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:
momentum effects of the discharge jet. Techniques for the determination of initial dilution were discussed in Section 1 of this appendix. 1.113-4 For nontidal rivers the flow is assumed to be uniform and approximately steady. Under these conditions, the diffusive transport in the flow direction may be neglected compared with the advective transport (Ref. 13). It has been shown that far-field transport of dissolved constituents in rivers can be satisfactorily treated by a two-dimensional model in which vertical variations of velocity and concentration are averaged out (Refs. 14, 15, and 16). Such a model, however, retains transverse variations of river bottom topography and velocity. Consider a section of a steady natural stream as shown in Figure 1. The origin of the coordinate system is placed on the near shore. The x-axis Is taken positive in the downstream direction, the z-axis is directed vertically downward from the water surface, and the y-axis is directed across the stream. The steady-state mass balance equation for a vertically mixed radio nuclide concentration may be written (Ref. 14) as follows: ud LC - l (Kd'3C) - (Xd)C (1) ax a where C is the radionuclide concentration (activity/volume); d is the stream depth; Ky Is the lateral turbulent diffusion coefficient (vertically averaged, two dimensional); u is the stream velocity; and A is the decay coefficient and is - (ln 2)/half life. Since, for a real stream, u and d will be functions of the transverse coordinate y, Equation (1) will generally not have a closed-form analytical solution. A more tractable form of the equation is obtained through introduction of a i.aw independent variable q, defined by q - (ud)dy (2) Jo The quantity q is the cumulative discharge measured frnu the near .shore. Hence, as y - B, q , where B is the river width and Q is the total river floe. Substitution of Equation (2) into Equation (1) yields the following transport equation: 2-_ . L-_ -(yu2 IC i C ."(3) In the decay term, the