Energy Secretary Chu on the Prospects for Carbon Sequestration

At the conclusion of the Carbon Sequestration Leadership Forum's 3rd Ministerial Meeting last week in London, the ministerial communique strongly endorsed the potential of carbon sequestration as a climate change mitigation technology, and urged member countries and other stakeholders to step up their efforts to research, develop and commercialize the technology on an aggressive timeline to 2020, calling for "many more" sequestration demonstration projects than are currently under way.

Carbon sequestration has unfortunately suffered from a rather narrow definition in the public perception, partly on account of one of its precursor technologies having arisen primarily in the oil sector, where enhanced oil recovery from existing fields was enabled by the injection of carbon dioxide directly into the oil fields. Being a heavier-than-oil supercritical liquid, carbon dioxide can force crude oil to the surface in oilfields where it would otherwise have remained trapped within geological formations. This version of carbon sequestration has come to be considered 'canonical' - while in truth, it is just a geological sequestration method, while there are also terrestrial-biologic and oceanic sequestration modes, among many others. Photosynthesis itself is a carbon dioxide sequestration technology (not yet mimicked effectively by human technology) and so are lungs, where gas exchange between blood vessels (alveoli) effectively separates carbon dioxide from blood supply and also replenishes it with oxygen!

In his letter to his ministerial colleagues, Secretary Chu further endorsed and encouraged the adoption of an aggressive timeline, importantly lending his considerable scientific prestige to a technology that so far had been viewed as somewhat tentative even by its proponents, going so far as to call for a deployment timeline to begin 10 years from now; cautioning also that success will not come easily, asking for a strong, highly focused R&D program, and making a 'call to action' to all US Department of Energy laboratories, as well as to corresponding organizations around the world. Secretary Chu's letter to his ministerial colleagues around the world follows his Oct 2, 2009 editorial in Science Magazine, where he outlined the arguments supporting a stronger push toward carbon sequestration technology directed to a scientific audience.

While work on carbon sequestration projects has been going on for the past while, it has so far been occurring on a more relaxed timeline and with a much greater degree of tentativeness. Secretary Chu's strong endorsement will undoubtedly increase the level of near-term effort and activity in the area, and spur the technology forward in the medium term, bringing it into the forefront of climate change mitigation options for the world community. Secretary Chu's letter also places sequestration technology in the middle of the power generation cycle - rather than at the very end. He formulates sequestration as a technology alongside such related others as cleaner oxygenated combustion as well as ultrasupercritical technology which, by using steam at higher temperatures and pressures, raises the thermodynamic efficiency of the power generation process, thus producing more power per unit of coal used, and contributing to a decrease in carbon emissions.

Secretary Chu also situates carbon sequestration more properly within the suite of climate change mitigation options - which would include economy-wide improvements in energy efficiency, conservation, as well as carbon-free generation of energy. Part of the challenge of assigning priorities (and funding) to different R&D options is also assessing the urgency of the sub-problem that the technology is designed to solve, relative to the intrinsic merit and state of development of the technology itself. What carbon sequestration can do, if successfully developed and deployed, is to cut the flow rate of carbon dioxide emission into the atmosphere drastically, even while the energy generation mix remains roughly the same as now (as it will for at least the next couple decades). Deployment timeframes for energy generation options that significantly reduce emissions relative to the current mix are all a decade or more beyond (with the possible exception of wind turbines). Therefore, a technology that promises to cut the net emissions from the existing generation mix must be moved up the priority, effort and funding list. This is the judgment call that I see Secretary Chu as having made. The subtext is the realization that Climate Change itself is in the here and now; arresting the net flow of carbon dioxide is urgent; even while technologies such as solar or fusion that promise to reduce the gross flow in the future are aggressively developed. What this endorsement will also do is make the entire field of sequestration science more 'sexy', attracting physicists, biologists and chemists into the field, that is otherwise dominated by petroleum geologists or engineers.

Just prior to the Ministerial meeting, the Carbon Sequestration Leadership Forum added ten new R&D Projects to its portfolio, including one each in Texas, British Columbia and Alberta.

