The challenges and opportunities of UK nuclear power, a materials perspective

One of the great things about our seminar series is the ability to bring in people from all over Imperial and further afield. This week’s seminar featured Dr Ben Britton very much a rising star here at the College and in the wider nuclear research community. His talk on the challenges and opportunities of UK nuclear power was very enlightening and he has written us the customary complementary blog. You can also download a copy of his slides[PDF].

I firmly believe that nuclear power is an important contributor to the future of the UK energy mix. This is borne not only from a trust in our ability to engineer complex and exciting technology that delivers societal change, but also underpinned by a belief that delivery of a low carbon future requires the UK to have a diverse energy mix. This energy mix includes renewables, energy storage, and nuclear power driving forward our economy.

In my talk, I took a simple approach in justifying that investment in the research and building of nuclear power stations is in the interest of the UK, and followed this with a technical insight into some of the research that my group and collaborators are conducting in providing predictive capability to understand the mechanical performance of engineering alloys.

As an engineer and material scientist in this domain, I am especially interested in how we can improve our knowledge of materials structures and their mechanical performance. I want to provide insights that enable us to understand how to make materials better, how to introduce them to the market faster, and how to make materials we currently use last longer by reducing conservatism in design and operation of high-risk high-value engineering components.

Figure 1: Energy consumption and population density rationalised against energy supply, originally by Prof David McKay
Figure 1: Energy consumption and population density rationalised against energy supply, originally by Prof David McKay

Firstly, to address why I think that nuclear in the UK is very important. Following the lead of the late Professor David MacKay, I consider the balance between our population, energy needs and our landmass (Figure 1), where I have added nuclear to the mix. Presentation of this data as a log-log format allows us to consider how each renewable energy solution can contribute, I have modified it to include nuclear power. My inclusion is to highlight that nuclear has the potential to contribute a substantive amount of base load electricity and support our energy mix.

If we consider that we rather like electricity, then we need to accept that we have to generate it. Our society is becoming more electrified (cars, heating) and our population is growing, so our total demand will go up. If we are to supply low carbon energy, we cannot build more fossil fuel power stations and we are left with choices regarding renewables (with storage or gas backing) or nuclear. Fundamentally, this motivates the UK’s interest in new build in nuclear, and current attention is focussed on the Hinkley Point C project(HPC). At present, the UK generates 20% of its electricity from nuclear power and consumes ~30-50 GWe per day. HPC offers a chance to build a reactor for generation in ~2025 (grid connection time estimates are scarce) and this is timely (see Figure 2), given the shutdown and retirement of the UK’s advance gas cooled reactor (AGR) fleet.

Figure 2: The life cycle of the current UK nuclear generating fleet.
Figure 2: The life cycle of the current UK nuclear generating fleet.

In the debate around HPC, I have tried to compare the offerings of the project against other electricity generation technologies. In these comparisons, I have purposely used order of magnitude calculations to provide a fair estimation of the offerings for different technologies and solutions.

Let’s assume that solar generates at 5 W/m2, 3.2 GWe HPC plant (that occupies an area of <1 km2) would require a solar farm that is 640 km2, or 1.6 times the area of the Isle of Wight. At £2k per kW this solar would cost £6.5bn and have a typical warranty of 25 years (HPC has an estimated lifetime of 60 years). The calculation for a wind farm is similar, wind power generates at 2.5 W/m2 and therefore a wind equivalent occupies 1,280 km2, an area equivalent to half the area of Derbyshire or the whole of Berkshire. This challenge is also made more difficult when we consider the intermittency of supply from renewables, and the less intermittent needs of UK consumers.

If we follow the argument that we want a 100% renewable scenario in the UK, we require 1 TWh generation, and ~1/3 of that as storage. One suggestion is to use batteries, and there’s some tremendously exciting engineering at Imperial and beyond into these technologies. However, making large scale battery technology we can deploy ‘today’ is challenging. As an example, the storage material in Li-ion batteries (at 2.5 MJ/L) for an energy demand of 0.33 TWh energy demand would occupy 200-600 Olympic sized swimming pools and at $600 per kWh would cost ~$180bn to construct.

These calculations illustrate, in my mind, that a 100% renewables solution to deliver power in the immediate future is not substantiated using current technologies, and therefore I believe that we must deliver low CO2 energy with a combined investment in large scale wind and solar power, together with an underpinning investment in nuclear electricity generation.

For my personal research interests, I am excited by opportunities to take fundamental understanding of mechanical performance at the microscopic level and to develop predictive capabilities that scale from the micro-meter length scale up to components.  My research group typically works on metals, and in the nuclear context zirconium is special as it is used as a fuel cladding material due to its good mechanical properties, low neutron absorption cross section (required for nuclear fission), and good corrosion resistance (important for a water reactor).

To highlight some recent success, together with colleagues from the University of Oxford, we successfully used small scale mechanical testing to predict the strength and flow of zirconium (Figure 3 and J. Gong, T.B. Britton, et al. Acta Mat (2015)).

In brief, I believe that optimising the use of engineering materials employed in high-value high-risk applications requires us to improve our predictive capability in materials deformation and performance, thus enabling us to safely reduce conservatism in component design. Furthermore, in nuclear applications, due to radioactivity of samples we typically want to handle small volumes of material. A metal is made up of individual grains (crystals of different atomic orientation), much like a wall is made up of bricks. Each of these units has a different performance – based upon their orientation with respect to the applied load. To provide predictive capability in understanding the structural integrity of zirconium metal, we have used small cantilevers of material which are ~µms in size to isolate individual units within a material.

Figure 3: Informing macroscopic properties from micro-cantilever measurements (reported more completely in Gong et al. Acta Mat (2015)) – going from small scale mechanical testing of individual grains within zirconium to predicting the performance of a real polycrystal of zirconium.
Figure 3: Informing macroscopic properties from micro-cantilever measurements (reported more completely in Gong et al. Acta Mat (2015)) – going from small scale mechanical testing of individual grains within zirconium to predicting the performance of a real polycrystal of zirconium.

Our micromechanical characterisation approach provides an encouraging leap in taking mechanical measurements from the microscale, to informing performance of real components through the generation of predictive models. Our initial experiments have been targeted at a nuclear context, as prediction of performance is important. Generating predictive capability enables us to cross cut employment of materials into different target environments and operation modes,  as many properties we are interested in will be related to the particular environments of each reactor (e.g. due to a high neutron flux and local corrosive environment). Furthermore, if we want to improve the time from design to grid connection, we must grow confidence through the development of physics based predictive capabilities. We believe that improving our understanding of current materials performance, as well as proving new techniques to explore the next generation of reactor grade materials, is critical in the evolving area of materials informed structural integrity assessment and design.

For more about my research group activities, please see our website: http://www.expmicromech.com or follow me on twitter @bmatb.

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