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:
xp (U1) [g(xt) - g(x,t - to)] for t t where eg(xt) " erfX +LIl t J+ 1 exp(L-) [erf tf L 1 exp - ) 7 • U2+4EL The function g(x,t - tO) has the same form as g(x,t), with (t - tD) replacing t. The sign within the brackets is chosen negative downstream of the source (positive x) and positive upstream of the source (negative x). Equation (31) holds for any pulse duration to. In the limit as (t,tD)+ -, the solution reduces to the steady-state solution given by Equation (25). Release rates other than square pulses are most easily computed by solving Equation (29) directly, using numerical quadrature. (See Sections 2.a.(2) and 3.a.(2) of this appendix.) (3) Tidally Averaged Numerical Models To simulate constituent transport in many types of estuaries, it Is necessary to include detail beyond the capabilities of analytical models. For example, the distribution of sources and sinks (both man-made and natural) may be important. Additionally, the estuary may have a nonuniform cross-section and tidal mixing proper ties that vary along its length. The next level of sophistication above the analytical models are one-dimensional numeri cal models, which can account for variable cross-sections, inputs, withdrawals, and tidally averaged longitudinal diffusion. These models solve what Is essentially the finite difference equivalent of Equation (23) in either the steady-state or transient (but tidally averaged) form. Models similar to the EPA AUTOSS and AUTOQD models fall into this category (Ref. 48). The estuary Is considered to be divided into variable-length segments. Each segment is coupled to the next upstream and downstream segment, as well as to external sources and sinks. Typically, the boundary conditions are chosen so that the concentrations of the first and the last segments are known constants. This is the most realistic assumption for this model, pro vided the model is extended to the headwaters of the estuary and to the ocean. In practice, the model can easily be