Postscript: After I wrote this post, I discovered a presentation by Prof. Sir Christopher Llewellyn Smith, FRS, on Energy Options. One of his slides particularly well illustrates the point I make above on carbon sequestration not being just a post-combustion technology, but being a suite of technologies potentially applicable before, during and after the actual combustion:

Canada: Nuclear Renaissance or Nuclear Vita Nova?

The Nuclear Renaissance has been a much-awaited thing in Canada, for at least the last four years, if not longer. Renaissance, of course, suggests the idea of 'rebirth', a beginning anew of a life once lived; with the subtext that things in this rebirthed life will be much the same as before, only newer.

Over the last several decades, the Canadian nuclear industry evolved to encompass three main sectors: Uranium Mining, Reactors for Power Production, and Radioisotopes for Medical Uses. Of these three, the reactor segment has had the greatest visibility, while, on a worldwide basis, it was actually the uranium mining and medical radioisotope segments which had the greatest relative market share. A 'renaissance' in the Canadian nuclear sector therefore came to be understood primarily in terms of new reactors, and new reactors essentially of the same CANDU pressure-tube configuration that Canada pioneered and which now are operating in many other countries as well.

But in his speech at the US Nuclear Regulatory Commission's Annual Regulatory Information Conference in March 2009, NRC-RIC-2009, the Deputy Director General of the International Atomic Energy Agency (IAEA), Mr. Tomohiro Taniguchi of Japan, speaking at the session on Global Perspectives on the Nuclear Renaissance, introduced a new phrase that he hoped would refocus the emphasis on new ways of doing things in the new nuclear age: Nuclear Vita Nova:

I, on the other hand, view this reality as a Vita Nova, or new life, because the nuclear community needs new ideas and innovative thinking to address new challenges, rather than a simple revival of the "good old days."

At the current juncture, when Nuclear New Build - which seemed imminent just a few months ago - has been indefinitely postponed in the main Canadian province; when the main Canadian reactor builder faces an uncertain future; and when the main private reactor operator in Canada has withdrawn its license applications for new nuclear reactors - it is certainly worth pondering what is in store for the Canadian nuclear sector - a Renaissance, or a Vita Nova? And if it is to be the latter, might the relative (and perceived) importance of the three main sectors change from what it was in the past? At the moment the answer is not clear, but the singular salience of the question must certainly be recognized.

(Dr. Taniguchi took care to mention at the end of his talk, for the benefit of those who might have missed the allusion, which, given his audience, was probably everybody - that his neologism 'Vita Nova' was actually the Latin form of the Italian La Vita Nuova, the title of a collection of verse that Dante Alighieri wrote in 1295, being an expression of the medieval genre of courtly love. Incidentally, the incoming Director General of the IAEA, beginning 01 December 2009, is also from Japan - Yukiya Amano. He will be taking over from Dr. Mohamed El-Baradei of Egypt, who has been named Director General Emeritus, an honor he shares with Dr. Hans Blix. Dr. Amano's appointment to the Director-Generalship of the IAEA will be ratified during the 53rd General Conference of the IAEA in Vienna, 14-18 September 2009. Like Dr. El-Baradei and Dr. Blix, Dr. Amano is also a lawyer. By coincidence, the current Director-General of ITER, Mr. Kaname Ikeda, and the current Executive Director of the International Energy Agency (IEA), Mr. Nobuo Tanaka, are also Japanese.)


Update: After I wrote this post, I discovered that on the TV Ontario program The Agenda, the season-opening episode on 8th September had been on Canada's Nuclear Future. I am pleased to embed the video, featuring an extremely spirited discussion (in which, as Steve Paikin, the host, quipped, they ran out of time but clearly not energy. The astute physicist reader of this blog will immediately see Steve Paikin's probably unintended pun here - since energy and time are classically canonically conjugate variables, they are related through a quantum uncertainty principle - the more precisely you bound one of them [in this case, time], the more uncertain the other will be!):

