About HFIR

The ORNL High Flux Isotope Reactor (HFIR) is the highest flux reactor-based source of neutrons for condensed matter research in the United States. Thermal and cold neutrons produced by HFIR are used to study physics, chemistry, materials science, engineering, and biology.

The 85-megawatt High Flux Isotope Reactor (HFIR) provides one of the highest steady-state neutron fluxes of any of the world's research reactors. The intense neutron flux, constant power density, and constant-length fuel cycles are used by more than 200 researchers each year for neutron scattering for probing the fundamental properties of condensed matter. The Neutron Scattering Research Facilities possess a powerful collection of spectrometers and unique thermal-neutron scattering capabilities used for fundamental and applied research on the structure and dynamics of matter. The reactor is also used for medical, industrial, and research isotope production; research on severe neutron damage to materials; and neutron activation to examine trace elements in the environment.

The HFIR is the western world's sole supplier of californium-252, an isotope with uses including cancer therapy and detecting pollutants in the environment and explosives in luggage. The Activation Analysis Facility is a powerful tool for analyzing environmental pollutants.

Since it began full-power operations in 1966, the High Flux Isotope Reactor (HFIR) at the Oak Ridge National Laboratory (ORNL) has been one of the world's most powerful research reactors. The major use of the HFIR is for neutron-scattering experiments to reveal the structure and dynamics of a very wide range of materials. The neutron-scattering instruments installed on the horizontal beam tubes are used in fundamental studies of materials of interest to solid-state physicists, chemists, biologists, polymer scientists, metallurgists, and colloid scientists. These instruments are open to use by university and industrial researchers on the basis of scientific merit.

One of the original primary purposes of the HFIR is the production of californium-252 and other transuranium isotopes for research, industrial, and medical applications. These materials are produced in the flux trap in the center of the HFIR fuel element where a working thermal-neutron flux of 2.0 x 1015 neutrons/(cm²·s) is available to irradiate the target material. Additional irradiation facilities are also provided in the beryllium reflector.

Beyond its contributions to isotope production, the HFIR also provides for a variety of irradiation tests and experiments that benefit from the exceptionally high neutron flux available. In the fuel element flux trap, a hydraulic rabbit tube provides access to the high thermal-neutron flux in the reactor for short-term irradiations, and other positions are ideal for fast-neutron irradiation-damage studies. A modification of the flux trap experiment facilities in 1986 has provided two locations in the maximum flux region that can accommodate instrumented capsules and engineering loops. The beryllium reflector contains numerous experimental facilities with thermal-neutron fluxes up to 1.0 x 1015 neutrons/(cm²·s). These facilities can accommodate static experimental capsules, complex fuel-testing engineering loops, and special experimental isotope irradiations.

Benefits from Research at HFIR

Picking the Right Material for the Job

Any airline passenger who has struggled to open those bags of peanuts and pretzels knows that thin polymer films can be strong. The frustratingly durable packages are often blends of high- and low-density polymers. High-density polyethylene is a strong, hard, bricklike material made of long linear polymer chains; low-density polyethylene materials are made of polymer chains with many branches. Not surprisingly, blends of high-density and low-density polymers are popular and important materials. About 100 million tons are now produced each year for other ubiquitous consumer products such as sandwich bags and high-strength garbage bags.

To develop new types of polymer blends for even higher-performance materials, a critical question is: Will the separate components of the polymer really blend to make a new material, or will they simply congregate in small intermingled globs of the original materials? More precisely, will the materials blend or will they segregate?

This critical question would likely be impossible to answer without small-angle neutron scattering. Neutrons--neutrally charged particles that help make up part of an atom's nucleus--have a handy ability to penetrate materials. To make use of that ability, researchers first replace the hydrogen atoms in one of the polymer components with deuterium, another form of hydrogen. The deuterium scatters neutrons passing through the material differently but does not affect the property of the polymer. Measuring how the neutrons "scatter" can reveal the difference between a real polymer blend and a segregated material.

It's important to know which is which. Segregated material deteriorates over time, whereas true blends do not. Exxon, Phillips Petroleum, and Dow Chemical are among manufacturers who use the neutrons produced in Oak Ridge National Laboratory's High Flux Isotope Reactor to sort polymer blends from segregates. They can then determine how long the material will last and thus tailor the material for its intended application. It's worth much more to these industries than peanuts.

Putting Your Car in a Quiet Gear

We all want our cars to run well and run quietly. Whether they do depends in part on the precision and uniformity of the gears that transfer power from the engine to the wheels.

