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Sensitivity Study of Reactivity Consequences to Waste Package Egress Area

John A. McClure
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The criticality consequence analysis for pressurized water reactor (PWR) waste packages (WP)
(Civilian Radioactive Waste Management System [CRWMS] Management and Operating
Contractor [M&O] 1997) focused on results obtained by maximizing postulated rates of
reactivity insertion to assure no synergistic reactions could occur among waste packages from
hypothetical criticality events. Other variables potentially influencing the criticality
consequences were held constant during the above referenced analysis. One of those variables
that may affect results is the exit area of the leakage paths from the WP. If the leakage area
through the WP wall is sufficiently small, inflow rates will be restricted; lengthening the time
required for flooding the WP and thus delaying potential criticality events, which require flooded
conditions. However, if a criticality event does occur, a limited leakage area will reduce the exit
flow volume. The immediate effect on the system from a limited leakage area is to reduce the
negative reactivity effect of voiding the WP because the water/vapor escape rate may be
lowered. This, in turn, leads to higher heat output, higher internal pressure, and higher
temperatures. The higher pressure and density of the water vapor will increase the mass flow out
of the waste package, so that eventually the negative reactivity from voiding the system becomes
dominant, and the criticality event shuts down.
The purpose of this calculation is to determine the relation between reduction in the leakage area
and possible increases in peak pressures and temperatures for such hypothetical criticality events.
This calculation was performed under the AP3.12Q Revision 0, ICN 0 Procedure and will
support WP design and analysis activities.

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