The Other Chandrasekhar Limit

As a schoolboy in India, one couldn't help knowing of the Chandrasekhar mass limit. I distinctly remember being challenge-quizzed by fellow schoolmates about it - as early as the sixth grade. That an Indian-born astrophysicist had discovered a fundamental limit - the stellar mass, that, if exceeded in a white dwarf, could lead to gravitational collapse - was something every Indian schoolboy in the 1970s seemed to know (at least in the schools I went to!). Later, in high school, I remember doing an elementary calculation, and later still, at college and university, more detailed calculations were done. Chandrasekhar himself became an idol of sorts, and his benign gaze, from a picture portrait framed on the wall above my desk, was deeply inspiring in the last two years of my university career. In the very last year - 1983-84, he was also awarded the Nobel Prize in Physics, for, it turned out, the very work he had done, as a nineteen-year old, in calculating his Mass Limit. [This seemed to ignore his work of a lifetime since, which did not sit at all well with him - but be that as it may for now, it can be the subject of several blog posts.]

That, apart from Subrahmanyan Chandrasekhar, there were other Indian physicists named Chandrasekhar as well, I also knew. One of them, who also shared his first initial, was Sivaramakrishna Chandrasekhar, a liquid crystals specialist, who was at the Raman Research Institute in Bangalore (which I visited often as an undergraduate, since my family happened to live near by). [The two were actually first cousins, both also being nephews of C.V. Raman.]

But it was Professor B.S. Chandrasekhar, (Bellur Sivaramiah Chandrasekhar) formerly of Case Western Reserve University and now at the Walther Meissner Institut at Munich – like me, a Delhi University alumnus (M.Sc. 1949) and a Rhodes Scholar as well - passing through some 35 years before me - for whom another Chandrasekhar limit is named. In 1962 (the year of my birth) he wrote a paper in the very first issue of the journal Applied Physics Letters: A Note on the Maximum Critical Field of High-field Superconductors. This paper defined a natural upper limit on the ambient Magnetic Field which, if exceeded, causes a complete loss of superconductivity. Independently, the idea was also suggested by A.M. Clogston, and has ever since then been known as the Chandrasekhar-Clogston (Field) Limit.

For reasons I cannot fathom, this limit on the upper critical field of superconductors has not received the type of (er ahem) critical acclaim that the first Chandrasekhar Limit received - not even noticed in the Delhi University Physics Department, of which Prof. B.S. Chandrasekhar, is a distinguished alumnus! He was felicitated for a lifetime of work in superconductivity and condensed matter physics, with a special award at the American Physical Society March Meeting in Indianapolis in 1992 (where I was fortunate to be present). I remember seeing him from afar but being too intimidated to approach him directly and introduce myself!

Professor B.S. Chandrasekhar has continued to work on superconductivity, and still does, at the Walther Meissner Institut (the Institute is of course named for the discoverer of the famous Meissner Effect - which describes the exclusion of magnetic flux from the interior of a superconductor below its critical temperature). He has worked on the critical field of Niobium, and on magnetic fields created by superconducting solenoids. As it happens, the magnetic fields required by the ITER tokamak - both the central solenoid and the toroidal field - are created by superconducting Niobium-Tin alloy - of which some 750 tons (seven hundred fifty tons) of wire, 200 km (two hundred kilometers) long will be required. Thus, considerations following from the Chandrasekhar-Clogston Limit are relevant to ITER design and operation. What is really interesting is that the other Chandrasekhar - Subrahmanyan Chandrasekhar - worked on the theory of fusion - especially laser fusion (or inertial fusion) - using the pressure of light to push two hydrogen atoms close enough that they fuse. (This is not the approach at ITER, which is a magnetic fusion reactor). Prof. B.S. Chandrasekhar has also written a popular book, Why Things Are The Way They Are.

Today, the Chandrasekhar-Clogston limit occurs most often in the physics literature in descriptions of work relating to spin-polarized fermionic atomic fluids - which display both superfluidity through a BCS-like pairing, as well as a Bose-Einstein Condensation (BEC) after dimerization (which makes them bosons) at ultra-low temperatures. A group at the University of Trento (Italy) and, appropriately, the Walther Meissner Institut (where Prof. Dr. B.S. Chandrasekhar is a 'Permanent Guest') is active in the field. The Chandrasekhar-Clogston limit appears in that context as a critical value of the ratio of up-and-down spin polarizations in a dilute fermionic atom gas, and determines phase separation of the dilute gas into a superfluid phase and a 'normal phase'.