Manufacturing processes, however, can introduce distortions and residual stresses deep inside the gear material. These flaws--difficult to measure with conventional techniques-- often cause poor performance or premature breakdowns, not to mention an annoying growl. Researchers can now use capabilities provided by Oak Ridge National Laboratory's High Flux Isotope Reactor and the Residual Stress User Center, which is part of the High Temperature Materials Laboratory user facility at ORNL, to determine residual stresses in an automobile transmission gear.

Neutrons from the reactor can penetrate far into most engineering materials without damaging the material, allowing engineers using sophisticated materials analysis equipment to identify residual stresses without destroying the gear. Measurements on a General Motors Saturn gear proved that residual stresses can be mapped at points separated by only one millimeter (less than 1/25th of an inch).

These promising initial results led General Motors Corporation, Ford Motor Company, and other industrial members of the National Center for Manufacturing Sciences to ask that ORNL's Residual Stress User Center and Los Alamos National Laboratory join them in collaborative research. For automobile owners, the result of this collaboration could be a quiet ride that lasts for miles and miles.

Saving Lives and Money with Isotopes

Both lives and money are being saved with isotopes produced by the High Flux Isotope Reactor at Oak Ridge National Laboratory. The HFIR, with its intense neutron flux, is the West's sole source of californium-252, an intense neutron-emitting radioisotope used extensively in medical and industrial applications: cancer therapy, neutron radiography, elemental analysis, and as a startup source for nuclear reactors.

Californium-252 is effective in treating certain cervical and brain cancers that are otherwise incurable. Using it, Dr. Yosh Maruyama at the University of Kentucky has treated more than 450 patients with advanced cervical cancers, improving the 5-year survival rate for this type of cancer from 12% to 54%. With this kind of progress in mind, researchers are investigating its applications to other cancers.

Other medical isotopes produced at the HFIR include potassium-43 (for evaluation of coronary heart disease), palladium-103 (for treatment of prostate cancer), gadolinium-153 (for measuring bone loss in women), and tungsten-188 (associated with the treatment of cancer and arthritis). Thousands of patients undergo clinical evaluation or treatment using these and other isotopes each year. In fact, more than 100 million Americans receive diagnosis or therapy annually using some aspect of nuclear medicine. Of those, 10 million radioimmunoassays are performed annually.

In addition to its role in combating disease, californium-252 is used for radiography of aircraft to detect metal fatigue. At McClellan Air Force Base, engineers use californium- 252 to examine fighter aircraft, a technique that saves $5 million a year in repair costs alone. As a lifesaver in a different sense, the isotope is also used to detect explosive devices.

Alvin Weinberg, a former ORNL director, once observed: "If at some time a heavenly angel should ask what the laboratory in the hills of East Tennessee did to enlarge man's life and make it better, I daresay the production of radioisotopes for scientific research and medical treatment will surely rate as a candidate for very first place."

New Cask, Racks will Help HFIR Fulfill Its New "Extended Mission"

The High Flux Isotope Reactor will remain an important asset for neutron research for ORNL and the nation for the foreseeable future. Two recent developments at HFIR reduce the concerns regarding spent-fuel storage and should help ensure the reactor's increasingly important continued operation.

The problem with spent fuel has been twofold: DOE has long been without an acceptable container for shipping spent fuel over the roadways, most likely to the Savannah River Plant. Unable to be shipped for lack of a certified container, spent fuel has been stored in the reactor's pool, which is an acceptable method of storage as long as there is room for it. Space, however, was running out. In a nutshell, the HFIR can't operate if there is nowhere to store its spent fuel. The General Electric-made spent-fuel container, examined by DOE's Dave Rosine, features a leak-tight cask contained witha fire- and impact-resistant outer shell. A spent-fuel cask made specifically for the Research Reactors Division by General Electric was exhibited in January cinched to the back of a "low-boy" semi trailer. The container's dumbbell- shaped exterior, fastened to the trailer with thick steel cables, conceals a cylindrical, leak-tight cask. The cask and curiously shaped overpack are designed to withstand impacts and fires that could occur during transport. The $2.6 million container meets stringent Nuclear Regulatory Commission requirements.

Loading the spent fuel into the container is an interesting process: The cask will be removed from the outer shell and lowered into the reactor pool. There, under about 6 meters of water, a spent-fuel assembly will be loaded into the cask. After some drying out, the cask will be checked for leaks, placed back in the overpack, and sent on its way. It is hoped that shipments of spent fuel will commence about midyear when DOE lifts a moratorium on such shipments.

