gents for cancer detection and treatment, stronger materials, better electronic gadgets, and other consumer and industrial products--these are assured benefits of a research reactor project proposed for Oak Ridge. Just as American companies have again assumed world leadership in producing semiconductor chips as well as cars and trucks, the United States is poised to retake the lead in neutron science by building and operating the $2.9 billion Advanced Neutron Source (ANS) research reactor by the start of the next century.
In the 1950s and early 1960s, the United States had the lead in neutron research. One reason was the work of pioneers like Ernie Wollan and Cliff Shull (winner of the 1994 Nobel Prize for physics). They performed some of the first neutron scattering studies in the late 1940s and early 1950s at Oak Ridge National Laboratory's (ORNL's) Graphite Reactor, the World War II pilot plant for the plutonium production reactors at Hanford, Washington. Another reason was the U.S. Atomic Energy Commission's (AEC's) support for construction of the High Flux Beam Reactor (HFBR) at Brookhaven National Laboratory (BNL) in 1965 and the High Flux Isotope Reactor (HFIR) at ORNL in 1966. A third reason was the variety of strong neutron science programs that were developed using these research reactors.
In 1969, the U.S. Department of Commerce's National Bureau of Standards built a research reactor specifically for neutron scattering experiments in Gaithersburg, Maryland. By the end of the 1960s, it had become apparent that a key to industrial leadership was the ability to produce neutrons for research aimed at development of new, improved commercial products and processes.
In 1971, Europe's new research reactor facility--the Institut Laue-Langevin (ILL) at Grenoble, France--began operation. Because it was a more powerful source of neutrons for research (including highly useful low-energy neutrons) and had more sophisticated instruments than the American reactors, researchers from all over the world were drawn to Grenoble to conduct neutron studies. In the 1980s, other neutron sources were built in Europe and Japan, and neutron research at these facilities also surpassed that at U.S. reactors. Furthermore, many American neutron scientists went abroad to conduct their research.
Although not obvious to many people, the fruits of neutron research include improvements in the range and quality of products used in our everyday lives. Examples are automobiles, jets, credit cards, pocket calculators, compact discs and magnetic recording tapes, computer disks, agricultural pesticides, geological maps of oil deposits, and satellite weather information for forecasts. (For a more detailed explanation of applications, see the article "Fruits of Neutron Research" on p. 19.)
In the past 20 years, neutron research brought about a revolution in plastics, once fragile materials that engineers considered useless except for toys. New high-tech plastics are lighter and stronger than steel. Examples of uses for these plastics are bulletproof Kevlar'-armored vests that have saved the lives of police officers and small bags that contain prepackaged foods or snacks (these extremely thin bags are now so strong they can be opened only by tearing at the precut notch).
For millions of people, neutrons provide a lifeline in the form of specialty radioisotopes produced by the HFIR and other sources; in the United States, radioisotopes are used in 36,000 medical procedures conducted each day and 50,000 treatment programs and almost 100 million laboratory tests conducted each year.
Neutrons are also an essential tool for researchers studying ways of improving materials that may have practical uses such as high-temperature superconductors and powerful lightweight magnets.
In 1985, the neutron community, led by ORNL researchers, proposed a pioneering project, later called the ANS. Scheduled to begin operation in 2003, the ANS is seen not only as a replacement for the aging HFIR and HFBR but also as the best laboratory in the world for conducting neutron-based research.
In Asia, while South Korea is completing construction of a new research reactor, Japan has strengthened its position by building the new JRR-3M research reactor, Indonesia has brought a new reactor on line, and Thailand is planning a new one for completion in 1999. Interestingly, Japan's investment of $300 million exceeds all U.S. investments in research reactors in the past 20 years.
No world-class research reactor has been built in the United States since the 1960s. The HFIR and HFBR are approaching the end of their useful lives. In the western hemisphere, the HFIR is the only source of californium, a radioisotope critical to treatment of certain cancers, and other isotopes used for medicine and industry. Without a new world-class research reactor, the United States will no longer be competitive in neutron scattering research and radioisotope production and will have to turn to sources abroad.
