The US National Energy Policy of 2001 advocated the development of advanced fuel and fuel cycle technologies that are cleaner, more efficient, less waste-intensive, and more proliferation resistant. The need for advanced fuel development is emphasized in on-going DOE-supported programs, e.g., Global Nuclear Energy Initiative (GNEI), Advanced Fuel Cycle Initiative (AFCI), and GEN-IV Technology Development. The Directorates of Energy & Environment (E & amp;E) and Chemistry & Material Sciences (C & amp;MS) at Lawrence Livermore National Laboratory (LLNL) are interested in advanced fuel research and manufacturing using its multi-disciplinary capability and facilities to support a design concept of a small, secure, transportable, and autonomous reactor (SSTAR). The E & E and C & MS Directorates co-sponsored this Laboratory Directed Research & Development (LDRD) Project on Mono-Uranium Nitride Fuel Development for SSTAR and Space Applications. In fact, three out of the six GEN-IV reactor concepts consider using the nitride-based fuel, as shown in Table 1. SSTAR is a liquid-metal cooled, fast reactor. It uses nitride fuel in a sealed reactor vessel that could be shipped to the user and returned to the supplier having never been opened in its long operating lifetime. This sealed reactor concept envisions no fuel refueling nor on-site storage of spent fuel, and as a result, can greatly enhance proliferation resistance. However, the requirement for a sealed, long-life core imposes great challenges to research and development of the nitride fuel and its cladding. Cladding is an important interface between the fuel and coolant and a barrier to prevent fission gas release during normal and accidental conditions. In fabricating the nitride fuel rods and assemblies, the cladding material should be selected based on its the coolant-side corrosion properties, the chemical/physical interaction with the nitride fuel, as well as their thermal and neutronic properties. The US NASA space reactor, the SP-100 was designed to use mono-uranium nitride fuel. Although the SP-100 reactor was not commissioned, tens of thousand of nitride fuel pellets were manufactured and lots of them, cladded in Nb-1-Zr had been irradiated in fast test reactors (FFTF and EBR-II) with good irradiation results. The Russian Naval submarines also use nitride fuel with stainless steel cladding (HT-9) in Pb-Bi coolant. Although the operating experience of the Russian submarine is not readily available, such combination of fuel, cladding and coolant has been proposed for a commercial-size liquid-metal cooled fast reactor (BREST-300). Uranium mono-nitride fuel is studied in this LDRD Project due to its favorable properties such as its high actinide density and high thermal conductivity. The thermal conductivity of mono-nitride is 10 times higher than that of oxide (23 W/m-K for UN vs. 2.3 W/m-K for UO{sub 2} at 1000 K) and its melting temperature is much higher than that of metal fuel (2630 C for UN vs. 1132 C for U metal). It also has relatively high actinide density, (13.51 gU/cm{sup 3} in UN vs. 9.66 gU/cm{sup 3} in UO{sub 2}) which is essential for a compact reactor core design. The objective of this LDRD Project is to: (1) Establish a manufacturing capability for uranium-based ceramic nuclear fuel, (2) Develop a computational capability to analyze nuclear fuel performance, (3) Develop a modified UN-based fuel that can support a compact long-life reactor core, and (4) Collaborate with the Nuclear Engineering Department of UC Berkeley on nitride fuel reprocessing and disposal in a geologic repository.

The physical and mechanical properties of GCRE-type fuel elements were determined from room temperature to 1650 deg F. The fuel elements were prepared by cladding Type 318 stainless steel sheet to a core containing 15 to 35 wt.% UO/ sub 2/ in either prealloyed Type 318 stainless steel or elemental iron-18 wt.% chromium-14 wt. % nickel-2.5 wt. % molybdenum. The tensile strength in the direction perpendicular to the rolling plane decreased from 24,600 psi at room temperature to 9,200 psi at 1650 deg F for the reference fuel plate, whose core contained 25 wt.% UO2 in the elemental alloy. The tensile strength in the longitudinal direction for this fuel element ranged from 54,800 psi at room temperature to 14,200 psi at 1650 deg F, with elongation in 2 in. ranging from 8 to 13 per cent. The extrapolated stress for 1000hr rupture life at 1650 deg F was 1800 psi, and a 1.4T bend was withstood without cracking. The mean linear thermal coefficient of expansion was 11.0 x 10−6 per deg F for the range 68 to 1700 deg F. (auth).

Nuclear Fuel Elements: Design, Fabrication and Performance is concerned with the design, fabrication, and performance of nuclear fuel elements, with emphasis on fast reactor fuel elements. Topics range from fuel types and the irradiation behavior of fuels to cladding and duct materials, fuel element design and modeling, fuel element performance testing and qualification, and the performance of water reactor fuels. Fast reactor fuel elements, research and test reactor fuel elements, and unconventional fuel elements are also covered. This volume consists of 12 chapters and begins with an overview of nuclear reactors and fuel elements, as well as fuel element design and development based on the reactor operator's approach, materials scientist's approach, and interdisciplinary approach. The reader is then introduced to different types of nuclear fuels and their irradiation behavior, considerations for using cladding and duct materials in fuel element design and development, and fuel element design and modeling. The chapters that follow focus on the testing of fuel element performance, experimental techniques and equipment for testing fuel element designs, and the performance of fuels for water reactors. Fuel elements for gas-cooled reactors, fast reactors, and research and test reactors are also described. The book concludes with an assessment of unconventional fuel elements. This book will be useful to fuel element technologists as well as materials scientists and engineers.