POPA Report

Neutrons for the Nation

Discovery and Applications while Minimizing the Risk of Nuclear Proliferation

July 01, 2018

Executive summary

For many decades, neutron fluxes from civilian nuclear research reactors have been important in the advancement of science and industry. Since 1978, the policy of the United States has been to reduce and ultimately eliminate the use of highly enriched uranium (HEU) in civilian research reactors, encouraging by example worldwide efforts to reduce nuclear proliferation risks. Significant progress has been made on this front, with many reactors having been converted to low enriched uranium (LEU) fuel or shut down.

However, there still exist HEU-fueled reactors in the United States and abroad. An important reason for their continued use is their capability to produce intense sources of neutrons that can probe matter and trigger interactions at a level that no other technique currently can achieve. This capability is critical to scientific research and industrial applications. HEU-fueled reactors are used in materials research that engenders economic development, tests of fundamental laws of the physical world that enrich our understanding of nature, and advanced treatments that improve medical outcomes.

This report, commissioned by the American Physical Society’s Panel on Public Affairs (APS POPA), focuses on the competing goals of reducing nuclear proliferation risk while maintaining intense controlled sources of neutrons for vital scientific and industrial work.

In developing this report, several issues were examined, including the current and future needs of neutrons for science and industry; the landscape of neutron facilities in the United States and worldwide; the complementary merits of spallation sources and nuclear reactors; the prospects for converting research reactors from HEU to LEU fuel usage; and the economic motivations for maintaining and growing neutron science and its industrial applications.

The examination culminated in the following six key findings and four recommendations:

Key findings

  1. Investigations performed at neutron sources are essential components of R&D in numerous areas of science and engineering.
  2. Neutron scattering is often an essential part of a broader experimental study that uses a complementary suite of tools (e.g., light sources, high-performance computers). Thus, neutron sources play a key role in overall U.S. innovation capacity.
  3. The United States has lost important capability in neutron R&D in the last two decades and is no longer the world leader. The United States cannot afford to lose its remaining capacity and capability without significant detriment to the quality and quantity of science, engineering, and even medical and manufacturing processes that rely on neutron sources.
  4. Reactor fuels containing HEU represent a risk for proliferation, which should be considered when planning for the future infrastructure for neutron R&D.
  5. Current HEU-fueled research reactors provide unique R&D capabilities relative to other neutron sources available today. Eliminating them without developing and deploying alternative methods of producing neutrons with the same properties (e.g., from high-density LEU-fueled reactors and/or a new generation of spallation sources) would compromise U.S. innovation capacity.
  6. World-class neutron science and engineering require the comprehensive benefits of spallation facilities, research reactors, and high-performance instrumentation. While there is some overlap in the capabilities provided by spallation and reactor sources, each provides certain capabilities that cannot now be duplicated by the other type of source.


  1. The United States should continue to support its diversity of neutron R&D capabilities, including both research reactors and spallation sources, for scientific, engineering, and economic capacity and capability. Decisions regarding potential new neutron sources should be guided by the principle of reducing and ultimately eliminating the use of HEU while retaining or enhancing current neutron capabilities.
  2. The United States should sharply increase its investments in neutron instrumentation development and deployment to partially compensate for the country’s dramatic decrease in neutron R&D capacity and capability in recent decades; to offset any loss of capability arising from the elimination of HEU fuel from research reactors; and to complement continuing investments in complementary tools such as light sources and high-performance computing.
  3. The United States should reaffirm its commitment to the timely development and deployment of high-density LEU fuels for use in existing high-performance research reactors. Any transition from HEU to LEU reactor fuel must not compromise neutron research and engineering capabilities, especially those that cannot be duplicated using spallation sources. The United States should also consider options to cost-effectively maintain reactor performance and simultaneously reduce HEU consumption while awaiting a suitable LEU fuel.
  4. The United States should initiate an effort to competitively design and build a new generation of LEU-fueled high-performance research reactors that would satisfy all needs presently met by current HEU-fueled U.S. high-performance research reactors and provide new capabilities.

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