To make the United States more competitive in a scientific field that has such important applications, leaders in science and industry recognized the need for a new world-class research reactor 10 years ago. In 1984, a National Research Council committee ranked a new reactor-based neutron facility as one of the nation's top two needs in materials science and related disciplines. In December 1985, some 40 scientists and engineers, including ORNL researchers, met at Gaithersburg, Maryland, and the basic concept of the ANS emerged as the preferred neutron source for meeting the needs of the U.S. scientific community.
In 1989, Paul Fleury, director of physical research at AT&T Bell Laboratories, told a Department of Energy (DOE) panel, "We simply are not competitive with the rest of the world at this point." He called construction of the ANS "absolutely necessary." He added, "It is a sad fact that. . . over the last couple of years, I have spent more of my neutron-related research money on airplane tickets for our scientists to go to Europe than on direct support of collaborative work at U.S. facilities."
In a January 1993 report, Neutron Sources for America's Future, the Basic Energy Sciences Advisory Committee of DOE's Office of Energy Research deemed construction of the ANS as an "overriding priority" to prevent a serious decline in the U.S. neutron research community in the next decade. In early 1993, President Clinton urged Congress to build the ANS in his report A Vision of Change for America.
The ANS Project is incorporating European improvements so that the ANS will be the world's best neutron facility for fundamental science, for engineering, for isotope production, and for materials irradiation and testing. Such a remarkable facility will be made available to a broad spectrum of scientists and students.
The ANS will ensure America's future in neutron-based studies and will reaffirm its position as an industrial leader through the many products that will result. The list of businesses and organizations that already depend on neutron research to develop better products and services contains household names such as IBM and Xerox, Goodyear and Firestone, Ford and General Motors, General Electric and AT&T, Exxon, Amoco, and even the American Dental Association. The Smithsonian Institution, a popular tourist attraction in Washington, has used neutrons to assess paintings and ancient bronze sculptures. These and other organizations have been sending their researchers to the best neutron facilities, especially those in Europe, to conduct their studies.
However, the ANS will be far superior to even the best neutron facilities in Europe, allowing the United States to recapture the lead in neutron production and research. Once operational, it will have 5 to 10 times the useful neutron flux--the number of neutrons that strike a given area each second--of any existing research reactor. Such a position would not be new to ORNL if the ANS is located here: the Oak Ridge Research Reactor (ORR) and HFIR were, in turn, world leaders in neutron flux when they were new. Through improved design and instrumentation, the ANS will offer up to 10,000 times more usable neutrons for some experiments than the HFIR and HFBR. Hence, the path for neutron research will lead back to the United States.
The ANS will offer the nation several benefits. It will be the foremost center in the world for neutron science. It will have a record number of neutron beam lines and world-class, state-of-the-art instruments. It will have a user-friendly design for scientists all over the United States--that is, it will be designed from the beginning with user access in mind. It will be a national testing center for new materials, it will facilitate engineering development, and it will produce new radioisotopes that may be approved for medical use when the ANS begins operation.
The ANS also will offer regional benefits. It is estimated that every year about 1000 university, laboratory, and industrial researchers from around the world will come to Oak Ridge to use the ANS, which is designed to be a DOE user center. Most of these visitors will stay a few days to several weeks to conduct their experiments. In addition to making valuable research contributions, the visitors will help bolster the area's economy and will contribute to regional colleges and universities through lectures, seminars, and research collaborations.
In addition, the ANS will be a magnet for industrial firms in need of neutron research for product development. Just as Coors Ceramics Company located in Oak Ridge to take advantage of the research capabilities of ORNL's High Temperature Materials Laboratory, other businesses and industrial firms are likely to settle in the region because of the unique research offerings of the ANS.
The ANS design proposal was based on a concept initially proposed by Dick Cheverton of ORNL's Engineering Technology Division (ETD) and strongly endorsed by Ralph Moon of the Solid State Division. It was dubbed the HFIR-II at first and then was called the Center for Neutron Research (CNR). The ORNL researchers had proposed a heavy-water-moderated reactor because they considered it the best choice for high thermal flux, minimum technical risk, and reliability of operation. They proposed using heavy, or deuterated, water to cool the nuclear fuel core; to slow down, or moderate, neutrons to make them useful for research and isotope production; and to reflect them back into the core to promote additional neutron-producing fission reactions. By contrast, the HFIR uses ordinary water as the moderator and coolant and beryllium as the neutron reflector.
