Heavy load: Large nuclear reactors incur big capital costs and offer huge building challenges
Several years ago, when the previous Labour government said Britain would embrace a nuclear renaissance and build a fleet of gigawatt-scale reactors, ministers were confidently stating that the first electricity would be generated by 2018. Fast forward to today, with not a foundation dug or the smallest amount of concrete mixed, and that prediction must be judged, with hindsight, as laughably optimistic.
The challenge of constructing large nuclear reactors, such as Westinghouse’s 1 gigawatt (GW) AP1000 or Areva’s 1.6GW EPR, have proved manifest, with issues of finance, regulation and technology all coming into play. The licensing and approvals process for such advanced pieces of equipment has proved tortuously slow. Indeed, with the AP1000, that process is still ongoing.
The enormous capital costs have also been an issue. Each reactor comes with a price tag of several billion pounds – a sum not easily found by even the largest industrial conglomerates. The companies looking to build the reactors have therefore sought long-term, predictable returns in the form of ‘strike-price’ agreements with the government for the electricity they produce. Cue never-ending wrangling between lawyers on all sides, slowing the newbuild process further still.
So now officials within Whitehall’s corridors of power are starting to wonder whether there might be an alternative way of adding nuclear capacity. What if clusters of smaller, modular reactors of less than 300MWe, with reduced costs and quicker build times, might provide a means of overcoming many of the challenges seen to date? That intriguing possibility has encouraged the government to launch a review of small modular reactors (SMRs), assessing the technological capability of the variants on offer and establishing whether the UK supply chain could play a central role in the construction of such devices.
That review is being overseen by Sue Ion, who has been installed as chair of the government’s Nuclear Innovation Research Advisory Board. Ion, one of the most respected nuclear engineers in the world, will look at SMRs for a range of applications, including electricity production, district heating, and plutonium management.
“There is no doubt that SMRs are, potentially, an exciting prospect,” she says. “What we need is a study that delivers evidence to show that SMRs can be as successful as their proponents claim. It’s also important to establish whether there is an international market for SMRs, to establish a route to that market, and to clarify whether the UK can develop a supply chain that can win out.”
Ion says that, while SMRs are unlikely to be as effective as larger reactors on a cost per megawatt basis, they do offer other advantages in terms of lower capital costs and shorter construction timescales. “Therefore the financing for SMRs could be much more manageable. You wouldn’t have to bet the company to build one,” she says.
Genuine modularity – with the bulk of the reactor being built at a plant and brought to site – could eventually bring real economies of scale, says Ion. “If you started to build fleets of 20-30 SMRs, you could expect those economies of scale to really start flowing though,” she adds.
The concept of a small reactor is not new. The first commercial reactors built and operated in the UK were small in energy output, typically a few tens of MWe. The Magnox reactors built in the 1950s were small in terms of electrical output, although they could not be considered modular, having cores of approximately 12m3 which required construction to be carried out in-situ.
Since the 1970s, though, several companies and academic organisations have developed designs that are both small and modular. Today, there are around 80 SMR concepts at various stages of development around the world from companies including NuScale, Gen4, Mitsubishi, Holtec, mPower, Westinghouse, General Atomics and the South African PBMR (Pebble Bed Modular Reactor) project. These include light water reactors, gas-cooled reactors, fast spectrum reactors and molten salt reactors. While all differ in design, they can be viewed as having common characteristics that make them intriguing alternatives to larger-scale variants.
The Nuclear Innovation Research Advisory Board study will be project managed by the National Nuclear Laboratory (NNL), which has already carried out significant research into SMRs. NNL says the major advantage that SMRs have regarding capital expenditure is that they allow more operators/investors the opportunity to consider a nuclear programme.
The level of investment for a single or twin large plant is of the order of several billion pounds – beyond the reach of most industrial groups. In smaller nations, such as in eastern Europe, such a figure would represent a large proportion of gross domestic product.
By using a staggered building programme and the ability to construct smaller units more quickly, says NNL, the total cumulative cash flow for an equivalent several-module unit in a single site has been shown to be in the order of one-fifth that of a single large plant. As one module is finished and starts producing electricity, it soon generates positive cash flow for the next module to be built.
“Historically, the difficulty with nuclear newbuild comes both in terms of capital cost and cost of capital,” says Dr Fiona Rayment, director of fuel cycle solutions at NNL. “With SMRs, the whole concept is about modular design. Smaller parts can be mass manufactured by a local supplier, or elsewhere, and then brought to site. If you start to think about what we are seeing with flatpack housing, then that’s the sort of concept we are moving towards with small modular reactors.
“Finance has always been difficult for a capital-intensive sector such as nuclear. A large nuclear power plant typically takes 10 years from design to making money from generating electricity.
