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The “Nuclear Renaissance” is at hand and the materials community is integral to its success. Increased reliability of current nuclear components and the construction of the next generation of nuclear reactors depend on advancements in materials knowledge. This article introduces some of the ways materials will enable the future of nuclear power.

The renewed global interest in nuclear power arises from balancing concerns for global climate change with the need to provide sufficient electricity for a growing global population. This means developing an energy strategy to satisfy a projected 160 percent increase in global electricity demand by the year 2050¹ while reducing greenhouse gas emissions. Nuclear power stands to play an important role in such a strategy by delivering a sustainable, large quantity of electricity with near-zero carbon-dioxide emissions.

Worldwide, over 130 new nuclear plants are projected with 28 new permit applications in the United States alone.² The Global Nuclear Energy Partnership (GNEP)³ and the United States Energy Policy Act of 2005⁴ promise a rebirth of nuclear power in the United States; however, the task is daunting. Much of the emphasis in the literature has been on the development of the next-generation, or Generation IV, nuclear power plant. While Generation IV reactors promise improved efficiency and plant simplification, including waste minimization, significant proof of concept work is needed before any of these designs meet regulatory approval. Therefore, shorter-term construction will predominantly be Generation III+ reactors, which represent incremental improvements to current designs.

New plant construction does not occur overnight. Significant lead time is required for plant construction, due in part to a limited supplier base and necessarily stringent quality control procedures. As such, extended lifetimes and increased productivity of the current fleet of nuclear power plants is planned.

Materials are the enablers for future nuclear technologies. New alloys, improved predictive models, and new component quality specifications are needed. This article highlights some examples of the critical role materials will play in the Nuclear Renaissance.

Materials degradation is the primary cause of unplanned outages in the nuclear industry. In fact, Paul Spekkans from Ontario Power Generation states that “managing degradation is central to achieving business success.”⁵ The U.S. Nuclear Regulatory Commission recently conducted a survey of materials degradation in light water reactors (LWRs).⁶ As shown in Figure 1, this study concluded that significant technology gaps still exist. In particular, concern was raised for those areas with insufficient knowledge of mechanisms and/or process interdependencies to mitigate risk.

With the limited time available to start bringing new capacity on line, the current body of knowledge, including service experience and life cycle predictions, needs to be critically evaluated. Recently, Peter Ford noted that we need to do a better job than was done 20–30 years ago when only general corrosion, irradiation embrittlement, and fatigue were considered in reactor design.⁷ Lessons learned from in-service performance and from laboratory studies must form the basis for improved risk-informed component inspection as well as for alloy selection.

As suggested by Figure 1, fundamental research for materials is needed. Radiation damage, deformation of irradiated material and irradiation assisted stress corrosion cracking (IASCC) remain focus areas. Emphasis is needed on understanding corrosion precursors as well as crack growth and arrest, especially in welded components. Andresen and Morra⁸ highlighted critical trends in high-temperature stress corrosion cracking (SCC), including:

• Mechanistic role of silicon
• Effects of chlorine on high-temperature SCC of low-alloy steels, even at 5 ppb
• Rapid crack growth rates upon reloading
• Effect of residual strains at welds

Generation IV reactor designs promise higher efficiencies than Generation III and III+ reactors. As shown in Table I, however, the service conditions will be more severe than those for current reactors. The key stage gate for the construction of a Generation IV plant will be the development and qualification of materials that are resistant to higher irradiation levels, higher temperatures, and more aggressive media.

In 2006, the United States Department of Energy summarized materials research needs for advanced nuclear systems as follows:

“The fundamental challenge is to understand and control chemical and physical phenomena in multi-component systems from femto-seconds to millennia, at temperatures to 1,000°C, and for radiation doses to hundreds of displacements per atom (dpa).”¹⁰

This obviously is no small task. Material system viability for Generation IV reactors is the focal point of development efforts. Using the supercriticial water reactor (SCWR) as an example, Figure 2 presents a summary of a materials qualification program. An extensive array of testing will be required in order to fully characterize material performance and meet the time demands for qualification.

Research and development programs are underway to investigate the behavior of candidate materials, operative damage mechanisms, and potential materials specifications for Generation IV reactor designs. Recent work^11–14 has shown accelerated IASCC crack initiation for materials in simulated SCWR conditions; however, quantification of crack growth behavior is still needed. Ultimately, accurate component specifications and robust material degradation models will be needed to facilitate plant operation.

As summarized by Steve Zinkle,¹⁶ critical materials needs for advanced fuels include spent nuclear fuel reprocessing, improved fuels for light water reactors, high temperature gas-cooled reactors and liquid metal fast burner reactors, high performance cladding materials, coolants for heat transfer and transport and waste form development.

