While many different fuels are used in combined heat and power generation, one that has yet to make its mark is nuclear fission. However, a UK consortium believes it will be able to break into the CHP market with its design, writes David Flin
In 2008, URENCO, a global uranium enrichment company based in the UK, initiated a project to develop a nuclear micro-reactor that is able to produce local power and heat for a range of energy needs. The intention is for the U-Battery reactor to target the market for industrial power units and off-grid applications.
The University of Manchester in the UK and Delft University of Technology in the Netherlands collaborated to design a nuclear micro-reactor that would work like a battery, allowing the modules to be manufactured in series and transported to the customer’s site. The universities completed the feasibility study in 2011, culminating in the U-Battery concept. URENCO is working with Amec Foster Wheeler, Atkins, Cammell Laird and Laing O’Rourke to develop the system.
The role of the U-Battery
The U-Battery is a unit that is capable of generating 4 MWe and 10 MWth, able to provide process heat up to 800°C. It is a modular system, with one potential model of operation being build-own-operate, with a specialist operator – for example, U-Battery Power Company – running the plant for the end user.
Figure 1. Generation hall schematic
Dr Paul Harding, chair of the U-Battery Consortium, says the system could be used in many ways: to provide backup power, as a source of off-grid power for remote locations and, because it can rapidly shift output levels, it could also work alongside intermittent renewables in a load-following capacity. He says there have been discussions about the system with a number of potential customers, including discussions with Canadian organizations regarding its use to provide power to remote communities in northern Canada, and with Polish organizations regarding its possible use at heavy industrial sites to help deal with the issue of fuel supply security and to enable decarbonization, reducing the level of coal-fired generation in the country. It is suitable for use in desalination projects in the Middle East and Africa and as backup power supply for large nuclear power plants, and it could also be used to power hydrogen generation.
Figure 2. Projection of future installations (figures from independent market study)
Operating in a harsh environment would not be a significant problem for the U-Battery. Heavy snowfall and exceptionally low ambient temperatures do not affect its ability to operate, and it does not need systems to prevent the freezing of fuel. The fact that it can provide continuous power from a fuel cartridge for at least five years without refuelling enables it to provide supply security in situations where fuel supply might be problematic, be it for climatic, geographical, logistical or geopolitical reasons.
How will the system work?
The U-Battery is a modular system, with each unit operating with an output of up to 4 MWe and 10 MWth. The reactor is powered by TRISO (Tri-structural Isotropic) fuel, a triple-coated spherical particle about the size of a grain of sand which is coated in layers of graphite and silicon carbide. The small spheres are embedded in a graphite matrix constituting compacts which are used to build prismatic fuel elements forming the core. The structure of TRISO fuel enables it to maintain integrity under temperatures of up to at least 1600°C, and the fuel is accident-tolerant. TRISO fuel was originally developed in the 1980s, and was demonstrated and used at the Dragon reactor in Winfrith, UK.
The reactor is cooled by helium gas, thus avoiding the use of water as a coolant and consequently reducing the use of water in the system to very low levels, which is important in water-poor environments. The coolant is used to heat up nitrogen in an intermediate heat exchanger, which is used to drive a turbine.
The modular design of the U-Battery will enable multiple units to be built at a factory, then fully tested before being shipped to site for simple construction. Compared to larger nuclear facilities, this greatly simplifies civil works at the site, allowing for installation in six to 12 months, enabling it to be cost competitive.
The potential markets and applications for the U-Battery vary by country. In the UK and many other industrialized nations, the main market is likely to be embedded generation at industrial sites. In addition, many sites will be able to make use of the cogeneration capability. A particular use mentioned by Dr Harding was as an emergency back-up generator for large nuclear power plants. In this instance, obtaining an operating license is simplified, and the owners of the plant and the local population are familiar with the presence of nuclear power. Studies have been carried out which show that it is generally the case that people who live close to nuclear power plants have a positive view of the technology involved.
|Figure 3. TRISO Fuel Source: URENCO|
One possible model for operating U-Battery is to use a build-own operator. This will significantly reduce the operating costs. There has been a rapid growth in the capability of remote monitoring equipment over the last ten years, and this has enabled operators to monitor and operate several different locations from a central site.
There has been interest from Canada to use the system in possibly hundreds of remote communities that are not connected to a national grid, and where transport infrastructure is sparse. The U-Battery, which requires minimal refuelling once in operation, avoids the need for a significant fuel supply infrastructure, be it by pipeline or by transport. This would also be true for many parts of the developing world, and would eliminate the need to extend the national grid into remote regions.
Desalination plants in the Middle East and Africa are also viewed as being a good potential market, along with generating hydrogen for hydrogen-powered vehicles.
The U-Battery has fast ramping capability, enabling it to run up from no-load to full power in seconds. This makes it suitable for use alongside intermittent renewables, and thus enabling it to balance power supply and demand. For example, use in locations, such as remote islands, which are isolated from the grid and which have a high level of intermittent renewables such as wind would be attractive. This is enhanced because the U-Battery will have low logistical requirements, which will be beneficial in remote locations in harsh environmental conditions.
Dr Harding also mentioned other possible applications for U-Battery, including its possible use in energy storage systems, such as in pumped storage hydropower plants, where it is used to pump water uphill into a reservoir, to drive hydropower turbines during periods of high power demand. It can also be used to generate hydrogen to enable energy storage through hydrogen-based fuel cells.
Timetable for development
U-Battery is still at an early stage of development but many of the component parts use already existing technology. It is currently in its Phase 1 design, to develop the basic design and costing. During the first quarter of 2016, many of the components of the programme had been reviewed as part of the design and cost estimation, and were confirmed to be at medium to high Technology Readiness Levels. Areas that have been recently developed include the concept design of the Reactor Pressure Vessel and the Intermediate Heat Exchanger.
U-Battery expects to start detailed design work in 2018, with a demonstration plant planned for the early 2020s, leading to the start of commercial operation in the mid-2020s. For the second half of the decade, U-Battery anticipates a market of ‘several tens of’ (40-100) units annually, rising to 200-300 annually by the mid-2030s.
Dr Harding said that the next two years will be a critical period for U-Battery, to undertake the design work, and get the product to a stage where the investment risk will be reduced.
The key question regarding whether or not the U-Battery system is successful comes down to whether or not it will be cost-competitive. According to U-Battery, they carried out two independent market studies in 2014 and 2015. These studies said that the system would be competitive with current fossil-fuelled CHP systems.
The U-Battery system will typically have a low operating cost, and the studies suggested that gas would be the closest competitor in the CHP field. Because of the variability of gas prices, one has to make some assumptions about the price of gas in the future. It is worth noting that it is currently at a 10-year low, and it is more likely to rise than fall in price in the future.
Possibly the biggest problem that system will have in gaining traction is that of public perception. At best, the general public are cautious regarding any form of nuclear power, and the U-Battery is intended to be located in heavy industrial settings as one of its prime markets.
Dr Harding said that the opinion of people who live close to nuclear sites was generally more positive towards nuclear power than the average, as they became aware of the benefits it brings to the local area.
Because of this, he said that the first units would be at pre-existing nuclear sites. Not only would it be easier to gain local acceptance, it would also simplify the licensing arrangements. In general, in discussions that have been held with potential customers, there was a positive attitude towards the use of nuclear power. The intention is that this will allow deployment of the first units of the system, and will enable the wider public to see its safe use, and thus facilitate greater public acceptance, leading to the wider application of U-Battery.
David Flin is a freelance journalist focusing on the energy sector This article is available on-line. Please visit www.decentralized-energy.com