Materials research and development specifically for potential application in fusion energy development had its origin in the early 1970s, following the impetus of the 1973 report to the President on “The Nation's Energy Future” by Dixie Lee Ray then chairman of the U.S. Atomic Energy Commission. The first scientific conferences on fusion materials took place in the summer and the fall of 1975 at Argonne National Laboratory and at Gatlinburg, Tennessee. Argonne's international conference set a direction for the use and development of irradiation testing facilities for fusion materials which continues today.

In his keynote to the Gatlinburg meeting on “Radiation Damage and Tritium in Fusion Materials,” E.E. Kintner, then deputy director of the U.S. magnetic fusion program, spoke directly to the hearts of the materials community:

“Materials is the Queen Technology of any advanced technical system. The economics eventually depend upon the materials, the reliability depends upon the materials, and the safety depends upon the materials. I assure you that before we are through with fusion, the physicists will give way to the materials engineers as being the leading lights of fusion.”

Kintner spoke from his experience in naval and civilian nuclear power systems, with reference to the special threats of the fusion reactor environment to the integrity of materials, and from practical engineering issues in a broad sense.

Fusion is the energy production process which drives the universe. Controlled utilization of this process for the benefit of man has been the illusive goal of the world's fusion power research since the 1950s. The most easily utilized fusion reaction is the fusion of deuterium and tritium. Every major fusion power research program is directed toward utilization of the energy released from this reaction.

When the hydrogen isotopes deuterium (D) and tritium (T) are fused, 80% of the energy released is carried by a single neutron. This neutron moves at 5 × 107 m/s and a kinetic energy of 14 MeV, so the designer of a magnetically confined reactor is faced with the reality that 80% of the power produced will impinge on the structure facing the burning plasma as a “current” of 14 MeV neutrons. The D-T reaction is illustrated in Figure 1.

Neutrons are not charged and do not interact with electrons in material through which they move. They collide with nuclei. The result of these collisions is always some combination of the in-situ creation of one or more energetic ions, alteration of chemistry through transmutation, and the introduction of radioactivity. Each changes material properties.

Nearly all the present experimental data base of neutron irradiation effects has come from fission reactor irradiations.

The successful development of fusion power critically depends on structural materials which can maintain their integrity and dimensional stability in an extremely hostile service environment involving high temperatures and heat fluxes, corrosive media, high stresses, and intense fluxes of neutrons. Neutron irradiation results in a variety of mechanical, physical, and chemical property changes that are collectively referred to as radiation effects. The primary sources of damage are neutron-induced atomic displacements and transmutation products.

High-energy neutrons produce primary recoil atoms (PKAs) with energies ranging from less than 1 keV to more than 100 keV. The energetic PKAs create a cascade of additional displacements. About 10% of the displaced atoms survive cascade recombination as isolated vacancies and self-interstitials or small clusters of these defects. The mobile defects migrate to pre-existing sinks such as grain boundaries and dislocations, or cluster to form a variety of extended defects such as voids (vacancies) or faulted dislocation loops (interstitials).

The Fusion Reactor Materials Program in the United States began in about the mid-1970s, in a world sensitized to energy production needs by the 1973 Arab Oil Embargo. In the program's early stages, materials problems were recognized to be as important as any of the other problems facing this new energy technology. The effects of irradiation on the behavior of materials to be used in the first-wall and blanket structure were of particular concern. Today, although the economic and political realities that define energy needs have changed, fusion energy still remains an important part of our vision for a better future. Global environmental effects such as the “greenhouse effect” from increased CO2 in the atmosphere and acid rain, coupled with safety concerns about fission reactors, make fusion very attractive as a clean and safe energy source.

Over the past 10 years, the range of candidate materials for structural application in fusion reactors has expanded to include new martensitic and ferritic steels with reduced activation characteristics, vanadium alloys, ceramics, and composite materials. However, because austenitic stainless steels are easily fabricated, nonmagnetic, reasonably strong and tough, commercially available, and familiar, they also remain as candidate materials for fusion. They have also been extensively studied for use in various fission reactor systems as well. The austenitic and stainless properties of Fe-Cr-Ni alloys and steels were discovered during 1900–1915. Commercial grades like AISI types 304 and 316 stainless steels were developed prior to World War II. The effects of irradiation on materials have been studied since 1942, when Eugene P. Wigner anticipated that fission fragments and energetic neutrons would damage crystalline materials by displacing atoms to create point defects (vacancies and interstitials).

Developing materials that resist degradation when exposed to neutrons is a key element in international programs to demonstrate the engineering and economic viability of fusion power. An additional requirement is that these materials exhibit low-induced long-lived radioactivity in order to enhance fusion power's environmental (and economic) attractiveness. This article briefly overviews current efforts to develop reduced activation structural alloys for fusion reactor applications.

