35 Nobel Laureates Urge Further Reductions in Use of Highly Enriched Uranium

This week, President Obama convened the fourth Nuclear Security Summit, a high level forum for international leaders to negotiate measures for strengthening the security of nuclear materials around the world.

To coincide with this meeting, 35 Nobel laureates—16 of whom won the prize for physics—signed onto a letter arguing that the risk of nuclear and radiological terrorism could be greatly reduced if the use of highly enriched uranium (HEU) were curtailed in two sectors: naval nuclear propulsion and research reactors. They also encourage development of alternatives to certain highly radioactive isotopes that are used for medical and research purposes such as cesium-137 and cobalt-60. The letter was led by Burton Richter, emeritus director of the Stanford Linear Accelerator Center and winner of the 1976 Nobel Prize in Physics, and Charles Ferguson, president of the Federation of American Scientists.

Uranium that has a 20 percent or higher concentration of the isotope uranium-235 is considered to be HEU, with concentrations greater than 90 percent considered as “weapons-grade” material. Uranium with less than 20 percent of this isotope is referred to as low-enriched uranium (LEU).

In a move to increase transparency, yesterday the White House released figures on the amount of HEU remaining in the U.S. The fact sheet reveals that from 1996 to 2013, U.S. HEU stocks decreased from 740.7 metric tons to 585.6 metric tons. Of the remaining amount, just under 500 metric tons is for national security purposes such as nuclear weapons production and naval propulsion. Of the civilian component, 44.6 metric tons are spent nuclear reactor fuel and 41.6 metric tons are available for potential down-blend to LEU or disposal as low-level waste.

In their letter, the laureates note that more than 80 percent of the world’s HEU is used for military purposes and recommend that “serious technical studies” be conducted on how to transition to LEU-fueled naval reactors. Next, they highlight a recent National Academies report which presents a roadmap for shutting down or converting the world’s 74 remaining HEU-fueled research reactors and recommend that nations devote sufficient “technical and non-technical resources” to addressing this issue. Finally, they encourage development of “commercially useful non-radioactive source alternative technologies that provide comparable benefits” to existing highly radioactive isotopes used for irradiaion in medical and research applications.

The 35 laureates are not the only ones using the summit as an opportunity to send letters on the subject of nuclear security. In particular, six Democratic senators also sent a letter to President Obama this week. Although their letter is largely focused on ensuring effective implementation of the Iran nuclear deal and reducing overall nuclear weapon stockpiles, they do highlight “converting or shutting down weapons-grade uranium fueled reactors” and “replacing high intensity radiological materials to safer substitutes” as important steps toward increasing nuclear security.

Recent reports contribute to enriching debate

The use of HEU in naval and research reactors has been the subject of much study and congressional scrutiny in recent years.

Congress requested the aforementioned National Academies study (pictured right) which concluded that conversion of HEU-fueled research reactors has slowed due to a combination of technical challenges and lack of Russian interest. The study panel also highlighted that conversion of the six remaining U.S. research reactors (located at the University of Missouri, MIT, the National Institute of Standards and Technology, Idaho National Laboratory, and Oak Ridge National Laboratory) will not be complete until 2032. They therefore recommend fueling these reactors with 45 percent or lower enriched uranium as an interim measure to reduce the consequences of HEU theft.

Congress has also requested multiple studies on the feasibility of LEU-fueled navy vessels in the past—receiving reports on the subject in 1995 and 2014 and currently awaiting yet another report requested by Sec. 3118 of the fiscal year 2016 National Defense Authorization Act. Yesterday, the White House released a statement containing the administration’s views on the feasibility of LEU-fueled naval reactors, saying that the U.S. “values investigations into the viability of using LEU in its naval reactors” and that the Department of Energy (DOE) is currently working on advanced fuel system concepts which could enable the use of LEU by naval vessels.

Reps. Marcy Kaptur (D-OH) and Bill Foster (D-IL) as well as Sen. Lamar Alexander (R-TN) all asked about the possibility of using LEU in navy vessels during recent hearings on the fiscal year 2017 DOE budget. Alexander, chairman of the Senate Energy and Water Development Appropriations Subcommittee, appeared interested in the relative priority of addressing HEU-fueled research reactors versus naval reactors, asking “Why don’t you spend your time and money developing a way to have LEU for the navy vessels instead of worrying about the last six high performance reactors?”

Admiral James Caldwell, Deputy Administrator for Naval Reactors, responded “from a military standpoint, there is no advantage to using [LEU] in a naval reactor plant,” then proceeded to outline various downsides to using LEU, namely that ships with LEU reactors would likely have to be refueled one or more times. He emphasized that the HEU reactor being developed for the next generation of submarines does not need to be refueled during the 42 year lifetime of each vessel, saving a total of $40 billion.

Caldwell did however note that developing a LEU-capable reactor would demonstrate U.S. leadership in nuclear non-proliferation and could be used as a means of ensuring the naval reactor workforce retains its skills into the future after work on the next-generation HEU reactor is complete.

Correction: An earlier version of this article incorrectly stated that the laureates encourage transition away from use of highly enriched uranium in production of medical radioisotopes such as molybdenum-99. In fact, the laureates only call for the development of non-radioactive alternatives to certain highly radioactive isotopes and do not discuss the use of highly enriched uranium in this sector as they do for naval and research reactors.