In the meantime, spent fuel has accumulated in the HFIR's storage pool almost to capacity. A redesign and installation of new fuel- storage arrays will conserve space in the pools and allow safe storage of more fuel elements. The new design uses jacketed assemblies to store fuel in silo clusters, connected in groups of four or five. RRD engineers designed the clusters and performed most of the analyses, taking into consideration criticality, thermal, seismic, structural, and shielding safety factors. Plant and Equipment Division craftsmen made them. The first new racks were installed on December 1; further installations will continue.

HFIR's spent-fuel storage arrays sit behind the reactor pool. With no acceptable container to ship spent fuel, pool space for the spent fuel was running out. The new racks, along with the new shipping cask, should clear a barrier to HFIR's continued operation. HFIR operations are a showpiece of strict adherence to procedures and conduct of operations, and the new cask and arrays are no exception. Their fruition took many months of work--with strict attention to detail--by the organizations involved. The benefits will probably go beyond the HFIR operation. Efforts are under way to expand the certification of the cask to ship fuel from other DOE research reactors. Also, the availability of a properly certified shipping cask should help speed the decommissioning of the Bulk Shielding Reactor and the Tower Shielding Reactor at ORNL.

HFIR's last shipping cask was retired in 1986, and spent fuel has been stored in the pool ever since. The new cask and the more space-efficient racks should help the HFIR continue to crank out neutrons on its now extended tour of duty.

Neutrons and JFK

Most Laboratory personnel learned of the assassination of President John Kennedy over the Laboratory's public address system on the afternoon of November 22, 1963. A week later, the Federal Bureau of Investigation (FBI) asked the Laboratory to study fragments of the bullets that struck the president and the paraffin casts taken of the hands and face of Lee Harvey Oswald, the accused assassin.

This request was made because the Laboratory had facilities and scientists available for performing neutron activation analysis. When neutrons from a reactor activate the atomic elements in a material, each element emits characteristic gamma rays, revealing its presence and concentration in the material.

About five years after John Kennedy had admired the Oak Ridge Research Reactor as a U.S. senator, evidence relating to his assassination came to the Laboratory, where William Lyon Jr., Frank Dyer, and Juel Emery, all of the Analytical Chemistry Division, tested it in the High Flux Isotope Reactor's neutron flux. The FBI hoped Laboratory researchers could match gunpowder particles on the paraffin casts with gunpowder from a rifle found at the crime scene. The fact that Oswald had fired a pistol, killing a Dallas policeman, the day of the assassination, and earlier tests made on the paraffin casts complicated the research and made the Laboratory's results inconclusive.

The FBI hoped that ORNL's neutron activation analysis of the bullet fragments taken from the president's limousine could determine whether the bullets were fired from a single weapon. Lead bullets have traces of silver and antimony, and the Laboratory's analysis of these traces indicated that the bullets did indeed come from the same rifle. Later independent study by a University of California neutron activation specialist confirmed the Laboratory's conclusion. ORNL's Nuclear and Radiochemistry Analysis group complied with many requests for neutron activation analysis in connection with crimes until the 1970s when commercial laboratories entered the field.

Presidential Visit from the Grave

Shortly after breaking ground for the Washington Monument on July 4, 1850, President Zachary Taylor, a hero of the Mexican War, fell ill. When he died suddenly a few days later, the cause was listed as gastroenteritis (inflammation of the stomach and intestines).

Some historians suspected that Taylor's death may have had other causes, and in 1991 one convinced Taylor's descendants that the president might have suffered arsenic poisoning. As a result, Taylor's remains were exhumed from a cemetery in Louisville and Kentucky's medical examiner brought samples of hair and fingernail tissue to Oak Ridge National Laboratory for study.

In the Chemical and Analytical Sciences Division, Larry Robinson and Frank Dyer headed the Taylor investigation, using neutron activation analysis to measure the amount of arsenic in the hair and nail samples. After placing the samples in a beam of neutrons from the High Flux Isotope Reactor, Dyer and Robinson looked at the gamma rays coming from the samples for the distinctive energy levels associated with the presence of arsenic. Arsenic is among the easier elements to identify through neutron activation and can be detected in a few parts per million. Most human bodies contain traces of arsenic, so the essential issue in the Taylor case was whether the samples from Taylor contained more arsenic than would be normal after 141 years in the crypt.

Working late in the evenings, Dyer and Robinson in a few days calculated the arsenic levels in the samples and sent them to the Kentucky medical examiner for his decision. After reviewing the test results, the examiner announced that the arsenic levels in the samples were several hundred times less than they would have been if the president had been poisoned with arsenic. This finding acquitted several of Taylor's prominent contemporaries of the suspicion of murder and proved that history and science share a common quest for truth.