Article - Issue 64, September 2015

Time to re-evaluate nuclear risks?, Responses to: SMR letter and Synthetic diamonds

Professor Gregg Butler, Grace McGlynn, John Campbell OBE FREng, Professor Jason Smith, and Alan Kemp.

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We read with interest Professor Gerry Thomas’s Health risks from nuclear accidents – fact or fiction? in Ingenia 63. The Opinion makes a good case for a re-evaluation of what the risks from nuclear energy actually mean for existing and future operations. These thoughts are offered about the consequences of the UK’s current approach.

In common with all industrial activities, the nuclear industry seeks to keep risks to the public well below 1 in 10,000 per annum for the public, and drives towards the broadly acceptable level of 1 in a million. Using the accepted calculations, this equates to a dose of 16.7 microsieverts per annum, but this has been ‘rounded down’ to 10 microsieverts. Despite, as Professor Thomas says, it being hard to show a categorical link between radiation and health below 100 millisieverts - UK policy and regulation measures seek to keep doses some 10,000 times lower.

In addition to this, the management of risk within the nuclear sector has resulted in a level of conservatism which has become a mindset: for every stage in a process, pessimistic assumptions are made as to the severity of any occurrence, and when these pessimisms are accumulated, actual risks can often be orders of magnitude less that those quoted. Such conservatism is understandable but, we believe, unnecessary and counter-productive.

One example typifies the problem. What about doses one gets through eating sea creatures with radioactivity in them? Find the creatures with the highest radioactivity levels and assume people eat them – for example, sea mice (Google them and shudder!) found off the coast of West Cumbria and included in a Centre for Environment Fisheries and Aquaculture Science/ Defra report. This was done, and an assumed consumption habit provided an impetus to further abate discharges, at a cost, when the chances of their consumption occurring were actually very small indeed.

This example might be considered to be trivial in isolation, but the process of introducing incremental margins is endemic in nuclear operations – and every extra precaution, or delay while additional impact assessments are performed, costs money – lots of money. The general public might think that the nuclear industry would seek to ‘cut corners and minimise costs’, whereas, in fact, the current culture and organisation seeks to maximise safety margins at every stage, to the detriment of progress and the economy, and with no real gain in safety or environmental impact.

The UK’s nuclear legacy must be cleaned up safely and quickly, while delivering best possible value for money. If that is to be the case, the actual risks, as clearly indicated from Professor Thomas’s article, need to be managed using the best available scientific evidence. That way, the waste cleanup would not cost the UK more than is necessary, giving us a minimum of unbuilt hospitals and unelectrified railways – because in the end the money is coming out of the same bank account!

Professor Gregg Butler
Director IDM Ltd, Head of Strategic
Assessment, Dalton Nuclear Institute,
University of Manchester

Grace McGlynn
Director IDM Ltd, Visiting Researcher Dalton
Nuclear Institute, University of Manchester

RESPONSE TO SMR LETTER

Figure1

Figure 1

In the June issue of Ingenia, Professor Fells makes a good case for an early start to produce small modular reactors (SMRs) in the UK – as did the original editorial Small but powerful in Ingenia 62. I, too, am keen that we make sensible use of nuclear energy. It gives me all the more concern, therefore, to note worrying technical problems such as the shutting down of two Belgian pressurised water reactors in March 2014 because of thousands of cracks in their pressure vessels. This dismal news was followed by the discovery of defects in the reactor pressure vessel of EDF Energy’s first European Pressurised Reactor in Flamanville 3, Northern France. These issues seriously handicap nuclear technology. In addition, of course, they do not help its public image.

Manufacturing issues are to be expected from some of our current steel casting techniques. This is particularly true of ingot casting as currently practised, and which is widely used for the production of special steels. Fortunately, it is much less true of continuous casting, but even this greatly improved casting method can probably be further improved. However, the practical problems of handling a ladle weighing up to 100 tonnes or more and setting it down on a receptor within a few millimetres, without damaging the target, are not trivial, and are traditionally avoided by pouring in air, at a distance from the entrance to the mould-filling system through a funnel.

Pour of steel

A pour of steel at the Falk foundry in 2007. The foreground operator is pulling down the lever to raise the stopper at the bottom of the ladle releasing the metal into the mould © Michael Schultz, author of Foundry Work

Figure 1 shows how a 50/50 mix of steel and air is created by the entry trumpet which acts as a venturi, pumping air into the steel during the pouring of the steel. The molten steel and air mix flows down into the mould, but as each entrained bubble bursts in the mould, it leaves its oxide skin as a permanent legacy. As the residual gas escapes, the walls of each bubble collapse together to make a double-oxide film, which I call a bifilm, an unbonded interface serving as a crack. The pouring method means that the steel ingot is filled with thousands of cracks. The cracks survive the subsequent working of the steel and enter service in the component.

Non-contact via a funnel (see photograph) is traditional but now known to damage the metal. Contact pouring is a proven solution to the problem. This technique requires that the ladle is lowered with sufficient accuracy to engage with the downgate and make a seal good enough to exclude the ingress of air. This requires improved engineering to avoid damaging the filling system, but the metallurgical benefits are dramatic.

Further engineering refinements and cost savings are possible. In addition, this mechanical technique can be supplemented with metallurgical techniques for lowering the melting point of the solid oxide on the liquid metal, converting it into a liquid, so that on its mutual impingement with other oxide films the two simply merge to create relatively harmless spherical droplets which mainly float out, avoiding the creation of a bifilm crack.

