2014 - Report on Low Enrichment Uranium for NR Cores

This report responds to legislative language set forth in House Report 112-479, which accompanied the FY13 National Defense Authorization Act. The report examines the potential of using low-enriched uranium (LEU, 20% or lower 235u) in place of highly-enriched uranium (HEU, 93% 235u) in a naval nuclear fuel system. Two options exist: (1) substitute LEU fuel for HEU into the current naval fuel system and (2) develop a new fuel system that can increase uranium loading to offset some impacts of using LEU fuel.

US Navy warship requirements determine naval fuel system design features that require HEU fuel to deliver optimum performance. These Navy requirements include ruggedness, endurance, stealth, maneuverability and compactness that are necessary to deliver safe, effective operation of nuclear reactors on board Navy warships. While LEU is used in commercial and most research reactors, naval requirements are far more demanding than those in land-based reactors.

Substituting LEU for HEU would fundamentally decrease reactor energy density, increase lifecycle and operating costs, increase occupational radiation exposure, and increase the volume of radioactive wastes. Thus, while it may be feasible to replace HEU fuel with LEU fuel in current US Naval reactor plants, it is not economical or practical to do so. For example, the OHIO-Class Replacement ballistic missile submarine is being designed for a 40+ year core life without the mid-life refueling needed in the current OH 10-Class. Eliminating the refueling allows the Navy to meet the strategic deterrent mission with two fewer SSBNs and saves about $408 in ship acquisition and life cycle costs. LEU fuel would

eliminate these savings while adding substantial cost and occupational radiation exposure. LEU in current naval reactor fuels and core designs would reduce core life by a factor of 3 to 4. Today's ships would then require 2 to 3 refuelings instead of no refueling, or at most one refueling. Conceivably, a much larger LEU fueled core could be developed, which might preserve core life but would negatively impact ship performance.

With respect to developing an advanced fuel system, recent work has shown that the potential exists to develop an advanced fuel system that could increase uranium loading beyond what is practical today while meeting the rigorous performance requirements for naval reactors. Success is not assured, but an advanced fuel system might enable either a higher energy naval core using HEU fuel, or allow using LEU fuel with less impact on reactor lifetime, size, and ship costs. Advanced fuel system development would be a long-term effort that must start well in advance of a ship application.

The capability to develop advanced naval fuel resides within a small cadre of highly specialized, experienced, and qualified engineers and scientists. These experts, laboratory facilities, and Program funding are currently dedicated to supporting the existing Fleet and advancing technology to meet Navy requirements for new designs including the new Land-based Prototype reactor and the OHIO-Class Replacement submarine. It will not be practical to sustain these capabilities or work on an advanced fuel system without additional sources of funding. Consequently, until this funding can be secured advanced fuel is not being pursued beyond the early concept stage.