Next month the Energy Technologies Institute is expected to deliver a report on the prospects of building small modular nuclear reactors in the UK. The report is key to the future of the technology.
Loosely defined as nuclear reactors below 300MWe, these factory-built devices potentially have many benefits compared with large nuclear power plants: speed of build, reduced costs, more flexible siting and a strong safety case, to name but a few. However, there is one major disadvantage. Although dozens of civil small modular reactors (SMRs) are being designed, not one has been built yet.
There are clear drivers for the introduction of SMRs in the UK that explain the government’s interest. Flexibility of siting is a major advantage. Big nuclear plants have to be built near large amounts of cooling water, only available along the coast. SMRs do not have this requirement. There are also more potential sites with adequate grid connections that could accept SMRs. There are a number of suitable locations at the sites of former Magnox and gas and coal plants, which were set up to output around 600MW and so have good grid connections.
The Energy Technologies Institute is therefore assessing several technologies. The report will inform future government policy on the development of SMRs. However, there are clear front-runners among the contending SMR designs.
The institute’s experts acknowledge that the first kind of SMR to be built will most likely be of the “integral light water pressurised reactor” type. These designs are based on the well-proven principles of current pressurised water reactors (PWRs). The main difference with integral PWRs is that all the major components that would normally be found outside a PWR – the steam generators, coolant pumps and pressuriser – are contained inside the pressure vessel with the reactor core.
Aiming for 2023 deadline
The two most advanced integral PWR SMR designs in development are both vying for backing in the UK. One is being developed by US firm Nuscale Power, the other by the more established nuclear vendor Westinghouse. Oregon-based Nuscale looks set to be the first to market. The company plans to switch on its first 50MWe reactor in 2023 in Idaho and is on course to submit its design for approval to the US Nuclear Regulatory Commission (NRC) this year.
Tom Mundy, executive vice-president at Nuscale Power, is the engineer responsible for managing the project to build the world’s first SMR. He says: “We’re the furthest forward in programme development, certainly in the US. We’re the only one that intends in the near term to submit an application to the NRC. That’s several hundred million dollars worth of work already.”
After a 40-month certification process at the NRC, Nuscale’s engineers will finalise the design and then produce the documentation necessary to start fabrication and manufacturing. The reactor should take three years to build.
Development of Nuscale’s reactor started in 2000 at Oregon State University. The most distinctive element of its design is that it uses natural circulation instead of coolant pumps. The primary coolant flows up through the tubes and down through a centre column. Heat is removed by helical coiled steam generators. The slow flow is compensated for by the large surface area of the heat exchangers.
Another key feature is that the containment vessel is submerged in the ultimate heat sink for core cooling. In the event of an accident where power is lost, the heat transfer goes from the reactor wall straight into the water. “It’s the only SMR that has the containment as part of the module,” says Mundy.
Ease of transport
Nuscale’s SMR is designed to run for 60 years and to output 160MW of thermal energy, with a power conversion unit that produces 50MWe, a relatively small electrical output even for a proposed SMR. The size of the reactor isn’t arbitrary. Mundy says: “Our chief technology officer started with a clean sheet of paper. His thinking was that the only way to make the reactor economic was to limit the size so it’s easy to move – by rail, truck or barge.
“So the containment was sized first. Because the containment is also the heat transfer surface, the containment determined the size of the core. That sized everything thereafter. It’s how we arrived at 160MW thermal.”
Mundy adds that the thermal output could be put to use in industrial applications, such as chemicals production, enhanced oil recovery or district heating. Nuscale’s power stations are also designed to house up to 12 modules each, producing up to 600MWe gross.
The three-year build time is achieved with modular construction. Three main modules are built and shipped from the factory. These are lowered into a stand and the modules bolted up through normal flanging. The reactor is split into upper containment, lower containment and the lower reactor vessel.
Access to the reactor core for refuelling is achieved by separating sections – the upper containment is lifted off and placed in a dry dock. The dock can be pumped down for inspection. Mundy says: “The components are all standard, the fuel is the same standard PWR fuel, it’s just half height. The control rod drives are standard mag jack mechanisms and are all used in PWRs. The valves are similar. It’s just innovative use of tried-and-tested PWR technology.”
Nuscale is backed by engineering giant Fluor, which acquired a majority interest in the company in 2011. The US Department of Energy has also pumped money into the project, awarding Nuscale £159 million in 2013 to pursue licensing approval and £152 million in 2014. The 2013 funding decision selected the design from among several others, including Westinghouse’s SMR.
