Document: NRC Regulatory Guide
Document ID: c9ebcbb0-96c4-4d29-be51-5acae9cc858a
Document Type: regulatory_guide
Title: Estimating Aquatic Dispersion of Effluents from Accidental and Routine Reactor Releases for the Purpose of Implementing Appendix I (Rev. 1)
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML0037/ML003740390.pdf
Revision Date: 2023-06
Chapter: 
Section ID: RG-1.113
CFR Part: 
CFR Title: 

Content:
ofthe iffuionfactrKu--d requires a separate determination of the dif Evaluation of the diffusion factor ;;I fusion coefficient.Ky. For steady open-channel flow, Ky can be determined from hydrodynamic properties of the channel by using Elder's empirical formula (Ref. 19): Ky w Bu*d (11) where d is the river depth; u* is the shear velocity; and 1.113-8 0 is a dimensionless constant. (The user is not restricted to this formula. A number of alternative approaches have been published.) For straight natural stream channels B has a value of approximately 0.23 (Refs. 14 and 16). For curved channels, however, secondary flows can lead to Increased lateral mixing and the value of B is larger (Refs. 20-22). Fischer (Ref. 20), for example, has shown that the lateral mixing coefficient is increased in bending streams, varying Inversely as the square of the radius of curvature. In general, to obtain realistic transport estimates, values of the lateral mixing coefficient should be determined by onsite tracer studies. Although transverse variations of Ky have not been adequately confirmed in field tests, longitudinal variation of Ky in a sharp bend has been reported by Sayre and Yeh (Ref. 22). Equations (7) and (8) may be modified as follows to account for a diffusion factor that varies in the direction of flow: Ux -,fXD(x)dx a0 If the diffusion factor is known for each river cross-section of concern, the integral can be evaluated by simple numerical integration. If the variation in D(x) is small over the river stretch under consideration, then Equations (7) and (8) may be used directly, with the quantity D being interpreted as the mean value over the river reach. It is useful to write Equation (7) in dimensionless form. I + 2 ef n2W2; cos nlr cos nwi (12) n=l where S= q/Q is the dimensionless cumulative discharge; i x/ý is the dimensionless concentration relative to the fully mixed value; and i - is the dimensionless downstream distance. The utility of the dimensionless form is