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The report is available on-line at: https://science.energy.gov/bes/community-resources/reports/

DOI: 10.2172/1647598
The Scientific Justification for a

U.S. Domestic High-Performance 

Reactor-Based Research Facility

REPORT OF THE BASIC ENERGY SCIENCES ADVISORY COMMITTEE

U.S. Department of Energy/Office of Science/July 2020

Revision 10-28-2020

Prepared by the BESAC Subcommittee to Assess the Scientific Justification 

for a U.S. Domestic High-Performance Reactor-Based Research Facility
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Subcommittee Membership List

Robert Birgeneau, University of California, Berkeley; Subcommittee Chair

Sue Clark, BESAC/PNNL

Pengcheng Dai, Rice University

Thomas Epps, BESAC/University of Delaware

Karsten Heeger, Yale University

David Hoogerheide, NIST

Marc Kastner, MIT, retired; BESAC Chair

Bernhard Keimer, MPI-Stuttgart

Despina Louca, BESAC/University of Virginia

Pete Lyons, NEAC member

Allan MacDonald, BESAC/University of Texas, Austin

Sean O’Kelly, Idaho National Lab

Brad Olsen, MIT

Julia Phillips, SNL, retired

David Robertson, Director, MURR reactor @ Missouri; Subcommittee Vice-Chair

Anthony Rollett, BESAC/Carnegie Mellon

Kate Ross, Colorado State University

Mike Rowe, NIST, retired

John Stevens, ANL

Brian Wirth, FESAC/University of Tennessee, Knoxville

Editor/writer: Al Hammond

Design/Production: Maggie Powell

BES Staff: Harriet Kung, Tom Russell, Katie Runkles

October 2020 revision corrected an error on page 1 of the Executive Summary.
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Table of Contents

Executive Summary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Recommendations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

THE SCIENTIFIC CASE

1. Neutron Scattering. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

1a. Solid State Physics Including Quantum Materials. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

1b. Soft Matter. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

1c. Biology. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

1d. Polarized Neutrons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

1e. Synchrotron X-rays vs. Neutrons. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

2. Industrial Applications of Neutron Scattering. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

2a. Industrial Applications. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

2b. Industry-Related Consortia for Use of Neutrons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

2c. Neutron Techniques with Potential Industrial Applications. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

2d. Barriers to Broad Industry Use of Neutrons. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

2e. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

3. Fundamental Physics at Reactors and Spallation Sources. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

4. Isotope Production. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

4a. Isotope Production at HFIR. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

4b. Heavy Element Chemistry. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

5. Materials Irradiation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

5a. Materials Irradiation — General. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

5b. Fusion Materials Irradiation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

HEU-LEU CONVERSION

Preservation of Reactor Capability with Low Enriched Uranium Fuel. . . . . . . . . . . . . . . . . . . . . . . . . . . 52

Selection of U3Si2 for HFIR Application, and the Path to Conversion. . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

Progress on High Flux Reactor Conversion since 2016 NAS and 2018 APS Studies. . . . . . . . . . . . . . . . 54
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MAJOR U.S. NEUTRON FACILITIES: STATUS AND FUTURE PLANS

High Flux Isotope Reactor (HFIR). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

NIST Center for Neutron Research (NCNR). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60

SNS Present and Future. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63

INTERNATIONAL NEUTRON FACILITIES

Institut Laue-Langevin (ILL). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66

Forschungsreaktor München II (FRM-II). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68

Jules Horowitz Research Reactor (JHR). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70

Belgian Reactor 2 (BR2). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71

Conclusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72

References and Notes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77

APPENDICES

1. Oak Ridge Proposed Strategy for HFIR. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83

2. The Global Effort to Convert Research Reactors to Low Enriched Uranium Fuels. . . . . . . . . . . . . . . . 94

3. HFIR, SNS, and NIST User Data. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102

About the cover image: 

HFIR Refueling: July 2015

The High Flux Isotope Reactor at Oak Ridge National Laboratory is the highest flux reactor-based source of neutrons for research in the United 

States, and it provides one of the highest steady-state neutron fluxes of any research reactor in the world. Operating at 85 MW, an average fuel 

cycle for the HFIR generally runs for approximately 26 days—depending on the experiment loading for that cycle—followed by a refueling and 

maintenance outage for various scheduled calibrations, modifications, repairs, and inspections.

The reactor underwent routine refueling in July 2015, as seen in these photos. While submersed, the spent fuel emits a luminescent blue glow 

due to Cherenkov radiation, in which shedding electrons move through the water faster than the speed of light in water. Once removed from the 

reactor, spent fuel is then relocated into an adjacent holding pool for interim storage.

This image shows the removal of a HFIR fuel element from the reactor vessel during defueling operations.

Image credit: Jason Richards/ORNL
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Executive Summary

Why neutrons are important. Neutrons are a research 

tool that scientists and industrial researchers use to 

probe the properties of materials. As their name suggests, they are neutral (carry no electric charge) and 

hence do not interact with the electric fields of atoms. 

Beams of neutrons can thus penetrate deeply into a 

material without damaging it, and they “scatter” or 

bounce off the atoms within a material in ways that can 

reveal its structure and dynamics. Neutrons are also 

uniquely suited to exploring the magnetic properties of 

materials. Indeed, whenever an important new material 

is discovered, its basic structural and magnetic properties will invariably be explored using neutron scattering 

techniques. In addition, neutron bombardment creates 

the radioactive isotopes used for medical treatments of 

cancers and other diseases as well as in a wide range of 

critical industrial and national security activities. 

Where they come from. Neutrons are generated within 

a nuclear reactor, such as the High Flux Isotope Reactor 

(HFIR) at Oak Ridge National Laboratory and the reactor at the NIST Center for Neutron Research (NCNR) 

at the National Institute of Standards and Technology, 

by the process of nuclear fission. Neutrons can also be 

generated by colliding a beam of high-energy protons 

with a metallic target to shake loose a pulse of neutrons, such as at the Spallation Neutron Source (SNS) 

at Oak Ridge National Laboratory. For some types of 

research, the reactor-based steady flux of neutrons and 

the spallation-based pulses of neutrons are interchangeable; more often they are complementary, each technique having an advantage in certain areas of research. 

The HFIR is a unique resource. It is the world’s most 

intense source of neutrons for research that is widely 

available to scientists, as well as the only source capable 

of generating certain critical radioactive isotopes; the 

only comparable source for isotope production, in 

Russia, is not available to western scientists. Despite its 

importance, the HFIR faces a number of current and 

prospective problems that threaten its continued availability, and which are the reason for this report. These 

problems include:

• The reactor’s age—the HFIR was put into service 55

years ago, and steady exposure of the reactor’s steel

pressure vessel to neutron bombardment is causing

embrittlement of the steel, so that the pressure 

vessel will have to be replaced (or the reactor shut 

down) within two to three decades. 

• In the short term, the U.S. and other nations are

committed by agreements, policy, and precedent to

stop using highly-enriched uranium (HEU) fuel for

research reactors—inclu-ding the HFIR—as an

international security measure against nuclear

weapons proliferation. Conversion to low-enriched

uranium (LEU) will involve significant changes to

the HFIR and, this report argues, should be

combined with replace-ment of the pressure vessel.

• Thirdly, demand by both academic and industrial

researchers for access to the HFIR and other major

U.S. neutron sources (SNS and NCNR) is already as

much as three times higher than current facilities

can accommodate, meaning that critical research is

either not done or delayed for long lengths of time.

In addition, national security demand for certain

radioactive isotopes produced by the HFIR is more

than the reactor can currently supply. During a

shutdown of the HFIR to replace the pressure vessel and convert to LEU fuel, it would be possible to

add more beamlines that extract neutrons from the

reactor and more experiment stations along those

beamlines together with enhancement of the

instrumentation, plus more isotope production

capacity, enabling a significant expansion of neutron-based research. Because of the importance of

high-flux neutron research both for fundamental

science and for industrial applications, this report

argues for such expansion.

The Scientific Case

This report describes a wide variety of important 

scientific and industrial research for which the intense, 

steady flux of neutrons generated by a research reactor 

such as the HFIR is either advantageous or essential. 

Neutron Scattering as an Essential Tool for Basic 

Materials Research

Ever since the discovery of neutrons in the 1930’s, neutron scattering has been extremely useful as a means to 

study the atomic and magnetic structure of materials 

and their behavior, resulting in a Nobel Prize in 1994 

Executive Summary
REPORT OF THE BASIC ENERGY SCIENCES ADVISORY COMMITTEE ON THE SCIENTIFIC JUSTIFICATION 

FOR A U.S. DOMESTIC HIGH-PERFORMANCE REACTOR-BASED RESEARCH FACILITY

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and a steadily growing array of applications. For some 

areas of research, such as magnetism, neutron scattering has become virtually the only way to investigate 

many phenomena. More broadly, reactor-based neutron sources such as the HFIR have certain advantages, 

including more rapid and efficient collection of data. 

In solid state materials, neutrons are particularly 

sensitive to two key constituents of battery materials, 

hydrogen and lithium, making neutrons an indispensable probe of the nanoscale structure and behavior of 

advanced batteries. Neutron beams are equally useful 

in the study of a wide array of other materials, such 

as advanced and more efficient photovoltaic materials for solar cells and thermoelectric materials that 

can convert heat into electricity, which may become 

important for grid-scale energy storage systems. Neutrons are also essential in determining the properties 

of high temperature superconducting materials which, 

although not yet fully understood, clearly involve 

magnetism; and are playing a critical role in the study 

of novel systems that may have application to quantum 

information science. 

In biology and soft materials such as polymers 

and thin films, which together constitute a significant 

fraction of neutron beam research, neutron scattering 

plays a role that cannot be replicated by any other 

type of probe. This arises from the high percentage of 

hydrogen atoms in organic materials, which can be 

easily mapped by substituting deuterium for hydrogen 

and contrasting the resulting scattering patterns. 

Neutron scattering enables the study of molecular 

structures such as proteins and the organization of 

biological molecules in organisms. Neutrons have also 

found application in medicine, through clarifying the 

mechanisms of disease and the structures of complex 

biopharmaceuticals and aiding the development of 

novel nanoscale vehicles for drug delivery and gene 

therapy. An important future area of research with 

neutron beams is the biotic/abiotic interface—such as 

the physical interface between semiconductor technology and biological tissue—where the ability of neutrons to probe both hard and soft condensed matter 

is likely to be important for designing biosensors and 

self-assembling biomolecules into useful materials. 

Polarized neutron beams (which have a uniquely 

defined spin state) offer the most complete characterization of both atomic and spin structure. That is 

important for fundamental studies of quantum phases 

of matter, including materials that exhibit quantum 

entanglement and that are likely to be essential for 

practical quantum computing devices. Polarized neutrons can also resolve complex spin structures that are 

important for understanding magnetism in single crystals and nanostructured materials, areas that may lead 

to future technological breakthroughs.

Industrial Applications of Neutron Scattering

Neutrons interact with the atomic nuclei in a material rather than its electrons and so easily penetrate 

dense materials and complex systems. That enables 

direct observation of an operating internal combustion engine or water flow in a fuel cell. Similarly, the 

utility of neutrons for probing organic or soft polymer 

materials has led to their use in optimizing paints and 

coatings, fabric softeners and adhesives. The pharmaceutical industry has used neutron scattering to 

understand the effect of drug preparation on stability 

and shelf life and to optimize drug processing and formulation. The oil and gas industries employ neutron 

scattering to understand the composition and molecular structures of non-traditional petroleum sources, 

leading to enhanced oil recovery, and to determine 

the properties of gas-bearing shale rock formations. 

Neutron studies have provided useful insights for 

high-performance turbine blades for the transportation 

industry, have been used to measure stress in welds in 

the auto industry, and have proved essential for developing new reactor fuels for the nuclear power industry. 

One measure of commercial interest is the development of an industrial collaboration to provide technology and expertise in neutron-based measurements 

to member companies for pre-competitive research 

at NCNR and to the stationing of industrial staff at 

that facility for extended periods to gain expertise in 

neutron-based research techniques. Pre-competitive 

industrial research proposals for the HFIR are considered on the same basis as university-based proposals; 

proprietary industrial research is allowed on a full-cost 

recovery basis. 

Fundamental Physics at Reactor and Spallation 

Neutron Sources

Reactors and spallation sources are unique sources of 

neutrons and neutrinos (neutral subatomic particles 

with a mass close to zero that rarely react with normal 

matter). Both play a key role in fundamental science, 

enabling scientists to study the constituents of atomic nuclei, to search for new forms of matter, and to 

Executive Summary
REPORT OF THE BASIC ENERGY SCIENCES ADVISORY COMMITTEE ON THE SCIENTIFIC JUSTIFICATION 

FOR A U.S. DOMESTIC HIGH-PERFORMANCE REACTOR-BASED RESEARCH FACILITY

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explore the symmetries that govern fundamental laws 

of physics and the evolution of the universe. 

The fission process in reactors such as the HFIR 

generates a large flux of electron antineutrinos along 

with neutrons. The neutrons are guided out of the 

reactor core in beamlines to experimental stations, 

but the antineutrinos are emitted in all directions, 

making it desirable to locate experiments as close to 

the reactor core as possible. The HFIR with its compact 

but powerful core and regular cycle of operations is an 

ideal source of electron antineutrinos and has enabled a 

broad program of studies with those particles as well as 

with neutrons. Spallation sources such as SNS generate 

a variety of neutrino types in beamed pulses. Together, 

these complementary characteristics enable precision 

experiments such as measurement of neutron lifetimes, which in turn is critical for understanding how 

the basic elements of matter are formed. Neutrinos, 

because they interact so weakly, stream freely through 

the cosmos and have played a key role in the evolution 

of the universe, yet much about them, including their 

tiny mass, is still a mystery. Nonetheless, progress is 

being made: a SNS experiment in 2017, for example, 

confirmed the characteristics of neutrino-nucleus scattering first predicted theoretically in 1947. A recent 

HFIR experiment to measure the neutrino spectrum 

emitted from the reactor core helps understand the 

properties of neutrinos, as well as providing data for 

improved modeling of reactor operation. Understanding the properties of neutrons and neutrinos holds 

the key to some of the most fundamental questions 

in physics, such as why the universe has matter, and 

its observed asymmetry in the amounts of matter and 

antimatter. 

A potential upgrade to HFIR provides an opportunity to establish an experimental laboratory close 

to the reactor dedicated to fundamental physics—in 

effect moving from opportunistic studies to a strategic 

research program. 

Isotope Production and Materials Irradiation

Since the advent of the nuclear era, the use of radioactive isotopes has brought tremendous benefits to 

society in a multitude of ways, from expanding our 

knowledge of the world around us to improving the 

lives of millions of people through medical diagnoses 

and treatment. No fewer than 16 Nobel prizes have 

been awarded in the fields of nuclear chemistry and 

applied radiochemistry. The use of radioactive isotopes 

has allowed researchers to answer a myriad of questions about wide-ranging subjects from plant metabolism and ocean currents to the behaviors of ancient 

peoples and indigenous trade routes. Radiation from 

such isotopes has also brought immeasurable benefits 

to industry, allowing the analysis of material densities, 

inspection of critical systems, and product sterilization. 

Radioactive tracers have been integral in oil and gas 

exploration, monitoring fluid flows, and detecting leaks 

in remote and inaccessible networks. The vast majority of radioactive isotopes used in medicine, industry, 

and research are produced by irradiating materials 

with neutrons in nuclear reactors. And because of the 

HFIR’s intense neutron output, it plays a unique role 

in producing many critical short-lived radioactive isotopes. 

In healthcare, for example, radioactivity and 

radioisotopes have been instrumental in diagnosing 

and treating disease, improving the lives of millions of 

people. Ever since the first radioisotope was approved 

by the U.S. FDA in 1951 for treatment of thyroid cancer, researchers and clinicians have employed numerous additional radioisotopes for both diagnostic and 

therapeutic applications. While HFIR makes numerous 

medical isotopes, its high neutron flux is required to 

produce the first alpha therapeutic approved by the 

U.S. FDA. Ra-223 is a targeted therapy for symptomatic bone metastases in prostate cancer patients that 

improves the overall survival with a 30% reduction in 

mortality.

Californium-252 is used by industry as a small, 

robust, self-powered, economical source of neutrons 

for a wide range of applications including energy, 

homeland security, and agriculture. The isotope is 

used by the nuclear energy industry to determine the 

fissile content of nuclear waste; it also provides the 

source of neutrons needed to start newly constructed 

nuclear reactors including those on nuclear powered 

submarines. The mining and minerals industry uses 

it to measure the amount of sulfur in coal, the ash 

and stone content of cement, and for oil well logging. 

Nickel-63 enables gas chromatography detector systems up to 1,000 times more sensitive than those using 

other types of detectors. Applications of these systems 

include food and pesticide analysis, forensic toxicology, 

controlled substances identification and environmental 

monitoring. In addition, Nickel-63 provides the electron source in ion mobility spectrometry systems that 

are extensively deployed by the Department of HomeExecutive Summary
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land Security and the U.S. military for detecting trace 

amounts of explosives, narcotics, chemical warfare 

agents and industrial chemicals. Both of these critical 

isotopes require a high neutron flux for their production and are only available from HFIR and the SM-3 

reactor in Russia; the demand for both greatly exceeds 

the available capacity of these two high-flux reactors. 

The heaviest elements on the periodic table—especially those with atomic number 90 through 103—are 

the ones least well understood. Fundamental research 

to understand their physical and chemical properties 

involves very small quantities of trans-plutonium isotopes, which can only be produced by irradiation in 

HFIR. These isotopes have short half-lives, however, 

and must be continuously produced. In addition, over 

the past few years, heavy elements produced at HFIR 

were used in international collaborations to discover 

elements 114, 115, 117, and 118. In addition, the HFIR 

is used to mimic the radiation conditions expected in 

advanced nuclear power reactors or fusion reactors and 

thus test structural materials and fuels for such reactors. 

Conversion of the HFIR to Low Enriched 

Uranium Fuel

Since 1978, the U.S. government has worked with civilian research reactors and medical isotope production 

facilities domestically and internationally to minimize, 

and, when possible, eliminate weapons-usable nuclear 

material around the world. The effort has successfully 

converted 71 reactors from Highly Enriched Uranium 

(HEU) fuel to Low enriched Uranium (LEU) fuel; 31 

other reactors have been shut down. 

A concern for conversion of the HFIR was the need 

for an increased volume of LEU fuel in the reactor to 

preserve its high flux capability. Ongoing research has 

identified and tested a fuel based on a uranium-silicon 

compound that, in combination with changes in the 

placement of the fuel in the reactor and other adjustments, would preserve the capability of the HFIR. 

Moreover, sophisticated models of the anticipated 

neutron fluxes and heat removal have provided strong 

assurance that the reactor can safely operate at the 

higher local power densities of the new design. Testing 

and qualification of the new fuel design is expected to 

start soon. 

This report recommends commissioning a joint 

feasibility study to explore whether replacement of the 

HFIR pressure vessel simultaneously with LEU conversion in a coordinated manner could simplify LEU 

fuel design through modest changes to the vessel and 

beryllium reflector design, thus reducing long term fuel 

costs for the refurbished reactor. 

The High Flux Isotope Reactor: 

Status and Plans

Oak Ridge National Laboratory, which operates the 

HFIR, has developed a preliminary plan to replace the 

HFIR reactor vessel, upgrade some reactor systems, 

and improve the neutron source in order to extend 

the operating life of the facility well beyond 2040. A 

potential LEU replacement fuel, for which testing is 

expected to begin soon, could be incorporated into 

an upgraded or enhanced HFIR reactor core design, 

potentially allowing a higher reactor power level. These 

activities could also support the installation of an 

additional neutron beam guide hall with a new suite of 

instruments, as well as additional isotope production 

and irradiation capacity, to capitalize on the enhanced 

HFIR, which would in turn enable high quality neutron 

science well into the 21st century. This would go a long 

way in enabling the United States to recover its world 

leadership position in this critical area of science and 

technology.

In parallel, however, this report also recommends 

that a “scoping study” be undertaken for a new highflux research reactor optimized for current needs but 

also incorporating flexibility of configuration to allow 

for future, unanticipated needs in neutron research and 

isotope production. Since such a reactor is likely to take 

several decades to design, construct, and commission, 

beginning now will ensure the continuing availability 

of such a critical resource in the U.S. 

Executive Summary
5

Recommendations

The subcommittee considered three options:

• Operate HFIR “as is.” There are unacceptable issues associated with this option:

> Consistent with U.S. policy, HFIR has committed to convert to LEU fuel when available, projected to be in 

2035. The conversion program has committed to an LEU design and power upgrade that will preserve the 

capabilities of HEU operation at 85 MW. The conversion will require an extensive shutdown at the time of 

LEU fuel deployment. Assuming no unforeseen occurrences, the pressure vessel of HFIR is projected to 

reach end of life about 2060. It should be noted that, given the age and history of HFIR, it is possible that 

the end of life of the pressure vessel could occur sooner. At best, HFIR will need another very significant 

shutdown within about 20 years of conversion.

> While investments in instrumentation in the absence of modifications to the pressure vessel design may 

add some capability and capacity to HFIR, they will fall far short of meeting the needs of the neutron 

science community. 

RECOMMENDATION: This is the least desirable option. Investment in fuel conversion or instrumentation 

without replacing the pressure vessel leaves an unacceptable risk of a short life of the reactor.

• Replace the pressure vessel of HFIR, which is the lifetime-limiting component of the reactor. If possible, 

coordinate this replacement with the conversion of the reactor to LEU fuel so that a single shutdown would 

accomplish both objectives. Redesign of the pressure vessel could enable:

> Enhanced capabilities for both in-reactor (isotope production, materials testing, etc.) and beamline work, 

which would provide an increase in both capability and capacity. Specifically, the new pressure vessel 

should support larger beam tubes and an improved cold source to enhance neutron scattering capabilities together with improved access for isotope production and materials irradiation. A significant investment should be made in advanced instrumentation for neutron scattering in parallel with infrastructure 

changes and possible changes in the reactor configuration to reduce dramatically the background for neutron scattering measurements. 

> Modification of the fuel assembly to make it more manufacturable and hence less expensive.

> The combination of pressure-vessel replacement and conversion may allow a power increase that would 

restore the flux-trap intensity of the original 100 MW HEU operations and an increase in reflector irradiation site and cold-source capabilities.

RECOMMENDATION: Pursue this approach immediately with the goal that the fuel conversion and 

pressure vessel replacement be performed during the same shutdown. The significant risk of HFIR failure 

will be removed, and important capabilities will result.

• Perform a “scoping study” for a green field research reactor optimized to perform neutron studies and isotope 

production that are uniquely suited to a very high flux reactor such as HFIR. The reactor would be designed 

to operate on LEU fuel. Reactor and fuel assembly designs should be evaluated to simultaneously optimize 

reactor performance and fuel assembly manufacturability. Further, the design should, to the extent possible, 

be optimized for neutron needs as currently understood and for flexibility of configuration to enable future, 

currently unanticipated, applications.

> A new research reactor is likely to take several decades from initial design through approval, construction, and commissioning. Beginning the process now will allow time to evaluate options and proceed with 

planning and approvals in time to ensure continuing availability of a multiply capable high flux research 

reactor in the U.S.

RECOMMENDATION: Pursue study of a new high-flux reactor in parallel with the shorter term 

replacement of the pressure vessel and conversion of HFIR to LEU fuel.

Recommendations
6

Introduction

High-performance reactor-based research facilities 

have been an essential part of the U.S. scientific and 

technological enterprise since the mid-1960s. These 

facilities contribute broadly to our national security, 

our fundamental and applied science knowledge base, 

our development of cutting-edge medical treatments, 

and our technological and industrial competitiveness. 

The flagship U.S. reactor facility is the High Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory 

(ORNL). This reactor is stewarded by the U.S. Department of Energy (DOE) under the auspices of Basic 

Energy of Sciences in the Office of Science. 

Operation of HFIR began in 1965 so the facility 

is 55 years old. It was initially designed primarily for 

isotope production and materials testing but four beam 

tubes were included making possible neutron scattering 

experiments with thermal and cold neutrons. HFIR 

runs with highly enriched U-235 fuel (HEU) with an 

enrichment of about 90%. There are two significant 

issues connected with the continuing operation of HFIR 

in the current mode. First, there are serious national 

security concerns about nuclear proliferation associated 

with the use of HEU. Second, the HFIR pressure vessel has a finite lifetime because of radiation induced 

embrittlement. This means that the vessel must be 

replaced by the middle of this century, or sooner if the 

embrittlement were to accelerate. A third concern is the 

continuing deficit in facilities for neutron scattering in 

the United States compared with Western Europe. This 

shortfall will be partially mitigated by the construction 

of the second target station at the Spallation Neutron 

Source (SNS), but it is certain that the available facilities 

will still fall far short of the national need.

Two recent reports have focused on the HEU 

conundrum. The first is the 2016 congressionally 

mandated study by the National Academy of Sciences 

(NAS), “Reducing the Use of Highly Enriched Uranium in Civilian Research Reactors.” This study 

recommended the conversion as soon as possible of 

existing U.S. high-performance research reactors to 

low enriched uranium (LEU) fuel operations as well 

as the enabling of a new generation of LEU research 

reactors. Here, LEU is defined as less than 20% U-235. 

This study was immediately followed by a second study 

completed in 2018, “Neutrons for the Nation: Discovery and Applications while Minimizing the Risk of 

Nuclear Proliferation” by the Panel of Public Affairs of 

the American Physical Society. This report emphasized 

the critical importance for the U.S. physics enterprise 

of world class neutron R&D capabilities and explicitly 

recommended initiating an effort to competitively 

design and build a new generation of LEU-fueled 

high-performance research reactors that meet current 

needs and provide new capabilities.

On March 3, 2019, J. Stephen Binkley, then Deputy 

Director for Science Programs, Office of Science, DOE, 

wrote to Dr. Marc Kastner, chair of the Basic Energy 

Sciences Advisory Committee (BESAC) seeking BESAC’s 

input on the long term strategy for HFIR. Specifically, 

Dr. Binkley asked BESAC to form a subcommittee to 

assess the scientific justification for a U.S. high-performance reactor-based research facility (implicitly LEU) 

taking into account current international plans and existing domestic facility infrastructure. The charge to the 

committee included six explicit questions:

1. What is the merit and significance of the science that 

could be addressed by a high-performance, steadystate reactor, and what is its importance in the overall 

context of materials sciences and related disciplines?

2. What are the capabilities of other domestic and 

international facilities, existing and planned, to 

address the science opportunities afforded by such 

a domestic research reactor?

3. What are the benefits to other fields of science and 

technology and to industry of establishing such 

a capability in the U.S.? In particular, consider 

applications such as isotope production, materials 

irradiation, neutron imaging, dark matter research, 

and neutron activation for trace element analysis.

4. What are the strengths and limitations of a steadystate research reactor compared to a pulsed spallation neutron source for science, engineering, and 

technology? What functions currently performed 

by research reactors can be assumed by spallation 

neutron sources?

5. Are there feasible upgrade paths for HFIR to provide world-leading capabilities in serving the Office 

of Science missions well into the future? What 

can we learn from the experience at the Institut 

Laue-Langevin (ILL)?

Introduction
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7

6. Can Low Enriched Uranium (LEU) and High 

Assay LEU (HALEU) fuels (defined as <20 % 

enriched U-235) replace Highly Enriched Uranium 

fuels in research reactors while preserving the 

needed characteristics of neutrons produced by 

steady-state reactors? What R&D would be needed 

to support LEU and HALEU fuels development?

In response to this charge, BESAC formed a 

subcommittee with 19 members having expertise covering the complete range of areas impacted by high-performance research reactors. In addition, the chair of 

BESAC, Marc Kastner, participated in the deliberations 

of the committee. The formal title of the committee 

was: “BESAC Subcommittee on the Scientific Justification for a U.S. High-Performance Reactor-Based 

Research Facility” (HPRBRF).

The committee held a series of meetings exploring 

all of the issues and opportunities associated with an 

HPRBRF. The first meeting took place in Berkeley, 

California on August 19–20, 2019. The meeting laid the 

groundwork for the study. It included presentations by 

DOE senior officials giving their perspectives, by Oak 

Ridge neutron scientific administrators on HFIR and 

the SNS, by the chairs of the NAS and POPA HEU-LEU 

committees, by officials from NIST and ILL on their 

reactor facilities, and finally by European leaders on 

FRM-II. The second meeting was held on Nov. 14–15 in 

Washington, D.C. This workshop included a series of 

talks by outside experts on virtually all of the different 

important areas of science, technology, and industry 

where high flux nuclear reactor facilities make important contributions. The final afternoon of this meeting 

was spent touring and hearing presentations at the 

NCNR at NIST. 

On January 7–8, 2020, the committee had a site 

visit to ORNL, touring the SNS and HFIR. In addition, 

there was a series of presentations by ORNL neutron 

leaders on their plans for the HFIR reactor vessel replacement and upgrade of the facility overall including the 

neutron scattering instrumentation. In late February, 

a subset of the committee visited the BR2 reactor in 

Belgium and the planned Jules Horowitz Reactor in 

France. A planned site visit to ILL and FRM-II by 

a second group of subcommittee members in early 

March was cancelled because of Covid-19.

The final meeting of the committee was held on 

April 24, 2020. The meeting was originally planned to 

be held in Washington D.C., but because of Covid-19 

was held virtually via Zoom. In advance of this meeting, each of the committee members prepared comprehensive reports on the current and prospective impact 

of an HPRBRF on important scientific and/or technological issues in their respective areas of expertise. 

The topics ranged from quantum materials to biology 

to heavy element chemistry to industrial applications. 

The committee members made brief presentations on 

each of these subjects. The committee then finished by 

producing a set of recommendations for BESAC which 

appear subsequently in this report.

These individual reports appear in the next section: “The Scientific Case.” The breadth and depth of 

the impact of nuclear reactor-based research is simply 

remarkable. The individual subjects include solid state 

physics and quantum materials, soft condensed matter, 

molecular biology, industrial applications, fundamental 

physics, isotope production, heavy element production, 

materials irradiation in general, and fusion materials 

irradiation in particular. In addition, there are sections on polarized neutron scattering techniques and 

a comparison of the relative roles of neutrons and synchrotron X-rays in probing condensed matter. There is 

a comprehensive discussion on the current state of progress on HEU-LEU conversion. These sections are all as 

comprehensive as possible. We intend this report to be 

a resource for DOE and for the research nuclear reactor 

community far into the future.

The report includes brief sections on U.S. neutron 

facilities HFIR, NCNR, and the SNS. In addition, 

there are sections on the international research reactor facilities: ILL in France, FRM-II in Germany, BR2 

in Belgium, and the planned JHR facility in France. 

Appendix 1 contains a comprehensive review by ORNL 

of the history, current status, and their proposed 

upgrades for HFIR. We are deeply grateful to ORNL for 

providing us with this strategic plan. Appendix 2 gives 

a comprehensive discussion of the current state of progress on HEU-LEU conversion. Appendix 3 contains 

user information from NIST and ORNL which shows 

that both facilities are vastly oversubscribed. These data 

show clearly the continuing shortfall in neutron facilities in the United States.

The report concludes with our recommendations to 

DOE for moving forward and with our overall conclusions.

Introduction
THE SCIENTIFIC CASE

Researchers Danielle Mai and Yun Jung Yang from Massachusetts Institute of Technology prepare samples for the HFIR neutron beamline CG-3.

Image credit: Genevieve Martin/ORNL
The Scientific Case 9

1. Neutron Scattering

1a. SOLID STATE PHYSICS INCLUDING 

QUANTUM MATERIALS

Neutron scattering has been highly impactful in the 

field of condensed matter and materials physics for 

several decades. Soon after the discovery of the neutron 

in the 1930s, neutron scattering was implemented to 

study structures, atomic or magnetic, and dynamics. 

The Nobel prize in Physics in 1994 shared by Shull 

and Brockhouse attests to that achievement. Over the 

decades, neutron scattering has evolved to an extent 

that it has become the only way to study certain problems. Applications of neutron scattering include (but 

are not limited to):

• The structures and dynamics of hydrogen-containing materials, such as hybrid perovskite photovoltaic materials, metal hydrides, molecules and 

proteins, and soft materials

• The structure and dynamics of functional materials, such as thermoelectrics, ferroelectrics, metallic glasses, multiferroic materials, photovoltaic 

materials, and batteries

• Fundamental studies of quantum phases of matter—

such as unconventional superconductivity, quantum 

magnetism, quantum phase transitions, and topological materials—areas that may lead to future technological breakthroughs. (These areas may each lead 

to future technological breakthroughs.)

• Anything related to magnetism, for which neutron 

scattering is the go-to technique.

Neutrons are produced either at reactors or by the 

process of spallation, and the instruments developed at 

both types of sources are very complementary, spanning wide length and time scales. When combined, 

they can provide a complete microscopic picture of 

the static and dynamic attributes of the systems at 

hand. The proposal to build a high-power research 

reactor (HPRR) carries certain advantages even when 

compared to a spallation source. These are: 1) efficient 

collection of data for parametric studies (focusing on 

a single feature such as the energy of an excitation at 

a particular wavevector, as a function of temperature, 

magnetic field, or other control parameters), and 2) use 

of neutron spin polarization analysis, including several 

types of instruments that are difficult to implement at a 

spallation source. Aside from these unparalleled strengths of an HPRR, linked directly to the continuous and 

high flux nature of the source, HPRRs are very strong 

in areas in which spallation sources are more directly 

competitive. Thus they provide some distinct advantages, as well as an overall increase in capacity for an 

extremely broad range of applications, which is desperately needed in the United States. 

Following are key scientific examples where an 

HPRR has considerable advantage over spallation neutrons. This list is by no means exhaustive, but highlights 

the complementary nature of HPRRs and spallation 

neutron sources.

Applications of neutron scattering at HPRRs

Advantages of HPRRs in the study of unconventional 

superconductivity 

“Unconventional superconductors,” such as high-Tc

copper oxides, iron-based, and heavy fermion superconductors, share several common characteristics, 

such as close proximity to a magnetically ordered 

parent state, very similar phase diagrams as a function 

of carrier doping, and unusual normal state properties.1-15 These features are distinctly different from 

the properties of Al, Sn, or some of the other simple 

superconductors that can be fully explained by the 

Bardeen-Cooper-Schrieffer (BCS) theory,16 in which 

the superconducting gap is isotropic in space, but 

orbital effects along with magnetism do not play an 

important role in the mechanism for superconductivity. Although the underlying mechanism for these 

so-called “unconventional” superconductors is yet to be 

established, it is clear that magnetism plays an important role in their anomalous electronic properties and 

superconductivity.1 This means that neutron scattering 

is fundamentally important in sorting out magnetic 

order and excitations in these materials, as neutron 

scattering is essentially the only probe that can completely determine the wave vector and energy dependence 

of the magnetic order and excitations throughout the 

Brillouin zone.17,18 Compared with a spallation neutron 

source, which is excellent in probing magnetic features 

over large energy and momentum ranges, HPRRs are 

ideal in studying magnetic and lattice features at a 
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10 The Scientific Case

particular energy/wave vector as a function of temperature/field/pressure and/or other tuning parameters due 

to its high average neutron beam flux. In addition, neutron polarization analysis, important for conclusively 

separating the magnetic and lattice contributions, can 

be much better done at an HPRR. In fact, several types 

of polarized neutron scattering instruments can only 

be constructed at an HPRR. These include the neutron Larmor diffractometer, which can be used to very 

precisely measure lattice parameter variations;19 the 

neutron triple-axes spin echo spectrometer,20 which 

has extremely good energy resolution (~1 meV) at large 

energy transfers and large wave vectors; and spherical 

neutron polarization analysis21 (i.e. cryopad), which 

can provide polarization analysis without having to use 

a guide field near the sample. In the following, some 

scientific examples are provided to demonstrate the 

unique capability of an HPRR in studying exotic properties of unconventional superconductors.

1. Exotic magnetic states in Pauli-limited superconductors. In general, static magnetism and 

superconductivity competes for itinerant electrons 

below Tc. In some cases, novel static magnetic order 

appears due to superconductivity, but does not 

exist without it. These superconductivity-driven 

pair-density waves (PDW), which are described by a spatially modulated superconducting 

order parameter, is referred to as a Fulde, Ferrell, 

Ovchinnikov, and Larkin (FFLO) state.15 There 

are several unconventional superconductors 

which may have FFLOs under a high magnetic 

field, including CeCoIn5,22,23 FeSe,24 and UTe2.25

As shown in Figure 1a.1, a possible FFLO state 

has been identified in FeSe. Such a state can be 

unambiguously detected by neutron scattering 

experiments using a high magnetic field, which is 

much better performed at an HPRR than a spallation neutron source. Neutron polarization analysis 

can also provide key information concerning the 

nature of the FFLO state.15

2. Neutron polarization analysis as a probe of 

spin-orbit coupling. Although unpolarized neutron 

scattering can identify the presence of magnetic 

features, it is generally difficult to use unpolarized neutrons to determine conclusively that the 

feature of interest is indeed magnetic and sort 

out whether spin excitations are isotropic in spinspace. In many cases, it is extremely important to 

determine the polarization direction and magnetic 

anisotropy of the observed magnetic signal, as this 

information will provide information concerning 

the strength of spin-orbit coupling in the system. 

For example, neutron polarization analysis played 

an indispensible role in determining the magnetic 

nature of the famous neutron spin resonance in 

cuprate superconductors.26 In the case of iron based 

superconductors, neutron polarization analysis 

found a strong anisotropic resonance, providing 

strong evidence that spin-orbit coupling is important for the electronic nematic phase and superconductivity.27,28 Moreover, the neutron polarization 

analysis using a cryopad can only be carried out at 

an HPRR.