“However, with an SMR, if you constructed two or three of them, you could generate the same electricity as a large power plant, but you could bring them online as they were ready. You’d generate revenue earlier, and as such reduce some of your finance costs.”
The benefits on the capital investment are not the only potential economic advantage for SMRs, says NNL. Simpler, smaller designs with a reduced number of components (using passive safety features, for example) also have the potential for lower operating and maintenance costs as well as more flexible operating strategies.
Despite a large variety of SMR designs, they tend to share a common set of design principles to enhance plant safety. Some of the typical features include incorporation of the primary system components into a single vessel; increased relative coolant inventory in the primary reactor vessel; and smaller radionuclide inventory per reactor. Other benefits include vessel and component layouts that facilitate natural convection cooling of the core and vessel; more effective decay heat removal; and smaller decay heat per reactor.
NNL argues that enhanced security can also be offered, by virtue of the fact that SMRs can be sited below ground. This is made possible by a much smaller reactor footprint, making it economically viable to do so.
Below ground siting lessens the potential impact of external events such as aircraft collision or natural disasters, while reducing the number of paths for fission product release following any accident.
More flexible siting is also a factor: because the footprints of SMRs are smaller than larger plants and they need less cooling (as they have lower heat outputs per plant), they can be accommodated on sites that otherwise would have been excluded. Recent research undertaken in the US suggested that use of SMRs, compared with large 1,600MWe plants, would increase the percentage of US land that was viable for new nuclear build from 13% to 24%. “Flexibility is a factor,” says Rayment. “SMRs wouldn’t necessarily have to go where the large nuclear power plants are at the moment. They are designed to be passively safe – so they wouldn’t require the same volume of cooling as larger plants. That, potentially, brings some real benefit around siting of reactors.”
NNL has also looked at whether the UK supply chain would have the required capability to provide the necessary components and expertise for SMR build. Essentially, the major components remain the same as for large plants (RPV, steam generators, pumps, fuel, etc) but the components are generally smaller, or there are at least fewer of them per unit. This, it argues, is likely to mean that a greater number of domestic manufacturers will be able to supply a much greater number of components. In addition, the modular, factory build philosophy behind SMRs will mean that a much more substantial manufacturing base will have to be created in each country or region.
“The UK manufacturing base understands how to make nuclear systems because it has a background in larger power plants,” says Rayment. “But an SMR programme could be opened up to a greater number of manufacturers making smaller parts.”
SMRs are adaptable to a broader range of energy needs than larger reactors, says NNL. As well as electricity generation, SMRs can be used for non-electric applications that require proximity to customers, like seawater desalination, district heating and other process heat applications. The specifics of these come down to technology choices, especially if high-temperature process heat is required.
Similarly, SMRs are proposed to have more flexible fuel cycle options, whether that is an “open” fuel direct-disposal cycle or a “closed” fuel reprocessing and recycle. For example, a fast reactor SMR fleet could be envisaged as a dedicated reactor concept to manage plutonium stocks and minor actinide incineration.
Finally, NNL has looked at decommissioning, stating that the modular nature of SMR reactor components could ease the decommissioning timescales. With smaller modules, the ability to dispose of the entire unit could be feasible. In addition, with many of the SMRs being based underground, there is the potential to backfill the site as is, removing the outer shell and buildings.
NNL clearly sees potential benefits of SMRs. But Rayment is realistic – no commercial SMR has yet been built. That’s why it’s important that the government takes a step-by-step approach to their uptake, she says. “There is no proof that SMRs have all the benefits that we have talked about. It is all around what they feel like on paper. We haven’t seen it in practice yet. That’s an issue – do we invest when we are not in a position to know if the benefits are real or not?”
NNL isn’t the only organisation leading a government review of SMR technology – the Energy Technologies Institute (ETI) is also running a study into their integration into the UK’s future energy mix. The £250,000 piece of work will assess the financial viability of building nuclear reactors up to 300MWe, comparing them with other forms of generation, such as biomass. The analysis is expected to inform government energy policy, specifically in relation to CO2 reduction targets.
Mike Middleton, the ETI’s strategy manager for the project, says: “The ETI doesn’t look to back a particular technology. We advocate analysis and give advice. And that’s what the research into small modular reactors is about.”
Middleton says that with obvious constraints to large nuclear, not least the huge upfront costs and ongoing concerns over the pace of construction, SMRs need to be considered for the role that they could play in a balanced portfolio of energy generation, going forward. Specifically, ETI will look at how small nuclear could help solve three major challenges of the energy system: the need for additional low-carbon electricity; how we might energise future heat networks; and how the energy system might become more flexible in terms of grid balancing.
“It’s important for us to establish where SMRs might fit,” he says. “They need to make sense, both economically and in a way that works in the energy system as a whole.”
