reducing costs, and unlocking the potential of nuclear for new markets. SMRs can be built in factories and assembled on site rather than having to be constructed as costly one-offs, and this factor, combined with their more frugal use of materials, is seen as key to bringing down the cost. It also allows for a more distributed energy generation model that could be attractive in regions with remote communities and distribution networks not geared to handling large amounts of electricity.
Leading the field in the UK are Rolls-Royce – whose manufacture of nuclear reactors for Royal Navy submarines makes it the only company to have produced, operated and maintained nuclear technology – and US firm Nuscale, based in Oregon and developing technology that originally came from US Department of Energy research supported by Oregon State University. Nuscale has declared an interest in developing manufacturing capability and capacity in the UK.
In technology terms, Nuscale and Rolls-Royce have both opted for pressurised water reactors cooled by light water (LPWR): scaled-down versions of the type of reactor that has dominated the nuclear sector for the past few decades in the US and Europe. The thinking behind this is that regulators both know and understand the technology and therefore are more likely to grant approval in a shorter time.
Nuscale goes for flexibility
However, the two designs stem from different approaches to reactor deployment. For Nuscale, flexibility of the nuclear installation is the most important factor, so it has opted for a low-power output module designed to be deployed in groups of up to 12, depending on power requirements. The reactor, with an output of 160MW of thermal energy or 50MWe, is fully integrated, with steam generation within the same housing as the reactor itself; the circuits for the primary coolant (which removes heat directly from the nuclear fuel and is in contact with the fuel rods) and the secondary coolant (used to generate steam and never coming into contact with radioactivity) are both within the reactor containment vessel.
The secondary heat exchangers use helical tubing to keep the volume needed for steam generation as low as possible; the steam generators can be connected directly to a steam turbine with no need for separate bulky and complex steam-generating heat exchangers, as are used in conventional nuclear power. This helical arrangement is one of the major engineering innovations in the Nuscale reactor, according to chief technology officer José Reyes, who was also the main designer of the module. Moreover, the entire reactor module acts as a heat exchanger because it is installed submerged in a water tank to which it can give up heat in an emergency; Reyes claims that, in an emergency shutdown situation, this reactor pond cooling will keep a failed reactor safe indefinitely.
Rolls–Royce opts for larger output
Rolls-Royce, by contrast, opted for a larger power output. Its reactor is sized so that a typical installation may have only one reactor, or maybe two. Although it is similar in size to the Nuscale module, its internal layout is more similar to a conventional reactor in operation and therefore needs to be connected to steam generators: two for a 220MW installation and four for 440MW. This, said David Orr, senior vice-president in the firm’s nuclear business, in a conversation with The Engineer, is deemed to improve the design’s “selectability” because of its similarity to existing LPWR installations.
Because of Rolls-Royce’s experience in supplying nuclear reactors for submarines, it’s a common assumption that this is the origin of its reactor design. However, Harry Holt, president of Rolls-Royce’s nuclear operations, at a recent SMR conference in London said this was not the case.
“Submarine reactors have to do very different things from civil power reactors. They have to be able to accelerate the submarine, which calls for variable power output that a civil reactor does not need, and they have to cope with the stresses of movement,” Holt explained. “Also, they are designed to last for the life of the submarine without the need to be refuelled. Civil reactors have to last much longer and are regularly refuelled. We operate a land-based prototype submarine reactor in Scotland and that’s given us familiarity with the ONR [Office of Nuclear Regulation], which will help us with the approval process,” said Holt.
In fact, Rolls-Royce’s policy is to ensure that no defence-related nuclear research transfers to the civil sector, he said. “The SMR was conceived as a separate project and is designed around the market requirements, with an eye to regulatory approval, manufacturability and selectability.”
Another difference between the two companies’ reactors is the way their coolant systems operate. The Nuscale reactor has no coolant pumps in the primary circuit, using only natural circulation. The heat given up to the coolant water by the reactor fuel causes it to rise by convection; then it falls back down to the fuel rods as it loses heat to the secondary circuit. This simplifies the electrical systems needed, with post-shutdown monitoring systems powered by arrays of batteries.
A further innovation is that the pressure inside the containment system is kept at near-vacuum levels, which, Nuscale claims, minimises reactor vessel heat loss, eliminating the need for insulation. It also reduces corrosion inside the vessel.
On the back of a truck
Despite this, the two reactors are of a similar size: Nuscale’s is 19m long and 2.75m in diameter, and Rolls-Royce’s only slightly bigger at 16m long (with the control rod drive system installed) and 4.5m in diameter. Both are sized to be carried on standard trucks, train carriages or barges; a key consideration for SMRs. They are composed of steel forgings in standard nuclear-grade materials, which it is anticipated would be produced by external specialist contractors and transported to a factory for assembly. Both companies are working with academics on methods for making the reactor assemblies, with the Nuclear Advanced Manufacturing Research Centre in Sheffield involved in research and prototyping. Reyes noted near-net forging and coating techniques as being of particular interest: these will require regulatory approval for nuclear use, but this can happen within the timescale envisaged for UK deployment by 2030, he said.