3. Neutron Larmor diffraction to study accurately 

changes in lattice parameter. X-ray diffraction is 

commonly used to determine the lattice parameters 

and structures of solids. However in many cases, 

X-ray diffraction does not have the accuracy needed 

to detect tiny changes in lattice parameters of a bulk 

sample. Neutron Larmor diffraction, which utilizes polarized neutrons to accurately detemine the 

lattice spacing, can have a Dd/d value on the order 

of 10-6, and is extremely bulk sensitive. Using this 

technique, one can accurately determine the tiniest 

lattice distortions induced by uniaxial pressure 

needed to de-twin iron pnictides.29 This technique 

can also be used to sort out distortions induced by 

FIGURE 1a.1. High-field phase diagram of FeSe for field parallel to ab-plane. The possible FFLO state is shown in red.

Source: S. Kasahara, Y. Sato, S. Licciardello, M. Culo, S. Arsenijevic, T. Ottenbros, T. Tominaga, J. Boker, E. Eremin, T. Shibauchi, J. Wosnitza, N. E. Hussey, 

Y. Matsuda, “Evidence for an FFLO state with segmented vortices in the BCSBEC-crossover superconductor FeSe.” Phys. Rev. Lett. 124, 107001 (2020).
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The Scientific Case 11

an electronic nematic phase as in the paramagnetic 

tetragonal state of an iron based superconductor, and 

its connection with lattice distortions is shown in 

Figure 1a.2.30 The neutron Larmor diffraction is very 

difficult to implement at a spallation neutron source, 

but is readily available in spectrometers at an HPRR.

4. Neutron Spin echo investigation of lattice and 

magnetic excitations. Typically, the instrumental 

energy resolution of a neutron spectrometer is inversely proportional to the energy of the excitations one 

wants to probe. This is understandable because in 

order to probe large excitation energies one needs 

higher incident beam energy, which inevitably gives 

poor instrumental energy resolution. However, by 

combining neutron spin echo with a triple-axis spectrometer, one can measure the intrinsic linewidth 

of elementary lattice and magnetic excitations with 

an energy resolution in the meV region over a broad 

range of momentum and energy transfers. These 

measurements can provide unique information that 

is not possible with any other technique. For example, the momentum and temperature dependence 

of the lifetimes of acoustic phonons in the BCS 

superconductor lead (Pb) have been measured, and 

new information obtained in these measurements 

suggests that many-body correlations beyond the 

standard BCS theory31 are present. The instrument 

can also be used to study magnon lifetime in classical antiferromagnets and ferromagnets.32

5. Instantaneous spin-spin correlation function of 

a system. The spin-spin correlation function measured by neutron scattering by integrating over 

a wide range of energy excitations can provide 

important information on the nature of the spin 

interactions. This is widely used to test different 

theoretical models proposed in cuprate superconductors.33,34

 More generally, measurements of the instantaneous spin-spin correlations in varied physical 

systems provide a direct measurement of the static 

wave vector dependent susceptibility (Q); the latter 

in turn is often directly amenable to theory. Such 

measurements, carried out with very high momentum resolution, are essential in characterizing the 

static critical behavior in second order magnetic 

phase transitions. 

 This technique is particularly powerful in oneand two-dimensional magnetic systems. In those 

cases, by arranging the scattering experiment such 

that the outgoing neutron is exactly perpendicular to the chain or plane the energy integration is 

essentially exact. It is just in those situations that 

one often has first principles’ calculations of the 

spin-spin correlation functions from statistical 

physical models, perhaps the most famous being 

the work of Chakravarty, Halperin and Nelson 

on the two dimensional Heisenberg model. These 

types of experiments can be done straightforwardly 

FIGURE 1a.3. Linewidths of transverse acoustic phonons 

along q = (ξ,ξ,0) in Pb.

Source: P. Aynajian, T. Keller, L. Boeri, S. M. Shapiro, K. Habicht, B. 

Keimer, “Energy gaps and Kohn anomalies in elemental superconductors.” Science 319, 1509-1512 (2008).

FIGURE 1a.2. Neutron Larmor diffraction can be used to 

accurately determine the temperature dependence of the 

lattice distortion of Ni-doped NaFeAs in the paramagnetic 

tetragonal phase. 

Source: W. Wang, Y. Song, C. Cao, K.-F. Tseng, T. Keller, Y. Li, L. W. Harriger, 

W. Tian, S. Chi, R. Yu, A. H. Nevidomskyy, P. Dai, “Local orthorhombic 

lattice distortions in the paramagnetic tetragonal phase of superconducting NaFe1−xNixAs.” Nature Communications 9, 3128 (2018).
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12 The Scientific Case

with a steady state source and would be much more 

difficult to realize with adequate signal strength 

with a pulsed spallation source.

 A more exotic example is the instantaneous 

correlations in physical systems with static random 

fields. In that case, the static susceptibility has two 

components, a simple dynamic Lorentzian arising 

from the thermal fluctuations and a perfectly elastic Lorentzian squared contribution arising from 

the random field fluctuations. As the temperature 

is lowered from high to low temperatures there 

is a progressive crossover from a Lorentzian to a 

Lorentzian squared lineshape in (Q) as the disorder 

evolves from being dominated by thermal fluctuations to random field fluctuations. Observation of 

such delicate changes in line-shape require both 

high Q-resolution and very high counting statistics. So far, such experiments have only been realizable with steady state sources.

Advantages of HPRRs in studying topological 

quantum materials and two-dimensional (2D) van 

der Waals materials 

The development of the next-generation quantum 

information systems requires the exploration of a 

variety of novel materials with enhanced quantum 

coherence. Topology35,36 and strong correlations are 

two of the foundational concepts in modern condensed 

matter physics, but they rarely coexist in the same 

system and therefore are not often investigated experimentally. The role of spin in topologically-protected states has implications on both our fundamental 

understanding of material properties and on the technological applications of certain materials. While most 

topological materials known so far have strong spin-orbit coupling, they can generally be understood within 

a Landau Fermi liquid picture and density functional 

theory (DFT) with weak electron-electron correlations 

(weak U).36,37 As electron correlations increase, magnetic interactions in topological materials start to become 

important, and one can ask whether spin waves in 

topological magnetic materials can play a similar role 

as electrons in topological insulators. Magnetic topological materials may be relevant for dissipationless 

transport of spin information, and important for quantum computation.38-41 Since neutrons are sensitive to 

the magnetic moment of the system and can directly 

probe spin excitations, neutron scattering will play an 

important role in determining topological magnetic 

properties of the system. Compared with time of flight 

chopper spectrometers at a spallation neutron source, 

triple-axis spectrometers at an HPRR can play a unique 

role in determining the temperature, magnetic field, 

and pressure dependence of the spin excitations at a 

particular wave vector and energy. In the following, 

we list several examples where an HPRR can play an 

important role in determining the magnetic properties 

of the system. 

1. Topological spin excitation in 2D honeycomb 

lattice van der Waals ferromagnets. For magnetically ordered 2D honeycomb lattice materials, 

spin waves (magnons) can behave like electrons 

in 2D graphene and form topologically protected edge states. In graphene, the conduction and 

valence electronic bands touch at Dirac points 

(the six corners of the hexagonal Brillouin zone). 

Adding spin-orbit coupling opens a bulk gap at 

the Dirac points, making the system an insulator 

except at the perimeter where conducting edge 

channels with certain fixed spin and momentum 

orientation appear.42 In the presence of a spin-orFIGURE 1a.4. Experimental (top, right panels) and calculated 

(top, left panels) neutron data for CrI3: the band gap at 

Dirac points along different cuts (bottom left)

Source: L. B. Chen, J. H. Chung, B. Gao, T. Chen, M. B. Stone, A. I. Kolesnikov, Q. Z. Huang, P. C. Dai, “Topological Spin Excitations in Honeycomb Ferromagnet CrI3.” Physical Review X 8, 041028 (2018).
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The Scientific Case 13

bit-coupling-induced next-nearest-neighbor Dzyaloshinskii-Moriya (DM) interaction that breaks 

inversion symmetry of the lattice, a gap can open 

in the magnon spectra at the Dirac points43 and 

the system may exhibit topological magnon edge 

modes. In contrast to the electronic spin, where 

dissipation can be large due to Ohmic heating, 

topological magnons have no charge and so in 

principle can propagate for a long time without dissipation.41 Consequently on the surface of a topological magnetic material, the magnons neither leak 

into the sample interior nor back-scatter, making 

them potentially useful for dissipationless spintronic devices. Recently, spin waves in a 2D honeycomb lattice ferromagnet, CrI3, were found to have 

a gap near the Dirac point, suggesting that spin 

waves in CrI3 may host topological magnons. If the 

magnon gap indeed arises from the next-nearestneighbor DM interaction, an in-plane magnetic 

field should rotate the ferromagnetic moment 

direction from the c-axis to the in-plane direction. 

This should cancel the DM interaction and therefore close the Dirac magnon gap. An inelastic neutron scattering experiment under a magnetic field 

is much better done at a triple axis spectrometer at 

an HPRR. This is because background scattering 

from a magnet can overwhelm the magnetic signal 

in a time-of-flight spectrometer at a spallation neutron source.

2. Candidate Kitaev Quantum Spin Liquid (QSL) 

materials. A QSL is a state of matter in which the 

spins of unpaired electrons in a solid are quantum entangled, but do not show magnetic order 

in the zero-temperature limit.44 Because such a 

state may be important to the microscopic origin 

of high-Tc superconductivity2 and useful for quantum computation,40 experimental realization of a 

QSL is a long-sought goal in modern condensed 

matter physics. Models supporting QSLs for 2D 

spin-1⁄2 Kagome, triangular, honeycomb, and 3D 

pyrochlore lattice systems indicate that all QSLs 

share the presence of deconfined spinons, elementary excitations from the entangled ground state 

which carry spin S = 1⁄2 and thus are fractionalized quasiparticles, fundamentally different from 

the S = 1 spin waves in conventional 3D ordered 

magnets.44 In particular, honeycomb and hyper-honeycomb lattice magnetic materials are of interest 

because a QSL can arise from the exactly solvable 

Kitaev model with S=1⁄2 Ising spins on a honeycomb lattice.40 Neutron scattering studies of spin 

excitations in α-RuCl3, performed at both spallation neutron source (SNS) and High-Flux-Isotope 

Reactor (HFIR), have identified this material to be 

a candidate material near a Kitaev’s QSL.45-48 Timeof-flight spectroscopy at the SNS has shown that, 

unlike conventional ordered magnets which have 

sharp signatures of their excitations in momentum 

and energy, -RuCl3 has a broad inelastic signature 

at relatively high energies, coexisting with the 

(conventional) lower energy sharp signatures.46

This broad spectral response is expected for fractionalized quasi-particles, since a single neutron 

creates two (or more) quasi-particles, and the 

neutron’s energy and momentum conservation is 

under constrained. This type of broad response is 

typically called a “continuum of scattering” and its 

connection to fractionalization hints that -RuCl3 is 

nearby a QSL. However, what is truly remarkable 

in this material is that the sharp (conventional) 

excitations disappear when a magnetic field is 

applied in the plane of the honeycomb layers, while 

the continuum remains.47 This strongly suggests 

that the magnetic field has induced a QSL phase by 

removing the long range magnetic order. In further 

support of the QSL scenario, triple axis spectroscopy at HFIR was used to understand the magnetic 

field dependence of the conventional excitations 

(and their disappearance), to identify the range 

of applied fields necessary for the QSL to exist.48

Commensurate with the expectation that -RuCl3 

really does display the required quantum manybody state, there are currently efforts to produce 

device-like structures with this material, by coupling a monolayer of -RuCl3 with graphene.49,50 The 

ability to probe extremely low sample masses with 

neutrons, requiring the extreme flux and focusing 

capabilities offered at HPRRs, will become essential 

for probing these next-generation QSL materials 

and devices. Although the detection of the fractionalized excitations and their unique transport properties is sufficient to show there is a Kitaev QSL 

in -RuCl3, new techniques are needed to validate 

older candidate materials, such as Herbertsmithite, 

as other types of QSLs. Innovations in neutron 

scattering, such as the use of entangled beams of 

neutrons, currently being pursued at spin echo 

spectrometers at HPRRs,51 may finally yield direct 
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14 The Scientific Case

evidence of the long-range spin entanglement, the 

defining feature of a QSL. Further into the future, 

for quantum information science applications it 

will be important to control QSL dynamics in a 

functional setting, which is likely to be one of the 

important frontiers for neutron reflectometry and 

INS from small (thin film) samples. 

3. Skyrmion materials. Magnetic skyrmions, particle-like spin textures (Figure 1a.5),52 are of 

interest due to their topological properties and 

potential for use in high density, low dissipation 

information storage applications. SANS studies, 

most efficiently carried out at HPRRs for the very 

long length-scales involved (5 to 100 nm), have 

been critical in the development of this research 

area. Their topological nature influences electronic 

motion, as well as ensures that they are protected 

against local perturbations. From the application 

standpoint, skyrmions are ideal magnetic “bits”, 

since they cannot be easily destroyed, and can be 

moved/manipulated using low energy-cost electrical or spin currents. The original identification of 

skyrmions in a material was in MnSi, using a SANS 

instrument at an HPRR (FRM II).53 SANS continues to be of utmost importance in identifying the 

presence of skyrmions in the bulk of new materials, 

but has also been successfully used recently on 

thin film samples, which are relevant for technological applications.54 Compared to complementary 

techniques such as Lorentz TEM, an advantage of 

neutrons is the ability to give access to a greater 

breadth of sample environments,55 allowing in-situ 

studies of skyrmion dynamics,56 or a determination 

of how the skyrmion phases are modified under 

pressure.57 Furthermore, spin polarized neutrons 

can be used to detect the detailed spin configurations within the skyrmions, which are invisible to 

other techniques.55

Advantages of HPRR in studying functional materials 

Inelastic neutron scattering is unparalleled as a comprehensive probe of lattice dynamics. Due to the 

energy and momentum transfer ranges for thermal 

and cold neutrons, phonon dispersions can be tracked 

throughout multiple Brillouin zones, which has proven 

essential for studying thermal conductivity in thermoelectrics. Meanwhile, extremely high resolution measurements have been useful in identifying the role of 

hydrogen dynamics in new photovoltaic materials. 

1. Thermoelectrics. Thermoelectrics are materials 

that can be used to convert a thermal gradient 

into electricity, and vice versa, and are of interest 

in increasing overall efficiencies of processes that 

produce significant heat waste.58 For a material 

to function well in this regard, it must have high 

electrical conductivity while maintaining low 

thermal conductivity. In order to optimize this, 

it is essential to understand how to limit lattice 

thermal conductivity by preventing coherent phonon transport. Using broad surveys of the phonon 

dispersions, obtained from time of flight chopper 

spectrometers at the SNS, combined with a detailed 

temperature dependence of certain key features 

from a triple-axis spectrometer at HFIR, researchers have been able to identify a large anharmonic 

phonon coupling in PbTe,59 which is one of the 

most popular thermoelectrics used in the temperature range of 400 to 800 K. This anharmonic coupling limits the ability for phonons to propagate. 

Triple-axis spectrometer data obtained at HFIR 

was used to investigate the temperature dependence of the anharmonicity in detail, which was 

crucial for understanding its microscopic origin. 

This is a prime example of the complementarity of 

the two types of inelastic neutron scattering measurements which are often used in conjunction. 

FIGURE 1a.5. An image of the magnetic skyrmion lattice as 

seen by small angle neutron scattering. After forming a 

stable, triangular lattice of skyrmions, magnetic field can 

rearrange them into a square pattern.

Source: T. Nakajima, H. Oike, A. Kikkawa, E. P. Gilbert, N. Booth, K. 

Kakurai, Y. Taguchi, Y. Tokura, F. Kagawa, T.-h. Arima, “Skyrmion lattice 

structural transition in MnSi.” Science Advances 3, e1602562 (2017).
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Both types can be carried out at HPRR sources, but 

chopper spectrometers (survey instruments) are 

well-suited to spallation sources, while triple-axes 

spectrometers are much more efficient at a continuous high flux source such as an HPRR.

2. Hybrid perovskite semiconductors. The organic-inorganic hybrid perovskites emerged in 

2009 as unexpectedly efficient semiconducting 

materials for photovoltaic and solid state lighting applications. These materials, exemplified 

by CH3NH3PbX3 and CH(NH2)2PbX3 (X = Br, I), 

consist of an inorganic anionic framework (e.g. 

PbX3) with organic molecules as the cations (e.g. 

methylammonium, CH3NH3

+ or formamidinium, 

CH(NH2)2

+). Despite their unoptimized nature, 

which is epitomized by the ability to easily and 

cheaply spin coat their films for devices, they 

have “out of the gate” solar conversion efficiencies rivaling the best known photovoltaics on the 

market (e.g. silicon). The converse of this effect is 

high efficiency light emission, and thus the hybrid 

perovskites are also being investigated as solid state 

lighting components. The role of the dynamics of 

the organic cations in the high efficiency of these 

materials has been under intense scrutiny, and neutron scattering has played a key role in elucidating 

these effects. Neutrons, being highly sensitive to 

hydrogen, are an ideal probe of the bulk structural 

and dynamic properties of the organic cations. The 

wide range of relaxation timescales involved 

require high resolution and high bandwidth quasielastic neutron scattering (QENS), achievable 

with a combination of cold neutron chopper 

spectrometers and backscattering instruments. The 

combination of the Disk Chopper Spectrometer 

(DCS) and High Flux Backscattering Spectrometer 

(HFBS) at the NIST Center for Neutron Research 

have proven to be exceptionally well suited to these 

studies, having recently produced two important 

results in this field: the cation dynamics in CH3NH3PbI3 were analyzed in terms of their “jump” 

symmetries, leading to an improved understanding of the long lifetimes of carrier recombination.60 Meanwhile, re-orientational transitions 

of the cations in CH(NH2)2PbBr3 were shown to 

correlate with the steady state photoconductivity 

of this material61 providing the first direct link 

between the functional property of interest and the 

cation dynamics. Given the intense interest in these 

materials for energy applications, it is expected 

that neutron scattering studies of the cation dynamics in hybrid perovskites will continue to play a 

pivotal role. Reactor-based backscatterers have the 

advantage that they are more flexible in their data 

collection strategies, offering the ability to quickly 

scan the temperature dependence in a fixed energy-window, for example, to produce high quality 

information on the dynamics across the multiple 

phase transitions known in these materials. 

3. Battery materials. Neutron reflectometry (NR) 

and SANS studies of the microscopic structures 

of layered battery thin film structures continue to 

play an essential and unique role in advancing a 

fundamental understanding of such systems and 

in the development of related technological applications. The fact that neutrons are particularly sensitive to two key constituents of battery materials, 

namely hydrogen and lithium, make NR and SANS 

studies of such thin film layered battery systems an 

indispensable probe of their nanoscale structure 

and behavior. An example is a recent SANS study 

that investigated electrolytes based on zinc and 

lithium salts, showing that they hold promise for 

constructing batteries with high efficiency, lower 

toxicity, and intrinsic safety.62 NR and SANS instruments have advantages at HPRRs, if they are 

designed so that a wide range of neutron energies 

can be used simultaneously. SANS instruments can 

simultaneously use 10% or more wavelength range, 

making the continuous flux of an HPRR highly 

advantageous. Meanwhile, development of NR instrumentation which can make full use of a white 

beam has been undertaken at NIST (CANDOR). 

Making use of the continuous, white beam from a 

HPRR, this instrument produces over an order of 

magnitude better signal to noise compared to previous monochromatic NR instruments. 

Advantages of HPRRs in studying the structure of 

materials 

Understanding structure-property relationships are of 

utmost importance in designing compounds or materials for specific purposes, whether the applications 

are proteins, high temperature superconductors, or 

anything in between. Neutron diffraction has been an 

indispensable tool in structural studies, as it is highly 
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complementary to X-ray diffraction due to its sensitivity to hydrogen, deuterium, and oxygen. HPRRs have 

played an essential role in structural studies, providing 

“workhorse” instrumentation for neutron powder diffraction. 

1. Hydrogen-containing materials. Neutron scattering is able to differentiate between hydrogen 

and its other isotopes, such as deuterium, due to 

the different scattering absorption and incoherent cross-sections. One of the earliest works on 

hydrogen containing systems was that of Nobel 

Laureate Cliff Shull on the hydrogenated lattice of 

palladium. Using neutron-diffraction measurements on powdered samples at a reactor predating HFBR, it was shown that both hydrogen and 

deuterium atoms in β-phase Pd-H and Pd-D were 

located in the octahedral positions of the palladium lattice. It was also determined that although 

the vibrational amplitudes of hydrogen and deuterium were similar to those observed in other 

compounds, the total neutron-scattering cross-section for hydrogen in this system was abnormally 

low, indicating that the protons were more nearly 

free than in other hydrogen compounds.63 The 

advantage of detecting hydrogen via neutrons over 

other techniques is particularly important to obtaining accurate crystal structures of hydrogenated 

systems. While X-ray diffraction can reveal the 

formation of metal-hydride phases, the position of 

the hydrogen atoms can only be indirectly inferred 

from the measurement. The difficulty in locating 

hydrogen atoms renders the structure determination very difficult along with the type of bonding 

and the nature of metal-hydrogen bonds. However, 

with neutron scattering, the location of hydrogen 

can be identified. This is due to the fact that neutrons are scattered by the nucleus, and both light 

and heavy elements can scatter neutrons equally 

well.64 Due to this strength, neutron scattering 

has infiltrated the field of protein crystallography, 

traditionally an X-ray diffraction stronghold. 

Neutron diffraction provides an experimental 

way to directly locate hydrogen atoms in proteins, 

a technique complimentary to ultra-high-resolution X-ray diffraction. Three different types of 

neutron diffractometers for biological macromolecules have been constructed in Japan, France, 

and the United States, and they have been used 

to determine the crystal structures of proteins. 

Results relating to hydrogen positions and hydration patterns in proteins include the geometrical details of hydrogen bonds, H/D exchange 

in proteins and oligonucleotides, the role of 

hydrogen atoms in enzymatic activity and thermostability, and the dynamical behavior of hydration structures. Combined with advancements in 

deuterating proteins, growing large single crystals, and the use of cryogenic techniques, neutron 

scattering offers new capabilities to deciphering 

biological systems. Neutron protein crystallography helps in the identification of all the hydrogen 

atoms in biological macromolecules and has helped 

to establish hydration patterns in proteins. More 

recently, technical innovations involving the development of the neutron imaging plate have made 

it possible to shorten the long amount of time 

required to collect a full diffraction data set. These 

instrumental improvements have been applied to 

Laue diffractometry (see Figure 1a.6), as well as 

to more conventional data collection techniques, 

such as those using monochromatized neutron 

beams,65,66 well suited at HPRRs.

FIGURE 1a.6. The BIX-3 diffractometer, equipped with a neutron image plate, is dedicated to protein crystallography 

using a monochromatized neutron beam source (installed 

at the JAERI reactor, Japan).

Source: N. Niimura, “Neutrons expand the field of structural biology.” 

Current Opinion in Structural Biology 9, 602-608 (1999).
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2. Oxygen positions in cuprate and nickelate superconductors. Neutrons are particularly vital to the 

study of oxygen-containing compounds. Neutron 

spectroscopy has been instrumental in understanding strongly correlated electron systems ranging from cuprates, nickelates, manganites and 

cobaltites. One example where neutron scattering 

has made significant contributions is the cuprate 

superconductor YBa2Cu3O7-y. Compared to all the 

elements in the system, oxygen has nearly the same 

coherent scattering lengths as the other elements 

in this compound and provides an unambiguous 

method for locating the oxygen atomic positions 

and determining the site occupancies. From the 

neutron diffraction analysis, the correct structure 

with the right oxygen positions were reported soon 

after this system was discovered. The crystal structure of the single-phase stoichiometric high-temperature superconductor in the Y-Ba-Cu-O system 

was determined using high-resolution neutron 

powder diffraction. This compound has an orthorhombic structure with space group Pmmm with 

buckled CuO2 layers.67 Oxygen ordering and the 

orthorhombic-to-tetragonal phase transition 

in YBCO became a very important issue soon 

after the discovery of this system. In situ neutron 

powder diffraction measurements showed that the 

orthorhombic-to-tetragonal phase transition near 

700°C in a pure oxygen atmosphere is an orderdisorder transition in which the disordering of 

oxygen atoms into a normally vacant site destroys 

the one-dimensional Cu-O chains present in the 

room-temperature orthorhombic structure. 

 The tetragonal structure has a partially occupied, nearly octahedral Cu-O arrangement, in 

contrast to the orthorhombic structure that has 

one-dimensional Cu-O chains. For both structures, 

the oxygen stoichiometry decreases monotonically with increasing temperature. It was found 

that the transition temperature depended on the 

oxygen partial pressure and occurred when the 

stoichiometry was near YBa2Cu3O6.5. Furthermore, suppression of the superconducting transition temperature in tetragonal YBa2Cu3O7−x was 

linked to the disorder of oxygen atoms which 

destroys the one-dimensional chains or from 

the absence of Cu3+ ions.68 The structural properties of oxygen-deficient YBa2Cu3O7−δ have 

been determined by neutron powder diffraction 

for 0.07<δ<0.91 (see Figure 1a.7). It was known 

at the time that superconductivity disappeared 

at the orthorhombic-to-tetragonal transition that 

occurred near δ=0.65. By following oxygen across 

the transition, it was determined that the superconducting behavior could be controlled by charge 

transfer between the conducting two-dimensional CuO2 planes and the CuOx chains, which acted 

as reservoirs of charge. None of this work could 

have been done by X-rays at that time.69

 Oxygen defects were also important in nickelates such as La2NiO4+δ. Using standard crystallographic techniques of neutron powder diffraction data, 

it was shown that the excess oxygen in La2NiO4+δ 

was incorporated as an interstitial oxygen defect. 

The defect was located with high accuracy in the 

orthorhombic Fmmm structure, which provided a 

favorable coordination to four La atoms but required 

FIGURE 1a.7. Results from Refs. 69 and 70 using pulsed 

neutron diffraction from IPNS. These experiments were 

among the first to accurately determine the structure of 

YBa2Cu3O7.
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four nearby oxygen atoms to be displaced from 

their normal positions. The defect concentration 

determined from structural refinement agreed well 

with the overall oxygen stoichiometry determined 

by hydrogen reduction. For intermediate oxygen 

contents (δ≊0.07), the system phase-separated 

with different defect concentrations. Structural data suggested that the nearly stoichiometric 

phase, 0<δ<0.02, incorporated excess oxygen by 

forming a different defect. La2NiO4+δ exhibited very 

similar behavior to superconducting La2CuO4+δ, 

suggesting that the oxygen defect structures were the 

same in both systems.70

3. Local structure. The local structure analysis, 

first pioneered by B. E. Warren close to 50 years 

ago, made use of X-ray diffraction. The technique 

became popular for studying disordered systems. 

With the advent of spallation neutron sources, the 

local structure analysis spread beyond disordered 

systems to highly ordered systems, with improved 

intensity and resolution. One class of materials 

where the local structure analysis has made important contributions is the relaxor ferroelectrics, 

which are at the border of order with disorder. 

Relaxor ferroelectrics exemplify a class of functional materials where interplay between disorder and 

phase instability results in inhomogeneous polar 

nanoregions (PNRs). The direct observation of the 

formation of PNRs in Pb(Mg1/3Nb2/3)O3 using the 

neutron pair distribution function analysis over 

the temperature range from 1,000 to 15 K demonstrated the existence of local polarization and the 

formation of medium-range PNRs with local 

rhombohedral order. The volume fraction of the 

PNRs was estimated as a function of temperature 

which steadily increased from 0% to a maximum 

of  30% as the temperature decreased from 650 

to 15 K. Below T~200 K, the PNRs freeze into the 

spin-glass-like state.71 Elastic diffuse scattering studies on Pb(Mg1/3Nb2/3)O3 revealed interesting features related to the polar nanoregions (see Figure 

1a.8). The intensity distribution measured near 

the (100) Bragg peak in the (hk0) scattering plane 

assumed the shape of a butterfly with extended 

intensity in the (110) and (1-10) directions. The 

temperature dependence of the diffuse scattering 

showed that both the size of the polar nanoregions 

and the integrated diffuse intensity increase with 

cooling even for temperatures below the Curie 

temperature TC~213K.72 Using neutron scattering, 

it was additionally shown that phonon localization 

drives polar nanoregions in relaxor ferroelectrics. 

Ferroelectric phonon localization drives PNRs in 

relaxor ferroelectric PMN-30%P. At the frequency 

of a preexisting resonance mode, nanoregions 

of standing ferroelectric phonons develop with a 

coherence length equal to one wavelength and the 

PNR size. It was determined that the size and shape 

of PNRs was not dictated by complex structural 

details, but by phonon resonance wave vectors.73

 Another exemplary system in which local 

lattice distortions were instrumental in understanding the competing mechanisms and strong correlation effects was the perovskite manganites. The 

discovery of colossal magnetoresistance, CMR, in 

the 90s led to considerable research to understand 

the competing spin, charge and lattice interactions, 

and the role of the static Jahn-Teller distortions. 

It was found that over certain ranges of composition, a transition from a paramagnetic insulator 

to a ferromagnetic metal occurred as a function 

of temperature and magnetic field. While the 

connection between ferromagnetism and electrical conduction was initially explained in terms of 

the double exchange mechanism, theoretical work 

pointed at the time to lattice involvement in the 

mechanism, possibly via polaron formation. Thus 

the manganites have become the canonical system 

for understanding polarons. Soon after, through 

FIGURE 1a.8. Neutron elastic diffuse scattering intensity at an 

HRPP on a relaxor ferroelectric (from Ref. 73)

Source: M. E. Manley, J. W. Lynn, D. L. Abernathy, E. D. Specht, O. Delaire, 

A. R. Bishop, R. Sahul, J. D. Budai, “Phonon localization drives polar nanoregions in a relaxor ferroelectric.” Nature Communications 5, 3683 (2014)
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The Scientific Case 19

neutron scattering experiments and the pair-density-function (PDF) analysis, it was demonstrated 

that the local structure in this system was quite 

distinct from that suggested by the crystallographic 

structure. It was shown that the Jahn-Teller distortion was locally present in the metallic as well as 

insulating phases, suggesting a direct link between 

the distortions and the polarons. Through the local 

structure analysis, it was also reported for the first 

time that the metallic state was not homogeneous, 

which led to a completely new picture of the metallic phase (see Figure 1a.9).74

 Finally, a very early example of charge ordering 

confirmation by neutron scattering was in magnetite Fe3O4 below the Verwey transition. Verwey 

initially discovered that magnetite undergoes a 

sharp, first order transition on cooling below 120 

K at which the resistivity of magnetite increases 

sharply by 2 orders of magnitude, and the structure 

distorts from cubic symmetry. He hypothesized 

that this effect was to charge ordering of the Fe2+

and Fe3+ states on the B sites in alternating layers, 

but was unable to confirm it. The charge ordering was determined to show a pronounced [001] 

modulation, consistent with the gap that opens at 

the Verwey transition, although other structural 

modulations might be present as well.75

Summary

HPRRs play an important role in solid state physics 

and chemistry, and the examples above illustrate that 

the applications range from the fundamental (quantum 

spin entangled states and unconventional superconductors) to the practical (magnetic storage, thermoelectrics, 

and photovoltaics). In the realm of the solid state, neutron scattering excels at probing lattice structure, particularly with regards to hydrogen and oxygen positions, 

lattice dynamics, and all aspects of magnetism. The 

primary advantages of HPRRs over spallation sources 

is the efficient collection of data over a targeted range of 

energy, and momentum space as a function of another 

control variable (such as temperature, magnetic field, or 

other parameters), as well as the use of spin polarization 

techniques. However, new instrument design concepts 

for HPRRs are always in the works, so that techniques 

can be improved dramatically and make excellent use 

of the continuous, high flux beams and in some cases 

can outperform comparable instrumentation at spallation sources. Thus, HPRRs and spallation sources 

can sometimes produce comparable efficiencies for the 

same types of measurements, depending on instrument 

design. This means that HPRRs not only offer complementary strengths to spallation sources, but also help to 

address the general oversubscription problem for neutron instrumentation in the U.S.

FIGURE 1a.9. The composition dependence of the Jahn-Teller 

polarons in CMR material, La1-xSrxMnO3 determined from 

pulsed neutron diffraction and the pair density function 

analysis from data collected at IPNS.

Source: D. Louca, T. Egami, E. L. Brosha, H. Röder, A. R. Bishop, “Local 

Jahn-Teller distortion in La1-xSrxMnO3 observed by pulsed neutron 

diffraction.” Physical Review B 56, R8475-R8478 (1997).

1b. SOFT MATTER

Soft matter research is one of the largest areas of investigation using neutron scattering instrumentation, and 

represents—along with biosciences—the soft ‘half’ of 

neutron scattering users. Key techniques used include 

small-angle neutron scattering (SANS), ultra-small 

angle neutron scattering (USANS), neutron reflectometry (NR), neutron spin echo (NSE), and the emerging 

method, offspecular neutron reflectometry (similar 

to grazing incidence scattering). There are other techniques used as well, however the majority of experi-
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ments in soft matter rely on SANS and NR, for which 

soft condensed matter research represents at least half 

of the experimental volume. 

Currently, the vast majority of neutron scattering 

experiments in the United States are performed at HFIR, 

SNS, and NIST. University-based research reactors do 

not make a substantial contribution to the total available 

experimental time for the neutron scattering community. 

This focus at Oak Ridge and NIST is due to the fact that 

the larger sources have the required flux and beam quality 

to perform experiments in a substantially shorter period 

of time, and they offer instruments with a better range of 

momentum space for the most popular soft matter-related 

experimental techniques. In the case of many smaller 

reactor sources, state-of-the-art instruments adaptable to 

effective soft matter research studies do not exist.

The Unique Role of Neutrons in Soft Matter

Neutron scattering methods play a unique role in soft 

matter research that cannot easily be replicated by any 

other category of experiment. There are three primary 

advantages that neutrons offer for this type of research. 

First, soft condensed matter tends to have a very high 

percentage of hydrogen within its structures, as it is 

predominantly based on organic molecules. This feature allows control of scattering contrast through the 

use of readily accessible H/D isotopic labeling, enabling 

many experimental designs that could not easily be 

achieved using other methods, such as:

• examination of chain confirmations in polymer 

melts and solutions1

• bi-continuous microemulsions2

• block copolymer diffusion experiments3

• contrast matching for structure determination4

• partial structure factor analysis5

• solvent and additive partitioning in nanoscale 

structures,6 and 

• the determination of hydration numbers.7

Furthermore, the fact that many soft matter systems 

(micelles, vesicles, coacervates, biohybrid systems, 

and gels) also exist in media with a substantial water 

content makes them ideal for this type of H/D contrast 

by simply varying the concentration of D2O within 

the water. This type of contrast variation provides 

extremely strong scattering contrast, enabling complex 

behavior such as self-assembly at air-water interfaces, 

ordering in polymer thin films, and concerted polymer 

dynamics to be readily accessed in a manner not easily 

accomplished via other techniques. 

Second, neutrons are considered ‘non-destructive’ 

as there is typically no radiation damage to exposed 

soft matter samples. This makes them the probe of 

choice for materials that may show substantial damage 

or degradation when exposed to X-rays or electrons, 

including many micellar systems, gels, and biological-synthetic hybrid systems. 

Third, the relatively large penetration depth of neutrons facilitates the in-situ and in-operando investigation 

of soft matter systems to uniquely probe time-dependent 

and path-dependent processes, such as the operation of 

fuel cell and battery membranes, mechanical deformation, or ordering dynamics in external fields. 8,9,10,11

Priorities in Soft Matter Research

In soft condensed matter research, the main priority 

is access to high quality neutron sources that can support world-class instruments, such as SANS,USANS, 

NR, and NSE, on which researchers can conduct 

experiments. The differences in source characteristics between spallation and reactor sources tend to be 

of secondary importance for soft condensed matter 

research, and the time/pulse structure of a spallation 

source offers relatively little advantage for most soft 

condensed matter studies. Conversely, the continuous-flux structure of a reactor source is highly 

beneficial for the rapidly emerging, high-resolution 

NSE approaches that can bridge the gap between soft 

matter and biophysics (e.g., measurement of membrane 

bending constants [cell membrane mimics] at air/water 

interfaces),12 and it is also ideal for low-Q (USANS)-

type studies. Overall however, the key characteristic is 

maximizing the intensity of the scattered beam, while 

maintaining the necessary momentum and energy 

resolution required for the experimental design.

The Current Role of Reactor Sources

Currently, reactor sources provide a large fraction of the 

available neutron time on the key instruments used in soft 

matter research. The reactor sources at HFIR and NIST, 

but particularly HFIR, provide a high flux of neutrons 

enabling soft condensed matter scattering experiments 

to be performed faster than other neutron sources in the 

United States. These high-flux reactor sources therefore 

form a critical part of the nation’s current neutron scattering infrastructure. The loss of either of the two reactor 

sources would critically compromise the technological 
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The Scientific Case 21

capability of the community if it were not replaced by a 

new source that provided an equal or superior experimental throughput. Given the large number of instruments 

of interest to the soft matter community, particularly 

SANS, supported at both of the nation’s largest neutron 

scattering reactor sources, it is difficult to imagine that the 

research community would continue successfully if either 

of these sources were to cease operation. 

Current instruments are already over-subscribed often by a factor of up to 3, making it difficult 

for academic and industrial research efforts that rely 

on neutron scattering or that focus on the development of neutron techniques. For instance, soft matter 

M.S. and Ph.D. theses are becoming increasingly 

dependent on neutron scattering information, as 

hierarchical structure determination and processing-dependent behavior become critical factors in 

next-generation soft materials design. 

With respect to industry, there are several key areas 

in which neutron scattering has led to transformative 

advances, and the importance of these techniques 

is evidenced by the 13 major corporations that are 

members of the nSOFT consortium. Impacts include 

improved transportation fuels, 13 improved polymer 

processing,14 and a better understanding of energy 

resource development.15 Perhaps more good proposals 

are denied beam time than are granted. 