In order to achieve higher efficiency in advanced reactors, research, development, and qualification efforts are needed, including those for coated particle fuel shown in Figure 3. Work is continuing to investigate metallic, oxide, carbide, and nitride fuel forms,¹⁷ with areas of focus being fuel fabrication techniques, performance evaluation, and modeling.

Waste disposal also remains an area of active research. Long-term nuclear waste repositories that will require containment system stability for greater than 10,000 years are an area of continued research.¹⁸ Corrosion studies for candidate materials for waste repository containers are also critical. General corrosion, hydrogen-induced cracking, and stress corrosion cracking behavior are being investigated and data being extrapolated over the 10,000 year specified timeframe based upon estimated environmental conditions (e.g., ionic species accumulation, microbial activity, radiation-induced degradation, thermal conditions, etc.).^19–23

It is obvious that much work is needed. As summarized by Roberto and Diaz de la Rubia, “addressing the basic research needs (of advanced nuclear systems) offers the potential to revolutionize the science and technology that underpins the development of materials.”²⁴ The following section discusses a few ways that the materials community can make a difference.

Research and Development Activities
While limited work has been conducted on materials for nuclear power in recent decades, marked advancements in experimental, analytical, and computational materials science methods have been made. Ab-initio, thermodynamic, and multi-scale modeling efforts are already advancing the understanding of radiation-induced microstructures.^25–29 Orientation imaging microscopy has also recently been used to assist in reliability assessments and fitness-for-service determinations.³⁰ These and other fundamental materials science and engineering methodologies can greatly compliment the traditional knowledge and research base for materials used in the nuclear power industry.

Communication and Collaboration
Karen Gott summarized it best, stating that “international experience will often provide advance warnings. It is therefore essential to participate in international exchange of information.”³¹ International collaboration is at the heart of research efforts for future reactor designs. Likewise, it is important that industrial experience continue to be shared in an effort to sustain and improve the current generation of materials in nuclear power reactors.

Education
With a relative hiatus in training engineers in nuclear-related fields and a near-term decrease in institutional knowledge, there is concern whether there will be enough qualified experimentalists and analysts to meet the challenges facing the nuclear power industry. Academic, government lab, and industrial organizations need to participate in educational efforts, transferring knowledge of intricate experimental techniques and operative mechanisms to a new generation of scientists and engineers.

Outreach and Advocacy
The development of new materials for advanced nuclear systems will take a sustained effort. Governmental advocacy efforts, such as Materials Information Luncheons,³² should highlight the integral role materials play in the future of nuclear power and the need for ongoing, stable funding. A portfolio approach that addresses current nuclear reactors as well as Generation III+ and Generation IV designs should also be advocated. Additionally outreach to the next generation of scientists and engineers is needed, emphasizing not only challenges and opportunities, but also the marked impact a career in nuclear power can make on global energy security.