Both reactors are designed to be refuelled every two years. The Nuscale module contains a 17 x 17 array of fuel rods. Orr preferred not to reveal the number of rods in the Rolls-Royce design, saying only that it was between 10 and 150. Both use standard light-enriched nuclear fuel in a similar fuel rod to that of a conventional PWR. The Nuscale installation uses a refuelling procedure with the exhausted module physically removed from the reactor pool; in practice, Reyes said, the refuelling schedule would be staggered, with the process probably carried out every year.
A key part of Rolls-Royce’s SMR strategy is that it hopes to be part of a consortium that delivers a whole nuclear power station within a turnkey project. The company is therefore seeking partners – most likely from China, Germany or the US, Orr said – to provide the other sections of the station that are not part of the nuclear island: notably, the steam turbines. The UK no longer has a capability to make turbines large enough for nuclear power stations, even the scaled-down ones supplied for SMRs.
Production engineering techniques are key to cost reduction. Tony Roulstone, course director at Cambridge Nuclear Energy Centre, said: “The cost of building nuclear plants is related to their complexity and the work you have to do on site to build them, and nothing the industry has tried has worked. So it’s time to try something else. The manufacturing approach works in every other industry. Nuclear is the only industry in which production engineering is not used.” He added: “It’s only by getting into a factory environment and building these things over and over again that you learn how to bring the cost down.”
Herein lies a potential problem for any UK project to manufacture SMRs. To produce the required economies, Roulstone said, the programme would have to be quite large, making exports essential. This would disadvantage the UK versus countries that could finance manufacture on a much larger scale for their domestic market.
The Rolls-Royce model seems to make production engineering more difficult because you are inherently going to make fewer of them.
And what will happen to the waste??
With the UK looking for any trade partner after Brexit, I’m sure ISIL will be interested to dispose of the waste.
The idea of modular reactors is long overdue but using pressurized water reactors is the wrong thing to do. High pressure reactors are not failsafe and add huge amounts of cost to a systems construction.
Liquid metal cooled reactors are much more efficient and because they operate at low pressure the construction is much simpler and cheaper. They don’t have to be shut down every couple of years for refueling and they generate an order of magnitude less waste.
It’s time the regulatory agencies get some fresh blood that understand technology that isn’t 60 years old.
beware braggart* obviously oblivious to criticalities in convective^ forced-free transitions & US-NRC alarming approvals” of unsafe LOCA codes: *helical heat exchangers claimed as major engineering innovation yet been used in nuclear industry since early 1970s; ^emergency shutdown reactor pond cooling will fail-safe indefinitely indicates unaware of Hall&Jackson’s seminal 70s stuff on buoyant laminarisation; “viz CamUni DAMTP 80s definitive demonstration of alarming added-mass error halving time for boiling bubbles to migrate from flow to wall.
An SMR that never needs refueling, hence far less radioactive waste and a higher thermal efficiency, hence lower cost electricity, General Atomics EM2. http://www.ga.com/websites/ga/docs/em2/pdf/EM2_datasheet.pdf
Same as the waste from the big beasts. Send it to Windscale, sorry Sellafield.
Just as the CO2 from wood burning stoves ends mixed up with that from fossil fuelled power stations.
Well it keeps the majority of the county employed, so they won’t be complaining, especially all the highly paid subcontractors in the area…. 😉
Here is what we know about SMRs. No one has built one yet, no one even has an approved design. The licensing process will take at decade at least. The military has been trying for 50 years to come up with an economical small reactor, all they have succeeded with is fantastically expensive ones for aircraft carriers and nuclear subs.
The modular reactors under construction in SC and GA (which were supposed to be built in a factory and not at the site) have simply moved production problems from the site to the factory. These are not small, but they still indicate that “modularity” is no magic fix. These 4 failed new reactor are billions over budget, years late and possibly bankrupting Westinghouse.
Transatomic nuclear was a highly visible new SMR company with designs promising to burn radwaste and use fuel 75 times more effectively than conventional reactors had to come back and say they could not burn waste at all and would come in close to twice as efficient. The promises got them huge media exposure and venture capital, the corrections got little press and basically vanished in a technical journal.
Very smart marketing, just the product does not work. SMRs are going no where fast.
Not true – the worlds first SMR was build by INVAP in Argentina
There is some competition over claims of who built the first SMR. Depending on definition, Britain’s AGRs could be classed as SMRs, in which case the UKAEA got there first in the 1960s.
