Tag Archives: power stations

Graphite for Very High Temperature Reactors (VHTR)

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One of the implications of the second law of thermodynamics is that the thermal efficiency of power stations increases with their operating temperature.  Thus, there is a drive to increase the operating temperature in the next generation of nuclear power stations, known as Generation IV reactors.  In one type of Generation IV reactors, known as the Very High Temperature Reactor (VHTR), graphite is designed to be both the moderator for neutrons and a structural element of the reactor.  Although the probability of damage in an accident is extremely low, it is important to consider the consequences of damage causing the core of the reactor to be exposed to air.  In these circumstances, with the core temperature at about 1600°C, the graphite would be exposed to severe oxidation by the air that could change its material properties and ability to function as a moderator and structural element.  Therefore, in recent research, my research group has been working with colleagues at the UK National Nuclear Laboratory (NNL) and at the National Tsing Hua University (NTHU) in Taiwan to conduct experiments on nuclear graphite over a range of temperatures.  Our recently published article shows that all grades of nuclear graphite show increased rates of oxidation for temperatures above 1200°C.  We found that large filler particles using a pitch-based graphite rather than a petroleum-based graphite gave higher oxidation resistance at these elevated temperatures.  This data is likely to be important in the design and operations of the next generation of nuclear power stations.

The work described above was supported by the NTHU-University of Liverpool Dual PhD Programme [see ‘Citizens of the world‘ on November 27th, 2019] and NNL.  This is the fifth, and for the moment last, in a series of posts on recent work published by my research group.  The others are: ‘Salt increases nanoparticle diffusion‘ on April 22nd, 2020; ‘Spatio-temporal damage maps for composite materials‘ on May 6th, 2020; ‘Thinking out of the box leads to digital image correlation through space‘ on June 24th, 2020; and, ‘Potential dynamic buckling in hypersonic vehicle skin‘ on July 1st, 2020.

The image is figure 5: SEM micrographs of the surface of petroleum-based IG-110 graphite samples oxidized at various temperatures from Lo IH, Tzelepi A, Patterson EA, Yeh TK. A study of the relationship between microstructure and oxidation effects in nuclear graphite at very high temperatures.  J. Nuclear Materials. 501:361-70, 2018.

Source:

Lo I-H, Yeh T-K, Patterson EA & Tzelepi A, Comparison of oxidation behaviour of nuclear graphite grades at very high temperatures, J. Nuclear Materials, 532:152054, 2020.

Reinforcement ensures long-term structural integrity

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Last month when I was in Taiwan [see ‘Ancient Standards‘ on January 29th, 2020] , I visited Kuosheng Nuclear Power Plant which has a pair of boiling water reactors that each generate 986 MWe, or between them about 7% of Taiwan’s electricity.  The power station is approaching the end of its licensed life in around 2023 after being constructed in 1978 and delivering electricity commercially for about 40 years, since the early 1980’s.  There is an excellent exhibition centre at the power station that includes the life-size mock-up of the reinforcement rods in the concrete of the reactors shown in the photograph.  I am used to seeing reinforcing bar, or rebar as it is known, between 6 to 12mm in diameter on building site, but I had never seen any of this diameter (about 40 to 50mm diameter) or in such a dense grid.  On the other hand, we are not building any nuclear power stations in the UK at the moment so there aren’t many opportunities to see closeup the scale of structure required.

Isolated systems in nature?

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Is a coconut an isolated thermodynamic system?  This is a question that I have been thinking about this week.  A coconut appears to be impermeable to matter since its milk does not leak out and it might be insulated against heat transfer because its husk is used for insulation in some building products.  If you are wondering why I am pondering such matters, then it is because, once again, I am teaching thermodynamics to our first year students (see ‘Pluralistic Ignorance‘ on May 1st, 2019).  It is a class of more than 200 students and I am using a blended learning environment (post on 14th November 2018) that combines lectures with the units of the massive open online course (MOOC) that I developed some years ago (see ‘Engaging learners on-line‘ on May 25th, 2016).  However, before devotees of MOOCs get excited, I should add that the online course is neither massive nor open because we have restricted it to our university students.  In my first lecture, I talked about the concept of defining the system of interest for thermodynamic analysis by drawing boundaries (see ‘Drawing boundaries‘ on December 19th, 2012).  The choice of the system boundary has a strong influence on the answers we will obtain and the simplicity of the analysis we will need to perform.  For instance, drawing the system boundary around an electric car makes it appear carbon neutral and very efficient but including the fossil fuel power station that provides the electricity reveals substantial carbon emissions and significant reductions in efficiency.  I also talked about different types of system, for example: open systems across whose boundaries both matter and energy can move; closed systems that do not allow matter to flow across their boundaries but allow energy transfers; and, isolated systems that do not permit energy or matter to transfer across their boundaries.  It is difficult to identify closed systems in nature (see ‘Revisiting closed systems in nature‘ on October 5th, 2016); and so, once again I asked the students to suggest candidates but then I started to think about examples of isolated systems.  I suspect that completely isolated systems do not exist; however, some systems can be approximated to the concept and considering them to be so, simplifies their analysis.  However, I am happy to be corrected if anyone can think of one!

Image: https://www.flickr.com/photos/yimhafiz/4031507140 CC BY 2.0

Thought leadership in fusion engineering

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The harnessing of fusion energy has become something of a holy grail – sought after by many without much apparent progress.  It is the energy process that ‘powers’ the stars and if we could reproduce it on earth in a controlled environment then it would offer almost unlimited energy with very low environmental costs.  However, understanding the science is an enormous challenge and the engineering task to design, build and operate a fusion-fuelled power station is even greater.  The engineering difficulties originate from the combination of two factors: the emergent behaviour present in the complex system and that it has never been done before.  Engineering has achieved lots of firsts but usually through incremental development; however, with fusion energy it would appear that it will only work when all of the required conditions are present.  In other words, incremental development is not viable and we need everything ready before flicking the switch.  Not surprisingly, engineers are cautious about flicking switches when they are not sure what will happen.  Yet, the potential benefits of getting it right are huge; so, we would really like to do it.  Hence, the holy grail status: much sought after and offering infinite abundance.

Last week I joined the search, or at least offered guidance to those searching, by publishing an article in Royal Society Open Science on ‘An integrated digital framework for the design, build and operation of fusion power plants‘.  Working with colleagues at the Culham Centre for Fusion Energy, Richard Taylor and I have taken our earlier work on an integrated nuclear digital environment for the nuclear energy using fission [see ‘Enabling or disruptive technology for nuclear engineering?‘ on january 28th, 2015] and combined it with the hierarchical pyramid of testing and simulation used in the aerospace industry [see ‘Hierarchical modelling in engineering and biology‘ on March 14th, 2018] to create a framework that can be used to guide the exploration of large design domains using computational models within a distributed and collaborative community of engineers and scientists.  We hope it will shorten development times, reduce design and build costs, and improve credibility, operability, reliability and safety.  It is a long list of potential benefits for a relatively simple idea in a relatively short paper (only 12 pages).  Follow the link to find out more – it is an open access paper, so it’s free.

References

Patterson EA, Taylor RJ & Bankhead M, A framework for an integrated nuclear digital environment, Progress in Nuclear Energy, 87:97-103, 2016.

Patterson EA, Purdie S, Taylor RJ & Waldon C, An integrated digital framework for the design, build and operation of fusion power plants, Royal Society Open Science, 6(10):181847, 2019.