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"Factor of 5” Plume Rise Adjustment/Stack (Vent) Flow Correction

Is it appropriate to apply both the stack (vent) flow correction described in the ARCON96 User Manual (NUREG/CR-6331 Rev. 1), Section 3.4, and the “factor of 5” plume rise adjustment described in Regulatory Guide 1.194? Specifically, would entering a stack (vent) flow value to calculate X/Q values for a ground-level release and then applying the “factor of 5” plume rise adjustment on the calculated X/Q values be acceptable? Does this result in double counting for the effect of flow and if not, why not?

The stack (vent) flow correction described in ARCON96 Manual (NUREG/CR-6331 Rev. 1), Section 3.4, is to ensure that the near field concentrations are no greater than the concentration at the release point. The “factor of 5” plume rise adjustment described in Section 6 of Regulatory Guide 1.194 is applicable for ground level energetic releases from steam relief and atmospheric dump valves and is intended to take credit for plume rise from these types of releases. These two corrections are not double counting; one accounts for initial dilution effects and the other accounts for plume rise effects.

Is the order in which the stack (vent) flow correction described in ARCON96 Manual (NUREG/CR-6331 Rev. 1), Section 3.4, and the “factor of 5” plume rise adjustment described in Regulatory Guide 1.194 are to be applied important? The reason I’m asking this is that if an effective release height (i.e., release height adjusted for plume rise) and a stack (vent) flow rate are both specified in an ARCON96 run for any release type, ARCON96 seems to apply the stack (vent) flow correction at the end, i.e., ARCON96 seems to first calculate the X/Qs given the impact of plume rise (accounted for by specifying an effective release height) and then uses the resultant calculated X/Qs as the X/Q’ input in Equation (18) presented in Section 3.4 in NUREG/CR-6331. Therefore, should the “factor of 5” plume rise adjustment described in Regulatory Guide 1.194 not be applied first to the calculated ground-level X/Q values and the resultant calculated X/Q values then be used as input in Equation (18) in NUREG/CR-6331?

ARCON96 does not calculate plume rise. If applicable, plume rise should be calculated by the user using Equations 11 through 13 in Regulatory Guide 1.194, Section 6, and then added to the actual stack height to create the release height for input to the code. The code will then calculate X/Q values and make the vent/stack flow correction described in NUREG/CR-6331, Section 3.4. This is an acceptable approach. The calculation of plume rise and the “factor of 5” adjustment are mutually exclusive. If the user adjusts the release height code input to consider plume rise, then the user should not also be using the “factor of 5” adjustment. In the case where the release height is not adjusted to consider plume rise, the ARCON96 code will calculate X/Q values using the vent/stack flow correction and the user can then apply the “factor of 5” adjustment. This is also an acceptable approach. As stated in Footnote 14 to Regulatory Guide 1.194, the “factor of 5” adjustment and associated velocity ratio criteria are deterministic in nature and their selection was based on sensitivity analyses performed for typical steam release points at light-water reactors.