Future Needs of the Soft Matter Community

Research in the soft matter community is limited by 

the number of high-quality instruments that are operated in the United States. While the community has 

several needs with respect to sample environments, 

data analysis tools, and the specific range of momentum and energy space to be probed, the main limit is 

accessibility to beam time on world-class instruments. 

Currently, reactor sources support a critical fraction 

of such instruments. Continued development and 

expansion of this instrumental suite on new or existing sources is the most important need of the community. Due to their ability to support a large number 

of instruments and provide for high scattered-beam 

intensity in the right momentum range with cold 

neutrons, reactor sources play an irreplaceable role in 

providing these neutrons. 

Some methods, such as NSE and offspecular 

neutron reflectometry, will also benefit from improved flux, allowing a wider range of samples to be 

studied as well as faster acquisition times, which will 

increase the number of experiments that can be run 

on the instrument. These methods would benefit from 

next-generation reactor designs. ■

BOX: Polymer Micelles

Until recently, a major unanswered question in colloid 

and soft matter science was how polymer micelles relax 

and how molecules might exchange between them. 

Using the unique capabilities of neutron scattering, 

Lodge, Bates and coworkers devised a clever experiment where they prepared a blend of purely deuterated 

and purely hydrogenated micelles in a mixed aqueous 

solvent. If chains interdiffuse between micelles, contrast 

will decrease until it reaches the match point which was 

set to be equivalent to a random distribution of chains. By 

using time-resolved neutron scattering, the investigators 

were then able to extract the rate of interdiffusion and 

show how it depended upon the chemical structure and 

thermodynamic interactions of the system. This study 

illustrates the critical role that reactor sources play in soft 

matter where they enable this type of experiment over 

long times with high intensity scattering.

FIGURE A. Time decay of scattered intensity from blends 

of deuterated and hydrogenated micelles

Source: Choi, Lodge, and Bates PRL 2010, 104, 047802
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1c. BIOLOGY

Neutron scattering has found application in a broad 

range of biological and biology-related research.1 A 

diagram of the current major application spaces for neutrons in biological research is shown in Figure 1c.1. The 

primary biological application of neutron scattering is in 

basic science, particularly structural biology,2 or the study 

of the molecular structures and organization of biological 

molecules in organisms, with the goal of establishing the 

relationship between structure and biological function.3

Structural biology research with neutrons includes: 

• examination of protein structure, particularly the 

chemical mechanism of enzyme active sites; 

• examination of the organization and dynamics 

of the bilayer lipid membranes that separate cells 

from their environment and enclose subcellular 

structures such as organelles; 

• examination of the association of membrane 

proteins with bilayer lipid membranes; and 

• examination of the organization of large molecular 

assemblies. 

Also, neutrons have found important applications 

in medicine, including in elucidating the mechanisms 

of disease, assaying biopharmaceutical formulations, 

and facilitating the development of novel nanoscale 

vehicles for drug delivery and gene therapy. Finally, 

neutron scattering is often useful in probing the interaction of biomolecules with solid-state materials, from 

designing biosensors and self-assembling biomolecules 

into useful materials to reducing biofouling.

Why Neutrons in Biology?

Four features of the interaction of neutrons with biological matter account for the widespread application of 

neutron scattering to the study of biological systems. 

Each of these features stems from the fundamental fact 

that in the sample material, neutrons scatter from the 

atomic nuclei, rather than from the electrons. 

• First, neutrons are highly sensitive to hydrogen 

atoms, which account for a large fraction of the 

atoms in biomolecules. 

• Second, neutrons are sensitive to nuclear isotopes. 

Thus the scattering properties of a biomaterial can 

be completely transformed (e.g., by isotopic substitution of deuterium for hydrogen) while having 

only a small effect on the biochemistry. Often this 

substitution is simply and effectively performed on 

the aqueous medium of the sample by exchanging 

water for heavy water, though it also can be done 

on the macromolecular portion of the sample. 

• Third, because neutrons do not disrupt binding 

electrons, beam damage from neutron scattering 

experiments is extremely limited. 

• Finally, neutrons interact relatively weakly with 

the sample material, often reducing the number of 

scattering events experienced by a single neutron 

in a sample to just one. This phenomenon results in 

simple theoretical treatments, small contributions 

from systematic errors in data analysis, and a wide 

range of neutron-compatible materials for sample 

environments. In biological molecules and assemblies, energy differences among states are often less 

than thermal energy; thus, samples comprise many 

independent states of varying occupancy. The weak 

interaction of neutrons with these materials produces an unbiased superposition of all such states. 

On the other hand, the weak scattering of neutrons 

from biological materials increases the required 

sample size or data collection times, limiting both 

the applicability and accessibility of the technique 

to the broader structural biology community, and 

highlighting the importance of high-flux neutron 

sources.

FIGURE 1c.1. Application space of scattering neutrons from 

biological materials. Applications at the intersections of basic science, materials research, and medicine are italicized.

Source: David Hoogerheide/NIST

Figure 1. Application space of scattering neutrons from biological materials. Applications at the 

intersections of basic science, materials research, and medicine are italicized. 

 
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Major Techniques

Neutron scattering in biology utilizes four major techniques or classes of techniques (see Table 1c.1). Small 

angle neutron scattering (SANS) is perhaps the most 

widely used, particularly for low-resolution (≈10 Å) analysis of structures associated with solvated biomolecules 

and biomolecular assemblies. SANS is both analogous 

to, and complementary to, small angle X-ray scattering 

and is often deployed in conjunction with other structural techniques such as NMR spectroscopy or electron 

microscopy to probe large macromolecular assemblies.4

Neutron reflectometry (NR) is used to provide low-resolution structural analysis of biological molecules 

and assemblies at the interfaces between solid, liquid, 

and air phases5,6 and is highly complementary to other 

interfacial techniques such as scanning force microscopy, as well as electrical and optical methods.7 NR studies benefit from the penetration of neutrons through 

materials such as single-crystal silicon, enabling the 

fabrication of samples with large areas while using relatively small liquid volumes. Neutron macromolecular 

crystallography (NMX) is analogous to X-ray crystallography and yields atomic resolution structural information, such as of the active sites of enzymes where the 

position of hydrogen atoms is important for enzymatic 

function.8 Finally, a range of dynamics techniques, 

including neutron spin echo spectroscopy and inelastic 

neutron scattering can probe a range of time scales from 

0.01 to 1000 ns, similar to that accessible by molecular 

dynamics simulations.9 These techniques are used to 

probe collective motions in lipid bilayers10 as well as 

the motions of protein sidechains and the dynamics of 

water at biomolecule surfaces.11

Future Opportunities and Requirements

In the future, neutron scattering is likely to continue to 

be a crucial component of biological research in three 

major areas: 

1. Structural biology. In structural biology, due to 

its unbiased sampling of distributions of structural 

conformations, neutron scattering will be particularly important in studying proteins and protein 

complexes with high disorder that are invisible 

in crystallographic techniques and difficult to 

assemble from electron microscopy images.

2. Biopharmaceuticals. In recent years, there has 

been a sharp increase in the economic footprint of 

biopharmaceuticals.12 Unlike small molecule pharmaceuticals, biopharmaceuticals are structured on 

the nanometer scale and are thus readily probed by 

neutron scattering techniques. As a recent example 

of the importance of neutron scattering, Amgen 

acknowledged the “valuable impact” of SANS measurements to probe the stability of formulations of 

the first oncolytic virus therapy approved by the 

FDA (https://www.nist.gov/industry-impacts/cancer-therapy-formulations). 

3. Biotic/abiotic interface. Finally, development and 

characterization of the biotic/abiotic interface (i.e., 

the physical interface between semiconductor technology and biological tissue) will require a probe 

that interrogates both hard and soft condensed 

matter materials and is likely to be an important 

application for neutron scattering in biology. 13

TECHNIQUE SAMPLE FORM LENGTH (TIME) SCALE INFORMATION

Small angle neutron scattering (SANS) Solubilized 1 nm – 10,000 nm Structure

Neutron reflectometry (NR) Thin film 1 nm – 1,000 nm Structure

Neutron macromolecular crystallography (NMX) Crystallized 0.1 nm resolution Atomic structure

Neutron spin echo (NSE) Solubilized 0.1 nm – 100 nm

(0.01 ns – 1000 ns)

Collective dynamics

Inelastic neutron scattering Powder 0.5 nm – 5 nm

(0.01 ns – 5 ns)

Diffusive dynamics

TABLE 1c.1

Suite of Neutron Scattering Techniques for Probing Biological Materials
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Realization of these opportunities will rely on a 

robust response to the challenges facing researchers 

interested in neutron scattering for the biological 

sciences. The most significant obstacles are slow measurement speeds and the lack of automation in sample 

handling and data analysis. Biological samples (and soft 

matter samples generally) have a limited lifetime, even 

with appropriate sample handling and refrigeration 

equipment. Protein samples are particularly sensitive to 

experimental conditions and handling protocols, and 

may lose functionality on the hours-long time scales 

of a conventional neutron scattering measurement. 

Because effect sizes are small for biological samples, 

multiple independent measurements are often desired 

for accurate uncertainty estimation. Similarly, biological samples are complex, with many components in 

the sample and its aqueous environment, and therefore 

they benefit from the multiple measurements required 

for parametric mapping. Precious samples, such as 

virus-based drug formulations, are available only in 

small sample volumes or at dilute concentrations. High 

capacity and sample throughput, for which high-flux 

sources with efficient detectors are a fundamental 

requirement, are thus essential for biological samples. 

A promising recent development in this area is the 

construction of wide-band energy-dispersive detectors 

for SANS and NR instruments at reactor sources.14

These combine energy discrimination (the primary 

efficiency advantage of pulsed-source measurements) 

with the uninterrupted flow of neutrons from a continuous source, increasing measurement speeds over 

conventional instrumentation by well over an order of 

magnitude.

In addition to the technical requirements for neutron sources and instrumentation, biological research 

requires an appropriate level of infrastructure and 

staffing support. Due to the limited neutron scattering 

resources in the United States, and the traditional role 

BOX: Membrane-Associated Proteins

Membrane-associated proteins are 

proteins that are embedded in, or 

transiently interact with, the lipid 

membranes that define the boundaries of cells and their compartments. 

As a result of their strategic location, 

membrane-associated proteins play 

an outsized role in how cells process 

and respond to their environment 

and thus constitute a large fraction 

of drug targets. Their confinement 

to the crowded two-dimensional 

membrane surface, however, limits 

the number of these proteins found in 

cells and makes them difficult to study 

by conventional solution-based biochemical and biophysical techniques 

in which their natural membrane 

environment is not present. An important contemporary example is the 

KRas4B GTPase (“KRas”) protein, a 

small, membrane-bound molecular 

switch that controls cell growth and 

division. Certain mutations of KRas 

inhibit its switching function, leading 

to cell proliferation and cancers of the 

lungs, pancreas, and colon for which 

no effective treatments are currently 

known. A critical step in the activity 

of KRas—and a potential target for 

therapeutic drugs—is the binding 

of the Raf effector protein; however, 

development of such an inhibitor for 

KRas has been hampered by the lack 

of a structural model for membranebound KRas. Recently, researchers 

in a collaboration involving the 

NIST Center for Neutron Research, 

Carnegie Mellon University, and the 

National Cancer Institute’s RAS Initiative performed a combination of 

neutron reflectivity, nuclear magnetic 

resonance, and protein footprinting 

measurements that, together with 

molecular simulations, elucidated the 

structure and dynamics of KRas at a 

membrane surface. The researchers 

found the KRas adopts an ensemble of 

molecular conformations in which the 

body of the protein, attached to the 

membrane via a flexible tether, dynamically explores the space above the 

membrane, with only brief excursions 

to the membrane surface (see Figure). 

The flexibility of this protein allows 

it to efficiently find and bind to the 

larger Raf protein; when this occurs, 

KRas is locked into a single conformational state. This mechanistic insight, 

enabled by neutron scattering, may 

prove critical to guiding the development of small-molecule or biopharmaceutical therapeutics inhibitors for 

Ras-driven cancers.
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The Scientific Case 25

of neutron scattering in the physical rather than the 

biological sciences, academic researchers and their 

trainees are unlikely to be familiar with both biological 

science and neutron scattering techniques. As a result, 

neutron beamline scientists are highly involved in both 

technical and scientific levels at the conception, execution, analysis, and final publication of neutron experiments for biological samples. In turn, this situation 

limits the number of research groups that can be supported at existing facilities. As a result, the rate of technique and instrumentation development for biological 

measurements—particularly automation of sample 

preparation, sample handling, and data analysis—has 

not kept pace with the growth of biological research 

applications. To achieve a self-sustaining research environment for biology akin to that for hard condensed 

matter, multi-pronged investment in neutron facilities, 

instrumentation, and both technical and scientific staff 

commensurate to the needs of the biological research 

community, will be required. ■

1d. POLARIZED NEUTRONS

In synchrotron X-ray and optical spectroscopy and 

imaging, polarized beams are widely employed to 

enhance the specificity and quality of data. Polarized 

neutron beams offer analogous benefits over unpolarized neutrons, but are not widely utilized. However, 

with the advent of more powerful neutron sources and 

more efficient means of delivering and analyzing polarized neutrons, there are opportunities for transformational impacts on a wide range of science through 

polarized neutron scattering.

Unpolarized neutrons can detect magnetic structure because neutron diffraction is a self-interference 

effect that survives averaging over the incident neutron spin state. But more specific information can be 

obtained by controlling and analyzing the incident 

and scattered neutron spin state respectively. Not only 

does this allow systematic separation of magnetic and 

nuclear scattering, but in spherical neutron polarimetry, each Bragg peak yields a second rank tensor that 

describes the rotation of the incident neutron spin state 

during diffraction. Polarized neutron diffraction and 

reflectometry can thus uniquely resolve the complex 

non-collinear spin structures that are important for 

understanding topological and multiferroic magnetism 

in single crystals and nanostructured materials. Also, 

by essentially solving the phase problem, polarized 

neutron reflectometry can be used to determine complex bio-membrane structures through first principles 

inversion.

Neutron spectroscopy brings into view collective 

quasi-particles with energies from micro-eV to eV, 

including phonons and magnons. However, we are 

increasingly interested in materials where magnons and 

phonons hybridize, or where quasi-particles are topological and can only be created in multiples. For the most 

interesting experiments, no theory is yet available to 

help understand the superposition of various particles’ 

contributions to the unpolarized neutron scattering 

intensity. Polarized neutrons can systematically separate into separate channels the vibrational component 

and each magnetic component of multiple or composite 

quasi-particles. Polarized neutrons may be the only way 

to convincingly isolate the subtle features of continuum 

scattering from Majorana quasi-particles in a Kitaev 

spin liquid from phonon scattering.

Polarized neutrons offer the ultimate in energy and 

momentum resolution. Spin echo techniques familiar 

from nuclear magnetic resonance can be exploited to 

access temporal or spatial correlations from the atomic 

to the 100 nanosecond or the micrometer scales respectively while employing a neutron bandwidth 5–6 orders 

of magnitude greater than conventional scattering 

methods. Spin echo methods provide a unique window 

on dynamic phenomena in soft and biological materials, and on glassy and critical phenomena in hard 

condensed matter.

While entanglement is the key resource of quantum materials and the basis for quantum computing, 

a direct experimental probe of entanglement within 

a quantum material has not been reported. Conventional polarized beam methods utilize product states 

of a plane wave and a spinor wave function. However, using methods from neutron interferometry that 

were previously used to probe the fundamental tenets 

of quantum mechanics, it is possible to form a spinpath entangled neutron beam. Probing whether the 

entanglement built into the incident beam is sustained 

during interaction with the sample might be the basis 

for a transformative probe of quantum entanglement in 

materials.
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FIGURE 1d.1. Dipolar Spin-Ice State in Ho2Ti2O7 Haldane-like Effect in Spin-1 Pyrochlore?

Sources: (left) Scheie, et al. (2019); (middle) Plumb, et al. (2019); (right) Shu, et al. (2019)

Experimental Exploration:

• Find other disorder free realization of 

spin-1 pyrochlore

• Does non-magnetic doping produce 

spin-1⁄2 like degrees of freedom?

• Examine Zeeman splitting of the gaplike excitation

Polarized neutrons offer unique capabilities with 

growing impacts on the full range of materials-based 

sciences

Recent developments in incident beam polarization 

techniques and wide angle polarized analysis indicate 

great scientific potential. Fully spin resolved diffraction 

resolves non-coplanar spin structures that are important for topological materials. Some examples follow.

Some additional advantages of polarized neutrons 

include:

• Larmor labeling methods can extend neutron scattering to regimes of energy and momentum resolution inaccessible with other methods. 

• Use of the neutron in “quantum sensing” methods 

could provide transformative access to quantum 

entanglement.

In view of these advantages, when developing 

new sources and instrumentation, polarized neutrons 

should be the default. Facility level investments may 

facilitate access to polarized neutrons (dedicated polarized guides that do not lose half the neutrons).

Polarized neutron beams can be generated and 

employed at both spallation and reactor sources. However, the extra layer of spin selectivity and the greater 

complexity of the subsequent measurements necessitates optimized instrumentation at the optimal high 

flux neutron source. The three-source strategy (short 

and long pulse target stations and HFIR steady state) 

for neutrons puts ORNL in a unique position to exploit 

polarized neutrons in the materials sciences. Fully 

polarized triple axis spectroscopy was first demonstrated at the HFIR facility, the highest flux neutron 

scattering facility in the world. An emphasis on science 

with intense polarized neutrons could be a scientifically 

productive focus at a revamped HFIR.

For example, one may consider a facility level provision of fully polarized neutron beam guides based 

on polarizing super-mirror guide sections. Bifurcating 

an unpolarized guide into two guides with opposite 

polarization may be an effective way to provide multiple high flux spin polarized end stations. Some uses of 

polarized neutrons, including for spherical polarimetry, larmor labeling, and entangled scattering, appear 

harder to combine with parallelized detection systems. 

For these the higher time-averaged beam flux of a reactor facility will be essential to achieve adequate data 

rates. However, massively parallel detection systems 

inevitably deliver higher data rates and should be the 

ultimate goal so that continued development of wide 

angle neutron spin analysis will be important to realize 

the scientific potential of polarized neutrons. ■
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FIGURE 1d.2. Wide Angle 

Polarization Analysis

Source: Collin Broholm, private 

communication

1e. SYNCHROTRON X-RAYS VS. NEUTRONS

Elastic and inelastic neutron scattering has been a critical part of experimental condensed matter physics 

since the 1950s. Initially that stemmed from the unique 

capability of neutrons to reveal the precise way in 

which moments order in particular magnetic materials 

(even if the order is complex); also because of neutrons’ 

ability to probe phonons, magnons, and other excitations of matter over a broad range of momentum. 

Over the decades since the first neutron scattering 

facilities were constructed, there has been tremendous 

progress in probing similar properties of matter using 

X-rays. This progress has been achieved1 mainly due 

to the development of synchrotron X-ray sources and 

advances in the instrumentation used to interpret synchrotron X-ray scattering. 

As we explain below, however, X-ray scattering is 

very far from being a drop-in replacement for neutrons 

in studies of magnetic materials. The two techniques 

have instead developed a complementary relationship, 

with one technique often filling holes in what can be 

explored with the other. Neutron scattering is still the 

technique of choice for studies of the magnetic properties of materials, and is increasingly important for studies of soft matter, including biological matter.

Neutrons couple to matter through their strong 

interactions with atomic nuclei and through the 

interactions of the neutron spin with magnetic fields 

created by orbital or spin moments in a material. X-rays 

couple to matter mainly through the interaction of the 

light wave’s electric field with charged electrons in the 

material. Because the two coupling mechanisms are 

unrelated and uncorrelated, the trends in the coupling 

strengths of the two-probes across materials classes 

are quite different. X-rays couple strongly to materials 

with a high-density of electrons per volume (i.e. heavy 

materials), whereas neutrons couple most strongly to 

materials with large nuclear cross sections and/or large 

densities of unpaired electron spins or large orbital 

angular momentum density. In general, the sensitivity 

of X-rays to magnetism is weaker than that of neutrons. 

Synchrotron X-ray scattering opens up a number 

of possibilities not available in neutron scattering. Most 

important, perhaps, is the possibility of achieving element specificity by taking advantages of resonances. 

Resonant X-ray scattering (REXS) and diffraction can 

easily identify which atoms or ions in a compound are 

most responsible for particular structural features, or 

if inelastic (RIXS), a particular excitation. It can also 

detect diffraction patterns associated with different 

types of electronic order, including not only magnetism 

but also charge and orbital order. 

In a very typical and important example, the resonance that is exploited in studies of transition metal 

oxides is between a metal ion-core p-level and a metal 

valence d-level. These transitions are in the soft X-ray 

range for 3d metals, in the tender X-ray range for 4d 

metals, and in the hard X-ray range for 5d metals. By 

tuning an X-ray source to a transition energy associated with a particular metallic cation, the contributions of different metals to structural, magnetic, or 
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28 The Scientific Case

other electronic features in a compound or artificial 

superlattice can be distinguished. (See box on Oxide 

Heterojunction Magnetism.) 

Other important possibilities are opened up by 

taking advantage of the pulsed and coherent character 

of modern high flux synchrotron X-ray beams. Using 

X-ray pulses and borrowing pulse-probe techniques 

from optics, it is possible to examine how the atomic 

scale electronic degrees of freedom of complex materials equilibrate after being excited by an X-ray or another beam. Taking advantage of X-ray coherence, X-ray 

photo-correlation spectroscopy (XPCS) can provide 

unique information on the slow dynamics of glassy 

materials. Coherent beams can also be easily focused 

down to their diffraction limit, adding spatial resolution to X-ray scattering experiments. 

Modern X-ray sources (particularly the X-ray free 

electron laser) are sufficiently intense to enable some 

studies that are simply impossible with neutrons (e.g., 

studies of thin films of Van der Waals materials down 

to the monolayer limit). Thanks to increases in available beam intensity and improved energy resolution, 

inelastic X-ray scattering can even be the technique 

of choice for studying phonons in crystals, a task normally accomplished using neutron scattering. The 

advantage of X-rays is that measurements can be successfully carried out in samples that are too small to 

generate detectable inelastic neutron scattering signals. 

In one interesting recent example, Dimitri Reznik 

and collaborators2 were able to use beamlines at 

RIKEN and at APS to measure the temperature dependence of acoustic phonon dispersion in small crystals 

of Fe-based superconductors that have nematic phase 

transitions. This important measurement took excellent 

advantage of steadily improving beamline characteristics and instrumentational flexibility to achieve an 

important scientific result. 

X-ray scattering can also be the only option available in some materials in which unusual nuclear 

physics details make it difficult to use standard neutron scattering techniques. One important example 

is compounds containing iridium, which are difficult 

to explore using neutron scattering because the most 

common iridium isotope has a large cross section for 

neutron absorption.

X-rays also have important limitations compared to 

neutrons, especially in probing magnetism and biological 

or soft condensed matter. In biological matter, the role of 

light elements like hydrogen, which are nearly invisible in 

X-ray studies, is essential. Because the neutrons interact 

only with nuclei and not with electrons, useful scattering 

signals can normally be achieved without causing radiation damage. Element specificity can sometimes be achieved in neutron scattering by isotope substitution, and this 

is particularly valuable in biological matter studies where 

deuterium can be substituted for hydrogen. 

X-rays see magnetic properties in a less direct way 

than neutrons, and typically with poorer energy resolution and weaker signals that are more difficult to interpret quantitatively. In X-ray scattering, the dominant 

magnetic signal typically comes from the response of 

the electronic system to the X-ray’s electric field, which 

FIGURE 1e.1. Real and momentum space lattices of several 

compounds. The circles surrounding zero momentum 

show the region of momentum space accessible to resonant inelastic X-ray scattering, while the squares mark complete Brillouin-zones studied by neutron scattering. 

Source: “Antiferromagnetic Order and Spin Dynamics in Iron-Based Superconductors,’”Pengcheng Dai, Reviews of Modern Physics, 87, 855 (2015).)
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is normally characterized by its conductivity at X-ray 

frequencies. In magnetic systems the conductivity at 

X-ray frequencies has an antisymmetric Hall contribution, analogous to the Kerr or Faraday response at optical frequencies. Although this response can be viewed 

as a magnetic order parameter, its relationship to the 

moment distribution in the material is not as direct as 

the corresponding relationship for neutrons. Typically 

the magnetic signal in inelastic X-ray scattering must be 

enhanced by taking advantage of a core-to-valence resonance. The energy of this resonance sets the X-ray wavelength, and hence the maximum excitation momentum 

that can be probed in a resonant inelastic scattering 

experiment. As illustrated by the examples in Figure 

1e.1, for some materials this can leave the momenta of 

greatest interest outside the range that can be explored. 

In addition to this fundamental limitation, the 

energy resolution that can be achieved with resonant 

inelastic X-ray scattering is not yet competitive with 

what can be achieved with neutron scattering. Furthermore, because X-rays are absorbed by most materials, 

it is technically difficult to surround samples within 

environments such as magnetic field coils, hydrostatic 

pressure cells, and dilution refrigerators. On the other 

hand, these are easily accommodated in neutron scattering setups. 

Finally, due to the large absorption coefficient of 

air at soft X-ray energies, X-ray scattering samples must 

be placed in a vacuum, imposing severe limitations on 

sample environments, scattering geometries, and sample 

changes. ■

BOX: Oxide Heterojunction Magnetism

Resonant X-ray scattering can sometimes reveal magnetic 

order that would not be detectable using neutrons. In an 

important experiment, Frano et al.* were able to measure 

magnetic diffraction from the magnetic order in a very thin 

films containing only two layers of LaNiO3 by scattering 

resonantly at a nickel p-core to d-valence transition. LaNiO3 

is a member of a family of rare earth nickelates, many of 

which have an interesting type of non-collinear magnetic 

order. However, bulk LaNiO3 is a non-magnetic but highly 

correlated metal. Frano et al. demonstrated that LaNiO3

films are magnetic when two layers thick, but that the 

magnetism is lost already at three layer film thicknesses. 

This experiment demonstrates the potential of oxide heterojunctions for tunable strong-correlation physics, and for 

tunable magnetism that may be valuable in spintronics. 

* Orbital Control of Non-Collinear Magnetic Order in nickel oxide 

heterojunctions,” Phys. Rev. Lett. 111, 106804 (2011).

FIGURE A. Schematic illustration of 

resonant X-ray diffraction from a 

thin film of LaNiO3 that is only two 

layers thick. Frano et al. were able 

to demonstrate that these films 

order magnetically, whereas films 

of larger thickness do not. 

Source: Illustration from Alex Frano, “Spin 

Spirals and Charge Textures in Transition 

Metal Oxide Heterojunctions,” Springer 

Theses [2014]. ISBN 978-3-319-07069-8

FIGURE B. Resonant X-ray magnetic diffraction 

peak which demonstrates magnetic order in 

two-unit cell thick films of LaNiO3 on LaAlO3. 

Magnetism does not appear when the LaNiO3

film thickness is larger than two layers.
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2. Industrial Applications of Neutron Scattering

This section offers a perspective on industry use of neutrons from reactors and spallation sources for research 

and development. These sources are available only at 

dedicated facilities. In the U.S., such facilities are found 

at a few national laboratories (Los Alamos, Oak Ridge, 

and Idaho National Laboratories, as well as the National Institute of Standards and Technology). They are 

also found at more than 20 universities with research 

reactors. Industrial research often involves staff both at 

the company and at the neutron center. Industry staff 

are typically generalists tasked with solving problems 

relevant to the company, whereas those at a neutron 

center are of course experts in their particular type of 

neutron research.

Research reactors and spallation sources have 

different characteristics. While some work can be done 

more or less equally well at either, some studies are better or uniquely performed with only one source type. 

Industrial uses that are uniquely suited to research 

reactors include isotope production and materials 

testing, both of which are covered elsewhere in this 

report. Many of the uses described in this chapter can 

be performed at either type of source. In many cases, 

research reactors—by virtue of the number of scattering stations they can support—offer more prompt user 

access or faster data collection than spallation sources, 

which is often important to schedule-driven users from 

industry.

2a. Industrial Applications

Neutron scattering and imaging provides unique 

contributions to the discovery, development, and processing of new and improved materials for industrial 

applications owing to the way in which they interact 

with matter. Neutrons interact only with the atomic 

nuclei in a material. As a consequence, dense materials 

are easily penetrated, so that complex systems (e.g., an 

operating internal combustion engine,1 batteries,2 or 

water flow in a fuel cell3 can be observed in operando. 

Frequently, neutron studies are components of a suite 

of measurement techniques that are needed to untangle 

a multi-disciplinary issue.

The large cross section for neutron scattering from 

hydrogen, and especially deuterium, make neutrons 

especially well-suited for exploring organic, polymer, 

and biological materials and structures. Industrial 

researchers, often in collaboration with others, have 

tackled such challenges as: 

• in situ studies of molecular alignment in 

semi-crystalline polyethylene during processing4

• the effect of branching and molecular weight on 

catalytic properties of polymers5

• the shear-dependent interactions on dispersion and 

viscosity in paint and coating formulations6

• the stability, structure, and flow properties of 

biodegradable surfactant vesicle dispersions used in 

products such as fabric softener,7 and 

• the atomic and molecular-level details of the interaction between different adhesives and their substrate.8

The biopharmaceutical industry applies neutron 

scattering to topics such as: understanding the effect of 

drug preparation on stability and shelf life;9 elucidating 

the structures and processing effects on drug viscosity, 

with implications for delivery;10,11 and optimizing drug 

processing and formulation.12

The oil and gas industries employ neutron scattering as one of a suite of techniques to understand the 

composition and molecular structures of non-traditional petroleum sources including heavier non-volatile components, leading to enhanced oil recovery.13

It is also useful for determining the architecture and 

connectivity in gas-bearing shale.14 Alternative energy 

technologies have also benefitted from neutron studies. 

For example, fuel cell development has been aided by 

neutron radiography studies that enabled visualization 

of water flow in a PEM fuel cell as a function of water 

channel geometry, material, and surface.15

In the transportation industry, neutron diffraction and imaging have provided useful insights into 

the residual strain in single crystal high-performance 

turbine blades.16 Neutrons are also useful for detecting 

corrosion, for example in aluminum aircraft components,17 although the major interest in that case is in 

a portable system rather than a reactor or accelerator-based system. Interest in neutron studies extends 
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to the automotive industry, where investigations have 

used neutron diffraction to measure residual stress in 

weldments, an essential characteristic for predicting 

fatigue life.18

General Atomics has demonstrated that it considers neutrons to be important for sustaining the 

infrastructure for nuclear research and work on 

radioactive materials. Their EM2 advanced reactor 

provides an example of a major development effort 

that has run experiments at both HFIR and SNS. These 

investigations provide critical information on swelling 

and thermal conductivity during neutron irradiation, 

which is essential data needed for qualifying new fuels 

for nuclear reactors. ■

BOX: Exxon and Neutron Scattering

Exxon was an early adopter of neutron scattering, investigating systems of interest to the corporation since the early 

1980s. This has resulted in science that impacts technology 

and also has impacted the broader scientific community 

through opening up areas of investigation now pursued by 

academic groups. The origin of soft-matter physics is traced 

to the researchers at Exxon from this period, and neutron 

scattering investigations significantly contributed to this 

area of study. Neutron investigations in this period and 

into the 90s were focused on several main themes: fluids 

for enhanced oil recovery, polymer blends, fluids in porous 

media, and fuel cells. Building on the impacts of these 

earlier studies, the corporation began to further explore 

areas in which neutron research could have an impact on 

technology. Starting in the early 2000s, the neutron work 

was extended to new areas: gas hydrate inhibitor polymers, 

polymers for cold flow of diesel, thermodynamics of 

petroleum, polymer composites, and residual strain in 

metal welds. The study of polymers for cold flow of diesel 

resulted in a commercial additive in use today, with extensive neutron scattering studies defining an optimized structure. In recent years, neutron investigations have helped 

with understanding the new class of hydrocarbon resource 

that has revolutionized the oil and gas industry via the rock 

structure of gas shale. There has also been a revolution in 

new understanding of polymer architecture, structure property, and deformation thanks to extensive new neutron 

scattering investigations.

ExxonMobil’s leadership in industrial uses of neutron-based 

R&D extended to the development and deployment of new 

capabilities at user facilities. The ExxonMobil Participating 

Research Team built the 30 m Exxon/NIST SANS beamline at 

NCNR that was completed in 1991. It immediately superseded other SANS capabilities in the U.S. Its impact was felt 

immediately across the research community, particularly 

for soft matter research. A team of Exxon researchers led an 

active, highly productive research effort, becoming one of 

the best neutron programs in industrial research ever carried out, as documented in some of the examples cited in 

the previous paragraph. The Center for Interfacial Engineering at the University of Minnesota also joined the Exxon/

NIST partnership and continues as a major user of NIST 

SANS instruments. The partnership continues to this day.

2b. Industry-Related Consortia for Use of Neutrons 

Neutron scattering and imaging are complex and 

continuously evolving techniques whose sophistication precludes casual use. Reasonable familiarity with 

the field and the information that different neutron 

techniques can provide is necessary to have a sense 

of the types of R&D questions that are well-, or even 

optimally-suited to exploration with neutrons. This has 

led major neutron facilities to establish pre-competitive 

consortia and other means of supporting first-time 

industrial users that enable them to work with neutron 

science experts to learn the capabilities of neutron 

science, and optimize and apply neutron techniques to 

address their challenges.

nSoft is a NIST-based industrial consortium1 with 

more than a dozen members across a range of industries. The consortium is designed to deliver technology 

and expertise in neutron-based measurement science 

to U.S.-based industrial researchers as they perform 

precompetitive research. The collaboration model is 

built around “expertise transfer” rather than traditional technology transfer, in recognition of the very 

significant knowledge and financial barriers to entry 

into neutron-based research. Researchers from member 

companies participate in non-proprietary research led 

by NIST staff at the NIST Center for Neutron Research 

(NCNR). Consortium members drive the research 
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topics, taking advantage of NIST expertise to develop 

new measurement methods, data models, and performance metrics in collaboration with member researchers. Member companies often station staff at NIST 

for extended periods. Staff at member companies gain 

expertise in the use of equipment and software appropriate for their business sector. The interaction also 

helps companies understand how neutron-based techniques might be applicable to other R&D challenges. 

In the U.S., the Shull Wollan Center2 provides a 

gateway for U.S. industry to use the High Flux Isotope 

Reactor (HFIR)/Spallation Neutron Source (SNS). Following the DOE Office of Science model for access to 

user facilities, industrial access for pre-competitive (i.e. 

non-proprietary) research is determined through the 

same proposal process that is used for all proposals for 

open research. Successful proposals are provided access 

at no cost to the researchers or their institution. Proprietary research is also possible on a full cost recovery basis.

The LANSCE accelerator at Los Alamos provides a 

test-bed for semiconductor irradiation damage used by 

many aerospace and computing companies.3 ■

2c. Neutron Techniques with Potential Industrial Applications

In addition to the cases where industry is already making 

use of neutron techniques to develop and improve products, there are many instances where researchers in 

other sectors are developing and deploying new methods 

that are providing fundamental understanding that 

should have impact on the industrial sector.

One example is provided by VULCAN, located at 

the SNS at Oak Ridge National Laboratory.1 The goal 

of VULCAN is to provide understanding of engineering and functional materials behavior under complex 

environments. The instrument is designed for deformation, phase transformation, residual stress, texture, 

and microstructure studies. In situ and time-resolved 

measurements are possible under many conditions, 

thanks to load frames, furnaces, battery chargers, and 

other auxiliary equipment that have been incorporated 

into the instrument. Capable of accommodating large 

specimens, spatial and time resolutions relevant to 

industrial problems are accessible. This unique instrument has been used for research of relevance to industry, frequently with industry collaborators, in areas 

including additive manufacturing, alloy development, 

and observation of manufactures parts under operating 

conditions.2 ■

2d. Barriers to Broad Industry Use of Neutrons

Many challenges remain that affect industry perception of neutrons. Quick and easy access to the correct 

facilities is challenging for a potential industry user 

who lacks direct experience because they are expected 

to be problem-solving generalists. Even for common 

applications such as residual stress measurement, it is a 

challenge for the industry user to gauge how well validated the technique may be, regardless of the source. 

Industry users need access to consultation services 

when things are unclear to the engineer who is unlikely to be an expert in the method to be used. Making 

it easy for people in industry to find an appropriate 

beamline without preexisting knowledge would facilitate expanded application of neutrons (and advanced 

characterization in general). It is notable that the neutron community in Europe has taken some actions 

in this direction (for example, the SINE initiative), 

although this has now ended. Proprietary research 

at a neutron user facility in the U.S. requires that the 

company pay the full costs associated with its studies. 

