Building Submarines Without Bomb Grade Fuel

Starting in the 1950s, the U.S. Navy began building nuclear-powered submarines and surface ships. These vessels were fueled by compact reactors that used highly enriched uranium (HEU). This fuel was chosen to maximize the time between refuelings, and to minimize the nuclear reactor’s weight and volume, but HEU fuel can also be used to make nuclear weapons with only trivial modification.
The Reactor of an Akula Class Submarine

Other nations interested in obtaining a nuclear-weapon capability have cited the United States' use of HEU as justification for their own pursuit of HEU-fueled submarines. If a country were to devleop this capability succesfully, then the country would also possess a near-instant nuclear-weapon capability. Exacerbating the situation, nuclear materials used for naval programs are exempt from international safeguards under the Non-Proliferation Treaty (NPT). The production and storage of HEU fuels also creates the risk of theft, which is believed to be the primary vector by which a terrorist group might acquire a nuclear weapon. HEU has been stolen from both Russia (in the 1990s) and the United States (in the 1960s).

Recognizing the risks posed by HEU, the United States began an international effort to remove HEU from the civilian fuel cycle in the 1970s. High-density fuels were developed that were able to replace HEU with low-enriched uranium (LEU) that is not weapons usable. About half of the world's reactors formerly fueled by HEU have now been converted to advanced LEU fuels.

The U.S. Navy, however, has resisted efforts to convert its reactors to HEU, partly out of technical concerns, and partly out of historical momentum. The United States lags the rest of the world in this regard: France, China, and Brazil now use low-enriched uranium in their submarines. Russia has developed a low-enriched reactor for its next generation of nuclear-powered icebreaker ships, and has reduced the enrichment of its submarines as well.

Recognizing that the U.S. Navy places especially high demands on its reactors, our research group is revisiting the technical aspects of submarine design to examine if a combination of new technologies might finally enable the U.S. Navy also to adopt LEU fuels. We are exploring the possibility of modular reactor designs that would enable rapid refueling without the need for an access hatch, and without impacting naval operations or deployed forces. If we can show conversion is possible without impacting the Navy's performance requirements, the United Staes could finally work to establish a new international norm banning the use of weapon-usable HEU in reactors worldwide.