REFERENCES

1. J.M. Deutch and E.J. Moniz, “The Nuclear Option,” Scientific American, 295 (3) September 2006, p. 76.
2. New Reactor Licensing, United States Nuclear Regulatory Commission, www.nrc.gov/reactors/newreactor-licensing.html.
3. Global Nuclear Energy Partnership, U.S. Department of Energy, www.gnep.gov/.
4. United States Energy Policy Act of 2005, www.gnep. gov/pdfs/epactActOf2005Final.pdf.
5. P. Spekkans, “Material Degradation—A Nuclear Utility’s View,” Proc. 13th International Conference on Environmental Degradation of Materials in Nuclear Power Systems, ed. T.R. Allen et al. (Toronto, ON, Canada: Canadian Nuclear Society, 2007).
6. Expert Panel Report on Proactive Materials Degradation Assessment (NUREG/CR-6923) (Washington, D.C.: Division of Fuel, Engineering, and Radiological Research, Office of Nuclear Regulatory Research, United States Nuclear Regulatory Commission, 2007), www.nrc.gov/reading-rm/doc-collections/nuregs/contract/cr6923/.
7. P. Ford, “Technical and Management Challenges Associated with Structural Materials Degradation in Nuclear Power Reactors in the Future,” in Ref. 5.
8. P. Andresen and M. Morra, “Emerging Issues in Environmental Cracking in High Temperature Water,” in Ref. 5.
9. T. Allen, “Scientific and Technological Challenges in the Development of Materials” (2004 Frederic Joliot and Otto Hahn Summer School, Cadarache, France, August 25–September 3, 2004).
10. Basic Research Needs for Advanced Nuclear Energy Systems (Washington, D.C.: Office of Basic Energy Science Workshop, U.S. Department of Energy, July 31 to August 3, 2006), www.sc.doe.gov/bes/reports/list.html.
11. D. Guzonas et al., “Corrosion of Candidate Materials for Use in a Supercritical CANDU Reactor,” in Ref. 5.
12. S. Teysseyre and G. Was, “Stress Corrosion Cracking of Neutron-Irradiated Stainless Steels in Supercritcal Water,” in Ref. 5.
13. E. West et al., “Influence of Irradiation Induced Microstructure on the Stress Corrosion Cracking Behavior of Austenitic Alloys in Supercritical Water,” in Ref. 5.
14. A. Kruizenga, “Investigation of Stress Corrosion Cracking in Supercritical Water Using Tubular Sample Configuration,” in Ref. 5.
15. G. Was, “Materials: The Bridge to Future Nuclear Power,” Materials Information Luncheon, Washington, D.C., May 3, 2007. (See T.M. Osman and I. Anderson, “Reawakening of United States Nuclear Energy: Materials Challenges for a New Generation of Power Plants,” Materials Technology@TMS, May 2007, http://materialstechnology. tms.org/TECarticle.asp?articleID=915 to view the presentation slides.)
16. S.J. Zinkle, “Fuel Systems for Future Generations of Nuclear Power,” Materials Information Luncheon, Washington, D.C., May 3, 2007 (See T.M. Osman and I. Anderson, “Reawakening of United States Nuclear Energy: Materials Challenges for a New Generation of Power Plants,” Materials Technology@TMS, May 2007, http://materialstechnology.tms.org/TECarticle. asp?articleID=915 to view the presentation slides.)
17. R.N. Hill (Presentation at the GNEP Fuels Performance Modeling Campaign meeting, Washington, D.C., 8 November 2006).
18. R. Devanathan and W.J. Weber, “Radiation Effects in a Model Ceramic for Nuclear Waste Disposal,” JOM, 59 (4) (2007), pp. 32–35.
19. K.G. Mon and F. Hua, “Materials Degradation Issues in the U. S. High-Level Nuclear Waste Repository,” Proc. 12th International Conference on Environmental Degradation of Materials in Nuclear Power Systems— Water Reactors, ed. T.R. Allen, P.J. King, and L. Nelson (Warrendale, PA: TMS, 2005), p. 1439.
20. V. Desai, “An Overview of the Yucca Mountain Project,” JOM, 57 (1) (2005), p. 18.
21. X. He and Y-M. Pan, “The Localized Corrosion Resistance of Alloy 22,” in this issue.
22. F. Hua et al., “The Effect of Temperature on the General Corrosion of Alloy 22,” in this issue.
23. R.M. Carranza, “Review on the Degradation Modes of Alloy 22 in Repository Conditions,” in this issue.
24. J.B. Roberto and T. Diaz de la Rubia, “Basic Research Needs for Advanced Nuclear Energy Systems,” JOM, 59 (4) (2007), pp. 16–19.
25. A. Caro et al., “The Computational Modeling of Alloys at the Atomic Scale: from Ab Initio and Thermodynamics to Radiation-Induced Heterogeneous Precipitation,” in Ref. 25, p. 50; also see www.tms.org/pubs/journals/jom/0704/caro-0704.html.
26. B. Wirth, “Multiscale Investigation of the Mechanisms Controlling Irradiation Effects in Materials and the Promise of Irradiation Resistant Materials” (Presentation at the 2007 ASM/TMS Annual Symposium, GE Global Research Center, Niskayuna, NY, August 20, 2007).
27. J. Tucker et al., “Ab Initio-based Radiation-Induced Segregation Predictions in Fe-Ni-Cr Alloys,” in Ref. 5.
28. D.J. Bacon and Y.N. Osetsky, “The Atomistic-Scale Modeling of Dislocation-Obstacle Interactions in Irradiate Metals,” in Ref. 25, pp. 40-45.
29. A. Misra, et al., “The Radiation Damage Tolerance of Ultra-High Strength Nanolayered Composites,” JOM, 59 (9) (2007), pp. 62–65.
30. E. Lehockey et al., “New Application of Orientation Imaging Microscopy (OIM) to the Characterization of Nuclear Component Failure Modes, Reliability Assessment and Fitness-for-Service,” in Ref. 5.
31. K. Gott, “Aging Management Requirements in Sweden” (Presentation at the 13th International Conference on Environmental Degradation of Materials in Nuclear Power Systems,” Canadian Nuclear Society, Whistler, British Columbia, Canada, August 21, 2007).
32. T.M. Osman and I. Anderson, “Reawakening of United States Nuclear Energy: Materials Challenges for a New Generation of Power Plants” (Materials Technology@TMS, May 2007), http://materialstechnology.tms.org/TECarticle.asp?articleID=915.

Todd M. Osman is the technical director at TMS. Dr. Osman can be reached at tosman@tms.org.