It is unthinkable that we should continue to specify steels for the new generation of reactors that do not comply with basic casting requirements to avoid these nearly invisible entrainment defects. The principles have been publicised for over a decade, and have been summarised recently. It is sobering to realise how easy it is to introduce into steel for reactor pressure vessels thousands of inclusions in the form of double oxide films which act as cracks. These cracks are not the result of stress, nor of solidification, but of the casting process itself. However, by improved casting techniques, it is just as easy to avoid such manufacturing issues with simultaneous reduced costs.

John Campbell OBE FREng
Author of Complete Casting Handbook
(Second Edition 2015)
Emeritus Professor of Casting Technology
Department of Metallurgy and Materials
The University of Birmingham

SYNTHETIC DIAMONDS

I read with interest the article by Professor Mark Newton about the uses of synthetic diamonds. Quantum technologies are an area of research in which diamond has shown considerable potential in the past 15 years. Now, work is being done to translate laboratory demonstrations into deployable systems.

One such area is quantum cryptography, which enables a security key to be generated in two remote locations in complete privacy. This is based on the impossibility of precisely measuring an unknown quantum state such as the polarisation of a photon. Other quantum technologies being developed will achieve enhanced performance of sensors or enable massively parallel computing, as mentioned in Professor Newton’s article.

The purely quantum mechanical phenomena used in these technologies are ‘superposition’ (where a physical system exists in two states simultaneously) and ‘entanglement’ (where a state describing multiple physical systems is not separable into states describing the systems individually). While these phenomena are present in all physical systems, it is only possible to harness them when states are preserved for long enough to be manipulated and recorded. This means that they must be free of rapid uncontrolled interactions which would change them in untraceable ways, a process known as decoherence.

Diamond provides an extremely ‘quiet’ environment for trapped atom-like defects, such as the nitrogen-vacancy defect referred to in Professor Newton’s article, that preserves their quantum state for long enough that functionality can be used. The quietness is obtained by the coincidence of three properties: diamond is stiff, so is low in thermal vibrations; it has a very wide electronic band gap, so has few thermally generated mobile charge carriers; and it is made of carbon, the most abundant isotope of which (relative atomic mass 12) has no nuclear spin. The result is that the coherence time for an electron spin in diamond can be of order milliseconds even at ambient temperatures, providing time for millions of operations at GHz clock rates, and equally providing exquisite sensitivity to local fields for sensing applications.

There is a technological problem to overcome though – diamond remains difficult to produce in large, high-quality single crystal wafers, and to process into devices. In addition, and in common with all quantum technology platforms, there are substantial challenges to be addressed in engineering systems that can operate beyond controlled laboratory environments.

Focused investments such as the new UK Quantum Technologies programme are bringing academic and industrial experts together to accelerate the emergence and uptake of quantum-enabled systems. For diamond, devices such as nanoscale sensors and single-photon sources are in relatively advanced stages of development, and are likely to be some of the first examples of quantum technologies to be put into practice over the next few years.

Professor Jason Smith
Workpackage leader, UK Hub in Networked
Quantum Information Technologies
University of Oxford


In Diamond Technology: Beyond Hardness in Ingenia 63, Professor Mark Newton identifies two factors that have taken the engineering application of diamond “beyond hardness”. These are the rapid improvement in the quality of synthetic diamond and the simultaneous exploitation of more than one of diamond’s exceptional properties. In my own area of laser engineering, diamond has gone from being intriguing, exotic, but ultimately impractical, to a credible engineering material that is starting to be commercially exploited.

The inconsistency of natural diamond does not lend itself to engineering; however, the ingenuity of diamond growth researchers means the crystal quality and impurity content of synthetic diamond can now be engineered with exquisite precision. This has provided laser engineers like me with a material we can routinely use within a laser.

At the Institute of Photonics, part of the Department of Physics at the University of Strathclyde in Glasgow, we have worked closely with the leading diamond grower Element Six Ltd in Harwell, and the wider diamond science community, to characterise synthetic diamond and prove it in laser applications.

Lasers typically produce considerable quantities of unwanted heat. Managing this heat effectively is usually the key to obtaining a high power, but still high-quality, output beam. The unrivalled thermal conductivity of diamond is therefore very attractive. Because this high thermal conductivity also comes with broad transparency and strong Raman scattering of light, it is possible to build efficient Raman lasers with diamond.

Professor Richard Mildren’s team at Macquarie University in Sydney demonstrated that this is a very efficient means to shift the wavelength of widely available pulsed lasers to hard-to-access spectral regions such as yellow and orange, which are important in dermatological and ophthalmological applications. We followed up this work by showing that conversion of continuously operating and tuneable lasers is also possible.

Recently, we demonstrated a monolithic diamond Raman laser that does away with the requirement for the alignment of external mirrors, potentially making diamond Raman laser easier to manufacture. This is achieved using microstructures on the diamond fabricated by inductively coupled plasma etching of diamond, in collaboration with Professor Martin Dawson and Dr Erdan Gu’s team, also at the Institute of Photonics.

The future for diamond science is bright, particularly if its multidisciplinary nature is underpinned by initiatives such as the EPSRC-funded Centre for Doctoral Training in Diamond Science and Technology. Where laser engineering meets diamond growth and defect physics, for example, this presents the intriguing possibility of harnessing diamond colour-centres – defects in the crystal structure that absorb and emit light – to develop a new generation of ultrashort pulse and tuneable lasers in the visible spectral region for precision spectroscopy.

Alan Kemp
Fraunhofer UK / RAEng Professor of Advanced Laser Engineering,
Institute of Photonics, Dept. of Physics,
University of Strathclyde

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