NUREG-1537, Part 2 - NRC

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APPENDKX 18.1
temperature and reactivity changes in the fuel or moderator. All credible potential
accidents should be considered when planning the reactor conversion.
If the comparisons by the licensee of the eisting HEU- and proposed LEU-fueled
reactors show sufficient similarity between the potential reactivity accidents and
the consequences for the two fuels, a comparison of the scenario analyses should
be performed, with quantitative checks at key points. The checks should examine
the effects on the course of the accident evolution caused by the reactor design or
operational parameters changed to accommodate the fuel conversion.
If the comparisons of the existing HEU- and proposed LEU-fiieled reactors show
significant differences in the types or consequences of potential reactivity
accidents, new independent analyses for the proposed LEU-fueled reactor may be
required. If new or revised analytical methods or assumptions are employed, the
licensee should validate them with an analysis similar to that used for HEU
accident scenarios.
In all cases, the analyses should include the initial reactor conditions; the
postulated initiating event; the evolution of the accident; assumed operational
condition (including failures, malfunctions, or normal operational finction) of any
barriers, protective systems, or actions; and the effect of any ESFs that stabilize the
reactor condition. The consequences during and after the postulated accidents
should be compared for the exsting HEU- and proposed LEU-fueled reactors
Acceptance Criteria
Acceptance criteria for the consequences of proposed reactivity accidents should
be based on the following considerations:
* The initiating events and scenarios for reactivity accidents should be
consistent with those assumed for the BEU reactor, and should be based
on physical principles and assumptions that are amenable to logical
analyses.
* Any significant differences in the initiating events or evolution of reactivity
accidents between the xisting HEU- and proposed LEU-fiieled reactor
should result from changes in reactor design parameers or operating
conditions required to accommodate the conversion of the reactor from the
use of HEU fuel.
* The potential consequences of reactivity addition accidents for the
proposed LEU-fueled reactor should be consistent with the acceptance
criteria for the HEU-fleled reactor.
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