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:
aulic radius; and C is the water surface location above an undisturbed level datum. Concentration boundary conditions can be treated realistically in the intratidal formu lation. The upstream boundary is usually the concentration at the head of the tide. The down stream boundary, however, usually differs according to whether the tide is flooding or ebbing. During ebb tide, the downstream boundary is chosen so that all constituents leave by advection. During flood tide, the entering concentration must be specified. This is determined by the physical situation assumed. If the downstrealp boundary is the ocean, the concentration of con stituents in ocean water can be the input. If the downstream boundary Is a bay or other water body where a discharged constituent can accumulate, an approximation of this concentration must be made. An advantage of the intratidal model is its ability to simulate releases coordinated with the tide. If the source of contaminant is close to the mouth of the estuary, it may be advantageous to discharge only during ebb tide to flush the contaminant rapidly out of the estuary. Such operation could not be simulated with a tidally averaged model. b. Multi-Dimensional Models In very wide estuaries and embayments, the one-dimensional assumption is not realistic. For such conditions, both transverse and longitudinal velocity components are important, and concentration gradients across the channel approach those along the channel. To simulate this case with one-dimensional models, unreasonably large longitudinal dispersion coefficients must be used. Two-dimensional vertically averaged numerical models are more suitable for these situations. Typical acceptable models were discussed in Section 3 of this appendix. 1.113-21 In some cases, numerical 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