The smallest of small nuclear reactors, about the size of a squash court, is finding big backers and global markets.
More from: Alternative Energy | UK independence
The U-battery micro-reactor is among 38 entries in the UK-government’s small modular reactor (SMR) competition, launched earlier this year. The competition is intended to begin a dialogue with this emerging industry and is attracting scores of designs from around the world.
Like other designs, U-Battery’s factory-built modular design would be manufactured for assembly – being cheaper and faster to deploy than large reactors.
But U-Battery’s main differentiator among SMRs is its size. At 10MW, it is 3% of the size and power of some of the largest SMR designs.
Enriched uranium manufacturer Urenco has backed it. Urenco performs about a third of the world’s nuclear fuel enrichment. U-Battery’s other partners for construction and shipping expertise include consultants Amec and Atkins, contractor Laing O’Rourke and shipbuilder Cammell Laird.
Not all SMRs are created equally. Light water reactors, liquid metal-cooled reactors and molten salt reactors – all are at various stages of development. The U-Battery concept has been developed a one of a group of “high temperature reactors”, which could run at about 800°C.
The heat generating nuclear reaction process is relatively simple, and kept in the core. From there it is a simple process of heating helium gas, through a heat exchanger which then heats nitrogen, which then drives a generator.
You’re putting all your safety in the fuel, so you don’t need any of the large complicated systems of the larger systems
Steve Threllfall, U-Battery
But at its heart are special tristructural-isotropic (Triso) spherical micro-fuel particles, each less than a millimetre in size. With enriched uranium at their core, they are covered in pyrolytic carbon and radiation-resistant silicon carbide. Each sphere is essentially a pressure vessel to trap the radioactive byproducts of nuclear fission. The spheres are fabricated into cylindrical “compacts”, which are housed inside layers of graphite.
U battery 1
“This makes it all very accident tolerant – you’re putting all your safety in the fuel, so you don’t need any of the large complicated systems of the larger systems,” says U-battery general manager Steve Threlfall.
The fuel and moderator are integrated into a single prismatic block. The prismatic blocks, 360mm across, 800mm high, would number 24 in the core – four high and six around. If run at higher temperatures, the outer layers of graphite expand, letting neutrons escape, shutting the process down.
It has been called “meltdown-proof” but testing continues at the University of Manchester.
“We haven’t been able to break it….they’ve proven it works up to 1,600°C, now they’re pushing it to 1,800°C,” says Threlfall.
The downside of the advanced Triso fuel is its added manufacturing cost. U-battery will not divulge just how much more, that is a trade secret. Firstly the fuel must be 19.5% enriched, rather than the 4% to 5% required of standard European Pressurised Reactors (EPRs). But more importantly, creating the multi-layered particles is expensive. And the fuel’s complexity makes it almost impossible to reprocess, potentially influencing future economics.
The first high temperature reactor, named Dragon, was built in the 1960s, so the technology has been around for a long time. But it did not get past the prototyping stage. China has taken up the baton, making small prototypes, in preparation for a large 200MW plant that is due to be commissioned next year.
Threlfall says the U-battery’s size lends itself to off-grid activities: providing heat and electricity, or just electricity, for industrial sites or remote communities.
“You can also use it for desalination, hydrogen separation, and another potential – taking out and replacing the diesel backup systems for large nuclear plants.”
But the markets gaining traction are Poland and Canada. Poland wants SMRs for industrial heat, replacing ageing boilers. Canada’s northern expanse hosts hundreds if not thousands of small communities with populations of up to 5,000, mostly
using diesel power because they are off-grid.
“So we were over there in Canada two weeks ago, we did a run around the provincial governments, federal government, met with the minister for natural resources, power companies… along with Canadian nuclear labs.
“The conclusion is [U-battery] is perfect for these communities where other SMRs are just too big.”
Threlfall notes that this decentralised model – putting the power at the point of use – removes much of the cost of delivering power, whether through a grid as in the UK, or from not having to truck gallons of diesel through Canada. These delivery costs often double the price of energy for customers.
Five year refuel cycle
The U-battery would also run for five years without needing to be refuelled, and Threlfall says it could run without on-site operators, being controlled remotely. “But a lot of this is down to discussions with regulators, what they require; a lot of countries require one person for security on site.”
Threlfall says the U-battery micro-model has virtually no competition. American company Ultrasafe uses the Triso fuel, but in a different configuration, where “pebbles” move around within the reactor.
“We both have a religious belief in one or the other method. Our belief is the best model is keeping everything stable, apart from the gas that flows through. [Ultrasafe] thinks it gets a better fuel burn-up with fuel that moves around. I’d say if you want to keep something in remote Canada for five years you want as few moving parts as possible.”
Growing to meet demand
As the UK government prepares to release a “roadmap” to guide the SMR competition entrants, U-battery is scoping how to build its design team, searching within the partner companies. It expects to go from about a dozen staff to about 50 in 2017.
The first three reactors would be built on site from supplied components, buying in the reactor pressure vessel, graphite blocks and turbine – all readily available from UK suppliers.
“And we want to do that [use UK suppliers], because once we move past the first three, we want to pre-assemble, probably involving five modules that each fit on the back of a truck,” says Threlfall.
“All of the jobs could be in the UK, equally though, other countries have an interest. It came up in talks in Canada: if it hosts them, can they also build them? Every country has its own industrial strategy to take care of.”
While Poland and Canada are keen, international public opinion is far from overwhelmingly positive. Following 2011’s Fukushima disaster in Japan, Germany decided to close its nuclear programme. But Threlfall says nuclear will be a useful part of the international energy mix “for another couple of hundred years”.
“If you look at developing countries, and as China and India expand, they really need to do something, otherwise they end up polluting… it’s [nuclear is] the only thing that can address the challenges ahead.