Whether and how the two Chandrasekhar limits, in speaking of different aspects of a gas of fermions (dilute in one case, and degenerate in another) are actually (or at all) related are interesting questions I might explore in a subsequent blog post.

Fusion Through a Hydrogen Economy Prism

Fusion has long suffered from the unfortunate impression of being a technology that is always 'thirty years into the future'. Reality has always been more complicated, even if sometimes the impression seems to ring true. Since nuclear fusion has been understood for longer than nuclear fission, the seeming lack of progress in commercializing fusion has appeared especially frustrating. While technical issues certainly remain to be addressed, the lack of a compelling future scenario within which nuclear fusion could be seen as a 'natural' energy solution has also been a barrier in the techno-scientific as well as policy discourse surrounding fusion.

If seen merely as an attempt to extract energy by fusing deuterium and tritium atoms (in the simplest conception), fusion appears less compelling than when seen as a natural part of a future carbon-free hydrogen economy. Deuterium (D) and tritium (T), after all, are isotopes of hydrogen, and the energy they yield on fusion is usefully seen as nuclear hydrogen energy. But what if the heat yielded by the neutrons in D-T fusion were further used in thermochemical schemes to create molecular hydrogen, from which chemical or electrochemical hydrogen energy could be extracted? If this is successfully done, the transportation sector of the future could well come to be powered indirectly by fusion.

I sketch out and elaborate this vision for a fusion-driven hydrogen economy of the future in my paper Nuclear Hydrogen Production: Re-examining the Fusion Option. I discuss more generally a vision for a Fusion Island (first sketched out by Nuttall & Glowacki), in which a complete hydrogen economy is envisaged - a scheme which uses all the isotopes of hydrogen (protium, deuterium, tritium) in all forms of matter (solid, liquid, gas, plasma). I discuss the new perspective in which fusion appears when seen through such a hydrogen economy prism, the policy implications thereof, and the likely present-day economic actors who might find such a vision of the future hydrogen economy sufficiently compelling to begin more actively participating in and funding fusion R&D today. Such a new perspective on fusion also sees both fusion and fission as complements instead of substitutes, and offers novel possibilities such as fusion breeders of fission fuels, as well as, for example, fusion-fission hybrids, and fission breeders of fusion fuels.



Update Presidential Science Adviser John Holdren, giving the Rose Lecture at MIT on 25 October 2010, discussed the role of fusion and fission in providing future energy options that would mitigate climate change. He mentioned that both fission and fusion represent energy sources with 'nearly inexhaustible' fuel supplies, and though the fusion fuel supply was 'much more inexhaustible' (paraphrasing), that was not much of an advantage over fission since fission was 'quite inexhaustible already'! However, he also stressed that he personally was in favor of funding fusion R&D, since the number of such 'nearly inexhaustible' fuel options was so small. However, this funding could only be sustained if the overall funding pie for energy R&D of all kinds was increased. Here's the video of part of his talk where he discusses this issue:



Dr. Holdren also presents a number of quantitative projections for the future of nuclear power that are worth summarizing in brief. The world currently has about 440 nuclear reactors which produce a total of 375 GWe of electrical energy, constituting about 13% of world total electricity supply, a percentage that is declining even as new plants are being built - since other sources of supply are growing faster in the aggregate. He feels that in the next 90 years, that is, out to the year 2100, the world total supply of nuclear power would fall considerably short of the 3500 GWe total that some analysts have hoped for [and which would have been an order of magnitude larger than current capacity].

He feels, however, that by the year 2050, a rough quintupling of current supply, to about 1700 GWe could happen. However, I found the most remarkable figure in his talk to be the estimate of Remaining Ultimately Recoverable Uranium (RURU) as 100 Million tons, based on a recent MIT study. What this means is that a once-through fuel cycle option using natural or lightly enriched uranium will remain competitive, and that reprocessing and breeding options may not need to be commercialized for several decades yet. Of course, the issue of how this recoverable uranium is actually distributed throughout the world, as well as how widely the technology of extraction will become available, remains. Different countries who feel uranium-constrained may still very well choose to pursue fuel cycle options that include reprocessing and breeding technologies.

