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:
models which simulate vertical concentration variations rather than horizontal variations may be more appropriate, for Instance, in the salinity intrusion region of an estuary, or a highly stratified reservoir. Although three-dimensional numerical models are currently being developed, their complexity and relatively high cost of observation are rarely warranted for the purpose of computations under Appendix 1. c. Exchange Coefficients The sectionally averaged, one-dimensional longitudinal dispersion coefficient, E, includes a combination of several individual processes. In the prototype, these processes include molecular exchange and flow- and wind-induced turbulent exchange. In most cases, these processes make a relatively minor contribution to the overall dispersion, which is in part an artifact resulting from the temporal and spatial averaging of the three-dimensional transport equations. In general, the greater the simplification of the model, the larger the exchange coefficient must be to simulate the prototype. The simplest model is the tidally averaged one-dimensional model. The actual three dimensional oscillating flow is drastically simplified Into a one-dimensional system in which the advective transport is determined by the fresh water flow rate. The diffusive transport includes the effects of deviations from sectional homogeneity and "turbulence" components of time scales on the order of the tidal period or less. In the Intratidal models, the true oscillating or unidirectional flow is simulated and is treated as part of the advective process. The diffusive term includes the effects of deviations from sectional homogeneity of the concentration and velocity fields. However, in this case, tidal effects are no longer included in the turbulence field. In the case of two-dimensional intratidal models, it is, in general, only necessary to include deviations of velocity and concentration in the vertical direction since, with sufficient resolution, the lateral