NUREG-1537, Part 2 - NRC

HEU To LEU CONVERSION
methods and assumptions are applicable and acceptable. The safety
analysis demonstrates that the fuel and cladding temperatures are within the
acceptance criteria for the LEU fuel, fuel integrity will acceptably be
ensured, and there will be no significant release of fission products.
Further, there is no significant difference in the radiation levels from the
uncovered LEU core following a postulated LOCA scenario. Therefore,
the changes do not increase the health'and safety risk to the public from the
postulated LOCA.
or
* The licensee assumed an acceptable loss-of-coolant scenario for the LEU
core, which is consistent with the LEU facility design. The licensee
calculated the fuel and cladding temperatures, associated fission product
retention capabilities, and radiological consequences. .The analyses and
assumptions are applicable to the proposed LEU-fueled reactor. The
radiological consequences are within the acceptance criteria for the lIEU
reactor. Therefore, the changes do not increase the health and safety risk
to the public from the postulated LOCA.
13.3.2 Loss-of-Flow Accident (LOFA)
Areas of Review
LOFAs are postulated accidents 'that result from the loss of reactor coolant flow,
but not the loss of the coolant itself For the case of forced coolant flow, LOFAs
may result from a loss of electrical power to a coolant pump or from an
obstruction in a coolant channel. For natural convection flow, a LOFA may result
from low head or obstructions in the coolant flow path If forced coolant flow
were lost, the system should revert to natural convection, which might involve a
reversal of flow direction and temporary degradation in core heat transfer to the
coolant. Loss of natural convection flow also would result in the degradation of
core heat transfer. An increase in fuel and cladding temperatures may lead to fuel
damage if(l) specified acceptable temperature limits are exceeded during the loss
of forced flow transient or after steady-state naial convective cooling is
established or (2) coolant flow stops' during a loss of natural convective flow
transient. The continued operabifity of the ultimate heat sink should be an area for
review, along with corrective'actions."
In the BIEU to LEU conversion, several parameters associated with the thermalhydraulic
characteristics of the core may change.' The areas of review should
inclu'de'the number or dimrensions of coolant channels a'nd fuel plites or rods, core
dimensions, power density, fuel and cladding temperatures, surface heat flux, and
thermal conductivity of the fuel. As a consequence, the time-dependent
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