US Energy Secretary Steven Chu Speaks at MIT 12 May 2009

MIT President Susan Hockfield introduces US Energy Secretary Steven Chu, who gave the Karl Taylor Compton Lecture at MIT, one of its most prestigious invited lectures. MIT's blurb to the video quotes Steve Chu in this talk: "Can we design a modern-day equivalent of Lincoln Labs or Los Alamos, focused on mission driven research, but also connected to fundamental research and the industrial world?". Steve Chu shows how all the great Nobel Prize winning work that was done at Bell Labs - all the people whose names you grew up hearing - Nyquist, Shannon, Penzias, Anderson, Bardeen, and many more - were actually trying to solve problems of quite an applied nature, but ended up revolutionizing their fields, making fundamental lasting contributions, that in most cases has been recognized by a Nobel Prize. (Chu himself was at Bell Labs at the beginning of his career, joining in the intake year 1977-78. Five people hired that year, including himself, are now Nobel Laureates.)

The talk is well worth hearing in its entirety. I really enjoyed it. There's both wit and wisdom in it, and aplenty. At one point Chu asks, for example: What does a Boeing 777 have in common with a Bar-tailed Godwit? A: They can both fly 11,000 km nonstop. (The B-t G is a bird that annually migrates from Alaska to New Zealand in the winter, and has 55% of its weight in body fat. Likewise the Boeing has 45% of its weight in jet fuel. The factoid is relevant to a point he makes about synthetic biology - using nature as an inspiration, but going beyond.)



One of the most impressive things about Chu is not only that he refocused his research toward Climate Change mitigation beginning 2004, but, partly in response, he has also increased his knowledge base in biology very significantly. Today, from biologically created fuels on the one hand, to artificial photosynthesis on the other, solutions to Climate Change mitigation inspired by biology are being actively researched. Chu emphasized in his talk that one of the reasons for the success of Bell Labs was the 'scientist-manager', who could quickly decide whether a given idea had merit or not - because he was a often a hands-on practitioner of the field himself. Chu clearly embodies this ideal.

Chu is an active Facebooker, and I salute him not only for the content he personally uploads there, but also for the infectious enthusiasm and compelling sense of mission he communicates to the world at large and to technically literate and younger audiences in particular.

Here's an earlier talk by Steve Chu when he was Director of the Lawrence Berkeley Laboratory, from back in 2005, on the same general subject of climate change science, possible biomimic solutions (both to sequestration and to energy production), and the culture of Bell Labs in the 1940s-1980s period:







And an even earlier talk given at UC Berkeley in May 2004, when he was still a Professor of Physics at Stanford: 'What can Physics say about Biology?'. This one is more technical, and is about how RNA transcription works at the sub-molecular scale. It is also about emboldening physicists to attempt answers to biological questions, and how ultimately, it might well be possible to explain life in terms of the 'jiggling and wiggling of atoms and molecules' (an old quote from Feynman that Steve Chu cites in the talk). Physics, he points out, is still young (only 400 years since Galileo) and the future of physics may well lie in biology. There is also the very faintest hint that climate change may be ultimately be stabilized by a biological solution, because he points out that the amplitude of temperature fluctuations on earth dropped markedly after agriculture was introduced. Cause and effect is not fully clear: for example, it could be that the temperature stabilization was exogenous, but made agriculture possible as a result. Equally, it is also possible that agriculture was a form of biological anthropogenic intervention that, operating on a large scale, stabilized climate, making life and civilization (and physics) possible. Here is the hint that if photosynthesis was properly understood as a 'physics problem', then an 'artificial photosynthesis' could be designed that could sequester (fix) carbon dioxide from the atmosphere more efficiently.

Oxide Dispersion Strengthened Steels (ODSS)

The fundamental elastic properties of metals are determined by the behavior of dislocations - which are systematic distortions introduced into the crystalline lattice. When the material is under stress, these dislocations can move. The ease with which they move, or more generally, by whether and if they can move, determines the elasticity (or plasticity) of the metal. The dislocations can be impeded in their movement by irregularities in the crystal - in the form of grain boundaries, or in the form of impurities - which can act as 'pinning centers' or 'sinks' for the dislocations.

