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:
ution for several reasons. Large portions of a pond may be unused for dilution if the pond is unstratified and irregularly shaped. If the same pond becomes stratified during certain times of the year, however, previously unused sections may become useful because of density flows (Ref. 57) and because of the strong mixing induced by seasonal turnover. In a flow-through cooling pond without recirculation, stratification may be detrimentalK because the thermal effluent and the radioisotopes may be confined to the upper layer, thereby reducing the effective volume of the pond. Thus, definition of the effective volume of a pond may be difficult. it should be possible, however, to pick a conservative volume for a "worst case" calcu lation. Calculation of the steady-state concentration of isotopes whose half-lives are long should cause little error because the concentrations approach that of a conservative substance w Co qb regardless of pond hydraulics. b. Numerical Models Stratified reservoir models are in most cases numerical evaluations of the one- or two dimensional equations describing convection and diffusion in stratified flow. The simplest numer ical models are the one-dimensional diffusion models, such as the MIT deep reservoir model (Ref. 57). In such models, concentration is assumed to be horizontally uniform. Vertical dif fusion and advection are modeled. The flow field is calculated by the equation of continuity and by accounting for inflows and outflows such as dams, tributaries, and outfalls to and from the different layers of the reservoir. Such models are useful where there is strong stratifi cation, especially where the reservoir is used for direct condenser cooling. In such cases, the stratification is reinforced by the additional heat, discharge is usually to the surface, with drawal is from the hypolimnion, and vertical gradients are more pronounced than horizontal gradients. These models are less accurate for reservoirs that have seasonal turnover