These SMR’s appear to solve many problems associated with nuclear generated electricity but what about security re terrorism etc. and will the public agree to a station “at the bottom of their garden” knowing their unfounded fears of nuclear technology?
In the UK, on site security would likely be provided by the Civil Nuclear Constabulary.
Hi Kevin, using Thorium Energy Amplifier Reactors and going over to Local Heat and Power would perhaps help in encouraging Public acceptance
What a lot of time wasting! The way forward is to use Thorium reactors in either liquid salts form, or as fuel mixed with present nuclear waste in Energy Amplifiers. Let us move Several steps forward rather than sticking to the polluting Uranium fuel route.
Its not ‘(general) public acceptance’ that is required but that of the star reporters in the popular media! I have always subscribed to Edward de Bono’s proposal in the 60s that as it was costing the USA $1,000,000 to remove each Viet Cong fighter from the battlefield, simple bribery would be much more cost effective. I presume journalists have a ‘strike-price’ just like any other ‘sham’ : so lets just pay-up and proceed with sanity to what [nuclear] will be best for ‘the greatest good to the greatest number!’ If that was good enough for Voltaire (who managed to trigger not one but two revolutions against entrenched stupidity) it’s surely good enough for us.
Some obvious and overlooked points.
One of the biggest problems with the utility scale reactors in the ’60’s was the high demand for capital before generating any income. Along with the massive number of reactors being built, this ‘drained’ the capital pool and causes double digit interest rates (supply/demand) that further increased the price of nuclear. SMR’s can be installed one at a time to start generating revenue while construction continues.
This is a way to move nuclear power to remote locations that currently need high priced diesel generators. Too small for a big nuclear plant, they are ideal for the modular reactor and this could MASSIVELY reduce energy costs for northern Canada, and some remote mining operations for example.
This is a very interesting article. Both designs seem like a good prospect for UK manufacturing, but there are a few clues that point toward the NuScale design being more advanced (and by that I don’t mean more ‘complicated’ or using ‘novel’ technology – simply the application of existing technology in a new design) than the Rolls-Royce design, the NuScale design simply appears to be more ‘passive’. The NuScale SMR is a integral reactor, whilst I infer that the Rolls-Royce design is essentially a scaled down AP1000 style of design – by that I mean dispersed – one that requires a pump etc. and with fairly conventional containment arrangements. It would be good to have more information on this as there is loads available on the internet on the NuScale design. Doing a bit more digging (assuming I can post some links): it appears Rolls-Royce have collaborated with NuScale and have therefore effectively endorsed their design concept; http://www.nuscalepower.com/pdf/nuscale-power-uk-prospectus-feb2016.pdf what isn’t clear to me is if this collaboration remains, I assume they’ve gone their separate ways if Rolls-Royce are pushing their own SMR? Seems odd, given that so much design work, testing and validation has already been done by NuScale/R-R – could Rolls-Royce not have licenced their design (or part owned it?) and pushed it through the ONR for the UK market? Surely this would be much more cost effective, and perhaps more importantly, more timely given the ever increasing UK energy demands. In addition, further digging suggests that there are many potential alternative SMR designs at different levels of design maturity, some are even under construction: https://www.uxc.com/smr/uxc_SMRList.aspx – to this end, is any government body doing an assessment as to what will actually meet our needs; i.e. MW output, development cost, build cost, timescales? Finally, one thing that confuses me with the SMR concept, or any new-build nuclear work is; where are all of these jobs that are promised? Where do these projects get the staff required to design and develop an SMR in an industry that is notorious for have a huge skills shortage? I’ve not seen many, if any, jobs advertised – for example, where have Rolls-Royce got their design engineers from? Is this ‘job creation’ just another sales pitch that ultimately won’t deliver? That would be a huge disappointment – surely the bottom line is UK jobs irrespective of where the design has come from?
They had research reactor working at oak ridge for four years without incident, it was shut down when Nixon’s administration decided to reward his home state rather than do what looked promising. It seems to me that continuing work on this 50 year old technology makes a lot of sense.
Companies are doing research on it https://www.technologyreview.com/s/542686/terrapower-quietly-explores-new-nuclear-reactor-strategy/ but vested interests on the uranium fuel rod side of things are throwing up roadblocks wherever they can – to much money to be made on the fuel side.
If your going to build a small reactor it seems the first thing you want to ditch is a pressure vessel that has to withstand hundreds of atmospheres of highly radioactive material. An atmospheric pressure design is going to be much smaller and orders of magnitude less expensive to build. Do the research and knock down the problems as you find them, don’t just go blindly on building the same design that the nave developed in the early 50’s for use on submarines. That was never meant to be more than a stopgap measure while research was done to develop better designs.
I wonder if great early locations for these might be UK military bases.
Security, space, resilience, planning, energy to power new laser weapons for ground based missile defence.
RAF helps make U.K. Nuclear industry fly 🙂