The size and orientation of the grains within the metal relative to the dislocations, determines whether, and how easily, the dislocations can be pinned at the grain boundaries. As the grain size decreases, the dislocations are more easily pinned, and this increases the yield strength of the metal (that is, it delays the onset of plasticity). However, below a grain size of about 100 nm, a reversal of this rule has been observed - with the decline in yield strength flattening out, or the yield strength even declining with decreasing grain size.

The idea that impurities within a crystal can act as pinning centers for dislocations has been intuitively grasped for centuries, as well as the idea that deliberate introduction of misaligned dislocations and defects in a metal through heat treatment or cold rolling can lead to an overall strengthening of the metal. For example, the strength of steel itself arises from the incorporation of carbon atoms in interstices within the iron lattice, which act as pinning centers for dislocations. A similar idea underlies the concept of alloying for increased strength.

Advances in metallurgy led to heat treatments of alloys, followed by differential quenching. Deeper investigations revealed that such treatments led to the formation of a precipitate of the alloyed species, with both the alloyed species and the matrix existing in a metastable supersaturated solution. When the quenching is followed by moderate heating, the precipitate finely diffuses into the matrix, forming a dense network of pinning centers that provides very high tensile strength for the alloy. This technique became known as precipitation hardening.

The idea of deliberately introducing as fine a powder of the pinning species as possible into the steel matrix was then taken up, and eventually led to the development of steels with nanoscale powders of transition metal oxides (such as those of Yttrium or Chromium) dispersed through the matrix. These are known as Oxide Dispersion Strengthened Steels (ODSS) which, in addition to displaying high yield strength, have also displayed low irradiation and thermal creep, as well as high corrosion resistance. This is why they are being intensively investigated as possible structural and cladding materials for next generation nuclear reactors.

In my presentation Multi-scale Modeling of Radiation-Induced-Dislocation Pinning in Oxide-Dispersion Strengthened Steels (ODSS)- Part 2 , I discuss these desirable properties in detail, as well as the scientific questions that arise given the existence of these properties. For example, the precise effect that the specific alloyed species has on the properties is not known. Similarly, the role played by the metal oxide dispersion in strengthening corrosion resistance is not known, nor the details of how the dislocation pinning actually occurs, or whether there are any other novel effects, such as spin interactions, which might conceivably impact the properties of these steels. Such understanding is not only scientifically motivated, but is also necessary to develop a predictive understanding of the properties of the steels that may then be rolled into probabilistic safety analyses of the reactors themselves.

Multiscale Materials Modeling, which I have discussed in another post, naturally lends itself to addressing these issues, and is the focus of my current work. At present, the behaviour of reactor materials is modeled by phenomenological methods involving approximate relationships and observed correlations, which may not extrapolate into the operating conditions (and desired design lifetimes) of the new generation (Gen IV) reactors. The research I am undertaking is intended to fill an important and critical knowledge gap in the path toward these reactors.

It is important to realize the compelling criticality of Materials Issues in the path toward the Nuclear Renaissance - no matter which path is taken - whether a new coolant is introduced or whether new fuel cycles are introduced - the stress on the structural and cladding materials for the new generation of reactors changes both qualitatively and quantitatively. New materials will be needed that can reliably withstand this stress, and their behaviour needs to be understood and modeled, before such materials can be qualified for use in these reactors.

The Materials Research Society Fall Meeting in Boston next month is devoting an entire session solely to a Discussion of Materials Science Solutions to Impediments to the Nuclear Renaissance, in addition to a Symposium on Materials for Future Fission and Fusion Reactors, which includes several sessions both on Multiscale Modeling and on Oxide Dispersion Strengthened Steels.

Multiscale Modeling for Nuclear Reactor Materials

For a variety of phenomena, it is true that physical interactions between constituents at a variety of length and time scales, starting from the smallest and cascading upward to the largest relevant scale - contribute to the macroscopic behaviour. While a strictly reductionist viewpoint would be misleading, it is nevertheless true that these interactions exist in a hierarchy of length scales, with the lower cutoff at the atomic scale and the upper cutoff at the 'continuum limit' in the millimeter length scale. This is true in particular of reactor materials that are subject to neutron irradiation (they may also be subjected to alpha or gamma radiation).