Colin West of ETD proposed that the ANS use uranium silicide (U 3Si2) as its fuel rather than uranium oxide employed in the HFIR. The uranium would be enriched, as it is in all high-performance research reactors, to 93% of the fissionable uranium-235 isotope. Researchers at Argonne National Laboratory, who had been trying to develop nuclear fuel for research reactors that contained a lower percentage (enrichment) of fissionable uranium because of nuclear proliferation concerns, had discovered in the 1980s that U3Si2 is a good choice for a fuel that contains a lot of uranium. The reason: The molecular structure packs the uranium atoms more closely together, enhancing neutron production.
DOE has asked Brookhaven National Laboratory to assemble a group of experts to assess the impact on ANS performance of using U3Si2 fuel enriched in lower amounts of uranium-235 to address proliferation concerns.
As with the HFIR and other research reactors, the ANS fuel will be clad with an aluminum alloy that is an excellent heat conductor, thus minimizing the temperatures within the nuclear fuel. Zirconium, which is used in Zircaloy cladding for nuclear power plants, is not as good a cladding as aluminum for research reactors that generate heat because zirconium doesn't conduct heat away from the fuel as well.
The maximum neutron flux of the ANS will be 7.5 10E19 m-2/s-1, or about 100 billion billion neutrons per square meter each second. This flux will be 5 to 10 times that of the ILL.
Features of the ANS will include 30 neutron beam lines, 48 neutron scattering stations, 50 irradiation facilities for isotope production and materials testing, 10 materials analysis facilities, a gamma irradiation facility, and a positron production facility. A Joint Institute for Neutron Studies building (in association with the University of Tennessee) will provide classroom space, small conference rooms, and some on-site accommodations.
When Congress passed an appropriations bill providing DOE funds for the first time for an "advanced neutron source," ORNL began to have a larger source of financial support for its CNR Project. Because of the bill's language, the CNR name was changed to the Advanced Neutron Source Project.
Since 1985, much progress has been made. The ANS Project management team has been working closely with the National Steering Committee for the Advanced Neutron Source to ensure that the facility meets the requirements of the scientific community. In addition, more than 3000 applicable federal, state, and local environmental, safety, and health regulations have been identified and have been, or will be, addressed. In 1991, Gilbert/Commonwealth, Inc., was selected as the architect-engineer for conceptual design of the ANS, working with ORNL researchers and other members of the team. Using a concept developed by architect Hanna Shapira of the ANS Project, the team came up with a user-friendly facility design. In June 1992, the ANS team completed a fully documented conceptual design for development of a cost estimate and schedule for detailed design and construction; the conceptual design report contains 12,000 pages. Based on the design, which has been approved by DOE, an environmental report was prepared, indicating some of the potential impacts of the project. That report was aimed primarily at the Oak Ridge Reservation--DOE's preferred site for the ANS, subject to evaluation of the environmental effects. Some of the information will also be useful in preparing the environmental assessment, which will include sites at Los Alamos National Laboratory (LANL) and Idaho National Engineering Laboratory, as well as Oak Ridge.
The environmental assessment will be prepared on the ANS by an independent group contracted by DOE. This group will examine the environmental and socioeconomic impacts of the proposed research reactor on all three candidate sites, with particular emphasis on the acceptability of the preferred Oak Ridge site.
During the past few years, West has been reporting to Bill Appleton, formerly associate director for Physical Sciences and Advanced Materials. In October 1992, Appleton headed an ANS task force responsible for getting the ANS initiated as a construction project, and in 1994 he assumed the new position of associate director for the Advanced Neutron Source.
In 1979, Wally Koehler of ORNL's Solid State Division obtained funding from the National Science Foundation to build a small-angle neutron scattering (SANS) instrument at the HFIR. The instrument was designed by William Taylor Clay and built by Charlie Fowler, both then of ORNL's Instrumentation and Controls Division. The instrument, combined with a small-angle X-ray scattering instrument designed by ORNL's Bob Hendricks, became part of the National Center for Small Angle Scattering Research at the Laboratory. Because industry is the nation's largest single taxpayer, Koehler invited representatives from American industry to make use of the center. Thus, the center became ORNL's first user facility, starting a tradition of government-industry partnerships that will continue to flourish with the operation of the ANS.
