Permalink Submitted by KNorman on Tue, 06/13/2017 - 16:10.

Section 2.3.5 in NUREG/CR-6331 Rev. 1 notes the maximum acceptable values for stack vertical velocity and stack flow as 50 m/s and 100 m3/s respectively. However, the regulatory and/or technical basis for these maximum values are not provided/explained in NUREG/CR-6331 or RG 1.194. 1) Is there a regulatory and/or technical basis for the maximum acceptable values for stack vertical velocity and stack flow as 50 m/s and 100 m3/s respectively and if so, could it be provided/explained? 2) If there is no justifiable regulatory and/or technical basis, can the maximum acceptable values for stack vertical velocity and stack flow be increased?

Permalink Submitted by KNorman on Wed, 06/14/2017 - 07:20.

In ARCON96, the value of the stack vertical velocity is used only in the stack downwash calculation; ARCON96 does not calculate plume rise. Stack downwash is caused by low pressure in the wake of the stack, resulting in the plume being drawn downward behind the stack. Stack downwash does not generally occur when the stack vertical exit velocity is greater than 1.5 times the wind velocity. Therefore, stack vertical velocities in excess of 50 m/s will have no to minimum impact on the resulting ARCON96 X/Q values. ARCON96 uses the value of the stack flow to ensure that the near field concentrations are no greater than the concentration at the release point. This value is significant only if the flow is large and the distance from the release point to the receptor is small. Placing an upper limit on this value produces conservative X/Q values for high stack flow rates.

## Max acceptable values for stack vertical velocity/stack flow

## Max acceptable values for stack vertical velocity/stack flow