While this may be reasonable for a business that has 

sufficient in-house expertise to know what neutron studies can (and cannot) provide, it is a significant barrier 

to entry for new users. Pre-competitive consortia or 

exploratory non-proprietary access is likely a reasonable first step for this population, since the financial 

barriers are low. Both experiences and new industry 

users need assurances and procedures that ensure that 

a number of conditions are fulfilled, including:

• IP will be protected (via, e.g., NDAs)

• Proper handling and control of data

• Export control is correctly followed

• Facilitation of remote operation so that multiple 

(industry) individuals can participate without 

having to travel
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• Users have access to data during an experiment 

and after they return to their company

• Results processed to the point where they are comprehensible to non-expert users, as opposed to raw 

data that has to be processed by a specialist at the 

facility

The nSoft consortium at NIST addresses these 

issues for non-proprietary work. DOE may find it useful 

to consider an analogous model to provide non-proprietary access to its user facilities. In Europe, the Sine2020 

Initiative (https://www.sine2020.eu) aimed to maximize 

industrial use of those neutron facilities but is no longer 

active. One target of opportunity was revenue generated 

from industrial use of their facilities to mitigate some 

of their funding issues. Another was to demonstrate 

their importance to sponsoring governments, along 

with encouraging internal investment in equipment and 

software appropriate to industry use such as handling 

heavy samples and remote operation. ■

2e. Summary 

This brief examination of industrial use of neutrons 

demonstrates its significance as well as the breadth and 

depth of the applications. Advances in neutron sources 

and instrumentation have dramatically increased the 

universe of industrial problems that are amenable to 

study using neutron-based techniques. Despite the 

various challenges, there is no doubt that industry will 

continue to exploit the available facilities. Actions that 

could increase industrial demand in the future include:

• Continued and increased communication about 

the capabilities of neutron user facilities, with particular attention to industrial problems which are 

especially amenable to neutron studies

• Extensive support for first-time industrial users 

to ensure that they have a positive experience and 

come to appreciate the value of neutron studies in 

addressing their problems

• Continued development of advances in instrumentation and timely processing of data to provide information that can address important industry problems

• Clear communication about neutron source availability to give industrial users confidence that a 

facility will be available when they need it, or to 

give them sufficient time to identify alternative 

approaches to address their problems in the event 

of a long shutdown.

Acknowledgments

Dr. Michael Glavicic (Rolls-Royce) and Hubert King 

(ExxonMobil Research and Engineering Co.) are 

acknowledged for their input on industrial needs for, 

and uses of, neutrons. ■
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3. Fundamental Physics at Reactors and Spallation 

Sources

Neutrinos and Neutrons from Reactors and 

Spallation Sources

Since the first observation of the free antineutrino by 

Reines and Cowan at the Savannah River reactor, fundamental physics at reactors in the United States has 

been at the forefront of discovery science. For decades, 

U.S. scientists have led experiments investigating the 

properties of neutrinos and neutrons from nuclear 

reactors and, more recently, spallation neutron sources. 

Neutrons and neutrinos play a key role in fundamental and applied science and enable scientists to 

study the constituents of nuclei, search for new forms 

of matter, and understand the symmetries that govern 

fundamental laws of physics and the evolution of the 

Universe. Neutrons are also powerful probe of materials, and neutrinos carry the signatures of nuclear 

decays in fission processes making them a probe of 

nuclear reactions and a monitor of nuclear fuel. 

Reactors and spallation sources are unique sources 

of neutrons and neutrinos. In reactors the fission products of heavy elements beta-decay and generate a large 

isotropic flux of electron antineutrinos along with the 

neutrons produced during the fission process. While 

the neutrons are guided out of the reactor core in 

beamlines to experimental stations, the antineutrinos 

are emitted isotropically. The antineutrino flux falls off 

with the inverse square law 1/R^2, making distances as 

close as possible to the reactor core a desired location 

for high-statistics experiments. The energy spectrum 

of emitted antineutrinos is determined by the nuclear 

beta decay energies. It peaks at ~4 MeV and ranges up 

to a maximum 10 MeV. Reactors are a pure source of 

electron antineutrinos making them ideally suited for 

neutrino oscillation studies and other experiments without backgrounds from other neutrino flavors. With its 

highly-enriched fuel, compact but powerful core, regular cycle of operations, and user facility, the High Flux 

Isotope Reactor (HFIR) at ORNL is a unique facility for 

research and scientific users from the U.S. and overseas. It has enabled a broad program of studies with 

neutrons as well as select neutrino experiments. 

Neutrons can be created by nuclear reactions in 

reactors and accelerators. Spallation sources are the 

most intense accelerator-based neutron sources. They 

use a high-powered proton accelerator to generate a 

beam of protons on a heavy metal target. During the 

collision, free neutrons are generated from the heavy 

metals creating a directed beam of neutrons and 

neutrinos. The accelerator facility allows spallation 

sources to be generally pulsed, unlike most reactors 

that generate neutrons and neutrinos constantly while 

operating. With GeV proton energies in the primary 

accelerator, spallation sources create neutrinos with 

energies of tens of MeV, a distinct time structure and 

variety of neutrino flavors. 

While research reactors and spallation sources are 

typically designed for the optimum production of neutrons, antineutrinos are a byproduct of these facilities. 

The abundance, energy spectrum, and flavor purity of 

antineutrinos from reactors and the pulsed time structure and direct beams of high-energy neutrinos from 

spallation sources make reactors and spallation facilities unique sources of neutrinos with complementary 

characteristics. They provide well-controlled laboratory 

environments that enable a suite of precision experiments for fundamental and applied science (See Figure 

3.1 and Box 3.1).

Fundamental Science with Discovery Reach 

Neutrons and neutrinos are key to our understanding 

of the constituents and forces of matter, the properties 

of elementary particles, and the symmetries of nature. 

Precision experiments using neutrons and neutrinos 

measure the neutron lifetime, probe the electric dipole 

moment, search for sterile neutrinos as a new form of 

matter, and constrain our understanding of nuclear 

reactions inside a nuclear reactor through precise measurements of the reactor neutrino spectrum. The neutron structure and the decay of neutrons are critical for 

describing matter and the visible world as we know it. 

The neutron lifetime is key to the synthesis of elements, 

and the charge distribution of neutrons may hold the 

clue to understanding the violation of CP symmetry 

and the resulting baryon asymmetry in the Universe. 

Neutrinos, on the other hand, are point-like elementary particle with no charge and little mass. They 
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only interact through the weak interaction making 

them a clean probe of the principles and physics that 

govern the Standard Model of Particle Physics. Their 

weak interaction and little mass allow neutrinos to 

freely stream effectively through the Universe close 

to the speed of light making them effective carriers of 

energy through the cosmos. Neutrinos have played a 

key role in the evolution of the Universe and the formation of large-scale structures since the beginning of 

time. 

Their tiny mass compared to other particles is a 

mystery, and a direct measurement of the neutrino 

mass is still outstanding. Since neutrinos have no 

charge, they may even be their own antiparticles. 

Understanding the Majorana nature of neutrinos 

through the search for neutrinoless double beta decay 

is one of the top priorities in neutrino science.

Since their postulate by Wolfgang Pauli in 1930, 

three Nobel Prizes (1995, 2002, and 2015) have been 

awarded for the observation and studies of neutrinos, 

the highest number of Nobel Prizes for any single particle. The 2015 Nobel Prize in Physics was awarded for 

the experimental observation of neutrino oscillation, a 

quantum mechanical transition of one neutrino flavor 

into another. 

Understanding the properties of neutrons and 

neutrinos holds the key to some of the biggest and fundamental questions in physics. 

• Why does the Universe have matter?

• How were the elements made in the Big Bang? 

• What is the nature of physics beyond the Standard 

Model? (See Figure 3.2)

FIGURE 3.1. Left: Fission process in a nuclear reactor. The fission products beta-decay to produce a flux of pure MeV electron 

antineutrinos emitted isotropically from the reactor. Right: Neutrino and neutrino production in a spallation neutron source. 

Several neutrino and antineutrinos are produced from the pulsed beam of pions generated in the spallation process.

Sources: Nuclearconnect

BOX 3.1. High Flux Isotope Reactor 

– A Compact Source for Neutrino 

Science

HFIR is one of the most 

compact but powerful 

reactors available for 

neutrino science in the 

world. With a size of < 0.5m 

in height, a radius of 0.2m, 

and a power of 85MW it is 

an abundant ”point” source 

of electron antineutrinos making it ideal for 

distant-depend neutrino 

oscillation studies and 

precision measurements 

using antineutrinos. With 

its highly-enriched fuel, > 

99% of electron antineutrinos come from the fission 

of 235U making it a spectroscopically clean antineutrino 

source. The regular operations cycle of HFIR allow for 

controlled signal and background studies. 

Image: Model of the HFIR core fuel assembly

Source: PROSPECT collaboration
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An Experimental Quest

Studies of neutrons and neutrinos require highly sensitive detectors to discern the interaction and faint 

signatures of these neutral particles. Advanced instrumentation and novel detector concepts are critical 

to the recent discoveries in the field. The fundamental 

physics studies with neutrinos and neutrons at reactors 

and spallation sources have led to a broad experimental 

program with a range in size, cost, and timeline. 

From the COHERENT project’s smallest neutrino 

detector (not larger than a milk carton) to the EDM 

mid-scale experimental facility for the study of the 

neutron, scientists have developed a variety of custom 

approaches to study the unique properties of these 

particles. Fundamental physics experiments with 

neutrinos and neutrons are typically custom-designed 

instruments following years of R&D advancing the 

frontiers of technology, materials and instrumentation. 

The development of neutron and neutrino experiments 

for fundamental science also enables a synergistic program in applied science ranging from the development 

of sensitive neutron detectors for portal monitoring to 

reactor monitoring and nuclear non-proliferation studies through neutrino detection.

For years, U.S. scientists and experiments at U.S. 

facilities have led the field in understanding the neutron lifetime and electric dipole moment and in probing the nature of neutrinos and properties of neutrino 

oscillation. The HFIR and the SNS facilities at Oak 

Ridge National Laboratory have provided a unique 

environment for studying fundamental physics with 

neutrinos and neutrons. 

The first unambiguous experimental observation 

of coherent elastic neutrino-nucleus scattering with 

the COHERENT experiment at the SNS confirms the 

prediction of a fundamental physics process predicted 

in 1974. The unique time structure of the accelerated 

beam and the synergistic use of neutrinos from the 

SNS made this discovery possible. (See Box 3.2.)

The Spallation Neutron Source is host to a suite 

of experiments in neutron science. Among them is 

the U.S. neutron EDM experiment, one of the most 

technically challenging and ambitious fundamental 

physics experiments in nuclear and particle physics. 

By pushing the technological capabilities of every 

single part of its experiment, the nEDM project aims 

to improve sensitivity in the study of the neutron electric dipole moment by a factor of 100, thereby resolving whether the neutron electric dipole moment can 

explain the observed matter/antimatter asymmetry in 

the Universe. (See Box 3.3.)

The High Flux Isotope Reactor is a unique source 

of reactor antineutrinos in the U.S. with user access. 

Over the years, it has enabled the study of reactor 

antineutrinos and nuclear processes with a variety of 

small R&D efforts. PROSPECT was the first particle 

physics project at HFIR designed and built in collaboration with ORNL leveraging the unique features of 

the HFIR facility. PROSPECT was designed to measure 

the flux and energy spectrum of reactor antineutrinos 

from HFIR in search of short-baseline oscillation as 

a signature of sterile neutrinos. PROSPECT reported 

its first results in 2018, leading the worldwide effort in 

the search for sterile neutrinos at research reactors and 

probing our understanding of the nuclear reactor data 

and models (See Box 3.4.)

The range of the experimental neutrino program 

at both HFIR and SNS is currently constrained by the 

size of the available experimental space near the reactor 

core and the beamline. The shielding requirements for 

surface-based neutrino detectors make the placement 

of detectors particularly challenging, and it is difficult 

FIGURE 3.2. Left: Neutrinos are 

elementary particles with no 

charge in the Standard Model 

of Particle Physics. Right: The 

neutron is a composite particle consisting of 3 quarks held 

together by gluons, the carrier 

of the strong fore.
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BOX 3.2. Precision Studies of Reactor Antineutrinos with PROSPECT

PROSPECT, the Precision Reactor Oscillation and Spectrum 

Experiment, is located at HFIR at a distance of < 10m from 

the reactor core. PROSPECT measures the relative flux and 

energy spectrum of antineutrinos emitted from the reactor 

as a function of distance from the core with a surface-based 

detector using a novel, segmented 6Li-doped liquid scintillator detector. PROSPECT demonstrated the successful 

measurement of reactor neutrinos with a surface-based 

detector with high signal-to-background, and made the 

first modern measurement of the reactor antineutrino 

spectrum from 235U in a highly-enriched reactor. The results 

form PROSPECT yield some of the world’s most stringent 

limits on the existence of eV-scale sterile neutrinos as a 

new form of matter and inform the nuclear modeling of 

the reactor neutrino spectrum. PROSPECT was designed, 

built, and operated with a collaboration of 10 universities, 

three national laboratories, and the National Institute of 

Technology. It draws on the multidisciplinary expertise of 

the collaborating institutions in particle physics, nuclear 

science, as well as instrumentation development and 

applied science. PROSPECT uses synergistically the “free” 

flux of antineutrinos emitted by HFIR. Its scientific results 

are critical for understanding the properties of neutrinos 

as well as informing nuclear data for reactor modeling and 

R&D for safeguard and reactor monitoring purposes. 

HFIR was chosen as the preferred site for the PROSPECT 

experiment following a detailed characterization of backgrounds at several high-powered research reactors in the 

U.S. and an extensive evaluation of site characteristics 

including ease of access, infrastructure, and user support. 

FIGURE A. Left: The 

PROSPECT detector 

inside its containment and shielding 

package inside HFIR 

next to the reactor 

wall. Right: Conceptual drawing of the 

PROSPECT detector 

with regards to the 

location of the HFIR 

reactor core.

Sources: PROSPECT 

collaboration

FIGURE B. Assembly of the segmented PROSPECT detector at the 

Yale Wright Laboratory prior to its 

shipment to ORNL/HFIR 

Source: Yale/PROSPECT collaboration
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BOX 3.3. Probing the Neutron Electric Dipole Moment and CP Symmetry

The neutron electric dipole moment (EDM) is a measure 

of its charge distribution. A permanent, non-zero electric 

dipole moment would violate both parity (P) and time 

reversal symmetry (T), and indicate that the neutron charge 

distribution is not perfectly round. A non-zero neutron 

EDM might explain the matter antimatter imbalance in the 

Universe. Violation of the CP symmetry has been observed 

in weak interactions and is part of the Standard Model of 

Particle Physics via a CP-violating phase, but its amount is 

too small to explain the baryon asymmetry. 

ORNL has had a long-standing history in this field. The 

first measurement of the neutron EDM in 1950 by Smith, 

Purcell, and Ramsey using neutrons from the Oak Ridge 

Reactor showed the roundness of the charge distribution 

to better than one part in a million. Since then, precision 

has improved by more than 6 orders of magnitude. The 

nEDM experiment under preparation at the Fundamental 

Neutron Physics Beamline at the Spallation Neutron Source 

will improve on this result by another factor of 100. The proposed measurement will utilize a large density of 

FIGURE B. Left: First measurement of the neutron electric dipole moment at the Oak Ridge Reactor in 1950. 

Right: Conceptual drawing of the planned nEDM experiment.

Source: Oak Ridge National Laboratory – The News

FIGURE A. Parity (P) and 

time-reversal (T) violation due to an electric 

dipole moment. 

Source: Wikipedia

ultracold neutrons (UCNs) that will be produced through 

a superthermal process involving scattering off of excitations in superfluid Helium. The UCNs will be stored in a 

material bottle in strong electrical fields for times longer 

than their decay lifetime. 
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to retrofit current available space. While the direct 

beam of neutrinos at the SNS and their time structure allows detectors to be farther away and provides 

experiments with an additional background rejection, 

the isotropic emission of antineutrinos from reactors 

demands experiments to be located as close as possible 

to the core. 

The PROSPECT experiment was designed into the 

available space inside the HFIR building next to the 

core containment wall, but its sensitivity and scientific 

reach were limited by the available space and floor loading capacity. A dedicated shielded room for neutrino 

detectors and detector R&D at HFIR would provide 

the U.S. community with a unique and world-leading 

capability to advance the field. It would provide the 

neutrino program at ORNL and HFIR with a range of 

opportunities spanning fundamental particle physics, 

nuclear physics, and applied detector development. 

Over the years, neutrino experiments at ORNL 

have made opportunistic use of the neutron (and 

neutrino) sources at HFIR and the SNS, leading to a 

series of impactful results and first measurements in 

neutrino science. The ease of access to HFIR and SNS, 

the ORNL user community, and to existing infrastructure were critical for the success of these experiments. The neutron program continues at dedicated 

beamlines, but would also benefit from increased space 

and user access. 

Future Opportunities, Synergies, and Outlook

Neutrons and neutrinos are a unique way to study the 

fundamental forces of nature. HFIR and SNS at ORNL 

are operated as user facilities for neutron and materials 

science and isotope production. Until now the scientific 

community has made creative and opportunistic use of 

these facilities for a fundamental physics program. And 

yet the neutron and neutrino programs in the U.S., 

at ORNL in particular, have obtained world-leading 

results with highly visible impacts. The recent results in 

neutrino physics from COHERENT and PROSPECT, 

BOX 3.4. First Observation of Coherent Elastic Neutrino-Nucleus Scattering 

of Neutrinos

Coherent Elastic Neutrino-Nuclear Scattering 

is a process predicted by the Standard Model 

of Particle Physics. It was first predicted in 1974 

by Freedman, and was finally observed in 2017 

by the COHERENT collaboration. The process 

depends on the nuclei used as a target, and 

is a sensitive probe of the underlying physics 

of coherent scattering of neutrinos off nuclei. 

The experimental detection requires a source 

of low-energy neutrinos and detectors that 

contain nuclei of optimal mass. The SNS provides an intense flux of neutrinos in the few tensof-MeV range, with a sharply-pulsed timing 

structure that is beneficial for background 

rejection. In 2017, Akimov et al. observed this 

process with 6.7sigma confidence by using 

a comparatively tiny, 14-6 kg sodium-doped 

CsI scintillator exposed to neutrinos from the 

spallation neutron facility. This measurement 

makes use of the distinct time structure of the 

neutrino beam from the SNS which enhances 

the background rejection in the signal. The 

discovery places tight bounds on exotic interactions beyond the Standard Model of Particle Physics.

FIGURE A. Left: Coherent scattering process of neutrinos off nuclei. 

Right: Assembly of the CsI[Na] detector at the SNS. The CsI[Na] detector is the world’s smallest working neutrino detector at 14.6 kg and 

has been operational at the SNS since July 2015. The CsI[Na] crystal 

is shielded with low background materials and instrumented with a 

super-bialkali photo-multiplier tube 

Source: COHERENT Collaboration
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as well as the planned nEDM project define the state of 

the art in their respective fields. Their proximity and 

co-location on the ORNL campus have created a new 

and growing user community for neutrino science. 

The fundamental physics program with neutrons 

and neutrinos is carried out by multi-institutional 

collaboration including other national laboratories, 

universities and research institutes, and has created a 

fertile environment for multi-disciplinary R&D and 

discovery science. The neutron and neutrino programs 

at ORNL are examples of truly synergistic programs 

that leverage BES facilities across the portfolio of activities in the Office of Science from experiments in High 

Energy Physics (HEP) and Nuclear Physics (NP) to instrumentation R&D for nuclear non-proliferation. 

With a potential upgrade to HFIR or a new 

research reactor facility, there is an opportunity to establish an experimental laboratory with a well-planned 

research program. We can move from being opportunistic to a more strategic plan for fundamental physics 

that includes discovery science, development of novel 

instrumentation and detectors, and workforce development and training.

Dedicated laboratory space for neutrino experiments, detector R&D, and fundamental physics at a 

reactor or spallation source are at a critical shortage 

and represent the most urgent needs to advance the 

field. A dedicated fundamental physics laboratory at 

an upgraded HFIR or a new reactor could have a transformative impact on the field of fundamental physics 

and the synergistic and collaborative effort of scientists 

within the Office of Science. ■
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4. Isotope Production

4a. Isotope Production at HFIR

Since the advent of the nuclear era, the use of radioactive isotopes has brought tremendous benefits to 

society in a multitude of ways, from expanding our 

knowledge of the world around us to improving the 

lives of millions of people through medical diagnoses 

and treatment. No fewer than 16 Nobel prizes have 

been awarded in the fields of nuclear chemistry and 

applied radiochemistry. The use of radioactive isotopes 

has allowed researchers to answer a myriad of questions about wide-ranging subjects from plant metabolism and ocean currents to the behaviors of ancient 

peoples and indigenous trade routes. Radioactivity 

has brought immeasurable benefits to industry as well, 

allowing the analysis of material densities, the inspection of critical systems, and product sterilization, while 

radioactive tracers have been integral in oil and gas 

exploration and monitoring fluid flows and detecting 

leaks in remote and inaccessible networks. 

In healthcare, radioactivity and radioisotopes 

have been instrumental in diagnosing and treating 

disease, improving the lives of millions of people. Ever 

since 131I became the first radioisotope approved by 

the U.S. FDA in 1951 for treatment of thyroid cancer, 

researchers and clinicians have employed numerous 

additional radioisotopes for both diagnostic and therapeutic applications. Technetium-99m is used in over 16 

million people per year in the U.S. as an imaging agent 

for numerous applications, with the most frequent use 

being heart perfusion studies and bone cancer diagnoses. Recently approved by the FDA, 177Lu is showing 

tremendous success in markedly improving progression-free survival in patients with metastatic gastroenteropancreatic neuroendocrine tumors, and is showing 

great promise in clinical trials in the treatment of 

patients with prostate cancer. 

The vast majority of radioactive isotopes used in 

medicine, industry, and research are produced by irradiating materials (targets) with neutrons in nuclear 

reactors. While numerous strategies are employed, the 

radioactive isotopes of interest are all created by atoms 

in the target capturing one or more neutrons. Our 

ability to generate radioactive materials in this way is 

primarily determined by two factors: the number of 

neutrons per second that impinge upon the target (the 

neutron flux density or n/cm2·s), and the kinetic energy 

of the neutrons that interact with the target. Hence, 

while power reactors generate an order of magnitude 

or more neutrons per second than isotope production 

reactors, their neutron flux density is several orders 

of magnitude below facilities designed to produce isotopes. Moreover, because the probability of capturing a 

neutron increases dramatically as the kinetic energy of 

the neutron decreases, isotope production reactors are 

designed to have a high neutron flux density of thermal neutrons or neutrons with a most probable kinetic 

energy of 0.025 eV. Because the High Flux Isotope 

Reactor provides the highest thermal neutron flux 

density (2.5 x 1015 n/cm2·s) of any reactor operating 

today in the western world, it plays a unique role in 

producing critical radioactive isotopes for industry, 

medicine, and research.

Californium-252 is used by industry as a small, 

robust, self-powered, economical source of neutrons for 

a wide range of applications including energy, homeland 

security, and agriculture. It has a half-life of 2.6 years, and 

1 milligram of this isotope emits over 1 billion neutrons 

per second. The isotope is used by the nuclear energy 

industry to confirm the fissionable content of nuclear fuel 

rods and for determining the fissile content of nuclear 

waste. In addition, 252Cf provides the source of neutrons 

needed to start up nuclear reactors, including those on 

nuclear powered submarines. The isotope is used by the 

mining and minerals industry to measure the amount of 

sulfur in coal, the ash and stone content of cement, and 

for oil well logging. It is also used as a calibration source 

to test the sensitivity of radiation detection equipment 

at ports of entry. The annual global demand for 252Cf for 

these and other applications ranges from 20 to 40 milligrams per year and the HFIR is the only reactor outside of 

Russia capable of producing this isotope. The importance 

of the high thermal neutron flux at HFIR for producing an 

isotope like 252Cf that requires multiple neutron captures is 

illustrated in Figure 4a.1. Aside from HFIR and the SM-3 

reactor in Russia, the other research/isotope production 

reactors in the world have a peak thermal flux around 1 

x 1014 n/cm2·s. As shown in Figure 4a.1, 252Cf cannot be 

produced at these lower thermal fluxes. Without HFIR, 

the western world would not have an independent, reliable 

supply of this critical isotope. 
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42 The Scientific Case

Nickel-63 is a low-energy beta emitter with a long 

half-life (100 y) that is available in a convenient physical 

form that enables repeatable, low-waste manufacturing 

of the radioactive source. Gas chromatography systems 

that utilize 63Ni electron capture detectors are up to 

1,000 times more sensitive than gas chromatography 

systems that use either flame ionization or thermal 

conductivity detectors. The applications of these systems include food and pesticide analysis, forensic 

toxicology, controlled substances identification, and 

environmental monitoring for greenhouse gasses. In 

addition, 63Ni sources are used as the electron source 

in field deployable ion mobility spectrometry systems. 

These systems are extensively deployed by the Department of Homeland Security and the U.S. military for 

detecting trace amounts of explosives, narcotics, chemical warfare agents, and industrial chemicals in the 

field. As with 252Cf, this critical isotope requires a high 

thermal neutron flux for its production and is only 

available from HFIR and the SM-3 reactor in Russia. 

Barium-133 has a half-life of 10.5 y and emits a 

large number of gamma rays (ranging in energy from 

30 to 400 keV) in its beta decay to stable 133Cs. This 

multi-line gamma ray source is used to simultaneously 

monitor the oil, gas, and water flow rates in a system 

without any phase separation. Multi-phase flow meters 

based on this radioactive source provide detailed, realtime flow data to the oil and gas industry. Like 63Ni and 

252Cf, 133Ba is only produced at the high-flux reactors 

HFIR and SM-3. Industry reported to the committee 

that demand for both 63Ni and 133Ba exceeds the current 

production capacity of these two high-flux reactors. 

Targeted radiotherapies based on alpha emitters 

are a promising new cancer therapy. Because of their 

short range in tissue, targeted α-radiotherapy (TAT) 

agents have great potential for application to small, disseminated tumors and micro metastases and treatment 

of hematological malignancies consisting of individual, 

circulating neoplastic cells. Because the energy deposited by the α particle in a cell is approximately four 

orders of magnitude greater than the energy deposited 

by a β- particle, the relative biological effectiveness of 

α particles is much greater than that of β- particles. 

In addition, the biological effectiveness of α particles 

does not depend upon hypoxia or cell cycle phase. As a 

result, far lower amounts of radioactivity are required 

to achieve the desired therapeutic outcome, which can 

be critical in those cases when the number of receptor 

sites is limited. The first TAT agent approved for clinical use by the U.S. FDA (May, 2013) is the in vivo α-generator radionuclide 223Ra, which has a half-life of 11.4 

d. In contrast to many single alpha-emitting isotopes, 

223Ra dramatically increases the therapeutic efficacy 

of endoradiotherapy as it emits four α particles in its 

decay chain, and the half-life of 223Ra is long enough 

for the isotope to accumulate at the target site. 223Ra-dichloride1 is a targeted therapy for symptomatic bone 

metastases in prostate cancer, a common cause of morbidity and mortality in patients with metastatic disease. 

In metastatic castrate resistant prostate cancer patients, 

223Ra therapy improves the overall survival with a 30% 

reduction in mortality. While still under active investigation, the utility of 223Ra therapy in bone metastatic disease in breast cancer and renal cell carcinoma 

appears very promising. The sole source of the parent 

radioisotope (227Ac) used by Bayer to provide 223Ra is 

from irradiation of 226Ra targets at the HFIR followed 

by processing of this highly radioactive target material at a radioisotope processing facility at Oak Ridge 

National Laboratory. Both the high thermal neutron 

flux of HFIR and the close proximity of specialized 

radiochemical processing facilities are required to meet 

FIGURE 4a.1. Cf-252 production from a 7 gram 

mixed curium target at different thermal 

neutron fluxes

Source: Dr. Marc Garland, DOE Isotope Program
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The Scientific Case 43

the current and emerging demand for this important 

medical isotope. 

In addition to the aforementioned isotopes, a highflux reactor will be required to produce new, emerging 

life-saving radioactive isotopes. For example, industry 

is currently evaluating the use of 227Th for the TAT 

treatment of multiple cancers including breast, prostate, mesothelin, and lymphoma. The advantage of 

using 227Th is that it can be chemically conjugated to 

established targeting vectors like HER2, PSMA, MSLN 

and CD22. Again, only HFIR can provide the amount 

of this isotope that will be required when one or more 

of these TAT agents is employed in the clinic. 

Another example is the use of 188Re as the therapeutic agent in theranostics based upon 99mTc and 

radioactive rhenium. A driving force behind the clinical 

application of radiopharmaceuticals in precision medicine is the ability to selectively direct—or target—radiolabeled molecules to active sites of human disease. In 

order to effectively accomplish this goal, both a diagnostic (99mTc) and therapeutic (188Re) radionuclide must be 

strategically attached to a biological targeting vector for 

delivery to a disease biomarker (e.g., a cancer-specific 

cellular receptor). Theranostic radiopharmaceuticals 

offer the unique opportunity to use information derived 

from patient specific diagnostic imaging studies to 

determine the therapy approach with respect to drug 

pharmacokinetics, biomarker density, and patient dosimetry. Because rhenium’s chemistry is nearly identical 

to that of technetium, the availability of this therapeutic 

isotope would build on the more than thirty approved 

99mTc imaging agents already approved by the U.S. FDA. 

As can be seen in Figure 4a.2, the high thermal flux of 

HFIR is required to produce any significant quantity of 

the parent isotope 188W from which 188Re can be generated in the clinic. ■

4b. Heavy Element Chemistry

The heaviest elements on the periodic table are the 

ones that we know the least about. The BES program 

on Heavy Element Chemistry (HEC) supports basic 

research on the fundamental chemistry of these elements, which are called actinide and transactinide 

elements. The goal of this research program is to 

understand the underlying chemical and physical principles that determine their behavior. The actinide series 

of elements are characterized as those elements with 

electrons in the 5f orbitals, which begins with thorium 

(atomic number of 90), and ends with lawrencium (atomic number 103) and a full inner 5f electron shell. Within this series of elements, thorium and uranium can 

be found in nature, but the remaining twelve actinides 

are not naturally occurring. The term “transactinides” 

is used to refer to all elements beyond the actinides—

that is, those elements with atomic numbers larger than 

103. According to atomic relativistic calculations, the 

filling of the 6d electron shell takes place in the first 

nine of the transactinide elements (those with atomic 

numbers 104 through 112). Consequently, they are 

currently placed as a 6d transition series under the 5d 

transition series. None of the transactinide elements 

are naturally occurring. 

Understanding the role of 5f electrons is an important frontier for chemists, as this knowledge is essential 

FIGURE 4a.2. A comparison of W-188 

production at HFIR to what can be 

achieved at other research/isotope production reactors

Source: Dr. Dave Robertson, University of Missouri 

Research Reactor
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to fully grasp the fundamental properties of all matter, 

as exemplified by the periodic table. This includes fundamental insights into bonding, which drives physical 

properties and reactivity of the heavy elements, across 

multiple length scales. For example, the 5f orbitals participate in the band structure of metallic and ceramic 

materials that contain the actinides, and the nature of 

this participation down the actinide series is an area 

of active research. Theory and experiment show that 5f 

orbitals participate significantly in molecular actinide 

compounds (e.g., compounds required for advanced 

nuclear energy systems). Resolving the role of the 

f-electrons is one of the three grand challenges identified in the report Basic Research Needs for Advanced 

Nuclear Energy Systems (2006) and echoed in the report 

from the Basic Energy Sciences Advisory Committee, 

Science for Energy Technology: Strengthening the Link 

between Basic Research and Industry (2010).

The unique molecular bonding of the heavy elements is explored using theory and experiment to elucidate electronic and molecular structure, along with 

reaction thermodynamics. Emphasis is placed on:

1. The chemical and physical properties of these elements to determine their bonding and reactivity in 

solution, at the interface, and in the solid-state

2. The fundamental transactinide chemical properties; and 

3. The overarching goal of resolving the f-electron 

challenge. (The f-electron challenge refers to the 

inadequacy of current electronic structure methods to 

accurately describe the behavior of f-electrons, in particular: strong correlation, spin-orbit coupling, multiplet complexity, and associated relativistic effects.) 

Because much of this research is experimental, it 

requires manipulation of pico- to milligram quantities 

of plutonium and trans-plutonium isotopes, which are 

generated for researchers by irradiation of targets of 

actinide elements in HFIR. Initial production at the 

start of the HFIR program involved irradiating 239Pu 

fuel to generate important activation products such as 

244Cm. Separations of elemental fractions of these isotopes were then completed. These separated fractions of 

trans-plutonium elements were then fabricated into new 

targets for subsequent irradiations to produce trans-curium activation products, as shown in Figure 4b.1.

This process of activating 239Pu, separating the 

heavier elements that are created, and re-irradiating them to produce even heavier isotopes is the 

framework by which trans-plutonium elements are 

generated. These elements are essential to the researchers in the BES heavy element chemistry program. 

FIGURE 4b.1. Producing Trans-curium Heavy Isotopes

Source: Oak Ridge National Laboratory
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Driving the activation of plutonium and curium isotopes to produce milligram quantities of the heavy 

elements requires larger neutron flux densities than 

that obtained by the fleet of U.S. commercial reactors. 

As illustrated in Figure 4b.2, the unique thermal neutron flux of (2.5 x 1015) of HFIR is required to produce 

measurable quantities of very rare trans-plutonium and 

trans-curium elements. The isotopes of these elements 

have relatively short half-lives, and therefore must be 

continuously produced for the research community. 

Because multiple neutron captures are required to 

produce these heavy elements, they cannot be created 

at the lower neutron fluxes available at other research/

isotope reactors.

Today, HFIR produces these isotopes in measurable 

quantities, as shown by Figure 4b.3. Over the last several years, heavy elements produced at HFIR were used 

in international collaborations to discover elements 

114, 115, 117, and 118, and HFIR is currently providing 

targets of 244Pu for the search for element 119.

Radiochemical Engineering Research Center (REDC) 

In addition to irradiation in HFIR, production of these 

isotopes requires the ability to chemically separate the 

irradiated materials. These separations are done in 

the REDC. The REDC is a Category II multipurpose 

radiochemical processing facility based around the use 

of heavily shielded hot cells and is located immediately 

adjacent to HFIR. The historical mission of the REDC 

has been to provide Cf, Bk, Es, and Fm for research 

purposes and industrial uses. Post-irradiation separations of elements and the preparation of targets for irradiation are completed in hot cells in the REDC, with 

the heaviest isotope typically produced being 257Fm. 

After separations and purification, actinide products 

are packaged and shipped to the research community 

as well as other users. 

Heavy element processing campaigns are conducted approximately every 24 months, and BES staff 

canvass investigators in advance to identify needs for 

specific elements and isotopes for upcoming processing 

campaigns. The co-location of REDC with the world’s 

highest thermal neutron flux reactor is critical for supplying researchers with the heaviest elements.

The BES program on HEC is the only source of 

funding for the discovery science associated with the 

actinide and trans-actinide elements. New knowledge 

generated by the HEC is fundamental to our understanding of matter and the periodic table, and the role of the 

5f electrons in physical properties and reactivity across 

multiple length scales. This program requires the use of 

small quantities of these elements, which must be produced through neutron activation using the neutron flux 

density of HFIR and separated for use in the REDC. ■

FIGURE 4b.2. Production of Es-254 at HFIR compared to the 

production that can be achieved with typical research and 

test reactors

Source: Dr. Marc Garland, DOE Isotope Program

FIGURE 4b.3.

Isotope 

Production 

Quantities

Source: Felker, 

ORNL, 2014
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5. Materials Irradiation

5a. Materials Irradiation — General

Isotope production and materials irradiation testing in 

HFIR are very similar activities and use many of the 

same or similar experimental positions. The primary 

irradiation position with the highest neutron flux is the 

HFIR central flux trap. There are 31 target positions 

in the flux trap utilized for radioisotope production. 

Six positions in the outer area of the target basket are 

designated as Peripheral Target Positions (PTP) and 

shown in Figure 5a.1. The PTP has the highest fast-neutron flux available in the reactor (~1.2 x 1015). A high 

fast neutron (> 1 Mev) flux is important for reactor 

materials irradiation testing because it accelerates the 

damage (as compared to lower power density reactors such as nuclear power plants) caused by the high 

energy neutrons. 

HFIR produces the highest displacements per atom 

(dpa) of any operating thermal reactor today. This 

accelerated damage mechanism enables researchers 

to see results much faster, or to partially mimic the 

neutron spectrum of a fast reactor (e.g. liquid sodium 

or gas cooled reactors) or the radiation environment 

of a fusion reactor. It should be noted that the planned 

fast neutron Versatile Test Reactor (VTR) will have a 

higher dpa but will not be designed to replace HFIR or 

any thermal reactor that produces radioisotopes or performs nuclear materials testing for light water reactors 

(LWR). In addition, high powered pulsed or spallation 

neutron sources are unable to simulate the energy distribution and radiation fields found within operating 

reactors.

Flux Trap capsules (PTP and central facilities) can 

be full-length or a series of shorter capsules. These 

full-length or short capsules are static and only removed when HFIR is shutdown. The short capsules are 

stacked inside of a holder tube for easy handling, and 

HFIR coolant flow through this holder tube is critical 

to heat removal from the capsule experiments. Each 

experiment is designed to have neutron absorption 

characteristics equivalent to 200 g of aluminum and 35 

g of stainless steel. These limits are established to minimize perturbation of the existing neutron flux in the 

target and a reduction in the fuel cycle length. 

FIGURE 5a.1.

Es-254 Production from 

7g Mixed Cm Target

Source: Oak Ridge National 

Laboratory

Pneumatic Facility NAA

Hydraulic Facility

Available Positions

Neutron Scattering Beamlines 

(available through ORNL Neutron 

Scattering User Facility)
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As shown in Figure 5a.2, PTP capsules are typically 

2.625 inches in length and are stacked in a secondary 

encapsulation for handling. The capsules have relatively 

limited internal volume to accommodate materials 

and fuels irradiation samples. There are currently six 

options for short capsule designs that are available with 

internal diameters less than 0.4 inch. All of these capsules are fabricated from aluminum with one capsule 

design perforated with 82 small holes to allow primary 

coolant flow to cool the internal sample.

To accommodate larger volumes for experiments, 

there are eight large and four small diameter positions 

in the removable beryllium (RB) reflector area. The 

large locations may have instrumented or non-instrumented experiments. Instrumented experiments may 

utilize thermocouples to monitor temperatures, and 

flow cooling or sweep gases as well as resistance heaters 

through the experiment to control temperature. Experiments in these locations may use neutron shields to 

tailor the spectrum for materials testing, but the quantity of neutron absorbing material is limited due to the 

proximity to the reactor fuel region and the potential 

impact to fuel cycle length and fuel element power 

distribution. Additionally, unshielded experiments 

in these positions are ideal for studying combination 

effects of fast neutron damage coupled with thermal 

neutron generation of helium (through transmutation) 

in certain reactor materials.