The ANS will be used primarily for neutron scattering experiments. Neutron scattering is used by a variety of scientific disciplines to study the arrangement, the motion, and the interaction of atoms in materials. Neutrons for scattering experiments will come from the heart of the ANS facility, which will be the world's most capable research reactor. The heart of the ANS is the reactor core, which is about the size of a 57-liter (15-gallon) can and which produces neutrons by fission of uranium atoms. Neutron beam tubes and guides, which serve as pipelines, will carry some of the neutrons from the reactor to adjacent instruments, where samples of material will be placed directly in the path of the neutron beam.
Neutrons are well suited for unlocking the secrets of materials made of light elements and of complex molecular structures. These materials include living matter and synthetics that are composed of the light elements carbon, hydrogen, and oxygen. Neutrons, particles in the atomic nucleus that lack an electrical charge, are strongly diffracted, or scattered, by light atoms in a sample. Because they are uncharged, neutrons penetrate to much greater depths than other radiation such as X rays and charged particles that interact with electron clouds in atoms of solids. On the other hand, X rays--the type of radiation commonly used in dentists' offices and emergency rooms--tend to shoot past light atoms, although they are more strongly deflected by the electron clouds around the nuclei of heavier atoms. So neutrons are a preferred probe for many materials, including DNA and synthetic molecules such as polymers.
As neutrons travel through the sample, some will ricochet at an angle off atomic nuclei. By measuring the relative fractions of the neutrons scattered at different angles from a sample, scientists can decipher even subtle details of the material's atomic structure. It is possible to deduce, for instance, the kind of atom doing the scattering, its energy of vibration, and its position and motion in relationship to other atoms in the material. This knowledge is the key to improving the material, making it stronger, lighter, more wear resistant, or more flexible, to meet specific needs.
Neutrons are also valuable because they behave as tiny magnets. Thus, they can reveal details about the magnetic properties of certain materials that cannot be obtained any other way. Such information can help determine if a material can be used for magnetic storage or superconductivity. Virtually everything we know about the behavior of magnetic materials has involved neutron scattering, and much of this information has come from studies at the HFIR.
Fast neutrons are the high-energy products of fissioning uranium atoms in the reactor core. By placing a sample of material very close to the core, where fast neutrons are most plentiful, scientists can study the effects of intense radiation on different materials. Thus, they can simulate in a few days or weeks the type of radiation damage that might be expected by long-term exposure of these materials to intense neutron radiation from fission and fusion reactions. Results from such studies help engineers select the best structural materials for fission and fusion devices being designed as future sources of electricity.
As fast neutrons leave the reactor core and pass through the surrounding heavy water, they lose energy through collisions with water molecules. As they slow down, they become thermal neutrons as their average energies reach the temperature of the water. Thermal neutrons can be used for scattering without altering the atomic structure of the target material. They are valuable also for neutron radiography for viewing the interiors of metallic components, such as aircraft wings, to identify signs of corrosion or hairline cracks. Unless these problems are detected and corrected early, they could lead to catastrophic failure under operational stress.
Very slow, or "cold," neutrons are desirable because they are even more sensitive probes than thermal neutrons for certain applications. For this reason, American neutron scientists have indicated that their greatest need is an intense source of cold neutrons, and the ANS will have the most advanced source of cold neutrons in the world.
Cold neutrons are produced by passing thermal neutrons through a region of the reactor containing a very low-temperature material, such as liquid deuterium (heavy hydrogen). In this process, the energy and velocity of the incoming neutrons are greatly reduced. Over the past 20 years, cold neutrons have been the key to new discoveries and developments in plastics, alloys, and biochemical systems made of living cells and membranes.
Cold neutrons are particularly useful for determining the structure of materials made from large molecules called polymers, long chains of smaller molecules. Such materials, including plastics, synthetic fibers, and wood, greatly influence our daily lives. Scattering techniques using cold neutrons even aid biologists in studying the building blocks of life. For example, DNA, which contains life's genetic code, is itself a polymer.