A neutron flux, for example, will impact an atom, and attempt to dislodge it from its lattice site, in what is called a 'primary knock-on' event. If the dislodgement is successful, the atom becomes an interstitial, and a vacancy is created at the original location. Such a primary knock-on event, which creates that point defect, is estimated to take as little as one-hundredth of a nanosecond (10^-11 seconds), while the atom is displaced over a length scale of the order of a nanometer(the lattice parameter of most metals is just under 1 nm).

The vacancy and interstitial atom function as a bound pair, known as the Frenkel pair. Many of the plasticity properties of the metal are determined by the behaviour of the population of Frenkel pairs that are created during the course of the irradiation. Point defects and Frenkel pairs can form clusters, and clusters grow by aggregation, forming voids where vacancies within them have accumulated. The formation of voids leads to swelling, which is an isotropic volume expansion of the metal that can be, for significant radiation doses, upto several tens of percent in magnitude. This can cause a considerable change in the linear dimensions as well (this scales as the cube root of the swelling percent).

Another phenomenon that can occur, depending on the mechanics of defect-vacancy formation, is growth, where volume remains constant but there is a change in shape of the metallic object. Usually, both swelling and growth occur, at different locations within the irradiated material. In addition, a phenomenon known as irradiation creep can occur, which is the slow deformation of the metal under constant mechanical and radiative stress.

It is interactions like these, and phenomena that occur when they aggregate over successively longer length (and time) scales within the reactor material that eventually have observable consequences on components that have dimensions of the order of meters, i.e., on the macroscopic scale. These consequences include onset of plasticity, fracture, or embrittlement.

Phenomena such as defect clustering and diffusion, formation of dislocations (a dislocation being formed whenever a regular pattern of defects significantly distorts the crystalline order), formation of separate phases and radiation-induced segregation also occur in the irradiated metal, each of which, depending on conditions, can contribute to the onset of plasticity or the start of fracture in a metal.

Zipping up a description starting from the lowest relevant length (and time) scale, up to the longest relevant length (and time) scale, using the most appropriate physical description at each scale - under conditions of high thermomechanical and radiative stress - is the challenge of Multiscale Materials Modeling under Irradiation (MMM-I). A certain amount of coarse graining is inevitable when this is attempted, and both sequential and parallel approaches are possible, as well as hybrid approaches that utilize elements of both methods.


My presentation Multi-scale Modeling of Radiation-Induced-Dislocation Pinning in Oxide-Dispersion Strengthened Steels (ODSS)- Part 1 and Multi-scale Modeling of Radiation-Induced-Dislocation Pinning in Oxide-Dispersion Strengthened Steels (ODSS)- Part 2 describe these ideas and my work in progress, in more detail, in the context of oxide dispersion strengthened steels, which have been suggested as possible reactor materials for new generation reactors in view of their superior creep strength under both radiative and thermomechanical stress, as well as corrosion resistance. This is the focus of my current work.

The Fall 2008 Meeting of the Materials Research Society in Boston has Symposium W on Computational Materials Design by Multiscale Modeling.

Safety Issues in Nuclear Hydrogen Production with the (Gas-Cooled) Very High Temperature Reactor (VHTR)

Nuclear Hydrogen Production (NHP) is the idea that the heat and/or electricity from a nuclear reactor can be used to electrolyse, thermolyse, or thermochemically analyse water - separating hydrogen and oxygen. The resulting hydrogen is useful for a variety of markets including hydrocarbon upgrading & refining, ammonia production, and transportation. The merit of the nuclear hydrogen production scheme is that it does not produce greenhouse gases. Alternative hydrogen production schemes currently in use invariably generate carbon dioxide at some stage. The most common technique is methane steam reforming - here carbon dioxide first arises from the burning of methane to produce heat to generate steam, then again in the reforming step that separates the carbon from the methane by successive oxidation to generate hydrogen. Even the alternative electrolysis method that is also common generates carbon dioxide when fossil fuels are burned in the generation of the electricity - whether from gas-fired or coal-fired plants.