The HFIR thermal neutron flux levels in the flux 

trap at 85 MW are too high for most nuclear fuel 

designs. However, nuclear fuels and materials are routinely tested in the various beryllium reflector locations. 

The large Vertical Experiment Facility (VXF) positions 

are the furthest from the reactor fuel with thermal flux 

levels lower by a factor of five. The addition of thermal 

neutron absorbers can further reduce those levels as 

needed. The Large Removable Beryllium Facilities 

(RB*) directly adjacent to the reactor core may have 

the thermal neutron flux reduced by the use of Eu2O3

shields for nuclear fuels testing, but this is generally not 

required for non-fuel materials testing. Various fast and 

thermal neutron flux levels in HFIR experimental positions are given in Table 5a.1.

HFIR is currently supporting the DOE Advanced 

Fuels Campaign with a primary focus on accident tolerant fuels and clad materials. Irradiation of Fe-Cr-Al 

alloys, materials that could potentially replace traditional zirconium-based cladding materials, has been 

performed recently in the HFIR flux trap to evaluate 

the radiation tolerance of the material. To support more 

experiment sample throughput and reduce the time and 

cost of irradiation experimental programs, ORNL has 

FIGURE 5a.2.

Target Basket and Example 

PTP Target

Source: Oak Ridge National 

Laboratory
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begun a new program to test nuclear materials. Rather 

than traditional nuclear fuel testing utilizing full-size 

pellets, the new approach uses much smaller samples 

(i.e. miniature) with more samples simultaneously 

irradiated to explore many more variations in fuel and 

materials design in one experimental campaign.

Various advanced fuel forms are currently being 

tested or planned for irradiation in the MiniFuel test 

facility. These materials include uranium nitride (UN) 

kernels, tristructural-isotropic (TRISO) UN particles, 

and fully ceramic microencapsulated (FCM) pellets. 

The facility allows concurrent and accelerated separate-effects irradiation testing of small fuel samples. 

These facilities may reduce the cost and time to 

perform nuclear fuel and material testing, but also 

compensate for the lack of irradiation test reactor 

capacity in the world today by increasing experimental 

throughput in the limited HFIR test positions. ■

TABLE 5a.1

Irradiation Test Parameters in HFIR Experiment Positions

PARAMETER FLUX TRAP RB* RB* SHIELDED SMALL VXF LARGE VXF

Fast Flux, E > 0.1 MeV (1014 n/cm2 sec) 11 5.3 4.9 0.5 0.13

Thermal Flux (1014 n/cm2 sec) 25 11 0.19 7.5 4.3

Peak displacements per atom (dpa) per cycle 1.8 0.67 0.58

FIGURE 5a.3. HFIR MiniFuel Experiment System

Source: Petrie, Christian M., et al. “Separate effects irradiation testing of miniature fuel specimens.” Journal of Nuclear Materials 526 (2019): 151783.

5b. Fusion Materials Irradiation

The performance degradation of structural steels in 

nuclear environments may limit the extended operation of current generation light-water nuclear reactors 

and restrict the design of advanced fission and fusion 

reactors.1,2,3,4,5,6,7,8 This neutron induced degradation 

to the physical and mechanical properties was first 

recognized by Eugene Wigner during the design of the 

Hanford production reactors during the Manhattan 

project. 9 The underlying physics controlling neutron 

radiation damage, and its consequence to physical and 

material property degradation, is inherently hierarchical and multiscale. Pertinent length and time scales 

controlling radiation effects range from neutron collision-reactions on the scale of the nucleus to the size 

and service lifetimes of structural components, spanning factors in excess of 1014 (length) and 1022 (time).10,11
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Correspondingly, a valuable, albeit often underappreciated, component of the scientific contribution 

of reactor based neutron sources is the irradiation of 

materials to support the fundamental investigation 

of radiation degradation mechanisms and to spur the 

development of advanced fuels and structural materials technology for future fission and fusion reactors. 

As pointed out in the November 2019 presentation of 

Dr. Kurtz, “a high-performance, steady-state mixed 

spectrum nuclear reactor is an indispensable tool for 

fusion materials science research.12 In particular, the 

HFIR provides a high dose capability associated with a 

high fast flux that enables material irradiations to produce more than 10 displacements per atom (dpa) per 

year in steels. This flux and damage production rate is 

currently the highest in the Western world, and enables 

scientific investigation into a number of challenging 

radiation damage phenomena, including questions 

related to:

• deciphering the irradiation and material variables 

controlling the nucleation onset of void swelling;

• developing predictive capability of phase transformations in complex alloys during irradiation; and

• determining the extent to which property degradation saturates under high dose neutron irradiation13

The study of radiation damage in fusion materials 

shares many commonalities with the degradation of 

fission structural materials in the neutron irradiation 

environment. As pointed out in the November 2019 

presentation of Dr. Back,14 this leads to a complementarity amongst the available research and test reactors 

within the U.S. (see Figure 5b.1) Smaller University 

based research reactors, like the MIT research reactor (MITR), provide lower neutron fluxes that can be 

appropriate for fundamental radiation damage studies 

and initial feasibility testing of novel materials. 

Likewise, the Missouri University Research Reactor 

(MURR) has a high thermal neutron flux that can be 

used for the neutron transmutation required to create 

special use materials, in addition to radioactive isotopes for medical and industrial applications. Along 

the upturn of the reactor power arrow in Figure 5b.1 

are the National Institute of Standards (NIST) Center 

for Neutron Research (CNR, although this reactor is 

labeled NBSR, National Bureau of Standards Reactor) 

that provides state of the art facilities for neutron scattering and non-destructive characterization. HFIR has 

a reactor power level and multi-program mission that 

enables it:

• the performance of basic research into neutron-induced materials degradation; 

• the critically important integration of basic science 

with engineering that is required to develop materials and technology for advanced fission and 

fusion energy sources.15,16

While common degradation mechanisms exist 

for fission and fusion materials, a confounding factor 

for fusion structural materials arises from the very 

high energy of the neutron spectrum, which peaks at 

14.1 MeV. High neutron fluxes at high energy (above 

2-3 MeV) can produce significant neutron induced 

transmutation reactions, most notably (n,p) and (n,α) 

reactions with neutron energy thresholds above 1 MeV. 

The H and He products, in addition to the transmuted 

elements, can alter microstructural evolution from 

the simultaneous radiation damage. In the absence of 

a high flux, volumetric source of 14 MeV neutrons to 

provide a representative fusion materials testing environment, the combination of the high thermal and 

fast neutron flux at HFIR provides a unique and indispensible role in both the U.S. and International fusion 

materials research programs. HFIR has been used for 

fusion materials irradiations in a long-standing U.S.-

Japan International collaboration, and more recently as 

part of a U.S.-EU collaboration. These collaborations 

have assisted with the qualification of the stainless steel 

vacuum vessel for ITER, and provide critically important neutron irradiations for developing materials that 

are capable of withstanding the harsh fusion neutron 

environment anticipated in a fusion demonstration 

reactor or pilot plant.

In fact, HFIR is the only mixed spectrum reactor 

in the world that has completed materials irradiations 

to doses exceeding 100 dpa.17 The high thermal neutron 

flux in HFIR has enabled fusion materials research 

to mimic certain aspects of H and He transmutation 

effects through the use of isotopic tailoring experiments (e.g., Ni-58, B-10, or Fe-54) using isotopes that 

undergo such transmutations either with thermal neutrons or a lower threshold energy, or through in-pile 

helium injection that takes advantage of a two step 

nuclear reaction in Ni from thermal neutrons. 

Thus, HFIR currently represents a unique and central facility for conducting fusion material research. 
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Existing and future fast spectrum reactors (e.g., BOR60 in Russia, or the VTR in planning and design in the 

U.S.) can provide high atomic displacement damage 

irradiations of fusion structural materials, but lack 

the ability to simultaneously study the nuclear transmutation effects since high thermal neutron fluxes are 

required to take advantage of isotopic tailoring. 

The research production of the fusion materials 

community with HFIR has been extensive, and indeed, 

historically, the number of peer-reviewed journal 

papers emanating from the HFIR in-core neutron 

materials damage studies has rivaled that of the neutron scattering community. As noted by the Kurtz 

presentation at the November meeting, HFIR has been 

a versatile and workhorse materials irradiation facility 

heavily used for fusion materials research, and contributes to U.S. leadership in the worldwide fusion materials research community.18

Finally, it is worth noting that a subset of the committee visited the Jules Horowitz Reactor (JHR), currently under construction at CEA-Cadarache. When 

completed and operational in 2025, the JHR will provide an alternative mixed spectrum reactor specifically 

designed to provide a high thermal and fast neutron 

flux that can provide in excess of 10 dpa per year, with 

the ability to utilize isotopic tailoring or in pile helium 

injection similar to HFIR. The JHR reactor costs in 

excess of 2.4 billion euros, and will also likely take a 

decade or more to demonstrate the diverse and extensive materials irradiation capabilities similar to what 

HFIR currently offers. ■

FIGURE 5b.1. Complementarity of research 

reactors based on the power output. The MITR, 

HFIR, and ATR reactors shown above the arrow 

are used for neutron irradiations to study 

materials degradation, while the MURR reactor 

provides irradiation to create special materials. 

The larger reactors also provide non-destructive characterization.

Source: C.A. Back, “Materials Irradiation,”, presented to 

BESAC Subcommittee on HFIR Long Term Strategy, Nov. 

15, 2019.
HEU-LEU CONVERSION

A button of uranium silicide (U3Si2) alloy prior to grinding to powder for use in Low Enriched Uranium (LEU) fuel. 

Uranium silicide is the fuel form being qualified for conversion of HFIR to LEU fuel.

Image credit: PNNL. Provided by C.A. Lavender, personal communication, July 23. 2020
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52 HEU-LEU Conversion

Preservation of Reactor Capability with Low 

Enriched Uranium Fuel

Since 1978, the U.S. government has worked with civilian research reactors and medical isotope production 

facilities domestically and internationally to minimize, 

and, when possible, eliminate weapons-usable nuclear 

material around the world.

As indicated in Figure HL.1, there has been a great 

deal of success converting reactors around the world, 

including 24 reactors with experimental peak thermal fluxes above E14 n/cm2/s. A total of 71 reactors 

converted from Highly Enriched Uranium (HEU) fuel 

to Low Enriched Uranium (LEU) fuel in the period 

1978-2019, and an additional 31 reactors that used HEU 

fuel have been confirmed permanently shutdown.

Though the global community has converted 24 

reactors with high flux, unique challenges remain for 

a group of highly optimized HEU reactors in the U.S. 

and Europe. The U.S. High Performance Research 

Reactors (USHPRR) and European High Flux Reactors 

(EUHFR) are each quite distinct, and have less fuel 

assembly design and/or grid-plate flexibility than prior 

conversions; high power density in the fuel in order to 

provide intense experimental fluxes; and high burnup 

in those reactors that reload fuel in order to minimize 

fuel costs. Appendix A2 describes many of the details 

of the efforts to convert the USHPRR and EUHFR reactors. This section summarizes aspects of that effort that 

are most relevant to the capabilities of HFIR, whether 

as a HFIR LEU conversion or a refurbished HFIR with 

LEU fuel.

It must be emphasized that to preserve capability, 

the Conversion Program addresses actual performance 

metrics rather than simple flux values. Such metrics 

are quite reactor-specific, but might include: isotope 

production rates; cold-source brightness; experiment 

temperature (gamma heating); silicon doping homogeneity; etc. Upon conversion, some specific performance 

metrics may decrease more than others, but the overall 

capability is preserved to the maximum degree. In 

a number of cases such as the Rhode Island Nuclear 

Science Center reactor or the VVR-K reactor in 

Almaty, Kazakhstan, the more compact cores possible 

with an LEU fuel that has U-235 density higher than 

the prior HEU fuel has allowed significant increases 

in flux intensity and associated mission capabilities. 

FIGURE HL.1. Timeline of the Global Reactor Conversions, 1978–2019

U3Si2 and TRIGA FLIP fuels were key higher-density fuels to allow conversion from HEU to LEU

GTRI: Global Threat Reduction Initiative organization within NNSA 

M3: Material Management and Minimization organization within NNSA

NNSA: National Nuclear Security Administration

Source: John Stevens, Argonne National Laboratory
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HEU-LEU Conversion 53

In other cases, such as the RPI reactor in Portugal, the 

flux in a specific energy range for a specific beam port 

was increased as part of conversion, with less emphasis 

on less utilized in-core irradiation sites.

The reactor conversions have been possible due to 

the development, qualification, and creative application 

of LEU fuels with uranium density higher than the 

HEU fuels already in use. The change in enrichment 

from 93% HEU to 19.75% High Assay LEU (HALEU) 

implies the need to increase uranium density in the 

same core volume by a factor of 4.7. However, the additional U-238 in LEU absorbs some neutrons parasitically, so a density increase greater than the factor of 4.7 

will be required to preserve reactivity worth of the core 

volume if nothing else about the system is changed. 

Fortunately, fuel reactivity is only one factor of effective 

operation. Since the reactivity worth of fuel and experimental performance are both highly dependent on 

neutron spectrum, changes to fuel geometry, reflectors, 

and/or multi-cycle fuel utilization strategy can mitigate 

the effect of the U-238 absorption in order to preserve 

mission capability. Changes to fuel layout on the grid 

plate and/or operating power of the reactor can also be 

used to preserve mission capability after conversion. 

Modernized safety bases that employ high-fidelity 

modeling for neutronics and heat removal analyses 

with a rigorous grounding in phenomenological safety 

basis rather than antiquated “conservatisms” can 

enable core operation at higher local power densities to 

facilitate compact cores and higher neutron fluxes.

In 2005, the U.S. organized the effort to convert 

the five USHPRR including HFIR into a coordinated 

subprogram. In 2008, the U.S. and the EUHFR formed 

a similar coordinated effort. The primary focus of the 

high-performance reactor groups was development and 

qualification of an LEU fuel that could be fabricated 

for use in the distinct systems. Uranium-molybdenum 

alloy fuel (UMo) was selected for the combination of 

high density and effective retention of fission gas upon 

irradiation. However, significant research and development was necessary to address an unstable interaction 

between UMo alloy and aluminum and to develop a 

sustainable fabrication capability for the UMo fuel.

The USHPRR team pursued a revolutionary monolithic fuel, in which a diffusion barrier is applied to 

a U-10Mo (where 10 indicates 10% Mo in the alloy) 

foil and then clad in aluminum using Hot Isostatic 

Pressing (HIP) rather than typical roll bonding. The 

EUHFR team pursued an evolutionary dispersion fuel 

with U-7Mo powder dispersed in an aluminum matrix 

and then clad by aluminum using typical rolling 

methods of plate-type fuel. 

In response to the challenges encountered for both 

monolithic and dispersion UMo fuel systems, in 2012-

2013 the NNSA Reactor Conversion fuel development 

and qualification efforts were significantly restructured 

for both the USHPRR and EUHFR. The European collaborators also restructured their approach. Both teams 

rebaselined the plans for the reactor conversions.

The USHPRR and EUHFR teams learned from 

each other regarding the UMo fuel systems. The 

EUHFR team adopted the diffusion barrier and heat 

treatment approaches that had proven vital for excellent 

irradiation performance of the U-10Mo monolithic 

fuel. The USHPRR team adopted inclusion of a commercial fuel fabricator and pilot-line-production 

that had proven predictable and effective for EUHFR 

experiment fabrication. Both teams slowed the pace of 

irradiation experiments to assure that maximum data 

value would be generated by each experiment, in terms 

of both fabrication data and irradiation performance 

data. In addition, both teams have had independent 

expert reviews to assure appropriate creativity, transparency, and rigor.

Selection of U3Si2 for HFIR Application, and the 

Path to Conversion

The independent expert review of the EUHFR plan in 

2015 suggested that the EUHFR pursue U3Si2 dispersion 

fuel as a backup to their work on U-7Mo dispersion. 

SCK CEN reconsidered their BR2 fuel element 

plate thickness and radius constraints, and determined 

that a modified geometry would allow preservation 

of mission capabilities with an LEU 5.3 g/cm3 U3Si2 

dispersion fuel incorporating gadolinium as an integral 

burnable absorber.

Since the promising results for LEU U3Si2 application to a redesigned BR2 fuel element, the conversion 

design teams for HFIR and the RHF reactor at ILL in 

France have both reconsidered geometric constraints 

and have developed design candidates for variants of 

U3Si2 details that would preserve mission capability.

In the case of HFIR, U3Si2 is not the backup solution, but was established as the baseline solution in 

2019. The unique fuel shape of HFIR will require 

fabrication capabilities quite distinct from the baseline U-10Mo monolithic plan for the other USHPRR. 

The U3Si2 dispersion fuel system will allow the HFIR-
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54 HEU-LEU Conversion

specific characteristics of the current HFIR design to 

be leveraged for the LEU design (i.e., fuel zone shaped 

rather than uniform inside the cladding and burnable 

poison distributed adjacent to the fuel). The U-10Mo 

fuel system will be a backup for HFIR conversion.

The HFIR design calculations for LEU conversion 

have included detailed simulation of a wide variety of 

metrics that represent the experimental capabilities of 

HFIR over the course of each operating cycle, including cold-source flux detail (intensity and cold-to-total 

flux ratio), 252Cf production rate, flux trap fast flux in 

material irradiation locations, flux trap fast-to-total 

flux ratio, reflector fast flux in material irradiation 

locations, and reflector fast-to-total flux ratio.1,2 In their 

presentation to this BESAC Subcommittee, the HFIR 

Conversion Team reported preservation of all missions, 

as summarized on Figure HL.2.

It is important to remember that no successful 

experimental results have been published for U3Si2 

at the challenging irradiation conditions required by 

BR2, RHF, and HFIR. The JHR confidence in EVITA 

results that have not been published is encouraging, 

but not a basis for qualification at any other reactor. 

Furthermore, the EVITA tests did not include integral 

burnable absorber in the fuel meat.

Thus, both the HERACLES Consortium and the 

HFIR team within USHPRR have initiated experiment 

campaigns to qualify U3Si2 with the appropriate fuel 

meat characteristics (density, specific integral burnable 

absorber if present) for the required operating conditions. The HFIR U3Si2 dispersion fuel qualification plan 

will move through a series of tests at BR2 and ATR to 

address the distinct fuel configuration and irradiation 

conditions of the inner and outer cores of HFIR fuel. 

The HFIR qualification may be adapted depending 

on the path forward selected by BR2 and RHF, to the 

degree that U3Si2 experimental synergies might accelerate the three conversions.

Progress on High Flux Reactor Conversion since 

2016 NAS and 2018 APS Studies

The 2016 NAS “Reducing the Use of Highly Enriched 

Uranium in Civilian Research Reactors”3 and 2018 APS 

“Neutrons for the Nation”4 studies each raised concerns 

about the credibility of conversion program schedules 

due to repeated delays prior to the rebaselines, followed 

by significant delays announced as part of the 2012 and 

FIGURE HL.2. Three Group Neutron Flux Radial Profiles on Core Midplane

Typical positions for Isotope production and materials damage testing irradiations illustrated BOC and 

EOC: Beginning and End OF Cycle. HEU operation at 85 MW is compared to LEU U3Si2 operation at 95 

MW. Safety margins have been preserved for the LEU at higher power..

Source: David Chandler, presentation to BESAC subcommittee, January 2000
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2013 rebaselines of the USHPRR and EUHFR efforts 

relative to the schedules that had been reported prior to 

rebaselines.

The need to restore schedule credibility with 

stakeholders was understood by reactor conversion 

leadership during the rebaseline processes, and the 

USHPRR and EUHFR teams have worked to maintain 

schedule despite the complexities of the programs. In 

July of 2015 the NNSA reported to the NAS review 

committee that the projected conversion dates of the 

5 USHPRR, the ATRC, and 3 EUHFR reactors would 

occur during the span from MURR in 2026 to FRM-II 

in 2033 (i.e., first licensed LEU fuel on the grid plates 

for operation). In January 2020, the NNSA reported to 

the BESAC Neutron Subcommittee that those 9 conversions will occur during the span from MITR in 2028 to 

HFIR in 2034.

Appendix A.2 lists a number of key deliverables 

toward high-performance research reactor conversions 

that have been accomplished in the US and Europe 

since the 2016 NAS report was published. Significant 

progress has been achieved in the areas of detailed LEU 

reactor design and safety analysis; fuel qualification of 

the UMo and U3Si2 fuel systems; and fabrication of the 

UMo and U3Si2 fuel systems, including cost projection 

and associated process optimizations.

The ORNL neutron science team (HFIR, SNS, and 

senior laboratory management) and the M3 Reactor 

Conversion team (NNSA, the collaborating national 

laboratories, and BWXT) agree that they are on a 

sound coordinated path to a U3Si2 conversion that will 

maintain the mission capabilities of HFIR, as reported 

in publications and the presentations by ORNL to this 

BESAC Subcommittee.
MAJOR U.S. NEUTRON FACILITIES: 

Status and Future Plans

360-degree panoramic of the HFIR Reactor at Oak Ridge National Laboratory in Tennessee

Credit: Jason Richards
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Major U.S. Neutron Facilities 57

High Flux Isotope Reactor (HFIR)

The need for a high neutron flux reactor to support 

transuranium isotope research and development was 

identified in 1958, and construction of the High Flux 

Isotope Reactor (HFIR) began in 1961. HFIR achieved 

first criticality in 1965 and reached full design power 

of 100 MW in August 1966. The reactor was designed 

around the concept of a neutron flux trap, which generally consists of an annular region of fuel surrounding 

a thermalization area to create a thermal neutron flux 

peak. The HFIR achieves the highest neutron flux density of any reactor operating today in the western world 

(2.5 x 1015 n/cm2/s at 85 MW) by utilizing a beryllium 

reflected, light-water cooled and moderated highly-enriched uranium fueled reactor core surrounding the 

center flux trap in the center (see Figure US.1).

HFIR Core

The HFIR core is a cylindrical assembly approximately 

2 feet tall and 17 inches in diameter consisting of inner 

and outer fuel elements. The center of the HFIR core 

contains a five-inch diameter flux trap. The inner fuel 

element contains 171 fuel plates, and the outer element 

contains 369 fuel plates. The fuel plates are curved in 

the shape of an involute to provide a constant coolant 

flow channel width between plates. To minimize power 

peaking, the uranium in the aluminum-clad fuel is 

non-uniformly distributed along the arc of the fuel 

plate. Boron-10 is added within the inner fuel plates to 

flatten the radial peak neutron flux and extend the operating cycle for the core.

The fuel region is surrounded by a cylindrical 

beryllium reflector approximately one foot thick and 

consisting of three regions or sections. These sections 

include the inner removable reflector, the semi-permanent reflector, and the outer permanent reflector. All 

sections of the beryllium reflector must eventually be 

replaced due to damage, growth, and cracking caused 

by irradiation from the reactor. The next beryllium 

reflector replacement is scheduled for 2024 and will 

require a nine-month outage. The reactor core and 

beryllium reflector are cooled and surrounded by 

light-water reactor primary coolant which is contained 

in the eight-foot diameter reactor pressure vessel.

FIGURE US.1. HFIR Axial and Radial Cross-Sections

Source: Oak Ridge National Laboratory
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In-Vessel Isotope Production and Materials 

Irradiation

HFIR was originally designed specifically to enable 

the production of transuranium isotopes for research, 

industrial, and medical applications utilizing the 

high thermal neutron flux in the center flux trap. The 

neutron flux energy spectrum across the HFIR reactor and the reflector is shown in Figure US.2. Today, 

HFIR is the only reactor outside of Russia capable of 

producing significant quantities of californium-252. 

Californium-252 is a very strong neutron source (with 

a half-life of only 2.645 years) used for well-logging, 

neutron radiography, reactor startup sources, and other 

industrial and medical uses. Other isotope productions 

for which HFIR is unique or particularly effective are 

discussed in The Scientific Case section of this study.

The HFIR flux trap has 30 target positions in the 

flux trap basket that are used for isotope production 

and materials irradiation testing or other experiments. 

Two of these locations will accommodate instrumented 

experiments which would allow, for example, temperature monitoring. 

One location in the HFIR target basket is reserved for a hydraulic facility which permits insertion 

and removal from the reactor during operation. The 

hydraulic tube (HT) transfers aluminum capsules from 

a loading station into the flux trap and back using the 

differential pressure across the HFIR core. HT samples 

and their effect on the reactor are carefully evaluated 

prior to approval to ensure that the insertion or withdrawal of the experiment does not cause a power transient that results in a reactor trip. 

By design, the peak thermal flux occurs near the 

center of the flux trap. There are six peripheral target 

positions (designated as PTP) in areas on the outside 

edge of the target basket. These positions receive the 

highest fast and epithermal neutron fluxes in the HFIR, 

making these locations useful for materials irradiation 

testing. Strong neutron absorbers are limited in the flux 

trap and some other positions as they could reduce the 

length of the HFIR experimental cycle.

HFIR has additional irradiation capacity located 

in the removable beryllium (RB) and permanent beryllium surrounding the HFIR core. Because the RB locations are closer to the reactor fuel, they are often used 

FIGURE US.2. Neutron Flux and Energy Across the HFIR

Source: Oak Ridge National Laboratory
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for instrumented and non-instrumented experiments. 

Within limits, the neutron spectrum in this area may 

be filtered to reduce the thermal neutron component of 

the spectrum. The vertical experiment facilities (VXF) 

in the permanent reflector normally will only contain 

non-instrumented experiments or target materials for 

isotope production.

HFIR has two pneumatic tube facilities supporting 

the neutron activation analysis program. These tubes 

allow the rapid insertion and removal of irradiation 

samples while the reactor is operating. One of the pneumatic tubes uses one of two engineering facilities that 

enter the edge of the beryllium reflector at an angle.

Neutron Scattering

HFIR has four horizontal neutron beams (HB-1 to -4) 

with the thimbles located in the beryllium permanent 

reflector. HB-1 and HB-3 are configured as thermal 

neutron beams that are tangential to the reactor core 

to reduce the gamma and fast neutron radiation in 

the beams. HB-2 is a radial beam tube which utilizes 

beryllium inserts and fast-neutron filters to increase 

the signal-to-noise ratio at the neutron scattering instruments. HB-4 is a tangential tube and contains the 

cold neutron source (commissioned in 2007) which 

is one of the brightest sources in the world today. The 

cold neutron source uses supercritical hydrogen operating near 17K to increase the available flux of neutrons 

at wavelengths 4 to 12 Angstroms for the cold neutron 

instruments. 

Together, the HFIR thermal and cold neutron 

beams support 12 neutron scattering instruments. A 

cold neutron guide hall was constructed in 2007 to 

provide greater space for small-angle scattering (SANS) 

instruments and other instruments optimized for the 

longer wavelength cold neutrons. As a continuous neutron source, HFIR’s fluency rate is 50 times greater than 

a Long or Short pulse source. The range of HFIR scattering experiments is discussed in The Scientific Case 

section of this report, together with the HFIR capability complementarity to the Spallation Neutron Source 

and other scattering facilities.

HFIR Status

The HFIR pressure vessel shown in Figure US.1 has a 

design lifetime of 50 effective full-power years (EFPY) 

for 100 MW operations. Tests performed on irradiation 

surveillance specimens in November 1986 indicated 

that the HFIR reactor vessel was being embrittled by 

radiation exposure at a higher than predicted rate. 

Following detailed evaluations and extensive reviews, 

HFIR was permitted to restart on April 18, 1989, but 

did not return to normal operations at a new maximum power level of 85 MW until May 18, 1990. The 

lower power level significantly reduces the rate of pressure vessel embrittlement and extends the operating 

life of HFIR, based on the vessel, to approximately 2050 

assuming six 23-day operating cycles per year.

HFIR has an extensive age management program 

that evaluates equipment and systems condition to 

determine a priority for refurbishment or replacement. 

Virtually all major components have been replaced, 

with many of those remaining scheduled to be replaced 

during the next reflector replacement in 2024. Since 

1995, this life extension strategy has improved HFIR 

reliability and assured a predictable (98.5% in FY19) 

operational schedule to support the ORNL neutron 

scattering science program. Predictability and reliability are essential for HFIR to support the strong neutron science user facility program.

Although the HFIR reactor pressure vessel has 

approximately 30 to 40 years of life remaining, it is 

considered the life-limiting component of HFIR. Similar to the 1995 replacement of the High-Flux Reactor 

pressure vessel at the Institut Laue-Langevin in France, 

ORNL has developed a tentative plan to replace the 

HFIR reactor vessel and extend the operating life of 

the facility beyond 2040. In a process already used for 

nuclear power plant decommissioning, vessel sectioning could be performed remotely using an underwater 

plasma torch and the segments could then be packaged 

FIGURE US.3. HFIR Target Basket Locations

Source: Oak Ridge National Laboratory

Peripheral Target 

Positions (PTP)

Target

Hydraulic Tube 

(HT)
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60 Major U.S. Neutron Facilities

for disposal. A replacement vessel could be fabricated 

using improved materials that are less susceptible to 

radiation embrittlement, such as stainless-steel, and 

allow HFIR to return to 100 MW operations. A project to fully design and procure a replacement reactor 

vessel, which would require three to five years for 

fabrication, could be aligned with DOE planning to 

coincide with LEU conversion in the 2030 to 2035 

timeframe and could include an early beryllium reflector replacement. HFIR and ORNL staff have drafted a 

preliminary project plan to replace the HFIR pressure 

vessel, upgrade some reactor systems, and improve the 

cold neutron source to improve brightness by 50%. A 

potential LEU replacement fuel, expected to begin testing soon, could be incorporated into an upgraded or 

enhanced HFIR reactor core design, possibly allowing 

a higher reactor power level to compensate for the LEU 

fuel neutron flux distribution. All of these activities 

could also support the installation of an HB-2 guide 

hall with a new suite of thermal and cold instruments 

to capitalize on the enhanced HFIR, which would in 

turn enable high quality neutron science research well 

into the 21st century. ■

NIST Center for Neutron Research (NCNR)

The NIST Center for Neutron Research (a major operating unit within the National Institute of Standards and 

Technology in the U.S. Department of Commerce) is a 

national user facility that operates world-class facilities 

for neutron-based research. The mission of NIST, “to 

promote U.S. innovation and industrial competitiveness by advancing measurement science, standards and 

technology...,” drives a robust engagement with industry in the application of neutron measurements to problems of technological interest and in the development 

of standard reference materials. Access to NIST neutron facilities is provided to scientists from industry, 

government, and academia through several different 

channels: 

• a general user program based on anonymous 

peer-reviewed proposals

• partnerships with government, private sector, 

or academic organizations

• collaborations on NIST-mission activities, and 

• proprietary research performed with full cost 

recovery

In 2019 alone, more than 300 articles were published that were fully or partly based upon research performed at the NCNR, and the facility served scientists 

from 50 U.S. corporations.

NCNR research facilities are centered around the 

NBSR, a 20 MW steady-state research reactor first 

commissioned in 1969, that has a heavy water moderator and reflector. The NBSR is licensed by the Nuclear 

Regulatory Commission; the current license was issued 

in 2009 and runs through 2029. No short-term issues 

that might limit operations beyond that time have been 

identified. The NBSR uses Highly Enriched Uranium 

(HEU) fuel, but a conversion to Low Enriched Uranium (LEU) will occur when such fuel is qualified. The 

liquid deuterium cold source now being constructed is 

partially funded by the NNSA Material Management 

and Minimization Program to compensate for the 10% 

reduction in neutron flux that will result from LEU 

conversion. 

The neutron beam instrument layout shown in 

Figure US.4 is the result of the cold sources developed 

and the research needs of the neutron community. 

Note that MACS views its own small cold source, meaning that more than 3⁄4 of the neutron beam instruments at the NCNR use cold neutrons.

Neutrons interact with both the nucleus and spin 

of atoms, which makes it possible to obtain information 

on atomic and magnetic structures, respectively. These 

interactions are weak, which result in some simplification in analysis but also weak signals. Thus, neutron 

scattering is an intensity-limited probe, and good instrument design is critical to successful studies.

The development of innovative instrumentation is 

a priority at the NCNR with a very high payoff. This is 

exemplified by the recent construction of CANDOR, 

a state-of-the-art instrument that multiplexes many 

HOPG monochromators in a row, each set to diffract 

a different wavelength. This allows much more rapid 

measurements of neutron reflectometry, as illustrated 

in Figure US.5 in the first scan taken with the new instrument compared to a single reflectometer.

In addition to the neutron scattering instruments, 

there are several thermal-neutron irradiation facilities 
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including pneumatic rabbit tubes, fixed vertical facilities, a thermal column, through tubes, and other facilities inside the reactor confinement building. Although 

these facilities may be used by outside users in a collaborative or service mode, they primarily serve the mission needs of NIST, including calibrations, activation 

analysis, and sample irradiations.

The Chemical Sciences Division of the NIST Material Measurement Laboratory uses these facilities for 

elemental analysis by neutron activation to support 

NIST’s role as the nation’s reference laboratory for 

measurements and standards of chemical composition. 

Neutron activation analysis (NAA) complements more 

common analytical methods and often serves as one 

of the two independent measurements required for the 

certification of Standard Reference Materials (SRMs). 

NAA is particularly advantageous for analyzing materials that are hard to dissolve, such as glasses, ceramics, 

geological specimens, metals, etc. Furthermore, NAA 

can quantify hydrogen in materials, a difficult measurement by other means. Since 2000, NAA has contributed to the certification of more than 120 SRMs with 

55,000 units sold, covering a wide variety of materials 

ranging from industrial commodities to food. 

Beyond SRMs, the research, development, and 

application of new non-destructive in-situ measurement capabilities are a major emphasis of this program. 

For example, an effort is underway to develop and 

demonstrate the measurement of chlorine distribution 

in concrete by prompt-γ activation analysis, a potentially field-deployable capability to assess the corrosion 

of concrete structures. A second example is the application of neutron depth profiling (NDP) to help elucidate 

battery failure mechanisms by measuring the complete lithium ion distribution during charge/discharge 

cycles.

The Neutron Physics Group of the NIST Physical 

Measurements Laboratory provides measurement services, standards, and fundamental research in support 

of NIST’s mission serving national interests, including 

industrial research and development, national defense, 

homeland security, and electric power production. This 

group provides measurement capabilities and services 

ranging from neutron imaging, instrument development and calibration, neutron source calibration and 

standards, detection of concealed nuclear materials, 

and radiation protection. Basic physics experiments 

probe the symmetries and parameters of the weak 

nuclear interaction, including measurements of the 

FIGURE US.4. NCNR Reactor Layout

Source: Dan Neumann NCNR
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lifetime of the free neutron, improved cold-neutron 

counting techniques, setting a limit on the time-reversal asymmetry coefficient, and the radiative decay of 

the neutron.

Neutron-imaging studies of water transport in fuel 

cells and hydrogen distribution in hydrogen storage 

devices have been performed using an imaging system 

(NeXT) that combines the power of neutron and X-ray 

3-D tomography into a single-pass probe for materials 

structure and composition analysis. This provides an 

entirely new approach to resolving longstanding problems in materials science, including concrete degradation, and advances the state of the art of energy 

technologies, including lithium batteries, and unconventional gas reservoir geologies.

The NCNR has established long-term partnerships 

with the National Science Foundation (Center for 

High-Resolution Neutron Scattering), the University 

of Delaware (Center for Neutron Science), and the 

University of Maryland to develop new instruments 

and science, and to expand the use of neutrons beyond 

traditional fields. Another collaboration that seeks to 

expand the use of neutrons by industry is the nSoft 

consortium, which is a group of industrial partners 

that currently comprises 3M, Amgen, Aramco Services 

Company, Braschem North America, Colgate Palmolive, Dow Chemical, Genentech, Procter & Gamble, 

Regeneron, Solvay USA, and Toyota Research in North 

America. The members have access to small-angle 

neutron scattering to conduct research on problems of 

industrial interest with results that are freely available 

to the general public. Membership fees support the 

development of new methods and instrumentation and 

the investigation of novel applications of neutrons by 

industrial partners. The operations are governed by a 

CRADA that establishes the terms of use.

In the short term, NIST is committed to continuing upgrades of the NBSR reactor and neutron scattering facilities. There are no known lifetime-limiting 

conditions for the NBSR, which is now over 50 years 

old. An aging management plan has been established 

to continually inspect and maintain the reactor for the 

foreseeable future. One major ongoing improvement 

is the design, construction, and installation of a new 

liquid deuterium cold neutron source in conjunction 

with the conversion of the reactor to Low Enriched 

Uranium (LEU). This will maintain and improve the 

NCNR facilities with increased flux for all cold neutron facilities, more than compensating for the losses 

expected as a result of higher absorption in the LEU. 

During the shutdown required for conversion activities, NIST will perform several maintenance activities, 

modifications, and replacements of aging components. 

At the same time upgrades to the existing scattering 

facilities (guides, instruments, and other capabilities) 

will provide the opportunity to increase performance 

even further.

FIGURE US.5. Neutron Beam Resources at 

NCNR

Source: NCNR/National Bureau of Standards and 

Technology
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For the longer term, a replacement of the NBSR 

will be required, and a project to explore and determine possibilities of an optimum design for cold neutron performance in an LEU reactor has been initiated. 

NIST expects to construct and commission such a 

reactor while the NBSR is still operational, so that there 

will be no interruption of the NCNR. NIST has begun 

the process of obtaining funding for this project.

