Skip to main content

Thank you for visiting You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

Safety in neutrons

To boost nuclear security, research reactors must eliminate highly enriched uranium.

Working with the United States, Japan has removed all of the highly enriched uranium (HEU) and the separated plutonium from one of its nuclear reactor facilities, to minimize the risk of theft and use by terrorists. The two countries have now pledged to convert a second research reactor to use safer, low-enriched uranium. These are among the latest in a series of accomplishments that have stemmed from US President Barack Obama’s biennial Nuclear Security Summit, which wrapped up on 1 April. More than 50 countries attended, most represented by heads of state, making a variety of commitments to reduce the risk of nuclear terrorism.

These projects are also a reminder of just how slow progress has been — and how much remains to be done.

Obama launched the agenda in a 2009 speech in Prague, calling on governments to secure or eliminate all vulnerable nuclear materials in four years. His speech underscored the fact that the threat of a nuclear attack has increased even as the danger of apocalyptic nuclear warfare has receded. Recent revelations that the Islamist terrorist group ISIS may have been targeting a nuclear facility in Belgium make this all too clear.

The initial focus has been on HEU, because of simple physics. Whereas plutonium must be compressed with explosives to produce a nuclear explosion — a feat that is probably beyond the technical capability of terrorist groups — the process is simpler for weapons-grade HEU, which is also used in many reactors. The United States and Russia, which have supplied the world with the bulk of HEU, have stepped up efforts to secure, remove or blend these materials into low-enriched uranium (LEU), which has 20% or less of the key isotope uranium-235. Security has been upgraded at 32 facilities, and 12 countries have been declared HEU-free since 2010.

Many of these materials are located at civilian research reactors. The risks were recognized long ago; in 1978, for example, the United States began eliminating HEU fuel in these reactors. In 1992, the US Congress enacted a law requiring countries that receive its HEU to commit to converting reactors to LEU fuel. To maintain reactor performance, however, scientists needed to develop a new generation of high-density LEU fuels, which are now available for most research facilities.

This is good news, but challenges remain. Existing high-density LEU fuels cannot be used without degrading performance in 11 specialized US and European research reactors. Certifying new fuels and converting these reactors could take nearly two decades. In January, the US National Academies of Science, Engineering, and Medicine recommended that specialized US reactors adopt an interim solution and convert to less-enriched fuel sources containing 30–45% uranium-235. This could — and should — be accomplished over several years, without impeding efforts to complete the shift to safer LEU fuel as soon as possible.

Researchers also need a comprehensive strategy to maintain research reactors. The European Commission is sponsoring a research consortium called HERACLES to do just that. The White House Office of Science and Technology Policy should convene agencies and research facilities to develop a path forward, and engage internationally. Many of these specialized research reactors are getting old; in some cases, given delays with new LEU fuels, it may make sense to start anew.

But research reactors are just one part of the puzzle, and the question now is how to carry the broader nonproliferation agenda forward once Obama leaves office. His four nuclear summits have boosted political attention and accelerated progress, but the world is awash with nuclear materials. Nuclear safety and security falls to a problematic patchwork of international institutions, including the International Atomic Energy Agency (IAEA), Interpol and the United Nations, and the latest summit produced a variety of initiatives to bolster these institutions.

That is a start. Ultimately, the world needs a new convention that sets specific standards for nuclear security and allows inspections and enforcement by the IAEA. In the meantime, governments must work through existing institutions to share and implement best practices. Regardless of cost, research facilities must ensure that their nuclear materials are safe and secure.

Additional information

Tweet Follow @NatureNews

Related links

Related links

Related links in Nature Research

Nuclear summit a test for Obama's legacy 2016-Mar-30

Iranian researchers welcome nuclear deal 2015-Jul-15

US warheads to get a facelift 2013-May-07

Time for a concerted nuclear approach 2009-Apr-01

Related external links

Nuclear Security Summit

International Atomic Energy Agency

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Safety in neutrons. Nature 532, 5–6 (2016).

Download citation

  • Published:

  • Issue Date:

  • DOI:


Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing