NUREG-1537, Part 2 - NRC

4.2.1 Fuel Elements
HEU TO LEU CONVERSION
The design and procurement specifications for the LEU fuel should be consistent
with the test fuels previously reviewed, evaluated, and accepted by NRC for nonpower
reactors. If an unapproved fuel type is proposed, sufficient information
should be provided to support evaluations and conclusions comparable to
NUREG-1281, -1282, or -1313, as applicable. The physical dimensions, uranium
loading, thermal capabilities, uranium burnup capabilities, and safety limits should
be consistent with the LEU fuels previously evaluated by NRC and the
assumptions and inputs used for the thermal-hydraulic and safety analyses for the
LEU-fueled reactor.
4.2.2 Control Rods
The control rods usually need not be modified or replaced for the HEU to LEU
conversion. If no change to any control rod is required,'the LEU safety analyses in
subsequent sections should show that the existing rods can provide excess
reactivity control and shutdown reactivities to maintain appropriate technical
specification limits and not compromise safe reactor shutdown. If a change is
required, the analyses should show that any changes in rod locations or in
environmental effects on the rods from changes in reactor operating conditions
(e.g., neutron fluence or spectrum changes) would not significantly decrease rod
reliability or integrity. If changes in design materials or function of control rods'
are required to accommodate the reactor conversion, the analyses should show
that the LEU-fueled reactor operating design bases, shutdown capability (to be
analyzed in subsequent sections), and control rod integrity would not be reduced
significantly below those for the existing lIEU-fueled reactor.
4.23' Neutron Reflector -
The reflector components or materials usually need not be modified or replaced in
connection with HEU to LEU conversion. -If the analyses show that reflector
changes are required to accommodate the conversion (e.g , for reasons of changes
in neutron flux levels or spectrum), the design bases, mechanical and functional
designs, construction materials, thermal capabilities, design life, and replacement
provisions should be analyzed to show that the kafety-related capability -vill not be
significantly reduced by the changes. If the reflector need not be changed in
connection with the reactor conversion, analyses should show that any changes in
environmental effects on the reflector from changes in reactor operating
characteristics, such as neutron fluence and spectrum, would not significantly
decrease reflector integrity or related safety analysis results.
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