In summary, NIST operates a full-capability, 

world-class neutron facility at the NCNR to serve 

U.S. researchers from industry, government, and 

universities. ■

SNS Present and Future

The First Target Station (FTS) at the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory 

is a third-generation neutron source capable of delivering the world’s brightest beams of pulsed neutrons 

that provide research capabilities across a broad range 

of disciplines including physics, chemistry, materials 

science, and biology. The FTS, operating at a power of 

1.4 MW, provides beams of neutrons in short pulses 

at a repetition rate of 60 Hz with the highest peak 

brightness in the world. Figure US.6 shows the layout 

of the instrumental hall at FTS of SNS. There are currently a total of 19 user instruments plus an additional 

5 instruments under consideration.

The user instruments at FTS cover a wide range 

energy and momentum space; they have opened new 

avenues for examining materials over greatly increased 

length, energy, and time scales. The materials that can 

be investigated by FTS include magnetic materials, 

FIGURE US.6. The Instrumentation Layout at FTS, SNS

Source: ORNL
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64 Major U.S. Neutron Facilities

polymers, engineering materials, as well as nanoparticles. In combination with sample environments, 

advances in neutron optics and detectors, and new computational methods, SNS has transformed the landscape 

of neutron science in the US. In the early part of the 

2000s, the number of neutron scattering scientists and 

their concomitant activities in Europe have significantly 

exceeded those in the US. The situation has changed 

considerably after the completion of the FTS of SNS in 

2006. Since that time, the numbers of users, operation 

hours, and publications from SNS have continued to 

increase with each passing year. For example, there were 

644 unique users in FY 2018, and 780 unique users in 

FY2019. Between SNS and HFIR, approximately 650 

scientific publications were produced in the calendar 

year 2019, 467 of which are instrument-based publications. SNS is currently undergoing a proton power 

upgrade (PPU), which will be completed in 2024, to 

double its power capability to 2.8 MW. This upgrade 

will deliver 2 MW of proton beam to the FTS, resulting 

in a significant increase in thermal neutron brightness 

to enable faster experiments and potentially time-resolved neutron spectroscopy experiments for materials 

research in the thermal energy (shorter wavelength) 

range. With this upgrade, FTS at SNS will be competitive with spallation neutron sources in Japan (J-PARC) 

and the future European Spallation Source (ESS), which 

is currently 68% complete and expected to have a user 

program starting in 2023. 

In addition to continued improvement of the FTS 

at SNS, which is mostly focused on thermal energy 

neutron users, there is tremendous interests in cold 

neutron spectroscopy. In fact, the 9 cold neutron spectrometers at the FTS are some of the most oversubscribed spectrometers (by a factor of 4). Currently, the 

Second Target Station (STS) at SNS is in the detailed 

design stage and will be under construction soon. 

Compared with the FTS, the STS will be pulsed at 15 

Hz (using one out of every four pulses from the target, 

the rest being used by FTS) and deliver cold neutrons 

with the highest peak brightness in the world (Fig. 

US.7). The construction of STS in the coming years will 

be expected to alleviate considerably the oversubscriptions of the cold neutron spectrometers at the FTS. In 

addition, STS will enable kinetic process and time-resolved measurements of quantum and biological materials. The ability to produce high flux cold neutrons will 

also make possible investigations of smaller samples 

and samples with large length scales of interest. In 

short, the continued improvement of the FTS and the 

near future construction of the STS at SNS, complemented by an upgraded and improved high-flux Isotope Reactor, will ensure the US leadership position in 

neutron sources. ■

FIGURE US.7. Peak and time-averaged brightness of current 

(closed circles) and planned (open circles) neutron sources, 

illustrated at 5 Å. CSNS: China Spallation Neutron Source, 

China; ESS: European Spallation Source, Sweden; FRMII: Forschungsreaktor München II, Germany; ILL: Institut 

Laue-Langevin, France; ISIS: ISIS Neutron and Muon Source, 

UK (TS: Target Station); J-PARC: Japan Proton Accelerator 

Research Complex, Japan. 

Source: ORNL
INTERNATIONAL 

NEUTRON FACILITIES

The Institut Laue-Langevin in Grenoble, France, and its reactor (in the dome) that provides an intense source of neutrons for research

Source: Wurzeller - English Wikipedia, Public Domain, https://commons.wikimedia.org/w/index.php?curid=6405870
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Institut Laue-Langevin (ILL)

Background

The ILL is located in Grenoble, France, in close proximity to the European Synchrotron Radiation Facility 

(ESRF), an outstation of the European Molecular 

Biology Laboratory (EMBL), the University Grenoble 

Alpes, and several institutes operated by French national research agencies CEA and CNRS. Funding for the 

ILL comes from a consortium of European countries 

including the “ILL Associates” (Germany, France, 

and the United Kingdom), which cover two thirds of 

its annual budget of about €100M. 10 other countries 

have signed shorter-term scientific membership agreements that give them privileged access to beam time 

in exchange for a more modest budget contribution. 

The ILL currently has a staff of about 520, including 

roughly 75 instrument scientists.

With a thermal power of 58.3 MW, the ILL Reactor 

delivers a flux of 1.5x1015 neutrons per second per cm2

to a suite of currently about 40 instruments, which are 

housed in the confinement building and two cold-neutron guide halls. It currently operates in four 50-day 

cycles per year. Reactor operations began in 1972, and 

the reactor vessel was replaced in the years 1993–1995. 

Since then, the reactor and instrument suite have 

undergone several upgrade programs. The two-phase 

“Millennium Program” (2000–2018) supplied funding 

of €85M for the replacement of the neutron guide system, 7 new instruments, and 25 instrument upgrades. 

The “Refit Program” (2002–2007) improved security 

and seismic reinforcement. In 2016, the ILL launched 

the two-phase “Endurance Program.” Phase 1 (2016–

2019) was funded at a level of €22M and enabled 14 

FIGURE I.1. Floor Plan of the ILL

Source: https://www.ill.eu/users/instruments/
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instrument upgrade projects as well as upgrades of the 

sample environment and data collection software. Phase 

2 (2019–2023) will fund 10 additional upgrade projects 

at a level of €40M. In addition to the neutron instruments, the ILL also operates a deuteration laboratory 

and chemical laboratories for sample preparation. In 

2002, the ILL, together with surrounding institutions, 

founded the “Partnership for Structural Biology” which 

promotes complementary use of scientific facilities. 

Most of the scientific instruments at the ILL are 

operated by staff scientists who are organized in four 

scientific groups: Diffraction, Large Scale Structures, 

Spectroscopy, and Nuclear and Particle Physics. The 

beam time is allocated via an external user program. In 

addition, eight instruments are operated by Collaborative Research Groups (CRGs), which either lease an instrument owned by the ILL and receive privileged access 

to 50% of the beam time (CRG-A), or build and operate 

their own instrument with privileged access to 70% 

of the beam time (CRG-B). In the following, the CRG 

instruments are described alongside those operated by 

ILL staff.

Diffraction

Powder diffraction accounts for a substantial fraction 

of the ILL’s publication output. The instrument suite 

includes three general-purpose diffractometers and 

three more specialized instruments. In the former category, D1B (a CRG instrument) and D20 are optimized 

for high intensity and are therefore in high demand 

for parametric studies and real-time experiments, in 

addition to standard crystal and magnetic structure 

determination. The flagship instrument D20 also 

allows stroboscopic experiments with duty cycles up to 

33 kHz, with a minimum counting time of 1 μs. D2B 

is optimized for high momentum-space resolution 

and thus allows efficient determination of mediumscale structures such as zeolites and quasicrystals. 

Among the specialized powder diffractometers, D4 

uses short-wavelength neutrons from a hot source to 

measure diffraction patterns of liquids and structurally 

disordered systems over a large Q-range. D7 focuses on 

diffuse scattering from magnetically disordered systems, using a spin-polarized beam and uniaxial as well 

as XYZ polarization analysis. SALSA is designed for 

strain imaging of engineering materials with dimensions ranging from a few millimeters to more than one 

meter.

Single-crystal diffractometers include the hot-neutron instruments D3 and D9 for accurate crystal and 

magnetic structure determination. D3 was upgraded 

in Phase 1 of the Endurance program, and includes a 

spherical neutron polarimetry (CRYOPAD) facility for 

determination of non-collinear magnetic structures as 

well as a dedicated setup for experiments on liquids. In 

addition, two thermal instruments, D10 and D19, are 

optimized for high flux and high Q-space resolution 

respectively. The Diffraction Group also operates two 

Laue diffractometers, CYCLOPS and Orient-Express, 

which allow users to rapidly characterize their samples 

on-site.

Large-scale Structures

Three small-angle neutron scattering (SANS) instruments (D11, D22, and D33) are dedicated to structure 

determination in soft and hard condensed matter as 

well as life sciences on length scales ranging from 1 nm 

to 1μm. With about 50–60 user experiments per year 

on each instrument, they are the workhorses of the 

ILL. All instruments have been extensively upgraded 

in both the Millennium and Endurance Programs. 

The flagship, D22, is currently the world’s highest-flux 

SANS machine. Its high flux and optimized detection 

capabilities enable applications in life sciences and 

microfluidics as well as time-resolved studies with 

μsec resolution (TISANE). Further special capabilities 

include a USANS option for extremely low momentum 

transfer on D11, and time-of-flight (TOF) and spin-polarization-analysis options on D33. 

The three reflectometers at the ILL (FIGARO, SuperADAM, and D17) were either newly built or extensively upgraded in the Millennium Program. FIGARO, 

a high-flux TOF machine with a horizontal sample 

geometry, is mostly used to study liquid interfaces in 

biophysics, soft matter, and environmental science. D17 

is a versatile machine that can be used both in TOF 

and monochromatic modes. With its vertical sample 

geometry, it is complementary to FIGARO. The CRG 

instrument SuperADAM, a monochromatic machine 

with a vertical sample geometry and polarization analysis option, is mostly used for solid thin films and 

multilayers. 

The Large Scale Structures Group also operates two 

Laue diffractometers dedicated to protein crystallography (LADI-III and LADI-B), as well as a diffractometer 

optimized for the investigation of partially ordered 

structures in soft matter and biology (D16).
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Spectroscopy

The ILL houses a suite of six three-axis spectrometers, 

including two dedicated cold-neutron machines (IN12 

and ThALES, both CRG instruments), three thermal 

machines (IN8, IN20, and IN22) and a hot-neutron 

instrument (IN1). Over the past few years, the beam 

optics of most of these instruments were upgraded, and 

new setups were installed to enhance the detection efficiency (e.g., the multi-analyzer “FlatCone” option on 

IN8, IN20, and ThALES), polarization-analysis capabilities (i.e., a spherical neutron analyzer on IN22), and 

energy resolution (e.g., a spin-echo option on IN20).

The ILL’s suite of time-of-flight spectrometers is 

being extensively refurbished in the Framework of the 

Endurance Program. Two ageing TOF spectrometers 

(IN6 and IN14) are being replaced by new instruments—the cold-neutron instrument SHARP and the 

thermal instrument PANTHER. In addition, the guide 

system and focusing optics of the general-purpose 

spectrometer IN5 has just been upgraded.

The Spectroscopy Group also operates several instruments for spectroscopy with high energy resolution, 

including two spin-echo spectrometers (IN11 and IN15) 

and two backscattering spectrometers (IN16B and IN13) 

for cold and thermal neutrons, respectively. With a 

sensitivity to relaxation times from 0.001 to 1000 ns, 

the spin-echo spectrometer IN15 is reported to be the 

world’s highest-resolution spectrometer of its kind. The 

newly commissioned WASP spin-echo spectrometer 

will complement the suite. WASP will cover a wider 

range of scattering angles than IN15 and thus bridge 

the gap to backscattering spectroscopy.

Nuclear and Particle Physics

The ILL also operates an extensive suite of spectrometers for nuclear physics (FIPPS, PN1, PN3-GAMS), 

cold (PF1B) and ultracold (PF2) neutron sources for 

high-precision measurements of fundamental properties of the neutron, and interferometers (S18, GRANIT) 

for experiments on fundamental physics, including 

gravitational bound states of the neutron. ■

Forschungsreaktor München II (FRM-II)

Background

The FRM-II is located on the campus of the Technical 

University of Munich (TUM) in Garching, a suburb of 

Munich, Germany, and is operated by the TUM. Funding for operation of the reactor and about half of the 

instruments is provided by the science ministry of the 

state of Bavaria at a level of €55M per year. Additional 

funding for operation of about a dozen instruments at 

the FRM-II comes from the German federal ministry of 

science (BMBF) via the Jülich and Geesthacht Research 

Centers, both members of the Helmholtz Association 

of Research Centers. The BMBF also funds instrumentation design or upgrade projects by nine German 

university groups currently, often in cooperation with 

the TUM. The Max Planck Society (MPG) operates 

two instruments. The Maier-Leibnitz-Zentrum (MLZ), 

a partnership of all instrument groups, coordinates 

research at the FRM-II and hosts regular workshops 

and conferences. The FRM-II currently has a staff of 

about 400, including roughly 130 scientists.

With its thermal power of 20M, the FRM delivers 

a flux of 8x1014 neutrons per second per cm2 to a suite 

of currently about 28 instruments, which are housed 

in the confinement building and a cold-neutron guide 

hall (Guide Hall West in Figure I.2). Access to 70% of 

the FRM-II beam time is managed through an external-user system. Instrument operators receive privileged access to the remaining 30%. A second guide hall 

with five instruments (Guide Hall East in Figure #.2) 

has been completed, but is awaiting safety approval by 

state authorities. Following the closure of the BER-II 

Reactor in Berlin at the end of 2019, 2–3 additional scattering instruments will be transferred to the 

FRM-II. With the transfer of the BER-II instruments 

and the opening of the second neutron guide hall, all 

available beam ports of the FRM-II will be occupied. 

Plans for a third guide hall have been discussed, but 

funding for conceptual design has not yet been secured. 

Diffraction

The FRM-II was initially equipped with only a single 

general-purpose powder diffractometer (SPODI), a 

monochromatic instrument that is optimized for high 

resolution rather than flux. A complementary high-flux 

monochromatic instrument (FIREPOD) will be transferred from the BER-II in the course of the next two years. 

Construction of two additional powder diffractometers 

(POWTEX and SAPHIR) has been largely completed, 
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International Neutron Facilities 69

and the instruments are ready for use once the second 

guide hall can be made operational. POWTEX is a TOF 

diffractometer with a texture analysis facility and associated sample environment targeted for use in solid-state 

chemistry and materials science. SAPHIR is also a TOF 

machine, specialized for diffraction and radiography of 

samples under extreme conditions of pressure (initially 

up to 15 GPa, with further upgrades anticipated) and 

temperature (up to 2000oC). Finally, STRESS-SPEC is a 

two-axis spectrometer optimized for residual-stress and 

texture analysis in engineering materials.

Single-crystal diffractometers include BIODIFF, 

which is situated on a cold-neutron guide and whose 

high momentum resolution is optimized for macromolecular crystals, as well as HEIDI and POLI, which are 

located on a hot source in the confinement building. 

Whereas HEIDI is mostly used for crystal structure 

determination, POLI is equipped with polarization 

analysis facilities for magnetic structure determination. 

An additional diffractometer, LaDIFF, will be transferred from the BER-II Reactor and will be used mostly 

for Larmor diffraction, a variant of spin-echo spectroscopy that provides extremely high momentum resolution (ΔQ/Q ~ 10-5) independent of sample mosaicity. 

Large-scale Structures

The FRM-II instrument suite includes four SANS 

machines with complementary (partially overlapping) 

capabilities. KWS-1, KWS-2, and SANS-1 are classical 

pin-hole instruments. KWS-1 is optimized for high 

Q-resolution and includes spin-polarization analyzers 

as well as a grazing-incidence (GISANS) setup. KWS-2 

is optimized for high intensity and wavelength coverage, and allows kinetic measurements with high time 

resolution. KWS-3 is a diffractometer designed for 

extremely small scattering angles and thus extends the 

coverage of real-space structures up to about 10 μm.

The reflectometers NREX and MARIA are monochromatic machines located on cold-neutron guides. 

Both instruments offer polarization analysis capabilities. Whereas MARIA has a vertical sample geometry, 

both horizontal and vertical geometries are possible 

at NREX. An x-ray diffractometer installed at NREX 

enables simultaneous x-ray and neutron scattering 

experiments, which is advantageous especially for 

degradable samples where consecutive measurements 

are impractical. The horizontal TOF reflectometer 

RESEDA is optimized for studies of liquid surfaces and 

interfaces, and also includes a GISANS option.

FIGURE I.2. Floor Plan of the FRM-II

TUM = Technische Universität München, FZJ = Forschungszentrum Jülich, HZG = Helmholtz-Zentrum Geesthacht, MPG = 

Max-Planck-Gesellschaft, FRM = Forschungsreaktor München (the FRM-II’s predecessor which is no longer operational)

Source: https://www.mlz-garching.de/instrumente-und-labore.html]
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70 International Neutron Facilities

Spectroscopy

Four triple-axis spectrometers are operational at the 

FRM-II. PANDA and PUMA are high-flux cold-neutron and thermal-neutron instruments, respectively, 

without polarization-analysis located in the confinement building. KOMPASS, a cold-neutron machine 

with extensive polarization analysis capabilities, has 

just been commissioned in the first guide hall. TRISP is 

a thermal triple-axis instrument with a zero-field spinecho setup that allows measurements of the lifetimes of 

dispersive excitations with 1 μeV energy resolution.

The flagship multi-chopper time-of-flight spectrometer TOFTOF, which sits at the end of a focusing 

neutron guide, combines high neutron flux and high 

energy resolution for a wide range of experiments in 

hard and soft condensed matter research. DNS is a TOF 

spectrometer with polarization analysis capabilities 

specializing in diffuse scattering measurements. An 

additional TOF spectrometer (TOPAS) with polarization-analysis will become operational as soon as the 

second guide hall is opened for experiments. Currently 

the FRM-II is considering the possible transfer of the 

high-flux TOF spectrometer NEAT from the decommissioned BER-II Reactor. Since a suitable beam port is 

no longer available, it would have to replace an instrument that is currently in operation.

The FRM-II also operates classical spin-echo

(J-NSE) and backscattering (SPHERES) spectrometers

for spectroscopy with high energy resolution. An additional spin-echo instrument (RESEDA) has just been 

extensively upgraded and now includes a longitudinal 

spin-echo setup that allows high-resolution spectroscopic measurements on ferromagnetic samples as well as 

experiments under high magnetic fields, which are not 

possible with standard spin-echo machines. A similar 

setup has also been installed at the cold-neutron tripleaxis diffractometer MIRA.

Imaging

The cold-neutron imaging instrument ANTARES is 

targeted for radiography and tomography of a wide 

array of industrial machinery in operation. A second 

imaging station is located in the confinement building 

and serves two irradiation rooms (MEDAPP and NECTAR). The front end of this station is equipped with a 

converter plate for the production of fission neutrons. 

MEDAPP has been designed for radiation therapy of 

cancer patients, taking advantage of the high biological activity of fission neutrons compared to standard 

hospital-based therapies. NECTAR uses the high penetrating power of fission neutrons for radiography and 

tomography of bulky industrial objects.

Elemental Analysis and Positron Spectroscopy 

A prompt-gamma activation instrument for elemental analysis (PGAA) is operational in the cold-neutron guide hall. The FRM-II also operates a high-flux 

positron source (NEPOMUC) that delivers positrons 

to three dedicated setups for positron annihilation 

spectroscopy of bulk solids (CDBS), Auger-electron 

spectroscopy of surfaces (PAES), and positron microscopy (SPM). A low-energy positron source intended for 

experiments on thin-film structures is under development. 

Nuclear and Particle Physics

Plans for instrumentation for nuclear and particle 

physics at the FRM-II include a spectrometer for 

spectroscopy of neutron-induced fission reactions 

(MEPHISTO), a setup for precision measurement of the 

neutron lifetime (PENELOPE), an experiment for the 

determination of the neutron electric dipole moment 

(EDM), and a source of ultracold neutrons (UCN) for 

neutron interferometric measurements. All of these 

experiments have experienced major delays, in part 

because of difficulties in the safety certification of the 

second guide hall. ■

Jules Horowitz Research Reactor (JHR)

The JHR is a 100 MW materials test reactor currently 

under construction at the French Alternative Energies 

and Atomic Energy Commission (CEA) site in Cadarache, France. It is scheduled to be commissioned by 

the end of this decade. When it comes on-line, JHR 

will alleviate much of the material test reactor capacity 

shortage created by the closures of the HALDEN and 

OSIRIS facilities. JHR is designed to provide a fast neutron flux of 5.5 x 1014 n/cm2·s in the core. In contrast to 

HFIR which yields up to 10 dpa/y, the fast flux in JHR 
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will generate up to 16 dpa/y. The core of JHR is being 

designed to accommodate up to 20 simultaneous experiments, many of which can be highly instrumented. 

The facility will also have the capability to perform 

in-core, on-line fission gas analysis from a pressurized 

fuel rod. 

The maximum thermal flux in the reflector region 

of JHR will be 5.5 x 1014 n/cm2·s. While useful for 

production of many industrial and medical isotopes, 

this value is well below the peak thermal flux HFIR. 

Six displacement systems are being incorporated into 

the reflector region to accommodate nuclear fuel 

experiments and isotope production. These include 

test devices for nuclear fuel behavior dedicated to 

characterization and qualification under nominal, 

off-normal, and accident conditions as well as a system 

for irradiating low-enriched uranium targets for the 

weekly production of up to 4,800 6-day Ci of 99Mo. 

Numerous fixed irradiation positions in the beryllium 

reflector will allow JHR to produce a range of medical 

and industrial isotopes. The reactor cannot, however, 

be used to produce those isotopes which can only be 

created at HFIR and SM-3. 

The JHR project is backed by an international 

consortium led by the CEA which is the project owner, 

nuclear operator, and contracting authority of the 

facility. The consortium includes AREVA and EDF 

for France, CIEMAT for Spain, NRI for the Czech 

Republic, SCK.CEN for Belgium, VTT for Finland, 

DAE for India, IAEC for Israel, NNL for Great Britain, STUDSVIK for Sweden, JAEA for Japan, and the 

European Commission. In exchange for their financial 

participation, JHR consortium members have guaranteed access to experimental capacities of the facility 

to conduct their own material test research. ■

Belgian Reactor 2 (BR2)

The BR2 light water cooled, beryllium moderated 

materials test reactor is located near Mol, Belgium and 

was first operated in January 1963. It has a very unique 

design with a central vertical channel and all other fuel 

and experimental channels inclined to form a hyperboloidal arrangement around the central channel. This 

compact geometry leads to a high fission power density 

with easy access at the top and bottom covers allowing 

for complex irradiation devices to be inserted and withdrawn. The reactor load is optimized for each cycle 

allowing for unique flexibility in the position of fuel, 

control rods, and experiments. When BR2 operates at 

its maximum power (100 MW), it provides thermal 

neutron fluxes up to 1 x 1015 n/cm2·s. The reactor has 

an active refurbishment plan for continued operation 

through 2026 and plans to run through 2036. Operations beyond this date will be determined by the lifetime of the current pressure vessel.

BR2 is used to simulate other reactor environments 

to perform tests of fuels and materials under representative conditions for light water reactors, gas-cooled 

or sodium-cooled fast reactors, and fusion reactors. 

The test reactor is also used to study accelerated ageing 

of materials under high neutron flux and behavior 

of materials under accidental conditions such as fuel 

transients and power excursions. While the facility 

has taken over a number of fuel experiments with the 

closure of HALDEN, it was reported during the committee’s visit that they are “struggling with capacity” to 

accommodate all of the requests from industry.

As an isotope producer, BR2 currently has the world’s largest installed irradiation capacity for the world’s 

most used nuclear medicine isotope; 7,500 6-day Ci per 

week for 99Mo. The facility also produces a wide array 

of other medical and industrial radioisotopes. While 

BR2 plays a critical role in meeting the world’s demand 

for these isotopes, it cannot provide several of the key 

isotopes produced at HFIR. For example, BR2 is used 

to make 188W as a generator for the production of 188Re 

(the therapeutic analogue of the most used nuclear 

medicine imaging agent 99mTc). The maximum specific 

activity of 188W from BR2 is on the order of 1 Ci/g whereas the 188W from HFIR is on the order of 100 Ci/g. 

As noted earlier in the report, higher activities will be 

required to take this promising isotope from research 

to clinical application. ■
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72 International Neutron Facilities

CONCLUSIONS

This comprehensive study was carried out in response 

to a request by J. Stephen Binkley, the Deputy Director 

for Science Programs, Office of Science, Department of 

Energy, to Marc A. Kastner, Chair of the Basic Energy 

Sciences Advisory Committee (BESAC). Dr. Binkley 

asked BESAC to form a subcommittee to assess the 

scientific justification for a U.S. domestic high-performance reactor-based research facility, taking into 

account current international plans and existing 

domestic facility infrastructure. Dr. Binkley then 

proposed six specific questions as the framework for 

our study. We will address these questions below. This 

study has provided, in great detail, the scientific justification which Dr. Binkley has requested.

An important part of the impetus for Dr. Binkley’s request was two previous studies. The first was 

a congressionally mandated study carried out by the 

National Academy of Sciences entitled “Reducing the 

Use of Highly Enriched Uranium in Civilian Research 

Reactors,” completed in 2016. The second was a Report 

commissioned by the American Physical Society’s 

Panel on Public Affairs (APS POPA) entitled “Neutrons 

for the Nation: Discovery and Applications while Minimizing the Risk of Nuclear Proliferation,” published in 

2018. These studies focused on the need for conversion 

of current research reactors from Highly Enriched 

Uranium (HEU >90% U-235) to Low Enriched Uranium (LEU <20% U-235) fuel to preclude any possible 

concomitant losses in U.S. scientific and technological 

capabilities. 

An additional issue for the Department of Energy 

is the known finite lifetime of its flagship research reactor facility, the High Flux Isotope Reactor (HFIR), at 

Oak Ridge National Laboratory. The steady exposure of 

HFIR’s steel pressure vessel to neutron bombardment 

has caused embrittlement of the steel. This, in turn, 

means that the vessel will have to be replaced within two 

to three decades, if not sooner (for example if the theoretical estimates for the rate of embrittlement are too optimistic or if failure occurs for some other reason).

As stated eloquently in the POPA study and as 

documented in detail in this report, neutrons are essential, precious, and powerful. Their unique properties as 

probes of the structure and dynamics of materials have 

led to numerous advances in basic materials science. 

Indeed, whenever a new class of materials is discovered 

or new properties are observed in an old class of materials, immediately the basic structural and magnetic 

properties of these materials are characterized using 

neutron scattering techniques. This has happened 

repeatedly over the past several decades. 

Neutrons have also become invaluable tools in 

industrial product development and manufacturing. 

The range of applications varies from studying the 

microstructure of high-performance batteries to optimizing drug preparation and delivery to determining 

the properties of gas-bearing shale rock. The penetrating power of neutrons has made possible direct observation of operating internal combustion engines, the 

optimization of high-performance turbine blades, and 

the measurement of stress in welds for the auto industry.

Nuclear reactors also play an essential role in providing both neutrons and neutrinos for studies in fundamental physics; they are key to our understanding 

of the constituents and forces of matter, the properties 

of elementary particles, and the symmetries of nature. 

For example, precision experiments using neutrons 

and neutrinos measure the neutron lifetime, probe the 

neutron electric dipole moment, and search for sterile 

neutrinos as a new form of matter. Understanding the 

properties of neutrons and neutrinos holds the key to 

some of the most important fundamental questions 

in physics, including the nature of physics beyond the 

standard model.

Nuclear research reactors also play an indispensable role in isotope production and materials irradiation. Indeed, initially HFIR’s primary mission was 

radioactive isotope production. The vast majority of 

radioactive isotopes used in medicine, industry and 

basic research are produced by irradiating materials 

with neutrons in nuclear reactors. Specifically, because 

of HFIR’s intense neutron flux, it plays a central role 

in producing many critical radioactive isotopes. These 

include the first targeted alpha therapy agent approved for clinical use by the U.S. FDA. Radium-223 is a 

therapy for symptomatic bone metastases in prostate 

cancer that improves overall patient survival with a 

30% reduction in mortality. Californium-252 and Nickel-63 are both used extensively in industry and by 

the Departments of Defense and Homeland Security. 
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Finally, the heaviest element radioactive isotopes are 

used in fundamental materials research to understand their physical and chemical properties. Materials 

irradiation studies are critical to developing accident 

tolerant fuels and clad materials for nuclear reactors 

and are essential to the fundamental investigation of 

radiation degradation mechanisms and, importantly, 

for the development of structural materials technology 

for future fission and fusion reactors.

We now turn to the questions posed by Dr. Binkley:

1. “What is the merit and significance of the science 

that could be addressed by a high-performance, 

steady-state reactor, and what is its importance 

in the overall context of materials sciences and 

related disciplines?”

As documented in great detail in this report, neutron 

scattering carried out at steady-state reactors plays a 

fundamental role in virtually all areas of the condensed 

matter sciences including solid state physics, quantum 

materials, high temperature superconductors, topological magnets, spintronic materials, polymer melts, 

microemulsions, block copolymers and gels. In addition, neutron scattering is playing a progressively more 

important role in biology including protein crystallography and studies of membranes, pharmaceuticals, 

and biotic/abiotic interfaces. Importantly, for both soft 

condensed matter and biological hydrogenous systems, 

scattering contrast may be controlled by H/D labelling 

providing structural information that is not available 

by any other technique. Progress in all of these fields 

would be greatly hindered if not stopped entirely if the 

information provided by neutron scattering was not 

available.

It is important to point out that the nature of 

research in the condensed matter sciences has changed 

dramatically over the past several decades. It is now 

rare for a single probe to elucidate completely the 

fundamental science underlying any given material. 

As an example, Fe-based superconducting systems 

are characterized by competing antiferromagnetism, 

electronic nematic order, charge density order, structural order, and superconductivity. Furthermore, each 

of these orders may be important on different length 

scales. In order to elucidate the fundamental science in 

such materials, one needs to carry out a wide variety 

of studies including crystal synthesis, measurements 

of the macroscopic electronic, magnetic and structural properties, neutron scattering studies of the static 

and dynamic structural and magnetic properties, 

angular resolved photoemission and inelastic x-ray 

scattering studies of the electronic excitations, electron 

microscopy for thin film materials, and optical studies 

using both laser and synchrotron light source. All of 

this information must then be integrated together to 

understand the physics underlying the material. Neutron scattering is almost always one of the essential 

tools in these studies; without world leading neutron 

facilities, both steady state and pulsed, the U.S. would 

be relegated to a secondary role in modern materials 

science and technology.

Separate from the above, steady-state reactors 

play a dominant and often unique role in both isotope 

production and materials irradiation studies. Radioactive isotopes contribute to science, technology, and 

medicine in a myriad of ways as documented in detail 

in this report. As mentioned earlier, they are used routinely in a wide variety of imaging technologies and 

to treat cancers. Steady state reactors also produce the 

heaviest elements on the periodic table. These heavy 

elements have fascinating electronic and chemical properties, representing one of the important frontiers in 

basic solid state physics and chemistry.

Clearly, in both the operation of current generation reactors and the design of advanced fission and 

fusion reactors, the performance of structural metals in 

nuclear environments must be understood. A critical 

role of reactor-based neutron sources is the irradiation 

of materials to support the investigation of radiation 

degradation mechanisms and to spur the development 

of advanced fuels and structural materials technology 

for future fission and fusion reactors. HFIR in particular plays a central and often unique role in such investigations.

Finally, steady state reactors provide both neutron 

beams and an isotropic stream of antineutrinos. This 

makes possible experiments which probe some of the 

deepest questions in physics including the nature of 

physics beyond the Standard Model. Neutrinos have 

played a key role in the evolution of the universe and 

the formation of large-scale structures since the beginning of time and yet much remains to be understood 

about their fundamental character. HFIR is a unique 

source of reactor neutrinos in the U.S. with user 

access and, as such, is a critical component of the U.S. 

research effort in fundamental physics.
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2. “What are the capabilities of other domestic and 

international facilities, existing and planned, to 

address the science opportunities afforded by such 

a domestic research reactor?”

In the main text, we have reviewed three major domestic facilities, namely NCNR at NIST and HFIR and the 

SNS at ORNL. In addition, we have reviewed the scientific capabilities at four European steady state reactor 

facilities, ILL at Grenoble, FRM-II in Munich, the BR2 

reactor in Belgium, and the Jules Horowitz Research 

Reactor which is currently under construction in 

France. The latter two facilities serve European materials testing and isotope production needs. We have 

not explicitly surveyed neutron facilities in China and 

Japan. We discuss first neutron scattering capabilities.

As stated succinctly in the POPA report, Europe 

has dominated neutron scattering in recent decades 

as measured by capabilities, capacity to support users, 

and scientific output. There are two European world 

class facilities namely ILL in France, and the ISIS 

Neutron and Muon Source in the United Kingdom. In 

addition, there is a network of both reactor and spallation sources throughout Europe which provide for 

the health of the European neutron scattering ecosystem. An example of the latter is the FRM-II with its 28 

well-instrumented spectrometers, cold source and two 

Guide Halls. Particularly notable is the investment in 

instrumentation that has been made at the European 

reactor facilities. Soon, the 5 MW European Spallation 

Source in Lund, Sweden will come on line. This facility is projected to be the world’s leading facility for 

research using neutrons; it should be operating with an 

initial suite of 15 instruments in the mid-20s.

The peak of U.S. capacity based on the number of 

scattering instruments occurred in 1996 with 55 scattering instruments. Currently the number of instruments 

is approximately 48; this plus the increasing importance of neutron scattering in frontier research and 

technology is the reason for the huge oversubscription 

at U.S. neutron facilities. This shortfall will be partly 

mitigated by the second target station at SNS, but only 

partly. If HFIR were to be closed down, some U.S. neutron scattering investigators would move their center 

of gravity to Europe. However, there are institutional 

and political constraints on U.S. researchers severely 

limiting available beam time on spectrometers at the 

lead European facilities. In brief, from the point of view 

of neutron scattering, losing a well-functioning steady 

state high flux reactor source would do irreparable 

damage to U.S. science and technology.

Loss of HFIR would generate similar concerns for 

the isotope production and materials testing community. In the main text we review the programs at the 

Advanced Test Reactor, ATR, the Belgian Reactor, BR2, 

and the French Jules Horowitz Research Reactor currently under construction. While ATR plays a vital role 

in materials irradiation and nuclear fuel qualification 

studies for the United States, it does not have the high 

neutron flux required to produce many of the radioactive isotopes and transuranic elements made in HFIR. 

BR2 plays an important role in Europe in terms of both 

materials testing and isotope production. However, it 

cannot provide a number of the key isotopes made in 

HFIR. Similarly, the JHR will be an invaluable facility 

but it will fall short of HFIR’s capabilities in many respects in part because its planned peak thermal flux will 

be well below that of HFIR’s.

3. “What are the benefits to other fields of science and 

technology and to industry of establishing such 

a capability in the U.S.? In particular, consider 

applications such as isotope production, materials 

irradiation, neutron imaging, dark matter research, 

and neutron activation for trace element analysis.”

This question has been answered in detail in both the 

main body of this report and in the response to the first 

question.

4. “What are the strengths and limitations of a steadystate research reactor compared to a pulsed spallation neutron source for science, engineering, and 

technology? What functions currently performed 

by research reactors can be assumed by spallation 

neutron sources?”

As discussed in detail in this report, there are many 

applications where a steady state source is either 

essential or preferable to a pulsed spallation source of 

neutrons. Examples of these include any investigations 

requiring polarized neutrons and studies of the phases 

and phase transitions in one- and two-dimensional 

materials. Currently, reactor sources provide a large 

fraction of the available neutron time on the key instruments in soft matter and biological research. Many 

investigators in hard condensed matter physics will 

characterize a material using both pulsed spallation 

neutron instruments and those at a steady state reactor, 
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the former to carry out a broad survey of the excitations in momentum and energy space, and the latter 

to obtain precise information in a particular region 

of phase space. We expect such dual investigations to 

continue for the indefinite future.

The question of which functions currently performed by research reactors can be assumed by spallation 

neutron sources is difficult if not impossible to answer 

except for isotope production and most materials irradiation studies which require the steady high-fluxes 

generated by a research reactor. Over the last decade, 

we have seen extraordinary developments in instrumentation and data analysis capabilities for neutron 

scattering at both steady state and pulsed spallation 

sources. Indeed, such instrumentation development has 

arguably been more important than increases in neutron flux. Thus, experiments which are currently carried out at only one type of source may, 10 years from 

now, be carried out at both types of facilities.

The fundamental challenge for the neutron scattering community is not which type of neutron source to 

use for a particular experiment, but rather obtaining 

beam time at all for any experiment. As shown by the 

user data for each of NIST, HFIR and the SNS, almost 

all of the neutron spectrometers are over-subscribed by 

as much as a factor of three. Further, the proposal cycle 

time is typically six months. This means that an important experiment can be delayed by a year or more—an 

unacceptable delay if the U.S. is to maintain leadership 

in the development of new materials. This is particularly 

challenging for both graduate students and postdoctoral fellows. Both are typically counting on carrying out 

experiments which will either lead to their Ph.D., or for 

the postdocs, enable them to obtain a coveted faculty 

position. The country needs a steady flow of outstanding 

young people entering the field of neutron scattering, 

and this in turn means that we need adequate state-ofthe-art facilities. In addition, oversubscription inevitably means that committees allocating beam time tend 

to favor proposals which guarantee results. This in turn, 

means that more speculative experiments which may 

fail, but if successful would produce spectacular results 

tend to be disfavored. 

Therefore, the most important issue is not steady 

state versus pulsed, but rather how do we ensure that 

the United States will recover its world leading position in the field of neutron scattering. This means that 

we need both well-instrumented high flux reactor and 

pulsed spallation sources of neutrons.

5. “Are there feasible upgrade paths for HFIR to 

provide world-leading capabilities in serving the 

Office of Science missions well into the future? 

What can we learn from the experience at the Institut Laue-Langevin?”