Following the energy department’s decision to fund Nuscale, Westinghouse “paused” efforts to develop its SMR design in the US. Instead, the company shifted its focus to the UK market. Last summer it offered to set up a UK-based company to develop its SMR. The offer catalysed the government’s interest in SMRs, but perhaps didn’t quite have the desired effect. In November the Chancellor announced that the government was to run a competition to identify the “best value” SMR design for the UK to build in the 2020s.
However, Simon Marshall, key accounts director at Westinghouse, is adamant that his company still holds the most important advantage – the economic one. As well as setting up a UK-based development company, Westinghouse would also supply all the intellectual property needed to advance the design. It has committed to partnering with British companies throughout the whole development process, including the Generic Design Assessment (GDA) licensing and detailed design.
Marshall says: “We will use engineers in the UK through the whole process to design and build the first unit with a supply chain that would be 70-85% British. “In particular, manufacturing Westinghouse SMR fuel at Springfields will secure the future of the UK’s nuclear fuel manufacturing capability and safeguard highly skilled UK jobs – something no other SMR provider offers. We think it’s a very attractive offer.”
The idea that SMRs could revitalise key parts of the UK nuclear industry is tantalising. Although there would not be a guarantee of work, Marshall says there would be opportunities for UK firms to make high-value components, such as the reactor pressure vessels and coolant pumps and the steam generators. The components needed for an SMR are relatively small,
which means more companies could potentially be able to supply parts.
He says: “Components like reactor coolant pumps on 1GW plants are huge, two storeys high, that the UK can’t supply. With the SMR they are significantly smaller and within the capability of UK suppliers.
“The government could take a golden share in the company we have proposed. In return they would require a significant fraction of the work to be done in the UK. That’s what we can commit to. It’s hugely exciting.”
Westinghouse describes its SMR as a “mature concept design”that reduces deployment risk. Marshall says: “Investors look at risk and that we’ve been doing this for 60 years. Half the operating reactors in the world are based on Westinghouse technology. Every day we learn more about modular construction from our Chinese and US plants. Would you buy a reactor from someone that’s never designed nor built one before?”
He anticipates that a political decision on SMRs could take another year to make. It would then take around a year to set up the UK company, a year to start the licensing process, and at the most four years for regulatory approval and then three years to build the first reactor. This would put commissioning for the first reactor at around 2027. Not first to market, but maybe close enough.
Timescales questioned
Westinghouse has experience of the UK’s regulatory environment, having gone through the GDA process for the larger AP1000 reactor already. “We have seen some of the timescales being suggested for SMR deployment in the UK which, based on our experience, lack credibility,” says Marshall. “Where some timescales are aspirational, ours are based on real current experience.”
There are similarities between Westinghouse’s and Nuscale’s designs because they share the same PWR heritage. Westinghouse’s SMR would use smaller versions of many of the AP1000 components, although Marshall is not comfortable calling the SMR a “mini-
AP1000”. It would, for example, use the same instrumentation and control and safety systems and the same fuel, at around half the height.
Maintenance would be carried out in a similar way – the top half of the unit would be removed for refuelling and maintenance access. From a fuel perspective, 24-month cycles are planned, making the reactor’s availability higher than 93%. However, unlike the Nuscale design, each Westinghouse SMR would be a standalone unit, with no shared systems or services. But there is nothing stopping SMRs being sited together if the grid allows.
Marshall says that all of the systems in the SMR are at Technology Readiness Level 6 or above: “It’s an innovative packaging of mature components. The instrumentation and control platforms are already operating. The fuel is already operating. The passive safety systems will begin operating in China next year. They are configured differently in the SMR, because it is integral, but the functionality is the same.”
The main “evolutions” are in the passive safety features and modular approach to construction. Whereas about a third of the AP1000 is designed to be of modular construction, the Westinghouse SMR design is entirely modular.
Westinghouse would build a module assembly factory in the UK. The sub-assembly modules would be transported to the site and assembled into super-modules, which would then be installed. The process should yield significant reductions in build time and cost through repeatability.
However, these potential benefits are largely unproven, says Marshall. “In France the cost didn’t reduce over time because of various reasons. But it did in the Korean and Japanese fleet. There’s lots of research saying the cost reductions happen between seven and 10 units. Whether that truly happens here is the academic question that needs answering.”
Ultimately, deciding which designs offer the best value for the UK is a complex judgement. What is clear is that the field of designs from which to choose the first to market is narrow, and that deciding between the two front-runners will require an informed and experienced technical and business assessment. The alternative, of course, would be to select both for construction.