A specific objective of the U.S. Fusion Materials Program is that all reactor components will meet the requirements for near-surface burial. Presently, this is interpreted to mean that all radioactive waste should satisfy Part 61 of Title 10 of the U.S. Code of Federal Regulations (10CFR61), prepared by the Nuclear Regulatory Commission (NRC). Specific activity limits are placed on particular long-lived radionuclides, which, when combined with activation calculations for conceptual fusion devices, place constraints on material compositions. Regulation 10CFR61 was prepared to cover low-level waste produced by the fission reactor industry; it has been necessary to extend it, in principle, to include additional radionuclides. Unlike anticipated waste from a fusion industry, only a small fraction of the fission waste stream is activated metals; hence, the applicability of the regulation is questionable. Further analysis of the probable disposal method for fusion wastes is needed, along with consideration of maintenance and decommissioning scenarios.

The next major step in the development of fusion power involves the design, construction, and operation of an experimental power reactor. The general objective of this type of device is to demonstrate key plasma physics, materials, and engineering performance under conditions that approach those considered necessary to establish the technical feasibility of fusion power. This device is generally perceived to be a tokamak configuration that operates on the deuterium-tritium (D-T) fuel cycle, which would produce several hundred megawatts of fusion power. Although a number of conceptual design studies on this type of device have been conducted, the current effort is focused on the International Thermonuclear Experimental Reactor (ITER) activity, a joint undertaking of the European Community (EC), Japan, the United States, and the Soviet Union, conducted under the auspices of the International Atomic Energy Agency (IAEA).

The development of fusion power as an energy source depends to a large extent on the proper selection of materials for the various components. these materials will be exposed to a wide variety of conditions such as plasma particle and neutron radiation, high thermal fluxes, large thermal and mechanical stress, various chemical environments, and high magnetic fields. In order to achieve the high performance desired for a commercial power reactor, considerable materials development will be required. Because of the relatively near term time scale projected for ITER and the limited objectives, more conventional materials with more extensive data bases will be used where possible. Even so, a substantial materials development program is required to support a test reactor like ITER.

More than 1,800 scientists from the United States and 33 other countries convened at the MRS Spring Meeting in San Diego, April 24-29,1989 to meet with their colleagues and discuss the latest research on a wide range of topics. According to Meeting Cochair Richard W. Siegel of Argonne National Laboratory, “It was a stimulating, broad-based, interdisciplinary scientific meeting of the high caliber that the materials research community has come to expect from the Materials Research Society.”

Siegel, along with Cochairs Robin EC. Farrow of IBM's Almaden Research Center and Angelica M. Stacy of the University of California led a cadre of 54 volunteer symposium organizers to present an impressive array of leading-edge topics in 17 different symposia, including a late-news technology update on diamond films. Topics ranged from the fundamental condensed-matter physics and chemistry of small atomic clusters, high Tc superconductors, and the processing of a wide variety of optica], electronic, and ceramic materials to the consideration of problems and solutions regarding materials for the world's infrastructure.

Complementing the wide range of scientific interests probed at the Spring Meeting were a three-day exhibit of the latest analytical and processing equipment, and a week-long series of 15 specialty, review, and survey short courses, many directly related to the symposium topics.

On Wednesday, April 26, 1989 at 6:00 p.m. Linus Carl Pauling, research professor, delivered the Plenary Address for the MRS Spring Meeting held in San Diego, California. He was introduced by John Baglin, Past President of MRS with the following words: “Linus Pauling…scientist, philosopher, and a thinker, whose fearless, pioneering research has made and continues to make vital and fundamental contributions to the sciences of chemistry, physics, mineralogy, biology and medicine. His work, frequently controversial, has stimulated thought and debate and research, promoting, indeed, the healthiest kind of scholarly activity within these many disciplines.”

With these thoughts and many more in my head 1 set out for the airport the previous afternoon to pick up Linus Pauling. I was about to meet someone who had deeply affected my scientific career from my early days as an undergraduate through the most important and fundamental aspects of 15 years of research. I was aware of almost all of Pauling's prizes and awards, but I couldn't quite remember what he won his second Nobel Prize for (he won the Nobel Peace Prize in 1962 for presenting a petition to the Secretary-General of the United Nations to ban atom bomb tests), and it was while I was wondering about this that Linus Pauling walked toward me after exiting the airport security gate.

Capping an exciting day at the 1989 Spring Meeting of the Materials Research Society in San Diego, a special three-hour session on “cold fusion” was held Wednesday evening, April 26, following the plenary lecture by two-time Nobel laureate Prof. Linus Pauling. (See “Linus Pauling Addresses MRS in San Diego” elsewhere in this issue.)

The session, the largest session in MRS history with over 1,700 participants, was sponsored by the Society to provide MRS meeting attendees with an unbiased scientific forum for the presentation and discussion of results and issues regarding recent “cold fusion” announcements in the press. The announcements had captivated the world's interest the preceding month while being met with a healthy amount of scientific skepticism. Such skepticism was not lost on the nation's cartoonists, many of whose works on “cold fusion” were shown during the evening's proceedings.

The special session was organized and moderated by Meeting Cochair Richard W. Siegel, with the help of Angelica M. Stacy and Robin F.C. Farrow (also Meeting Co-chairs) and MRS President R.P.H. Chang. A distinguished panel of invited speakers from the nuclear fusion and materials research communities was assembled to discuss the purported fusion of deuterium nuclei dissolved in palladium or titanium at or near room temperatures.