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:
are simpler than the closed-loop pond, since no recirculation occurs between intake and discharge. In this case, the only hydraulic time constant is that associated with the travel time from the plant discharge to the receiving water. a. Simple Analytical Models Simple models may be used to obtain conservative estimates of the radioisotope concentra tions. Four models can be used to describe all cooling ponds: the completely mixed model, the plug-flow model, the partially mixed model, and the stratified model. In each case, the effect of evaporation is neglected. (1) Completely Mixed Model SFigure 8 shows the first case (the closed loop), in which the pond is represented as a completely mixed tank. All inputs of material makeup are-instantaneously mixed throughout the tank, so that the concentration is homogeneous. By performing a mass balance on the volume of the pond, a solution for concentration is obtained, assuming zero initial concentration and complete mixing: q b - exp T - I (42) T where q b is the pond blowdown rate and V T is the volume of the pond. The concentration C0 is the steady-state concentration that would exist for a nondecay Ing substance and is given by C .W_ 0 qb where W is the rate of addition of radioactivity (in Ci/sec). 1.113-26 o. Makeup *P ° BIowdown FIGURE 6. CLOSED-LOOP COOLING POND 1.113-27 v, f I" I Ko FIGURE 7. FLOW.THROUGH COOLING POND 1.113-28 Eupoati Radwaste w Makeup In a qb + Evaporation concsnt*Wtjn -0 FIGURE 9.. IaaslI - a - - - - - a - - Volume  . - a - r - - - - -- I COMPLETELY MIXED MODEL .S~ovwdownm Out ma mConcentration i C j For the steady-state concentration of a decaying substance, Equation (42) reduces to qb C T X (43) f0 qb VTX +1 In terms of the half-life, t%, of the added radioactivity, Equations (42) and (43) reduce to CO t 0 - exp - +.1n2] (44) (at steady state) Co .- l (45) where "" and T t- (ln2)/0 The dimensionless yariable - is the radioisotope half-life expressed in multiples of the flushing tiie (VT/qb).