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:
cautioned that this equation can only be relied upon for order of magnitude estimates and is not necessarily conservative. 1.113-22 (2) One-Dimensional Real-Time Models Less "tuning" is necessary for real-time models than for the tidally averaged models. In the well-mixed region of the estuary, Taylor's formula (Ref. 53) for dispersion is acceptable for reasons discussed in Section 4.d of this appendix. The salinity intrusion region of the estuary is still poorly defined on physical grounds. Since the presence of gravitational circulation casts doubts on the applicability of sectional averaging, it is this region for which tuning is most important. An approximation for the longitudinal dispersion coefficient that is applicable to the whole length of the estuary is based on the work of Thatcher. and Harleman (Ref. 54). This approach is based on a combination of Taylor's dispersion formula applicable to the well-mixed portion of the estuary combined with an empirical correlation for mixing in the salinity intrusion region based on observed salinity distributions. The dispersion coefficient is E(x,t)" KI 00' 1 + 77nUtRh 516 (36) - ~d(~ where L is the length of estuary; n is Manning's coefficient (local); R is the hydraulic radius (local); *S is the salinity (local); So' is the salfnity at mouth; ,Ut is the RMS velocity (local); and x is the distance from mouth. The factor K is given by K - 0.00215VmaLED 0 ".2 5 (37) and Is shown in Figure 5. The quantity ED is the so-called "estuary number" and is given:by DED 2 (38) where F 0 Is the densimetric Froude number evaluated at the estuary mouth; PT is the tidalprism, in ft 3 ; Qf is the freshwater flow rate; and T is the tidal period. The dispersion formula given in Equation (36) may be used with good results as a first approximation in the tuning of a real-time model. In an oscillatory flow such as a hydroelectric or pump storage reservoir where there is no salinity intrusion region, the Taylor formula alone may be used