Feasibility studies of LEU fuel conversion for the BMRR and HFBR. Page: 5 of 6
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instead of 0.51 mm. The uranium density in the U3Si2 - Al fuel meat is 2.5 g/cm3 and this
fuel is fully-qualified for routine use in the BMRR. Both cores use approximately the same
number of fuel assemblies per year, and the neutron fluxes and the neutron spectra in the
two irradiation facilities are nearly the same.
Initial studies indicate that it may not be possible to convert the HFBR to LEU fuel
with its current core configuration. The HFBR core is under-moderated and has a hard
neutron spectrum. Direct substitution of LEU fuel meat for HEU fuel meat further hardens
the neutron spectrum and decreases excess reactivity available to achieve a reasonable fuel
cycle length. A core configuration with better neutron thermalization appears to be
necessary in order to utilize LEU fuel.
Alternative core configurations with better neutron thermalization are being
investigated. For example, removing 10 of the 28 fuel assemblies from around the central
six core locations, adds enough excess reactivity such that reasonable LEU fuel densities
are possible. At a power level of 40 MW, an LEU assembly with 20 fuel plates would
provide fuel cycle lengths of 16 days and 22 days with 2"U loadings of 450g "5U (4.5
gU/cm3) and 600g 3'U (6.0 gU/cm3) per assembly. Fast and thermal neutron fluxes in the
central irradiation positions and thermal fluxes in the beam tube positions are nearly the
same in these LEU alternative configurations as in the HEU standard configuration. While
the LEU alternative core configurations are neutronically possible, the thermal hydraulics,
safety and operation of these HFBR configurations haye not yet been investigated.
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ANL/RERTR/TM-23, Argonne National Laboratory, Argonne, IL (July 1995).
3. J. F. Briesmeister, Ed., "MCNP'. - A General Monte Carlo N-Particle Transport
Code," Version 4A, LA-12625-M, Los Alamos National Laboratory, Los Alamos,
NM (November 1993).
4. B. J. Toppel, "A User's Guide For The REBUS-3 Fuel Cycle Analysis Capability,"
ANL-83-2, Argonne National Laboratory, Argonne, IL (March 1983).
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Hanan, N. A.; Matos, J. E. & Pond, R. B. Feasibility studies of LEU fuel conversion for the BMRR and HFBR., article, November 14, 1997; Illinois. (digital.library.unt.edu/ark:/67531/metadc794417/m1/5/: accessed December 12, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.