This question is answered in detail in the HFIR strategy 

document provided to our committee by Oak Ridge 

National Laboratory. It is reproduced in full in Appendix 1. The lifetime of HFIR is limited by the progressive 

embrittlement of the pressure vessel. The vessel will 

most certainly have to be replaced by the middle of this 

century and possibly sooner. Fortunately, HFIR was 

designed for pressure vessel replacement. The complete 

replacement of a research reactor vessel has been previously accomplished at ILL in 1995 and at the Petten 

research reactor in 1983–85. There is a detailed plan 

for a similar vessel replacement for HFIR. Almost certainly, any vessel replacement would occur at the same 

time as the conversion from HEU to LEU fuel, likely in 

the 2030 to 2035 time frame. 

The pressure vessel replacement would allow a 

number of upgrades and improvements. The new pressure vessel would support large beam tubes and an 

improved cold source. This would make possible an 

increase in the number of neutron scattering instruments from 12 to 20. Importantly, it would also allow 

the construction of a second guide hall with concomitant lower background for neutron scattering experiments. It is envisaged that there would both a thermal 

neutron and cold neutron guide hall. 

The increased irradiation capacity enabled by the 

new pressure vessel would provide a corresponding 

increase in isotope production and damage rates for 

materials irradiation experiments. The changes to the 

reactor vessel head would facilitate introduction and 

removal of capsules, including during reactor operations. This would allow increased isotope production, 

especially for short-lived isotopes, such as Pt195m, 

Lu-177, W-188/Re-188, and Th-227 for medical applications, Se-75 for radiography, and Es-253 for heavy 

element chemistry. The improved access would also 

enable a significant increase in instrumented materials 

irradiation experiments to advance radiation effects 

research including the development of accident-tolerant 

fuels and fusion reactor materials.
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6. “Can Low Enriched Uranium (LEU) and High 

Assay LEU (HALEU) fuels (defined as <20 % 

enriched U-235) replace Highly Enriched Uranium 

fuels in research reactors while preserving the 

needed characteristics of neutrons produced by 

steady-state reactors? What R&D would be needed 

to support LEU and HALEU fuels development?”

The research and development of HEU-LEU conversion 

is discussed in detail in the “HEU-LEU Conversion” 

section of the main text and in Appendix 2. Many successful conversions have already been accomplished 

around the world. There is a variety of fuel compositions and configurations. In 2019, it was decided that a 

fuel based on U3Si2 in a dispersion geometry would be 

the baseline solution for HFIR. The U3Si2 dispersion 

fuel system would allow the HFIR-specific characteristics of the current HFIR HEU design to be leveraged 

for the LEU design. The HFIR HEU-LEU Conversion 

Team reported preservation of all missions to our 

BESAC subcommittee. They believe that they are on 

a sound coordinated path to a U3Si2 conversion that 

would maintain the mission capabilities of HFIR and 

they recommend that the pressure vessel and beryllium reflector replacement occur at the same time as 

the LEU conversion. The necessary U3Si2 fuel element 

research and development is ongoing.

Finally, there is always the possibility that, for 

either technical or political reasons, HFIR will have to 

be closed down and the vessel replacement and HEULEU conversion proposed above will not be possible. 

Indeed, our country has already suffered a major loss 

with the permanent closure of the High Flux Beam 

Reactor at Brookhaven National Laboratory. Because of 

the long times involved between the initial design and 

the final commissioning of such a reactor, DOE must 

have an alternative strategy. Specifically, DOE needs to 

initiate a scoping study for a green field research reactor optimized to perform neutron studies and isotope 

production that are uniquely suited to a very high flux 

reactor such as HFIR. The reactor would be designed to 

operate on LEU fuel. Reactor and fuel assembly designs 

should be evaluated to optimize simultaneously reactor performance and fuel assembly manufacturability. 

Further, the design should, to the extent possible, be 

optimized for neutron needs as currently understood 

and for flexibility of configuration to enable future, 

currently unanticipated, applications. Beginning this 

process now will allow time to evaluate options and 

proceed with planning and approvals in time to ensure 

continuing availability of a multiply capable high flux 

research reactor in the U.S.
77

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4. Isotope Production

4a. Isotope Production at HFIR

1. Xofigo®; Bayer HealthCare Pharmaceuticals

5. Materials Irradiation

5b. Fusion Materials Irradiation

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HEU-LEU Conversion

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reports/popa-reports/upload/APSNeutronsfortheNation.pdf.
APPENDICES
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Appendices 83

APPENDIX 1. Oak Ridge Proposed Strategy for HFIR

The High Flux Isotope Reactor 

Opportunities for Sustained Leadership In High-Flux Research Reactors and 

Related Neutron Science and Technology

Introduction

HFIR is a national scientific user facility funded by the 

Department of Energy (DOE) Office of Basic Energy 

Sciences (BES) within the DOE Office of Science. 

HFIR and the SM-3 Reactor in Dmitrovgrad, Russia, 

produce the highest steady-state neutron fluxes in the 

world, with a peak thermal neutron flux of 2.5×1015 

neutrons/cm2⋅s. HFIR is unique and flexible, providing 

the highest neutron fluxes for missions in neutron 

scattering, isotope production, materials irradiation, 

neutron activation analysis, and nuclear physics. SM-3 

matches HFIR’s peak flux but does not have neutron 

scattering capability. The Institut Laue Langevin (ILL) 

reactor in France, with a peak thermal flux of 1.5×1015 

neutrons/cm2⋅s, is optimized for neutron scattering 

and has limited capability in other mission areas. The 

HFIR peak flux exceeds that of all remaining research 

reactors by a factor of 2.5 or more. Table A1.1 provides 

a summary of higher-flux research reactors currently in 

service.

Facility Description

HFIR is a pressurized, light water-cooled and -moderated, flux-trap-type reactor with a beryllium reflector. 

The reactor core, illustrated in Figure A1.1, consists of 

TABLE A1.1.

High-flux Research Reactors Currently In Use

REACTOR LOCATION

INITIAL 

OPERATION

POWER 

(MW) FUEL REFLECTOR

PEAK 

THERMAL 

FLUX1 

(1015 N/

CM2·S) PRIMARY MISSIONS

HFIR US (ORNL) 1965 85 HEU Be 2.5 (1.0 fast)

Scattering (12 instruments)

Isotopes (including heavy actinides)

Materials testing

SM-3 Russia 1961 100 HEU Be 2.5 (1.0 fast)

Materials testing

Isotopes (including heavy actinides)

ILL France 1972 58 HEU D2O 1.5 Scattering (33 instruments)

BR2 Belgium 1962 100 HEU Be 1.0 (0.7 fast)

Materials testing

Isotopes

ATR Idaho 1967 250 HEU Be 1.0

Materials testing

Isotopes

FRM-II Germany 2005 20 HEU D2O 0.8 (0.5 fast)

Scattering (23 instruments)

Isotopes

CARR China 2010 60 LEU D2O 0.8 (0.6 fast)

Scattering (6 instruments)

Isotopes

Materials testing

NBSR US (NIST) 1967 20 HEU D2O 0.4 Scattering (19 instruments)

OPAL Australia 2007 20 LEU D2O 0.4

Scattering (13 instruments)

Isotopes
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84 Appendices

two concentric cylindrical fuel elements, each approximately 61 cm in height, surrounding a 12.7 cm diameter central flux trap. The fuel is contained in 171 inner 

and 369 outer aluminum-clad fuel plates curved in 

the shape of an involute to provide a constant cooling 

channel width between plates. HFIR currently uses 

highly enriched 235U fuel and operates at a power level 

of 85 MWt.

The fuel region is surrounded by an annular 

beryllium reflector approximately 30.5 cm thick. The 

beryllium reflector is in turn surrounded by a water 

reflector of effectively infinite thickness. The reactor 

core assembly is contained in a 2.44 m diameter pressure vessel located in a 5.5 m diameter cylindrical pool 

of water. The pool walls are reinforced concrete with a 

stainless-steel liner.

The central flux trap includes 37 cylindrical target 

positions where multiple capsules can be irradiated 

in the highest-flux region of the reactor. There are an 

additional 42 target positions distributed in the beryllium reflector where the neutron fluxes are lower. Four 

horizontal beam tubes penetrate the reflector to transport beams of neutrons to 12 scattering instruments 

located outside the biological shield. One beam tube 

incorporates a liquid hydrogen cold source and transports cold neutrons to instruments in an adjacent guide 

hall, while the other beam tubes transport thermal 

neutrons to instruments outside the reactor shielding 

in the beam room. Two pneumatic tubes provide access 

for neutron activation analysis, and four slant tubes are 

available for engineering studies.

In addition to having the highest thermal neutron 

flux, the HFIR complex includes a unique capability for 

radioisotope separations, the Radiochemical Engineering Development Center (REDC). REDC is essential 

to the chemical separation and purification of alpha 

emitting isotopes produced at HFIR, as well as other 

isotopes making up more than 400 radioisotope shipments annually to universities, hospitals, industry, and 

other research institutions. This HFIR/REDC complex 

(Figure A1.2) is essential to the DOE isotope mission 

and unique in the world.

User Communities

HFIR serves five distinct user communities, each with 

unique characteristics. They include neutron scattering, 

isotope production and research, materials irradiation and radiation effects research, neutron activation 

analysis, and neutrino research. The flexible design of 

HFIR allows these communities to be served simultaneously at the highest neutron fluxes with minimal 

interference. A summary of numbers of experiments, 

users, and publications for each of these communities 

is given in Table A1.2. 

Neutron Scattering

HFIR and ILL in France produce the highest continuous neutron flux in the world for neutron scattering, 

a factor of two or more higher than any other facility. The brightness of the HFIR source for both cold 

and thermal neutrons slightly exceeds that of ILL, as 

shown in Figure A1.3. Table A1.1 provides a listing of 

FIGURE A1.1. Photo and schematic of the HFIR core, showing the flux trap (yellow), fuel region (gray), and reflector 

(purple and green). 

The various target positions for isotope production and materials irradiation are shown as well as the four horizontal 

beam tubes for neutron scattering (the cold source is incorporated in the HB-4 beam tube)

Source:  Oak Ridge National Laboratory, U.S. Dept. of Energy

Peripheral Target Positions (PTP)

Target

Hydraulic Tube (HT)
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Appendices 85

selected high-flux reactors in service today, including 

the number of scattering instruments at each facility 

with neutron scattering capability. Europe has twice as 

many scattering instruments at high-flux reactors as 

the United States. 

HFIR is the highest flux steady-state neutron 

source for neutron scattering in the world, and is a key 

asset in providing the United States with this much 

needed tool for materials research. The U.S. competitive position in neutron scattering could be substantially strengthened by making improvements to HFIR 

instruments and related beam systems, expanding 

low-background experimental space, and increasing 

the number of instruments.1 Reactor-based and pulsed 

neutron sources are complementary, with reactor-based 

sources preferred for experiments that require the 

highest neutron counts in specific, predetermined 

regions of experimental space. Both types of sources 

are needed for a globally competitive neutron scattering program. 

Isotope Production and Research

HFIR, together with SM-3 in Russia, produces the 

highest thermal neutron flux for isotope production—

more than a factor of two above any other facility worldwide. HFIR and SM-3 are the only facilities capable 

of producing milligram quantities of heavy actinides, 

including Cf-252. Californium-252 is widely used for 

industrial applications, with ~70% of the world’s supply 

provided by HFIR. By-products of Cf-252 production, 

including Bk-249, Cm-248, mixtures of Cf-249, 250, 

and 251, Es-254, and Fm-257, are used for heavy element chemistry and for superheavy element research 

and discovery. Elements 115 and 117 were discovered 

using Bk-249 from HFIR, and HFIR isotopes have been 

involved in the discovery or confirmation of eight additional elements since 1970. Curium-248 from HFIR 

is currently being used in a discovery experiment for 

element 119, and mixed Cf recovered from HFIR Cf-252 

sources is planned for use in the search for element 120. 

The very high flux of HFIR also enables the production 

of many other isotopes with the high specific activity 

that is often preferred in industry and medicine.

HFIR isotopes are processed in the adjacent REDC, 

a large complex that includes heavily-shielded hot cells 

for remote handling and chemical processing of highly 

FIGURE A1.2. ORNL’s High Flux 

Isotope Reactor (HFIR) campus 

including the Radiochemical 

Engineering Development 

Center (REDC)

Source: Oak Ridge National 

Laboratory, U.S. Dept. of Energy

TABLE A1.2. 

HFIR Experiments, Unique Users, and Journal Articles (2017)

USER 

COMMUNITY

NUMBER OF 

EXPERIMENTS

UNIQUE 

USERS

JOURNAL 

ARTICLES

Neutron scattering 561 561a 192a

Isotopes ~50b ~50c 2

Materials irradiation ~400d ~50c 48

Activation analysis ~900d ~10c 1

Neutrino physics 1 14e 2

Other HFIR 10

Totals 1747 635 243

a. Unique users performing neutron scattering research on site at ORNL 

in 2018

b. Number of unique irradiation campaigns

c. Principal investigators and unique customers

d. Unique capsules

e. Consortium institutions
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radioactive materials. HFIR isotopes are distributed 

to hundreds of research, medical, and industrial customers each year. Many of these isotopes are unique to 

HFIR and are incorporated into industrial and medical 

products with tens of thousands of end users. A list of 

HFIR isotopes currently in worldwide distribution is 

shown Table A1.3. In addition to the heavy actinides, 

unique and high-specific-activity isotopes from HFIR 

include Pu-238 (to power National Aeronautics and 

Space Administration deep space missions), Ac-227 (for 

targeted alpha therapy), Ni-63 (for luggage screening at 

airports), and Se-75 (for nondestructive testing of pipelines and other infrastructure). 

Materials Irradiation and Radiation Effects Research

HFIR provides the highest fast-neutron damage rate 

in the world for materials research in areas such as 

accident-tolerant nuclear reactor fuels and materials 

for future fusion reactors. Hundreds of specimens are 

irradiated each year for multiple DOE programs and 

other sponsors. More than 30 positions are available 

in the central flux trap of HFIR for high-flux experiments involving a total of up to 200 individual capsules. Neutron irradiation capabilities include neutron 

flux tailoring and temperature control for many experiments; more than 400 unique neutron irradiation 

experiments were performed at HFIR in FY 2017. This 

represents several thousand individual specimens 

ranging from fundamental irradiation effects to qualification of advanced materials supporting dozens of 

sponsors.

A gamma irradiation facility is also available that 

produces the highest dose rate for gamma radiation 

damage to understand materials behavior and qualify 

materials in high-gamma radiation environments (such 

as in nuclear reactors). 

Neutron Activation Analysis

HFIR neutron activation analysis capabilities are the 

best in the world, providing the highest-sensitivity 

trace analysis for national security programs, international treaty verification, environmental compliance, 

and other applications. Two pneumatic tubes, one 

leading to a higher flux region of the reflector and the 

other to a lower-flux region, transport samples to the 

reactor for irradiation and then on to shielded counting 

stations. Primary customers include the International 

Atomic Energy Commission and DOE and National 

Nuclear Security Administration sponsors. More than 

900 samples were analyzed in 2018.

Neutrino Research

The combination of a very high neutrino flux and 

the capability of locating a neutrino detector close to 

the reactor make HFIR uniquely attractive for reactor-based neutrino research. In 2015, 14 universities 

led by Yale University formed a consortium with 

ORNL to design, build, and operate a neutrino expeFIGURE A1.3. Source brightness for thermal and cold neutron scattering at HFIR and ILL

Source:  Oak Ridge National Laboratory, U.S. Dept. of Energy
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riment at HFIR (the Precision Reactor Oscillation and 

SPECTrum Experiment, or PROSPECT2). The goal is 

to measure short-baseline neutrino oscillations with 

implications for fundamental nuclear physics and the 

standard model. Related advances in neutrino detection and properties offer potential for the development 

of stand-off reactor monitoring.

HFIR in the 21st Century

HFIR has been substantially refurbished and upgraded 

over the past two decades with new infrastructure, a 

high-brightness cold source, and a guide hall and new 

instruments. Continued operation of HFIR beyond 

mid-century will require replacement of the pressure 

vessel—an upgrade previously accomplished at several 

other research reactors. Pressure vessel replacement 

would extend HFIR operation into the next century 

and would provide options for significant mission-related upgrades.

HFIR was designed to facilitate the replacement 

of all reactor systems, including the pressure vessel. 

HFIR executes an extensive corrective and predicted 

maintenance program including more than 700 preventative tasks each year. Components that have been 

refurbished/replaced include primary and back-up 

pumps, the beryllium reflector, beam tubes, heat 

exchangers, cooling tower, control plates, and electrical and safety systems. The program also includes 

the fuel cycle, including offsite production of fresh 

fuel and fuel elements and disposition of spent fuel. 

The HFIR maintenance program is up-to-date and 

has supported an operational predictability exceeding 

92% since 2007.

TABLE A1.3. Medical, Industrial, and Research Use of Selected HFIR Isotopes 

HFIR produces more than 50 different isotopes for hundreds of customers that supply products to tens of thousands of end users each year. Selected examples of isotopes currently in high demand are shown.

ISOTOPE DESCRIPTION APPLICATION UNIQUENESS TO HFIR

Californium-252

(Cf-252)

Compact neutron source Nondestructive analysis of 

nuclear fuel rods;

Analysis of product streams in 

mining and cement industry;

Oil well logging;

Safe reactor startup

HFIR supplies 70% of global 

demand 

(only other source of Cf252 

is in Russia)

Plutonium-238

(Pu-238)

Radioisotope power source Power and heating systems for 

NASA deep space and outer 

planet missions

HFIR (supplemented by 

Idaho National Lab) is the 

sole supplier for NASA

Nickel-63

(Ni-63)

Compact irradiation source Security screening of luggage 

at most airports

HFIR is sole supplier outside 

Russia

Actinium-227

(Ac-227)

Alpha radiation source 

together with its daughter 

Ra-223

FDA-approved for targeted 

alpha therapy of advanced 

cancers

Can only be produced in 

HFIR; demand growing 

with >$1B in private sector 

investment 

Barium-133

(Ba-133)

Gamma radiation source Specific oil well logging applications; calibration source for 

medical imaging devices 

Produced only in HFIR at 

desired specific activities 

and quantities

Selenium-75

(Se-75)

Gamma radiography source Nondestructive testing of welds 

in bridges, shipbuilding, and 

other infrastructure

HFIR produces very high 

specific activity Se-177 

widely preferred in industry

Other heavy actinides 

(byproducts of 

Cf-252 production)

Berkelium-249, Einsteinium-254, etc.New element discovery (including elements 117 and 115); 

heavy element chemistry

Actinides from HFIR currently being used in searches for 

elements 119 and 120

Lutetium-177

(Lu-177)

FDA approved for treatment 

on neuro-endocrine cancers

Multiple clinical trials for other 

advanced cancers;

>$1B in private investment

HFIR uniquely capable 

to produce with minimal 

impurities at high specific 

activity
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Pressure Vessel

HFIR was designed for pressure vessel replacement. 

The existing crane used for vessel installation can be 

used for removal and replacement. The existing truck 

airlock can be used to admit the new vessel. A photograph from the original vessel installation is shown in 

Figure A1.4. There are only three welded pipe connections (all other connections are flanged), and the vessel 

can be disconnected and sectioned under water in the 

existing reactor pool. The vessel is less activated than 

other waste that is routinely disposed at HFIR. Vessel 

sectioning and replacement have been demonstrated 

in industry and at the ILL and Petten research reactors 

in Europe. A plan for vessel removal was developed for 

HFIR in the 1980s.

Replacement of the pressure vessel will be required 

by mid-century due to embrittlement, possibly earlier 

if embrittlement trends depart from theoretical predictions. A new vessel would allow return to HFIR’s 

100 MWth design power level and would enable 

mission upgrades, including larger beam nozzles for 

enhanced neutron scattering, vessel head changes to 

support the isotope and materials irradiation missions, and improved cold source design for up to a 50% 

increase in source brightness. These changes would 

also support additional scattering instruments, improved online insertion/removal of isotope production 

and materials irradiation samples, better temperature 

control and instrumentation for in-core experiments, 

and improved facilities for handling irradiated materials. 

In 1987, it was discovered that the HFIR reactor 

vessel welds and base materials were embrittling due to 

irradiation damage at a faster rate than anticipated by 

the original designers, such that certain portions of the 

reactor vessel in the vicinity of the beam tube nozzles 

no longer met the American Society of Mechanical 

Engineers (ASME) Boiler and Pressure Vessel Code. In 

order to resume operations, reactor power was lowered to 85 MWth from 100 MWth, some operational 

parameters were changed, and a hydrostatic proof test 

of the reactor vessel was instituted to ensure vessel 

integrity. This test is performed every two effective full 

power years.

One of the corrective actions proposed at the time 

was to determine if the HFIR pressure vessel could be 

replaced with a new vessel. An engineering assessment 

was performed, and it was determined that the vessel 

could be replaced. This included removing the old vessel, cutting it up in the pool, disposing of the irradiated 

material in an appropriate DOE low-level waste facility, 

fabricating a new vessel with new materials that were 

known to resist radiation damage (304L stainless steel), 

and reconnecting all the piping and support structures. 

In many ways, the reactor vessel restricts upgrades 

to the reactor because it is the most permanent fixture 

in the facility. The current vessel nozzle sizes are 8.0 

in. ID for HB-1, HB-3, and HB-4, and 12.0 in. ID for 

HB-2. Increasing the HB-1, 3, and 4 nozzle sizes to the 

same as at HB-2 would allow larger beam tubes at these 

locations, enabling larger beams for neutron scattering. 

The vessel head design of the current reactor restricts 

easy access to certain locations in the permanent beryllium reflector that are used for material irradiation 

and/or isotope production. If vessel replacement is 

pursued, the vessel head and beam tube nozzles will be 

redesigned to improve mission performance.

The 1987 replacement study concluded that the 

vessel could be replaced on an accelerated schedule that 

took about 3 years at a cost of $18M. The results of the 

study included a new vessel engineering specification 

(replacement vessel shell and extension region only), 

and a set of preconceptual design drawings. With cost 

escalation from 1987 dollars, more recently in January 

FIGURE A1.4. Original Installation of the HFIR Pressure Vessel 

The HFIR building and pool were designed to support 

pressure vessel replacement.

Source: ORO Construction Division, M.K. Ferguson Co.
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2020, it was estimated that the redesign/procurement 

of a new stainless steel reactor pressure vessel shell with 

new upper and lower head, seismic upgrades, associated minor upgrades, larger nozzles to allow larger 

beam tubes at HB-1, -3, and -4 (HB-2 equivalent size), 

and top head changes to better support isotopes and 

materials irradiation missions, would be $300M.

The complete replacement of a research reactor 

vessel has been previously accomplished at the Institut Laue Langevin (ILL) and Petten research reactors 

in Europe. In 1983–1985, the pressure vessel at the 

45MWth High Flux Testing Reactor (HFR) at Petten 

was replaced. The Petten replacement study3 contains a 

complete description of the replacement campaign for 

that reactor. In 1995, the reactor vessel at the 75 MWth 

ILL reactor was replaced. ILL has an aluminum vessel 

with a core region similar to HFIR. In addition, extensive experience exists for heavy component replacement at nuclear power plants.

Second guide hall

The APS report, Neutrons for the Nation,4 makes the 

case that reactor-based neutron scattering continues 

to be essential for U.S. scientific competitiveness, and 

recommends a sharp increase in investments in neutron 

instrumentation. A revitalization of HFIR, with improvements to the reflector design and a new pressure vessel, presents an outstanding opportunity to improve the 

U.S. capabilities in materials research using neutrons. 

One of the main challenges at HFIR is the relatively 

cramped space and high fast neutron background in the 

existing thermal beam room. Thus, significant gains can 

be attained by adding a second guide hall. This would 

enable the construction of more instruments with great 

improvements in the signal-to-noise. 

An additional guide hall at the HB-2 position with 

ten instruments would require the removal of three 

existing instruments for a net gain of six. With the 

possible addition of a couple of new instruments in the 

HB-4 guide hall, one can envision that an increase of 

instruments in the user program from 12 to 20 is possible. It must be recognized from the outset that the 

true benefits of improvements to the neutron source 

can only be realized if they are coupled with upgrading 

and constructing neutron scattering instrumentation to 

world competitive levels. Indeed, most of the improvements in neutron scattering over the past 50 years have 

been realized via enhancements in instrumentation. 

With this in mind, several possibilities for a 

reconfiguration are possible. One model that has been 

discussed is to build a cold guide hall at HB-2, and 

recast the HB-4 guide hall as a thermal neutron facility. Moving thermal instruments into a guide hall 

enables significant improvements in signal to noise, 

and is essential for building the best instruments to 

complement the facilities envisioned at the SNS. Up to 

20 world class instruments could be accommodated in 

this configuration.

In 2003, a cold guide hall for HB-2 was among 

the long-term priorities outlined in the DOE Office of 

Science report, Facilities for the Future of Science: A 

Twenty-Year Outlook.5 A cut-away view of the instrument level of HB-2 Guide Hall as envisioned at that 

time is illustrated in Figure A1.5. The preliminary 

design made use of the perceived wisdom that the 

performance of the instrument suite is greatly improved if essentially all instruments occupy end-of-guide 

positions. It was envisioned that up to 10 new instruments could be constructed in the guide hall. Adequate allowance was made for the requirement of the 

ancillary laboratories and office space needed to make 

the best use of these instruments. The estimated cost 

of constructing the HB-2 facility, including the cold 

source, guide system, instruments, guide hall, project 

management, and 20% contingency was just under 

$100 million dollars (in constant 2003 dollars) over a 

5-year period. An additional examination of the HB-2 

cold source possibility was carried out in 2012 and 

confirmed a new cold source at HB-2 could easily be 

50% brighter than the more compact cold source extant 

FIGURE A1.5. Early HB-2 Guide Hall Concept

Source:  Oak Ridge National Laboratory, U.S. Dept. of Energy
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90 Appendices

at HB-4. A more recent examination presented to the 

BESAC Subcommittee on High-Performance Reactor-based Research Facilities in January 2020 estimated 

the cost $375M. 

New reflector

In the past, the possible instrumentation upgrades 

for HFIR have been considered under the assumption 

that the essential configuration of the reactor pressure 

vessel and Be reflector would remain unchanged. A 

new reflector would be particularly advantageous for 

a cold source in the HB-2 location. Changing a major 

component of the reactor can affect several aspects 

of operation, including cycle length, as discussed 

elsewhere. Many options are under consideration and 

much optimization may be possible. To get a general 

idea of the possible effects of a new moderator on the 

brightness delivered to neutron instruments, it is worthwhile to examine the gain factors obtained simply by 

replacing the Be reflector with a D2O reflector. The net 

result is that brightness of cold and thermal neutrons 

is increased by 30–40%, while the fast neutron background is reduced by a similar amount, suggesting that 

the signal to noise can be improved by roughly a factor 

of two, independent of other improvements.

The HFIR beryllium reflector is composed of three 

regions including, in order of replacement frequency 

and distance from core centerline, the removable beryllium reflector, the semi-permanent beryllium reflector, 

and the permanent beryllium reflector. The expected 

lifetimes of these components are approximately 83.7, 

167.4, and 279 GWd, respectively (or approximately 6, 

12, and 20 years). In preparation for the HFIR permanent beryllium change-out in 2024, ORNL redesigned 

the permanent beryllium reflector to include six additional irradiation sites, be more versatile with respect 

to irradiation and scattering experiments, and enhance 

its thermal-structural performance. The new design 

increases the number of vertical experiment facilities 

from 22 to 28, and arranges them in a way to maximize 

their availability for radioisotope production (e.g., 238Pu 

production targets) and materials irradiation experiments without interfering with the neutrons delivered 

to the cold and thermal neutron scattering instruments. 

Replacing HFIR’s beryllium reflector with heavy 

water (D2O) offers the potential to further enhance 

neutron scattering performance. The D2O could be 

introduced as either a physical tank located within the 

pressure vessel, or as the coolant beyond the control 

element region. The absorption cross section and thermal diffusion length of D2O are much less than those 

of beryllium; thus, the neutron mean free path in D2O 

is much longer. Consequently, a D2O tank has the possibility to significantly increase the reflector region’s 

volume-averaged neutron flux and provide a more 

constant flux profile across its radius in comparison to 

the beryllium reflector. This enhancement could result 

in increased neutron fluxes on scattering samples, and 

additional space for larger beam tubes. However, the 

direct change from beryllium to D2O results in reactivity and cycle length degradation due to the change 

in neutron reflection properties. Thus, a combination 

of beryllium and D2O reflectors may provide optimal 

performance.

At a minimum, conversion to a D2O reflector 

would require:

1. an initial study to better characterize the performance impacts of the change

2. an evaluation of potential impacts to the safety basis

3. an engineering evaluation and design

4. as-required safety basis evaluations/calculations 

and updates to the documented safety analysis 

(DSA) with U.S. DOE approval

5. construction of the designed system, and 

6. startup testing. 

The DSA would need to be evaluated to determine 

safety aspects that would need to be removed, updated, 

or added as a result of the modification. The nuclear 

design aspects of the reactor including power distributions, shutdown margin, and reactivity coefficients 

would need to be addressed. Additionally, tritium produced via nuclear activation of the D2O would need to 

be managed. 

Fuel cycle

The HFIR fuel cycle can be broken down into five separate phases: HFIR Uranium Oxide Production, HFIR 

Fuel Assembly Fabrication, HFIR Fuel Production 

Equipment Upgrades, fresh and irradiated fuel shipment, and HFIR Spent Fuel Storage and Disposal.

HFIR’s uranium oxide is provided from feedstock 

at the Y-12 National Security Complex. The oxide 

processing takes place at Y-12’s 9212 Facility. This antiquated facility is scheduled to be decommissioned in 

the middle to late 2020s and will be replaced by a new 
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facility, the Uranium Processing Facility (UPF), currently under construction at Y-12. HFIR fuel elements 

are fabricated and assembled at BWXT in Lynchburg, 

Virginia. 

HFIR recently experienced a fuel deformation 

event that caused a manual shutdown due to increased 

radiation readings in the primary coolant system in 

November 2018. Upon opening the reactor vessel, fuel 

plate deformation on outer fuel element O-488 was 

observed. The cause of the fuel deformation has been 

attributed to machining errors on the outer side plate 

and subsequent fuel element assembly issues that led to 

inadequate welding and attachment of the fuel plates to 

the inner side plate. Enhancements to HFIR operations 

are underway to address potential vulnerabilities noted 

from the event. 

HFIR restarted in October 2019 following completion of corrective actions that were made as a result of 

the fuel deformation event. The restart of the fuel element manufacturing and assembly processes at BWXT 

is planned for 2020. 

LEU conversion

ORNL is funded by the U.S. DOE NNSA’s Office of 

Material Management and Minimization to perform 

HFIR HEU to LEU conversion studies as part of 

their nuclear nonproliferation mission. HFIR is one 

of six domestic high-performance research reactors 

(USHPRRs) that cannot be converted with existing 

LEU fuel forms and corresponding qualification envelopes. HFIR is committed to converting to LEU once 

a fuel form capable of ensuring that operations will 

continue at the current functional, scientific performance level in a safe, reliable, and affordable manner.

HFIR LEU conversion will take place in five phases 

with the appropriate safety basis preparation by ORNL 

and U.S. DOE SC approval for each. 

• The first phase is to present U.S. DOE SC with a 

Preliminary Documented Safety Analysis (PDSA) 

in the early 2020s. 

• The second phase consists of running at least one 

cycle with the current HEU fuel at the higher 

power required for LEU conversion (e.g., 95 MW) 

to demonstrate the ability of the reactor cooling 

systems to remove the higher heat load. 

• Third, in-vessel, low-power tests of the LEU lead 

test core (LTC) will be conducted to confirm calculated neutronic parameters. 

• Then, a single cycle with the LTC will be run at the 

higher power to demonstrate continued ability to 

perform HFIR’s scientific mission safely. 

• The fifth and final phase consists of operating 

HFIR long-term with LEU fuel at the higher power 

following conversion. The low-power LTC tests and 

conversion to LEU are currently scheduled for 2030 

and 2033, respectively.

Fuel design studies have been conducted by ORNL 

to evaluate performance and safety metrics for two 

proposed fuel systems for HFIR: uranium-molybdenum monolithic alloy fuel (U-10Mo) and uranium-silicide dispersion fuel (U3Si2-Al). Although the other 

five USHPRRs are planning to be converted with the 

U-10Mo monolithic fuel system, due to the complex 

nature of the HFIR fuel system (e.g., radially contoured 

fuel zone), it was anticipated that the fuel manufacturing R&D process for HFIR U-10Mo monolithic fuel 

would be long and expensive and might not deliver a 

manufacturing process with adequate yields to maintain an economically viable fuel. Therefore, in 2017, the 

conversion program asked ORNL to evaluate U3Si2-Al 

dispersion fuel systems6 because the fuel manufacturing R&D effort was believed to be shorter and less 

expensive, and the resulting manufacturing process 

was thought to be capable of higher yield/lower cost 

than U-10Mo monolithic fuel.

Advantages of the silicide dispersion fuel over 

monolithic are that it:

1. has been fabricated for several years by several 

vendors using a process that is similar to the one 

currently used to fabricate the complex fuel design 

of the HFIR HEU U3O8-Al dispersion fuel

2. was qualified and approved by the U.S. Nuclear 

Regulatory Commission for use in medium-power 

research reactors (NUREG-1313, 1988), and 

3. offers better uranium utilization (i.e., less uranium 

required per day of operation). 

However, fabrication of fuel plates with the complex HFIR design features has yet to be demonstrated 

and additional irradiation testing is required to qualify 

this fuel system for use in HFIR. 

BWXT is currently developing U3Si2-Al fuel plates 

for the HFIR-FUTURE irradiation tests to be performed in the SCK-CEN BR2 reactor. Fabrication is 

expected to be completed in late 2020, with irradiation 

to follow shortly thereafter. Results from these tests 
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will help provide input to subsequent fabrication and 

irradiation phases, which will consist of fabrication 

down-selections, plate demonstrations, full-size HFIR 

plate irradiations, fuel assembly fabrication demonstrations, design demonstration element testing, LTC fabrication and testing, and HFIR conversion. 

Seismic upgrades

Seismic upgrades for the reactor building could be 

accomplished at the same time as the vessel replacement. These upgrades are required to meet current 

seismic standards for the building—the reactor itself 

meets current seismic standards including reactor 

safety in the event of a building collapse. The upgrades 

primarily involve reinforcement of several columns and 

roof beams using technology that has been successfully 

demonstrated at other facilities.

Enhanced Mission Performance

The improvements and upgrades described above offer 

opportunities to substantially enhance the mission performance of HFIR. The new pressure vessel will support larger beam tubes and an improved cold source, 

strengthening and expanding neutron scattering capabilities. The redesigned pressure vessel head will enable 

improved access for isotope production and materials 

irradiation. The new pressure vessel will also allow a 

return to 100MWt operation, providing an immediate 

~20% increase in neutron flux. The higher power level 

will also be essential for maintaining current performance levels with low enrichment fuel should a suitable 

fuel technology become available.

In Figure A1.6, the average neutron brightness 

and peak brightness are compared for leading steadystate and spallation neutron sources worldwide. The 

upgraded HFIR will have world-leading time-averaged 

brightness for both thermal and cold neutrons. The 

high average steady-state brightness complements the 

intense peak brightness available at pulsed spallation 

sources, with the steady-state sources providing distinctive advantages for neutron scattering studies at 

specific length and time scales. The very high cold 

and thermal neutron fluxes at the upgraded HFIR will 

extend experiments to new frontiers, particularly for 

weak scattering systems and samples available only in 

smaller sizes.

The second guide hall will provide an opportunity 

to increase the number of instruments from the current 

12 to 20. All instruments will be state-of-the-art, and 

fed by world-leading cold and thermal neutron beams. 

Particular instrument choices and designs will be developed with broad community input. A new cold source 

will provide a ~50% boost to cold neutron brightness, 

and improved beam systems will increase available flux 

at cold and thermal instruments by factors of two or 

more. Low backgrounds in the guide halls will increase 

measurement sensitivity enabling faster data acquisition and detection of weaker signals. This will enable 

FIGURE A1.6. The Upgraded HFIR Will Provide World-leading Time-averaged Brightness 

for Both Cold and Thermal Neutrons

Source:  Oak Ridge National Laboratory, U.S. Dept. of Energy
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Appendices 93

new and better experiments to probe the structure and 

dynamics of materials that will drive future energy 

technologies, including energy storage materials, catalysts for production of fuels and chemicals, structural 

materials for transportation, next generation polymers, 

and quantum materials. Moreover, these instruments 

will provide the highest resolution for phase transitions 

at extreme conditions of magnetic field and temperature, quantum phenomena, residual stress mapping of 

engineered systems, and imaging of operating systems 

including batteries, fuel cells, and engines. 

The increased neutron flux enabled by the new 

pressure vessel will provide a corresponding increase 

in isotope production and damage rates for materials 

irradiation experiments. In addition, the changes to 

the reactor vessel head will facilitate introduction and 

removal of capsules, including during reactor operations. This will allow increased isotope production, 

especially for short-lived isotopes, such as Pt195m, 

Lu-177, W-188/Re-188, and Sr-89 for medical applications, Se-75 for radiography, and Es-253 for heavy element chemistry. The improved access will also enable a 

significant increase in instrumented materials irradiation experiments to advance radiation effects research, 

including the development of accident-tolerant fuels 

and fusion reactor materials.