- Materials irradiation, a technique which will be used to design and test the best candidate materials for use in fission or fusion reactors. These reactors may be a significant energy source in the future. Such tests also help determine the best materials for maintaining today's power reactors. Neutron radiography, which is similar in principle to X-ray analysis. Neutron radiography uses the penetrating power of neutron beams to examine the interior structures of materials in much the same way that X rays reveal the structures of human bones and organs. However, because neutrons are uncharged particles, they can penetrate to much greater depths in materials than X rays.
- Neutron radiography can be employed, for instance, to inspect the microstructure of steel girders used in the construction industry, to detect hairline cracks or early signs of corrosion in the wings of an airplane, or to analyze the flow of oil in an operating engine. The ANS can also be used to produce the isotope californium-252 for portable sources of neutrons for performing on-site radiography.
How do neutrons detect early signs of internal corrosion in aluminum and other metals? Corrosion is caused by the presence of water, and since water is made of the light elements of hydrogen and oxygen, it is detectable by neutron radiography. This is the only method that can detect the extremely small pockets of corrosion that may arise within airplane wings or other machine parts after manufacture.
- Neutron activation analysis, which is proving essential to environmental studies. Activation analysis can be used to determine the presence and the amount of targeted substances in soil samples. Neutron activation analysis has been used at the HFIR to detect mercury and other metallic pollutants in 100,000 soil samples. The method developed at ORNL has been refined into a technique that saved almost $3 million in analyzing 4000 samples of mercury-contaminated soil in the East Fork Poplar Creek floodplain in Oak Ridge.
To measure mercury concentrations in soil samples by neutron activation analysis, the soil samples are irradiated with neutrons. By absorbing neutrons from the reactor, the soil mercury is transformed into the unstable isotope mercury-203, which emits gamma rays as it decays. The gamma-ray energies measured by a high-resolution gamma spectrometer indicate the presence and concentration of mercury in the sample.
At ORNL, neutron activation analysis was used in late 1963 to study fragments of the bullets that killed President John F. Kennedy. In 1991, analysis was performed at the HFIR on hair and fingernail samples from the body of President Zachary Taylor. It was determined that he did not die from arsenic poisoning as had been suggested by a historian.
In addition to being used for in-reactor neutron activation analysis, the ANS will produce californium-252 for portable sources of neutrons for on-site activation analysis to detect and measure hazardous contaminants in support of environmental remediation programs.
- Isotope production, for making radioisotopes that are used for medical, military, industrial, and scientific purposes. Many radioisotopes produced in the ANS in the first decade of the 21st century may be approved by the Food and Drug Administration (FDA) to treat a wide range of cancers, including cancer of the prostate, breast, and cervix. Two studies report that the anticipated growth of FDA-approved commercial radio-pharmaceuticals will be in the areas of therapeutical agents for cancer. Because most therapeutic radioisotopes are reactor-produced, the projected growth suggests that the ANS will play a vital role in developing new radioisotopes for cancer treatment.
An important contribution of the ANS to the medical community will be production of already approved medical radioisotopes such as californium-252, which is used to treat cancer. In the entire western world today, the only significant source for californium-252 is the HFIR.
Californium-252 is in demand because its half-life of 2.6 years gives it a useful service life and because it provides a high amount of radioactivity for a small amount of mass--2.3 109, or about two billion, neutrons per second per milligram. Discovered by Nobel Laureate Glenn Seaborg in 1950, this element is produced at the HFIR by neutron irradiation of curium targets.
Medical facilities in the United States, Russia, and Japan use californium-252 to treat a variety of cancers, including those in the brain and cervix. It is particularly useful against large tumors that cannot be successfully treated with other types of radiation therapy.
At the University of Kentucky Medical Center, oncologist Yosh Maruyama has reported that use of californium-252 treatments resulted in five-year patient survival rates of 94% for victims with low-stage cervical cancer and 54% with advanced-stage cervical cancer, with some cures even for advanced severe-stage cervical cancers. For patients having malignant glioma, a type of brain tumor that was previously untreatable and invariably fatal, five-year survival has been achieved.
