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:
e 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). Figure 9 illustrates the steady-state concentration defined by Equation (45) as-a function of r. This figure shows that for small half-lives (compared with the flushing time, VT/qb)S the concentration depends strqngly on half-life, but for long half-lives, this dependence diminishes. The completely mixed tank model (see Figure 8) Is'adequate for substances with long half-lives, where the internal circulation timetis Short compared with the half-life. In this case, the concentration in the pond is fairly homogepeous, satisfying the "completely mixed" limitation of this model. (2) Plug-Flow Model For the flow-through cooling pond, the plug-flow model illustrated in Figure 10 may be adequate if it is presumed that there Is no recirculation. The concentration is expressed as C- CO exp (-xVT/qb) * Co exp ( ln2/r) (46) where qb is now the flow rate .thrugh the pond. This expression is evaluated in Figure 9 and compared with the completely mixed case. Agreement is best for large r. Although not easily seen in Figure 9, the models deviate for small T. (3) Partially Mixed Model Where a significant part of the flow is due to both blowdown and plant pumping, neither of the above models is adequate. A suitable model that includes both the plant pumping rate q and blowdown rate qb is illustrated in Figure 11. The recirculation factor R is defined as Rwqb RU q p The steady-state concentration is then defined as 1.113-30 K1 K 1.( 0.I O.I 0.? o.e 0.5 0.4 0.3 0.2 0.1 0 - " ,v- Plg l ;~~~w , .YI&,,,. - 1 111NA I ISili I I I gillI 0 1up 10, "HALF-LIFE/FLUSHING TIME VT 10)2 FIGURE 9. STEADY-STATE CONCENTRATIONS IN COMPLETELY MIXED AND PLUG-FLOW MODELS \I- K hi 0 lF u z ur-l . . . ..... | Evaporation - I - Malmuo I". % + Evapoation Concetrt~OionC =1CJO BtOwdOwn Out - Q Concentrationl -C