For over 50 years, HFIR has addressed important 

and often unique missions supporting the DOE Office 

of Science and the Nation. The proposed upgrades 

will significantly enhance the value of the reactor in 

carrying out these missions, and ensure its continued 

availability for the foreseeable future.Preliminary 

estimates indicate that the vessel replacement and 

improvements described above could be accomplished 

in a multi-year effort including a reactor outage of 

approximately two years. New scattering instruments 

would come online in stages following the outage. The 

upgraded HFIR will offer new and expanded state-ofthe-art capabilities for cold and thermal neutron scattering, isotope production and research, and materials 

irradiation using the world’s most intense steady-state 

neutron beams. Preliminary estimates indicate that the 

full HFIR upgrade project including pressure vessel, 

top and bottom head, reflector, cold source, redesigned 

nozzles and beam tubes, second guide hall, guides, 

instruments, building seismic upgrades, and various 

life extension projects would be in the general range of 

$500–800M, including contingency.

References

1. G. Ilas, C. Bryan, and J. Gehin, Needs and Requirements for 

Future Research Reactors, ORNL/TM-2015/654, Oak Ridge 

National Laboratory, February 2016.

2. J. Ashenfelter et al., “The PROSPECT reactor antineutrino 

experiment,” Nucl. Instrum. Methods A922, 287, 1808.00097 

(2019).

3. N. G. Chrysochoides et al., High Flux Testing Reactor Petten: 

Replacement of the Reactor Vessel and Connected Components, 

Commission of the European Communities, ISBN 92-825-

5710-3 (1985).

4. Neutrons for the Nation: Discovery and Applications while Minimizing the Risk of Nuclear Proliferation, Panel on Public Affairs, 

American Physical Society, July 2018. https://www.aps.org/policy/reports/popa-reports/upload/APSNeutronsfortheNation.

pdf.

5. Facilities for the Future of Science: A Twenty-Year Outlook, 

Office of Science, U.S. Department of Energy, November 2003.

6. D. Chandler, B. Betzler, D. Cook, G. Ilas, and D. Renfro, “Neutronic and thermal-hydraulic feasibility studies for High Flux 

Isotope Reactor conversion to low-enriched uranium silicide 

dispersion fuel,” Ann. Nucl. Energy 130, 277 (2019).
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94 Appendices

APPENDIX 2. The Global Effort to Convert Research 

Reactors to Low Enriched Uranium Fuels

The U.S. technical effort to replace the use of High 

Enriched Uranium (HEU, U-235 enrichment ≥ 

20%) fuel with Low Enriched Uranium (LEU, U-235 

enrichment < 20%) fuel began in 1978 as the Reduced 

Enrichment for Research and Test Reactors (RERTR) 

program, immediately working as a global community 

of reactor operators, fabricators, and their governments. From the first RERTR International Meeting in 

1978, the program has been focused upon preservation 

of reactor mission capability as a central tenet of the 

conversion program. Indeed, the reason the program 

continues forty years later is because the community 

continues to collaborate on projects to preserve mission 

capability, rather than forcing degradation of performance. The RERTR program management within the 

Department of Energy matured to the Global Threat 

Reduction Initiative (2004-2015) and now the National Nuclear Security Administration (NNSA) Office 

of Material Management and Minimization (M3, 

2015-present). 

As indicated in Figure A2.1, there has been a great 

deal of success converting reactors around the world. 

A total of 71 reactors converted from Highly Enriched 

Uranium (HEU) fuel to Low Enriched Uranium (LEU) 

fuel in the period 1978-2019, and an additional 31 

reactors that used HEU fuel have been confirmed permanently shutdown. Table A2.1 lists the reactors with 

a peak thermal flux > E14 n/cm2/s that converted in the 

period 1978-2019. The list includes many high impact 

reactors that represent a wide variety of scientific and 

isotope production capabilities. Table A2.2 indicates 

the variety of research reactor fuels used in reactors 

that have converted or that are under development and 

qualification for conversion of the remaining reactors. 

Overview of U.S. and European High Flux 

Reactor Conversion Efforts Since 2005

Though the global community has converted 24 reactors with high flux, unique challenges remain for a 

group of highly optimized HEU reactors in the U.S. 

and Europe. The U.S. High Performance Research 

Reactors (USHPRR) and European High Flux Reactors (EUHFR) are each quite distinct, but have less 

fuel assembly design and/or grid-plate flexibility than 

prior conversions; high power density in the fuel in 

order to provide the intense experimental fluxes; and 

high burnup in those reactors that reload fuel in order 

to minimize fuel costs. This Appendix describes many 

of the details of the efforts to convert the USHPRR 

and EUHFR reactors. The aspects of that effort that 

are most relevant to the capabilities of HFIR are described in the HEU-LEU Conversion section, whether 

FIGURE A2.1 

Geography of the 

Global Reactor 

Conversions, 

1978–2019

Source: John Stevens, 

Argonne National 

Laboratory
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Appendices 95

as a HFIR LEU conversion or a refurbished HFIR with 

LEU fuel.

In 2005, the NNSA Reactor Conversion Program 

formed the USHPRR sub-program to maximize 

synergy during conversion of the five U.S. reactors 

using HEU to meet their high flux, high national impact 

missions: The MITR at Massachusetts Institute of 

Technology in Cambridge, Massachusetts; the MURR 

at University of Missouri in Columbia, Missouri; the 

NBSR at the National Institute of Standards and Testing 

(NIST) in Maryland; the ATR at the Idaho National 

Laboratory (INL); and the HFIR at Oak Ridge National 

Laboratory (ORNL) in Tennessee. (The ATRC critical 

facility will also be converted to remain appropriate 

for the ATR reactor programs). The NNSA USHPRR 

sub-program has assembled expertise from nine national laboratories and sites (Argonne, Brookhaven, Idaho, 

Los Alamos, Oak Ridge, Pacific Northwest, Sandia, 

and Savannah River national laboratories and the Y-12 

national security complex) as well as the reactor operating institutions, fuel fabricator BWXT, and the U.S. 

Nuclear Regulatory Commission (NRC).

In parallel to the USHPRR effort, the NNSA Reactor Conversion Program has been collaborating with 

the EUHFR and their fabricator CERCA as a group 

since 2008 to develop and qualify the high density LEU 

fuel that will allow conversion of the EUHFR reactors: 

the BR2 at SCK CEN in Mol, Belgium; the RHF at 

Institut Laue-Langevin (ILL) in Grenoble, France; and 

the JHR under construction at the French Alternative 

Energies and Atomic Energy Commission (CEA) in 

Cadarache, France. The U.S. technical effort to support 

the EUHFR conversion has always involved a team 

of Argonne and Idaho National Laboratories, under 

the International Reactor Conversion sub-program at 

NNSA. The Y-12 national security complex has been 

instrumental for fresh uranium supply and transport. 

Savannah River National Laboratory provides strategic 

assistance.

USHPRR Feasibility Studies conducted in 2005-

2009 developed conceptual LEU designs for each of 

the reactors to preserve their mission capabilities 

with a revolutionary high-density LEU fuel, U-10Mo 

monolithic fuel. This monolithic fuel form is a foil of 

TABLE A2.1. High Flux Reactors Converted to LEU 1979–2019 (i.e., peak thermal flux > E14 n/cm2/s)

COUNTRY FACILITY NAME TYPE STATUS CONVERTED

THERMAL

POWER (MW)

Canada NRU HEAVY WATER PERMANENT SHUTDOWN 1992 135

China HFETR TANK OPERATIONAL 2007 125

France OSIRIS POOL UNDER DECOMMISSIONING 1979 70

Sweden R2 TANK UNDER DECOMMISSIONING 1990 50

Japan JMTR TANK PERMANENT SHUTDOWN 1993 50

Netherlands HFR TANK IN POOL OPERATIONAL 1998 45

Poland MARIA POOL OPERATIONAL 2012 30

South Africa SAFARI-1 TANK IN POOL OPERATIONAL 2008 20

Romania TRIGA II PITESTI - SS TRIGA OPERATIONAL 1992 14

Czech Republic LVR-15 REZ TANK WWR OPERATIONAL 2010 10

Germany BER-II POOL PERMANENT SHUTDOWN 1997 10

Hungary BUDAPEST RR TANK WWR OPERATIONAL 2009 10

Pakistan PARR-1 POOL OPERATIONAL 1991 10

Ukraine WWR-M KIEV TANK WWR OPERATIONAL 2008 10

Libya IRT-1 POOL, IRT TEMPORARY SHUTDOWN 2006 10

Uzbekistan WWR-SM TASHKENT TANK WWR OPERATIONAL 2008 10

Austria ASTRA POOL DECOMMISSIONED 1983 10

Denmark DR-3 HEAVY WATER UNDER DECOMMISSIONING 1988 10

Switzerland SAPHIR POOL DECOMMISSIONED 1990 10

Australia HIFAR HEAVY WATER PERMANENT SHUTDOWN 2004 10

Germany FRG-1 POOL UNDER DECOMMISSIONING 1991 5

United States GTRR (Georgia Tech) TANK DECOMMISSIONED 1997 5

Greece GRR-1 (Demokritos) POOL EXTENDED SHUTDOWN 1999 5

Canada MNR MCMASTER POOL, MTR OPERATIONAL 1999 3

Note that that the Conversion Program addresses actual performance metrics rather than simple

flux values. The data presented in this table is from the IAEA database on 22 April 2020, https://nucleus.iaea.org/RRDB/RR/ReactorSearch.aspx
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96 Appendices

TABLE A2.2. Uranium Density of Research Reactor Fuels Qualified and Under Qualification

URANIUM LOADING DENSITY

(GU/CM3)

19781 NOW2

IN

PROGRESS

TRIGA UZrH Pins 0.5 2.1 — 30/20 qualified in NUREG-1282 (1987)3

UO2 Pins 9.3 — — not fabricable for plate geometry

UAlx-Al Dispersion 1.7 2.3 — HEU fuel in use at MITR, MURR, ATR, BR2, RHF

U3O8-Al Dispersion 1.3 3.2 — HEU fuel in use at NBSR and HFIR

U3Si-Al Dispersion — 6 — only suitable for limited irradiation conditions

U3Si2-Al Dispersion — 4.8 — Qualified fuel in NUREG-1313 (1988), but at much lower power density 

than USHPRR and EUHFR4

— — 4.8–5.6 HERACLES/LEU FOREvER at EUHFR Conditions

 (experiment irradiated, awaiting PIE)5

— — 5.3 SCK COBRA EUHFR Conditions including Gd integral

 burnable absorber (irradiation in progress)6

— — 4.8 USHPRR HFIR-Relevant Conditions (experiment being fabricated)12

UO2-Al Dispersion — 2.5 — WWR-M2 Qualified (2002)7

— 2.8 — VVR-KN Conversion (2013) Coextruded tubes8

— 3.0 — IRT-4M Qualified (2002) Coextruded tubes9

UMo-Al Dispersion — 5.4 — IRT-3M Qualified (2016) Coextruded tubes10

— — 8 KJRR LTA (2 LTAs irradiated, PIE in progress)11

— — 8 HERACLES/US5,6 (EUHFR experiments irradiated, PIE in progress)

UMo Monolithic — — 15.3 USHPRR HIP Clad Process (in qualification phase of experiments)12-15

— — 15.3 HERACLES C2TWP Clad Process (in development, miniplates irradiated)5,16

Sources:

1. A. Travelli, “The U.S. Reduced Enrichment Research and Test Reactor (RERTR) Program,” 1st Intl. Mtg. RERTR, Argonne, Illinois, 9-10 November 

1978.

2. A. Travelli, “The RERTR Program and Status,” 18th Intl. Mtg. RERTR, Paris, France, 17-21 September 1995.

3. NUREG-1282 (1987): U.S. Nuclear Regulatory Commission, “High-Uranium Content, Low-Enriched Uranium Zirconium Hydride Fuels for 

TRIGA Reactors,” NUREG-1282, August 1987.

4. NUREG-1313 (1988): U.S. Nuclear Regulatory Commission, “Safety Evaluation Report Related to the Evaluation of Low-Enriched Uranium 

Silicide-Aluminum Dispersion Fuel for Use in Non-Power Reactors,” NUREG-1313, July 1988.

5. S. Valance et al., “Innovative and Safe Supply of Fuels for Reactors,” EPJ Nuclear Sci. Technol. 6, 40 (2020).

6. S. Kalcheva et al., “BR2 Fuel Evolution toward Sustainable Fuel Cycle,” RRFM 2018 Intl. Mtg., Munich, Germany, 11-15 March 2018.

7. K. A. Konoplev et al. “LEU WWR-M2 Fuel Qualification”, 24-th Intl. Mtg. RERTR, Bariloche, Argentina, 3-8 November 3-8, 2002.

8. A.A. Shaimerdenov et al., “The 50th Anniversary of the WWR-K Research Reactor,” Physics of Atomic Nuclei, Vol. 81, No. 10, pp. 1408–1411 (2018).

9. V.M. Chernyshov et al., “Results of IRT-4M Type FA’s Testing in the WWR-CM Reactor (Tashkent),” 24th Intl. Mtg. RERTR, Bariloche, Argentina on 

3-8 November 2002.

10. A.L. Izhutov et al.,” Lifetime Testing of Two IRT-3M (High Density U-9%Mo) LEU Lead Test Assemblies in the MIR Research Reactor,” 37th Intl. 

Mtg. RERTR, Antwerp, Belgium, 23-27 October 2016.

11. J.S. Yim et al., “On-Going Status of KJRR Fuel (U-7Mo) Qualification,” RRFM 2017 Intl. Mtg., Rotterdam, Netherlands, 14-18 May 2017.

12. E.H. Wilson et al., “U.S. High Performance Research Reactor Preliminary Design Milestone for Conversion to Low Enriched Uranium Fuel,” 2019 

RRFM Intl. Mtg., Jordan 

13. B. Rabin et al., “Preliminary Report on U-Mo Monolithic Fuel for Research Reactors,” INL/EXT-17-40975 Rev. 1, Idaho National Laboratory, 

Idaho Falls, USA, December 2017.

14. N.E Woolstenhulme, et al., “Irradiation Tests Supporting LEU Conversion of Very High Power Research Reactors in the US,” 37th Intl. Mtg. 

RERTR, Antwerp, Belgium, 23-27 October 2016.

15. J.M. Wight et al., “USHPRR Fuel Fabrication Pillar: Fabrication Status, Process Optimizations, and Future Plans,” RRFM 2018 Intl. Mtg., Munich, 

Germany, 11-15 March 2018.

16. B. Stepnik et al., “UMo Monolithic Fuel Development Progress in Areva-CERCA,” RRFM 2014 Intl. Mtg., Ljubljana, Slovenia, 30 March – 3 April 2014.
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Appendices 97

uranium-molybdenum (UMo) alloy (U-10Mo indicates 

an alloy with 10% molybdenum by weight) coated by 

a zirconium diffusion barrier, then clad in aluminum 

alloy by hot isostatic pressing. The U-10Mo monolithic 

fuel offers exceptional uranium density of approximately 15.3 gU/cm3 of foil. The U-10Mo fuel is often termed revolutionary since multiple fabrication techniques 

necessary for consistent production are new to commercial production of research and test reactor fuel.

EUHFR Feasibility Studies conducted in 2008-2010 

developed conceptual designs for BR2 and RHF to preserve their mission capabilities with an evolutionary 

high-density LEU U-7Mo dispersion fuel, since the JHR 

being constructed in France was designed to deploy 

LEU U-7Mo Dispersion Fuel that was under development. The dispersion fuel form is a mixture of particles 

of uranium-molybdenum alloy (U-7Mo indicates an 

alloy with 7% molybdenum by weight) mixed with an 

aluminum powder matrix and compacted to form the 

“fuel meat”. That fuel meat is then clad in aluminum 

alloy by a rolling process. The U-7Mo dispersion fuel 

offers high density of approximately 8 gU/cm3 of fuel 

meat (where the uranium density can be adjusted by 

altering the volume ratio of fuel particles and the aluminum matrix). The 7% Mo level was chosen for the 

dispersion fuel in order to balance the fission gas retention benefit of Mo in the alloy against the reduction 

in uranium loading density as the Mo weight fraction 

is increased. The U-7Mo fuel is often termed evolutionary since most fabrication techniques necessary for 

consistent production are consistent with the existing 

qualified dispersion fuels (UAlx, U3O8, and U3Si2).

Early testing of UMo fuel systems indicated creation of an amorphous intermetallic interaction layer 

between the UMo alloy and aluminum. That interaction layer allowed fission gas bubbles to grow and interconnect, leading to a problematic level of plate swelling, 

or failure by “pillowing” or “delamination” if the interconnected bubble region reached a scale at which material strength was compromised.

For dispersion fuel, the addition of silicon to the 

aluminum matrix was effective at controlling the interaction between UMo and the matrix for experiments 

irradiated at moderate power to full burnup. Tests of 

the U-7Mo with silicon in the matrix performed well 

for moderate-power experiments including miniplates 

in ATR, pin experiments at HANARO, full-size plate 

experiments in ATR, and the KJRR Lead Test Assembly elements at the ATR. However, the fuel irradiation 

efforts of the EUHFR collaboration between 2008 

and 2013 (during which the international team was 

named LEONIDAS) exposed continuing irradiation 

performance problems with the Uranium-Molybdenum (U-7Mo) dispersion fuel product subject to the 

combination of high power density and high burnup 

required for the EUHFR application. Two irradiation 

tests during that time frame (E-FUTURE and E-FUTURE-II) that used silicon in the fuel matrix to mitigate the interaction between the U-7Mo alloy and the 

aluminum matrix failed to meet the burnup required 

for EUHFR application.

For monolithic fuel, a zirconium layer between the 

UMo foil and the aluminum alloy clad proved highly 

effective at avoiding the interaction layer. Between 

2007 and 2011, the USHPRR program conducted seven 

irradiation campaigns consisting of 14 large size plates 

and over 60 mini plates with U-10Mo fuel with a zirconium interlayer. Those tests included power densities 

and burnups to envelop the NRC-regulated USHPRR 

(MITR, MURR, and NBSR) and significant portions 

of the ATR and HFIR envelopes. Unfortunately, in the 

same time period, the USHPRR Fuel Fabrication effort 

had experienced significant challenges with fabrication 

scale-up of the novel U-10Mo monolith fuel form for 

full-size plate experiments and increased rates, with 

very low yields that caused many long delays and did 

not seem to be converging toward a sustainable cost.

Thus, in 2012-2013, NNSA Reactor Conversion fuel development and qualification efforts were 

significantly restructured for both the USHPRR and 

FIGURE A2.2. The Concepts of Dispersion 

and Monolithic Fuel Plates

Source: Kim, Y.S. and Hofman, G.L., Journal of 

Nuclear Materials, Volume 419, Issues 1–3, December 2011, Pages 291 -- 301.
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98 Appendices

EUHFR. The European collaborators also restructured their approach, evolving LEONIDAS into the 

HERACLES Consortium by the addition of the FRM-II 

reactor of Technical University of Munich (TUM) in 

Garching, Germany, and engagement with EURATOM 

Framework funding mechanisms.

The USHPRR and EUHFR teams learned from 

each other regarding the 2008-2013 challenges encountered. The EUHFR team adopted the diffusion barrier 

and heat treatment approaches that had proven vital 

for excellent irradiation performance of the U-10Mo 

monolithic fuel. The USHPRR team adopted inclusion 

of a commercial fuel fabricator and pilot-line-production that had proven predictable and effective for 

EUHFR experiment fabrication. Both teams slowed the 

pace of irradiation experiments to assure that maximum data value would be generated by each experiment, in terms of both fabrication data and irradiation 

performance data. In addition, both teams have had 

independent expert reviews to assure appropriate creativity, transparency, and rigor.

The independent expert review of the EUHFR 

plan in 2015 suggested that the EUHFR pursue U3Si2

dispersion fuel as a backup to their work on U-7Mo 

dispersion. Though the uranium density of U3Si2 is 

considerably lower than U-7Mo, three attributes were 

of interest to the EUHFR as a backup. First, U3Si2 dispersion was qualified for modest power densities in 

1988 and has since been used to convert many research 

reactors and has been deployed in several new reactors, 

including a number with peak fluxes above E14 n/cm2/s 

(such as HFR Petten, SAFARI, MARIA, and OPAL). 

The JHR in France will begin operations with U3Si2, 

and the CEA completed the high-power-density EVITA 

experiments at the BR2 reactor in Belgium to support 

fuel qualification for the JHR. (Unfortunately, EVITA 

results are not available outside of the JHR project since 

the fuel qualification case is still being reviewed by the 

French regulator.) Second, the fabrication of U3Si2 is 

well established and will be simpler than the U-7Mo 

dispersion fabrication. Thus, fuel cost per element 

should be lower, even if more elements are needed each 

year due to lower density. Third, Orano has recently 

deployed a backend solution for U3Si2 fuel, while the 

backend for U-7Mo dispersion fuel would require development and deployment.

SCK CEN reconsidered their BR2 fuel element 

plate thickness and radius constraints, and determined 

that a modified geometry would allow preservation of 

mission capabilities with an LEU 5.3 g/cm3 U3Si2 dispersion fuel incorporating gadolinium as an integral 

burnable absorber.

Since the promising results for LEU U3Si2 application to a redesigned BR2 fuel element, the conversion 

design teams for HFIR and the RHF reactor at ILL in 

France have both reconsidered geometric constraints 

and have developed design candidates for variants of 

U3Si2 details that would preserve mission capability.

In the case of HFIR, U3Si2 is not the backup solution, but was established as the baseline solution in 

2019.

Notable USHPRR and EUHFR deliverables since 

the 2016 NAS study was published include:

U-10Mo Monolithic Fuel 

• U-10Mo Monolithic Fuel Fabrication Pilot Line was 

deployed and commissioned at commercial fabricator BWXT in Lynchburg, Virginia.

• The BWXT Pilot Line was used to make the 

USHPRR monolithic fuel miniplates for the MP-1 

qualification experiment from full-size foils. After 

completing two irradiation cycles, the irradiation 

of MP-1 fuel was stopped during the third cycle. 

A small number of miniplates for MP-1 that were 

made utilizing laboratory-scale equipment experienced performance issues, while all of the BWXTmade miniplates performed as expected. 

• Preliminary safety analyses for all three NRC-regulated USHPRRs (MITR, MURR, NBSR) have 

been performed that establish a safety case for each 

LEU design and operating plan that preserves the 

mission capabilities of the reactors. The USHPRR 

sub-program is working with the NRC to receive 

feedback on these analyses. (The preliminary designation acknowledges that the U-10Mo monolithic 

fuel qualification is still in progress, and the fabrication tolerances of the final fuel products are subject to change.)

• A Preliminary Report on U-Mo Monolithic Fuel for 

Research Reactors submitted to the NRC for review. 

The report provides a comprehensive account of the 

research and development (R&D) performed by the 

USHPRR sub-program and signifies the shift from 
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Appendices 99

R&D to the implementation phase of U-10Mo fuel. 

The report summarizes characterization and irradiation performance data that was obtained from 

early scoping and development irradiation campaigns and demonstrates that the U-10Mo monolithic fuel system is suitable for fuel qualification.

• The ATR conversion team has completed a conceptual fuel design and is preparing a Safety Analysis 

Report addendum to test first LEU element.

• Within the HERACLES Consortium TUM, CEA, 

and CERCA are pursuing a European variant of the 

U-10Mo monolithic fuel. Their “C2TWP” approach 

applies the zirconium diffusion barrier by Physical 

Vapor Deposition and then rolls the coated foil and 

clad to bond them. The first mini-plate samples of 

C2TWP product were irradiated in the EMPIrE 

experiment at ATR.

U-7Mo Dispersion Fuel

• EMPIrE Fabrication and Irradiation Condition 

Parametric Miniplate Experiment fabricated at 

CERCA and irradiated at the ATR at conditions 

that included the envelope of BR2 and RHF. 

EMPIrE irradiated 48 miniplates to explore the 

impacts of variations in both fabrication and irradiation conditions. Non-destructive PIE indicates 

good performance for nearly all variants examined, 

with no failures. Destructive PIE is in progress. 

CERCA is installing pilot devices capable of fabrication variants in order to respond efficiently if 

EMPIrE destructive PIE shows an advantage of one 

variant over the other.

• SEMPER FIDELIS Full-Size Plate Experiment 

fabricated at CERCA and irradiated at the BR2. 

The experiment did suffer from a faulty irradiation 

device design that led to damage of a number of 

the plates before they reached their target burnups. 

However, one plate was irradiated successfully 

to more than 80% local burnup at power levels 

that envelope BR2 and RHF. The plates that were 

damaged are still yielding significant data about 

how fuel performance evolves at different power 

densities to different burnups. Initial destructive 

examination is favorable for the plate that reached 

80% burnup. The PIE continues for the overall 

experiment.

• The HERACLES Consortium has been developing scaled-up fabrication capability at CERCA in 

parallel with the Comprehension Phase SEMPER 

FIDELIS and EMPIrE experiments. Pilot devices 

for UMo powder atomization, heat treatment, and 

coating are being deployed in the CERCA R&D 

Facility at their Romans site. The fuel meat compaction, rolling to apply clad, and fuel element 

assembly all use standard equipment of the CERCA 

fabrication facility.

U3Si2 Dispersion Fuel for High Power/High Burnup 

Applications

• BR2 has qualified and deployed a modified element 

design (named COBRA) with HEU fuel fabricated 

by BWXT. The modified geometry will allow preservation of mission capabilities with an LEU 5.3 

g/cm3 U3Si2 dispersion fuel with gadolinium as an 

integral burnable absorber.

• The COBRA-FUTURE Full-Size Plate experiment 

at BR2 to test the proposed LEU fuel meat at BR2 

irradiation conditions has been fabricated at BWXT 

and irradiation is in progress. Three nominal cycles 

were completed by May 2020. A final bounding 

irradiation cycle will begin in August 2020.

• The HiPROSIT Full Size Plate experiment at BR2 

to test U3Si2 fabricated by CERCA at EUHFR irradiation conditions with loadings of 4.8 gU/cm3, 

5.3 gU/cm3, and 5.6 gU/cm3 was fabricated and 

irradiated. The plates should have achieved local 

burnups greater than 80%. PIE will commence in 

2020 after cooling.

• Initial HFIR silicide design options have been completed that preserve full mission capability.

• LEU fabrication demonstrations for HFIR U3Si2

design options are underway at BWXT.

• The FUTURE HFIR experiment at BR2 to test 

U3Si2 with fuel meat characteristics and irradiation 

conditions relevant to HFIR is has been designed 

and is being fabricated.
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100 Appendices

LEU Fuel Cost Projections

• Fabrication yields have been dramatically improved since the 2015 NAS review.

• USHPRR cost projection modeling has been 

improved based on a Process Flow Diagram that 

details each fabrication step at BWXT.

• As of January 2020, LEU U-10Mo monolithic fuel 

is projected to cost more than the current HEU 

fuel, but the increase should be less than 40%.

• The initial cost projection for HFIR LEU U3Si2 dispersion fuel is that the fuel costs will be similar to 

current HEU costs since U3O8 powder production 

will no longer be needed.

Remaining Work Needed to Support LEU Fuel 

Qualification

A number of irradiation tests are still required to qualify the high-density U-10Mo monolithic and U-7Mo 

dispersion for application in research and test reactors, 

and U3Si2 dispersion fuels for application to reactors 

with high power density. Furthermore, reactor-specific 

irradiations are required for each of the USHPRR and 

EUHFR reactors due to the scale and distinct complexity of each of those reactors.

The USHPRR program U-10Mo monolithic fuel 

is in the qualification phase rather than fuel development phase. The program is no longer investigating 

process changes to baseline production of the U-10Mo 

monolithic fuel. It will be Vacuum Induction Melt 

(VIM) Cast, Hot Rolled to bond the zirconium diffusion barrier to the U-10Mo, Cold Rolled to desired foil 

thickness, then Hot Isostatic Pressed (HIPed) to bond 

the aluminum clad. Two miniplate tests will provide 

samples with a variety of variations and irradiation 

conditions in order to allow PIE data showing that the 

fuel behavior as fabricated by BWXT is predictable and 

stable. The MP-1 test began irradiation in 2018 and has 

been completed. The MP-2 test will follow MP-1. The 

FSP-1 full-size plate experiment will also follow MP-1, 

in order to demonstrate consistent performance of 

miniplates and full-size plates as fabricated by BWXT. 

A series of reactor-specific tests will follow FSP-1 to 

demonstrate the acceptability of the specific geometry 

in the LEU-design irradiation conditions.

The HFIR U3Si2 dispersion fuel qualification plan 

will move through a series of tests at BR2 and ATR to 

address the distinct fuel configuration and irradiation 

conditions of the inner and outer cores of HFIR fuel. 

The HFIR qualification may be adapted depending 

on the path forward selected by BR2 and RHF, to the 

degree that U3Si2 experimental synergies might accelerate the three conversions.

Within the EUHFR collaboration, BR2 and RHF 

plan to downselect either U-7Mo dispersion or U3Si2

during 2021 based upon completion of the HERACLES 

Consortium U-7Mo Comprehension Phase and the PIE 

results of the EMPIrE, SEMPER FIDELIS, HiPROSIT, 

and COBRA-FUTURE experiments. After the downselection, there will be at least one full-size plate experiment and one full-size, curved and constrained plate 

experiment pursued by the consortium in parallel with 

CERCA fabrication industrialization. The BR2 will 

irradiate Lead Test Assemblies (LTAs) with the downselected fuel fabricated by the industrialized processes. 

RHF will then irradiate a Lead Test Core.

TUM plans to pursue the European U-10Mo 

monolithic approach in a manner analogous to the 

HFIR experimental plan since it is an involute-plate 

reactor like HFIR.

In the case of each of the fuels, modeling will 

continue to evolve as new PIE data becomes available 

in order to document and demonstrate a thorough 

understanding of the fuel behavior to the regulators.

The LEU fuel development for conversions will 

undoubtedly be useful for new research reactor builds. 

Prior U3Si2 qualification facilitated deployment of the 

ETRR-2 reactor in Egypt and the OPAL reactor in 

Australia by Argentina’s INVAP and National Atomic 

Energy Commission (CNEA). Argentina, Brazil, and 

the Netherlands are all currently pursuing INVAP 

U3Si2 reactors (RA-10, RMB, and PALLAS reactors, 

respectively). KAERI of Korea deployed the JRTR in 

Jordan with CERCA U3Si2 fuel, and is constructing the 

KJRR reactor in Korea to use U-7Mo dispersion fuel. 

Indeed, KJRR is expected to be the first research and 

test reactor to qualify UMo fuel since their recent Lead 

Test Assembly irradiations at the ATR were successful.
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Appendices 101

Acronyms

APS: American Physical Society

ATR: Advanced Test Reactor at the Idaho National Laboratory

ATRC: Advanced Test Reactor Critical facility at the Idaho National Laboratory

BR2: Belgium Reactor 2 at SCK CEN in Mol, Belgium

BWXT: BWX Technologies, the research reactor fuel manufacturer in the U.S.

C2TWP: CEA CERCA TUM Welding Process (a process to bond layers of nuclear fuel and clad)

CEA: French Alternative Energies and Atomic Energy Commission (operators of JHR)

CERCA: Research reactor fuel manufacturing unit with Framatome of France

EMPIrE: A U.S./HERACLES joint mini-plate irradiation experiment 

EUHFR: European High Flux Reactors (BR2, FRM-II, JHR, RHF)

FRM-II: Research Neutron Source Heinz Maier-Leibnitz (FRM-II) at Technical University of Munich in Garching, Germany

GTRI: Global Threat Reduction Initiative within NNSA, the U.S. conversion program 2004-2015

HALEU: High Assay Low Enriched Uranium (i.e., uranium with between 5% and 20% U-235)

HERACLES: Consortium of Europe’s High Performance Research Reactors to support the worldwide non-proliferation efforts by minimizing their 

usage of HEU material HEU: High Enriched Uranium (i.e., 20% or more of uranium is U-235)

HFIR: High Flux Isotope Reactor at the Oak Ridge National Laboratory in Tennessee

HIP: Hot Isostatic Pressing (a process to bond layers of material, such as nuclear fuel and clad)

ILL: Institut Laue-Langevin (operators of RHF)

INVAP: Argentine research reactor vendor

JHR: Jules Horowitz Reactor under construction at the CEA’s Cadarache research center in France

KAERI: Korea Atomic Energy research Institute

KJRR: Kijang Research Reactor under construction by KAERI

LEU: Low Enriched Uranium (i.e., less than 20% of uranium is U-235)

M3: Material Management and Minimization within NNSA, the U.S. conversion program 2015–present

MITR: Massachusetts Institute of Technology Reactor in Cambridge, Massachusetts

MURR: Missouri University Research Reactor in Columbia, Missouri

NAS: National Academies of Sciences, Engineering and Medicine

NBSR: National Bureau of Standards Reactor in Gaithersburg, Maryland 

NNSA: National Nuclear Security Administration

RERTR: Reduced Enrichment for Research and Test Reactors, the U.S. conversion program 1978–2004

RHF: Reactor a’ Haut Flux at the Institut Laue-Langevin in Grenoble, France

SCK CEN: Belgian research foundation (operators of BR2)

SEMPER FIDELIS: A HERACLES/U.S. joint full-size plate irradiation experiment 

TRIGA: Training, Research, Isotopes, General Atomics, a UZrH pin-type fuel deployed by General Atomics

TUM: Technical University of Munich (operators of FRM-II)

U3Si2: Uranium Silicide alloy

UMo, U-7Mo, U-10Mo: Uranium Molybdenum alloy, where U-xMo notation indicates the weight percentage that is molybdenum

USHPRR: United States High Performance Research Reactors (ATR/ATRC, HFIR, MITR, MURR, and NBSR)
REPORT OF THE BASIC ENERGY SCIENCES ADVISORY COMMITTEE ON THE SCIENTIFIC JUSTIFICATION 

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102 Appendices

APPENDIX 3. HFIR, SNS, and NIST User Data

HFIR Facility GU Days Requested and Days Delivered

Number of GU days requested in GU Proposal Calls and number of actual GU days run in that calendar year

2997

2497 2410

2574

1283 1173 1063

1400

1221

126

CY 2015 CY 2016 CY 2017 CY 2018 CY 2019

HFIR GU Days Requested in Proposal Call and Days Run by CY

Days Requested Days Run

NIST Beamtime between January 2015 – January 2020

Oversubscription values (defined as total days requested/total days offered) shown above days requested.

FIGURE A3.1. HFIR Facility GU Days Requested and Days Delivered

Source: Oak Ridge National Laboratory

Note: Number of GU days requested in GU Proposal Calls and number of actual GU days run in that calendar year.

FIGURE A3.2. NIST Beamtime Between January 2015–January 2020

Source: National Institute of Standards and Technology

Note: Oversubscription values (defined as total days requested/total days offered) shows above, Days Requested

DAYS REQUESTED VS. DAYS APPROVED, HFIR AND NIST
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Appendices 103

*Note: Proposals are rated by an external Science Review Committee using a rating system of 1 

to 5, lowest to highest. Data includes most recent 6 HFIR proposal calls. 

32% of HFIR proposals rated ≥ 3 are not awarded beamtime*

1966

1643

1124

519

Total HFIR Submitted Proposals

Proposals rated ≥3 by Science Review (84% of total submitted)

Proposals rated ≥3 Approved (68% of proposals rated ≥3)

Proposals rated ≥3 not awarded time (32% of proposals rated ≥3)

Number of HFIR proposals rated ≥3 accepted and % declined

Oversubscription rate over time

Subscription Rate = Number of days requested divided by the number of days available in the General User Program

FIGURE A3.3. 32% of HFIR Proposals Rated ≥3 Are Not Awarded Beamtime

Source: Oak Ridge National Laboratory

Note: Proposals are rated by an external Science Review Committee using a rating system of 1 to 5, lowest to highest. Data includes 

most recent 6 HFIR proposal calls.

FIGURE A3.4. Oversubscription Rate Over Time

Source: Oak Ridge National Laboratory

Note: Subscription Rate = number of days requested divided by the number of days available in the General User Program.

ORNL: HFIR AND SNS DETAILED USER DATA
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104 Appendices

Number of SNS and HFIR users by fiscal year

258

358 375

477

442

395

453

491

450

511

561

0

165

307

430

890

799

726

893

845

893

764

644

758

FY08 FY09 FY10 FY11 FY12 FY13 FY14 FY15 FY16 FY17 FY18 FY19

HFIR and SNS User Numbers

HFIR SNS

Note: In FY 2019 the User Program at HFIR was not operating 

Subscription rate by field: Researchers are asked to indicate one or more research areas when they submit a proposal, which we 

combined into these larger fields. The ‘subscription rate by field’ shown in this chart is calculated as the number of received 

proposals that indicate a research field, divided by the number of proposals allocated that indicate the same field.

210%

237%

226%

175%

186% 184%

171%

152%

214%

Bio and Life

Sciences

Chemistry Earth Sciences Engineering Environmental

Sciences

Material

Sciences

Medical

Applications

Physics Poymer

Sciences

HFIR subscription rate by field over recent 5 year period

FIGURE A3.5. Number of SNS and HFIR Users by Fiscal Year

Source: Oak Ridge National Laboratory

Note: In FY2019, the User Program at HFIR was not operating.

FIGURE A3.6. HFIR Subscription Rate by Field Over Recent 5-Year Period

Source: Oak Ridge National Laboratory

Note: Subscription rate by field: Researchers are asked to indicate one or more research areas when they submit a proposal, which we 

combined into these larger fields. The “subscription rate by field” shown in this chart is calculated as the number of received proposals 

that indicate a research field, divided by the number of proposals allocated that indicate the same field.

ORNL: HFIR AND SNS DETAILED USER DATA
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Appendices 105

HFIR INSTRUMENT GENERAL USER PROPOSAL METRICS

1

CG-1D, IMAGING

271

221

203

180

89

118

98

114 103

21

CY-2015 CY-2016 CY-2017 CY-2018 CY-2019

IMAGING - Days Requested in Proposal Call and Days Run

Days Requested Days Run

FIGURE A3.7. HFIR Instrument General User Proposal Metrics

Source: Oak Ridge National Laboratory

ORNL: HFIR AND SNS DETAILED USER DATA