But in each case, says Middleton, the economics need to stack up. “Look at heat networks, for instance,” he says. “On the face of it, small modular reactors would offer more flexibility in terms of where they could be located, as they would have smaller footprints and would require less cooling water. So it might be possible to site them where you would never have considered a large plant. That means it might be possible to locate smaller reactors much nearer to where there is a requirement for heat networks, resulting in shorter pumping distances and pipe lengths. That could make them more cost competitive.”
Middleton says that with the ETI study into small modular reactors now under way, he has to remain neutral as to whether he thinks they will ever make an important contribution to the UK energy system. “What I would say, though, is that if these things are as good as everyone says they are, why hasn’t a commercial utility built one?
“You have to look hard at the economic analysis to understand how they can be attractive to developers, consumers and taxpayers. They have to make sense – you can’t embark on a programme for the benefit of the science and technology. You have to be clear what problem you are trying to solve with a particular technology. And that’s what we are trying to do with the research we are conducting.”
Reactor types
Light water reactors
The light water reactor concepts are the most mature as they are based on existing technology, operational experience and lessons learnt. The LWR designs are also where most of the significant investment money has been spent to date and work is still extremely active in this area, with companies such as Westinghouse and NuScale moving these designs from concepts, and through the licensing process. One of the main themes in these designs is to have the key primary systems internally integrated – steam generators, pumps, control rod drive mechanisms. In addition to electricity production, the LWR concepts have potential applications primarily to district heating and desalination, as well as a possible role in plutonium management.
Gas-cooled reactors
A number of gas-cooled reactors are being looked at, in particular in China with the HTR-PM project, with the pouring of concrete for the base of the first unit at Shidaowan, Shandong province, now completed, and in the US with the Next Generation Nuclear Plant. The new designs could potentially generate high-
temperature helium either for industrial application as part of an indirect cycle via a heat exchanger or to make steam conventionally via a steam generator, or via a direct cycle to drive a turbine to increase thermal efficiency.
Fast spectrum reactors
There have been several demonstration fast reactors developed, including the Dounreay Fast Reactor (DFR) and Prototype Fast Reactor (PFR), and others include designs in France, Russia, Japan and the US. The major difference with fast reactors compared with LWRs is that they are designed to use the full energy potential of uranium via a full reprocessing recycle route – closing the nuclear fuel cycle with the management of plutonium and consumption of minor actinides, which also means that any reactor technology development has to be in association with a similarly large programme on the fuel cycle technology. Typical coolants include liquid metal such as sodium, lead, or lead-bismuth, with high conductivity and boiling point, each of which has its challenges. They operate at or near atmospheric pressure and have passive safety features (most have convection circulating the primary coolant).
Molten salt reactors
The molten salt reactor technology comes into two distinct forms that need to be noted; one uses the molten salt solely as the coolant (the fuel is then in block form) and the other has fuel mixed with the coolant, as part of the molten salt (the fuel is a molten mixture of lithium and beryllium fluoride salts with dissolved enriched uranium, plutonium, thorium or U-233 fluorides). The fission products dissolve in the salt and are removed continuously in an online reprocessing plant and replaced with new fuel or fertile material. Actinides remain in the reactor until they fission or are converted to higher actinides, which also then fission. A demonstration design was run at the Oak Ridge National Laboratory in the 1960s (Molten Salt Reactor Experiment or MSRE), but there has been little development or investment in the MSR technology since then. Potential roles for MSRs, in addition to electricity production, include minor actinide and plutonium consumption.
SMRs review
An assessment of small modular reactors has been published by academics at the University of Lincoln to help policymakers decide on their potential for use in the UK.
The main findings are that economies of scale make small modular reactors a suitable choice when the power to be installed is in the 1-3GWe range. This would require several SMRs to be clustered together and built on an incremental basis.
Dr Giorgio Locatelli, from the university’s school of engineering, says: “One SMR by itself is not economical because there would be a lot of fixed costs such as site licensing and design approvals. But if you can put in more than one, getting to at least an output of 1GWe, it becomes cost effective. Under that you build a gas-powered plant, making it easier and cheaper to build.”
Locatelli says that SMRs with an installed range of 1-3GWe could prove highly desirable for smaller nations, such as Belgium or Switzerland, or emerging nations in Africa. They could also have application where the energy sector is dominated by private rather than state-owned utilities which have less money to invest. “In such cases, an SMR could be built, and the money made from generation could fund the next one.”
He says that the reason no utility has so far opted for a small modular reactor is that investors are nervous of new technology: “So they opt for a mature solution, like a gas-fired power station. That’s the easiest route for them.”
Locatelli says SMRs have many benefits. “They are simple designs – both the pressuriser and the heat exchanger are inside the reactor pressure vessel – so they have safety benefits.
“And they can be built underground, which reduces security threats.”