When treating brain cancer at the University of Kentucky center, physicians implant 30-microgram "seeds" of californium-252 into large tumors. The isotope's powerful neutron radiation destroys the cells of the tumor from within, causing less damage to the healthy tissue nearby than conventional treatments using gamma radiation or X rays. A different technique is used to treat cancerous tumors of the cervix. Stainless steel tubes containing californium-252 are implanted directly into the patient's uterus or vaginal canal; X rays guide the physicians in positioning the tubes to maximize radiation doses to the cancer cells. This method is highly effective in eradicating tumors, Maruyama says.
Interest in using californium neutrons for cancer therapy continues to increase. Recently, the Nuclear Regulatory Commission approved a license for evaluation of californium-252 for cancer therapy at Wayne State University, a comprehensive cancer center of the National Cancer Institute. ORNL will ship californium sources from the HFIR in 1994 to initiate the new clinical trials.
Radioisotopes from the HFIR and later the ANS also will help extend our knowledge of our domestic energy sources. Radioisotopes can be injected down an oil well to trace oil flow. Low-level radioactivity from the flowing oil, which decays away reasonably quickly, can be detected in the ground using a gamma-ray camera. This information helps American petroleum companies determine the direction of oil flow and, thus, the best locations for new oil wells.
Other applications of radioisotopes from the ANS will be neutron radiography, medical diagnosis, power sources for space satellites, and detection of airport explosives.
The term nuclear reactor usually refers to a large reactor that produces electrical power. The ANS, however, does not generate electricity. It is a research reactor, not a power reactor.
The two reactor types differ in size and heat generation, for example. The core of a typical power reactor would fill a two-car garage, whereas the ANS's core will be roughly the size of a medium-capacity home water heater. The 330-MW ANS will generate only one-tenth the amount of heat produced in a typical 1200-MW power reactor.
A power reactor is similar to a giant pressure cooker. Its primary purpose is to make steam that will drive turbines for producing electricity. Tremendous amounts of heat and high pressures are required for electricity generation. Thus, the core must be big, and the facility must be complex. Equipment failures at power reactors are usually the result of damage either to valves, to pipes, or to other mechanical systems and are caused by intense pressures or the complexity of the equipment needed to ensure cooling of the plant's key systems.
By comparison, the ANS is a low-temperature, low-pressure operation because making steam is not its purpose. In fact, the ANS is designed to be a cool system because one goal is to provide cool low-energy neutrons.
The ANS has been designed with safety as the highest priority, using a principle known as defense-in-depth. There are at least two different systems capable of providing each safety-related function; critical systems have backups that are both redundant and diverse. Very simply, the idea is (1) to design the facility from the outset so that no systems will fail; (2) to ensure that if a system did somehow fail, backup systems are immediately available to bring operations back to normal; (3) to construct a containment building with double walls (2-meter- or 6-foot-thick reinforced concrete backed by a separate steel liner) to prevent the escape of any material in the reactor area to the environment and to the public; and (4) to have well-established, well-rehearsed emergency plans, regardless.
The ANS Project team incorporates the combined expertise from DOE's national laboratories and from U.S. industry to design the ANS. The design relies on proven technology and has considered compliance with more than 3000 federal, state, and local regulations. This, combined with years of experience in building and operating research reactors, is additional assurance that the ANS will be a productive facility.
Despite the fact that a commercial reactor is much more powerful and is subject to much higher pressures, the containment building of the 330-MW ANS will be bigger than that for a typical 1200-MW power reactor because ANS needs a large floor space for experiments. Furthermore, the ANS is being designed to meet the reactor licensing specifications of the Nuclear Regulatory Commission, although there is no legal requirement to do so for DOE's research reactors. It's simply a matter of putting safety first.
This way of thinking has been consistent throughout the planning of the ANS Project and will continue until the facility has run its useful course, probably sometime in the mid-21st century. It is a standard that has led to more than 50 combined years of safe, successful operation at the HFIR and ILL, which have been design models for much of the ANS. Although the HFIR began operating in 1966 when the potential of neutron beams for research was only beginning to be understood and tapped, it has laid the groundwork for the future of neutron-based studies that will be realized through the ANS.
By building and operating the Advanced Neutron Source, Oak Ridge will reaffirm its status as one of the nation's most prominent centers for scientific exploration and will lead the United States back to the rank of world leader in the field of neutron research.
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Neutron Scattering at the High Flux Isotope Reactor