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:
r and Harleman (Ref. 54) should be adequate. d. Applicability of Models Choice of one of the above models involves several factors. Although these models are classi fied as estuary models, they may be used for other types of water bodies, such as reservoirs with hydroelectric power generation flow reversals and, in most cases, unidirectional rivers. However, the assumptions implicit in one-dimensional models may be invalid In some cases, as explained below. Fischer (Ref. 55) analyzed the mechanics of dispersion In nontidal rivers and concluded that Elder's formula yielded dispersion coefficients that were low by as much as two orders of magni tude. He concluded that longitudinal dispersion in rivers is primarily due to velocity variations in the lateral direction, while Elder's formula accounts only for velocity variations in the vertical direction. An approximate diffusion coefficient for unidirectional rivers derived by Fischer (Ref. 55) is L2 E 0.3 u' (40) where I is approximately the cross-sectional distance from the point of maximum velocity to the further bank; Rh is the hydraulic radius; u,2 is the mean squared deviation of the river flow from the sectional mean velocity V; and u* is the shear velocity. The one-dimensional model is valid only for downstream distances corresponding to travel times greater than the so-called "Taylor period": t 1.8 (41) at which point the constituent introduced at t - 0 is sufficiently well mixed in the cross-section for the transport to be considered one-dimensional. In an oscillating tidal flow in a wide, shallow estuary, however, the tidal period is large compared to the vertical mixing time scale, but small compared to the lateral mixing time scale. In this case, velocity variations in the lateral direction add little to the longitudinal mixing, and Equation (39) is appropriate. 1.113-25 E(x~t) - 77nUtRh 5/6 (39) 5. IMPOUNDMENTS There are two basic types of cooling ponds. The first is a closed-loop system in which the