and Yu.S. Cherepnin (Dollezhal Scientific Research and Design Institute of Energy Technologies [NIKIET]) described progress and prospects for reduction of fuel enrichment in Russian-origin reactors (Cherepnin, 2011).
Fuel Design for U.S.-Origin Reactors
Highly enriched uranium (HEU) fuel elements in U.S.-origin research and test reactors consist of aluminum-clad plates (see Chapter 1) that contain a UAlx or U3O8-aluminum dispersion fuel meat clad in aluminum or a uranium-zirconium hydride (UZrHx) fuel meat clad in stainless steel (TRIGA fuel). Work carried out by Argonne National Laboratory and the Idaho National Laboratory, in cooperation with other American, European, and Korean organizations, has resulted in the development of three LEU dispersion fuel systems1 for conversion of plate-type reactors:
• UAlx (density = 2.3 grams of uranium per cubic centimeter [gU/cm3])
• U3O8 (3.2 gU/cm3)
• U3Si2 (4.8 gU/cm3)
These fuel systems are adequate for converting all but “high performance” research and test reactors.2 There are six HEU-fueled high-performance research reactors in the United States3 as well as four HEU-fueled high-performance research reactors in Europe that cannot be
1 The Reduced Enrichment for Research and Test Reactors (RERTR) program (see Chapter 1) also participated in the qualification of a fourth LEU fuel system: a uranium-zirconium hydride with an erbium burnable poison (UZrHx-Er) fuel system that is used for the conversion of TRIGA (Test, Research, Isotope production—General Atomics) reactors. General Atomics began developing a higher-density fuel (up to 3.7 gU/cm3) before the RERTR program was started in 1978. The RERTR program performed irradiation tests on 20/20 (i.e., 20 weight percent uranium, 20 percent enriched), 30/20, and 45/20 fuels. The 30/20 fuel was used to convert the Oregon State TRIGA Mark II reactor, discussed later in this chapter, and the University of Wisconsin Nuclear Reactor, discussed in Chapter 3, as well as a number of other TRIGA reactors in the United States and abroad.
2 These high-performance reactors have high-power-density (i.e., high-flux-density) cores. Fuels having higher uranium densities than are available with existing LEU fuels are required to convert these reactors.
3 As noted in Chapter 1, there are two additional HEU-fueled research reactors in the United States (NTR General Electric and TREAT; see Footnote 20 in Chapter 1) that appear to be convertible using current-type LEU fuels. The Department of Energy (DOE) is completing studies to confirm the feasibility of converting these reactors using current-type LEU fuels. Additional research will be required to more fully develop the capability to fabricate these LEU fuels.