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:
ionuclide concentrations are not required, it is possible to construct quasi steady-state transport models that are valid for time scales larger than the tidal period and smaller than those associated with major nontidal fluctuations in flow. For regular shoreline geometry, or discharges removed from the shoreline, steady-state Gaussian models based on Equation (17) may be used (Refs. 38-41). The results based on these models require careful interpretation, however, because of the large uncertainty In input param eter values, particularly the turbulent diffusion coefficients. Since these coefficients arise from time averaging, their values for any given case will depend on the averaging period used to define the mean velocity field. Furthermore, there is evidence to indicate that in the ocean the rate of spread of a contaminant plume depends upon the plume age. Hence, in general, turbu lent diffusion coefficients will be time and space dependent. The methodology for obtaining reasonable estimates for these coefficients is based primarily on the interpretation of the results of tracer studies in the light of modern turbulence theory (Refs. 38-45). More realistic detailed descriptions of radionuclide transport in ocean coastal waters will require the use of numerical models. The advantage of such models is that they are applicable to fully time-dependent flow fields in receiving waters having complex geometry. In particular, these models have the capability of treating tidal currents as advective rather than diffusive mechanisms ("real-time" models), hence removing a large element of uncertainty in the deter mination of turbulent diffusion coefficients. Typical acceptable numerical models (Ref. 29-37) were discussed in Section 3.a.(3). In the "real-time" modeling approach, tidal currents are explicitly included as advective transport mechanisms. Leendertse and co-workers (Refs. 29-34) have shown that in this case, reasonable estimates of longitudinal and lateral