While nuclear hydrogen production (NHP) schemes thus are carbon-dioxide emission free, they do involve the use of corrosive fluids (such as sulphuric acid) at high temperatures; generation of noxious & poisonous gases (such as sulphur dioxide and hydrochloric acid); and issues from the possible generation of radioactive products such as tritium. As well, heat transfer fluids carrying heat from the reactor to the thermochemical plant may interact with the chemicals in the plant. Or, in the current conceptual version of the Very High Temperature Reactor, the coolant might be helium, as might also be the heat transfer fluid. Some contamination of tritium in helium is possible and more might arise from transmutation of helium isotopes. In addition, the very idea of having a thermochemical plant located close to a nuclear reactor is unprecedented. Both the hydrogen and the oxygen produced in the thermochemical scheme will need to be safely stored, to prevent the possibility of leakage, deflagration or detonation.

Such considerations impose a number of requirements on the layout of nuclear plants and thermochemical plants, they impose requirements on the amount and quantity hydrogen and oxygen that may be created and stored on site, and on the location of the control room in a nuclear power plant. They also have implications for probabilistic safety analyses (PSA) for combined nuclear-and-thermochemical plants.

The idea of nuclear hydrogen production is especially attractive also in the context of extraction and processing of crude oil from the Alberta Tar Sands. Several reactor-hydrogen production configuration schemes are currently being examined and considered for this project at the present time. Nuclear steam methane reforming (which generates steam from nuclear heat, and uses nuclear heat in the reaction), for example, is a possible transitional technology that decreases the overall carbon footprint of the process (it does not completely eliminate the carbon dioxide production, since it retains the reforming step). For all of these considerations, it is possible that the Tar Sands may emerge as the locus of the first commercial nuclear hydrogen production project anywhere.

I discussed issues surrounding this in my paper Safety Issues in Nuclear Hydrogen Production with the Very High Temperature Reactor (VHTR) presented at the Canadian Nuclear Society Annual Conference 2008, Toronto.

Materials Challenges for the Supercritical Water-cooled Reactor (SCWR)

The Supercritical Water-cooled Reactor (SCWR) is the most promising evolution of the water-cooled reactor technology that currently dominates the commercial market for nuclear reactors. Essentially the idea is to increase the thermodynamic efficiency of the reactor type by going to higher temperatures and pressures, and thus also going to the supercritical state. Supercritical water also has a much higher specific heat, enabling a higher heat transfer per unit mass. By going to higher pressures and temperatures, it is also possible to avoid phase changes within the coolant loop altogether. This substantially reduces the requirements for pumps and compressors within the coolant loop, simplifying it considerably and introducing even greater economy in the whole power plant.

The merit of the supercritical coolant idea has been tested and the concept has actually been deployed for fossil fuel power plants (coal-fired) already, where thermodynamic efficiencies have considerably risen as a result. Some jurisdictions have also mandated that all future coal-fired power plants be of the supercritical type. The supercritical water coolant imposes more stringent requirements for plant materials used in fossil fuel-fired power plants as well, and this experience is relevant to the Supercritical Water-cooled Reactor (SCWR) concept.

However, what is different about nuclear reactors, of course, is the radiation dose that reactor materials will experience, in addition to the thermochemical stress that the supercritical water environment might impose. This is even more the case when new fast neutron spectrum fuel cycles are introduced, with radiation doses upto a hundred times higher than the thermal spectrum neutrons that current generation reactors use.

Superior irradiation creep strength, and superior thermomechanical behavior in general then becomes a a very desirable critical property to have for cladding materials. I discuss the Materials Challenges for the Supercritical Water-Cooled Reactor in my paper published in the Canadian Nuclear Society Bulletin, Vol. 29. No. 1 pp. 32-38 March 2008.

The supercritical water environment is also chemically different in that it dissolves organic species but not inorganic ones, the reverse of ordinary water. Thus the supercritical water environment is expected to create novel corrosion challenges as well, and these also must be studied and understood.

Materials such as Oxide Dispersion Steels (ODS Steels) have been proposed for use as structural and cladding materials in the Supercritical Water-cooled Reactor SCWR (as well as other Generation IV Reactor concepts). These materials appear to display very desirable irradiation and thermal creep properties, as well as desirable electro-chemical properties (corrosion resistance). Understanding the physical origin of these properties by developing suitable multiscale materials models (MMM) is the focus of my present research.