Document: NRC Regulatory Guide
Document ID: 42f2dcf0-38ba-4f75-84d4-e60f4bbf9162
Document Type: regulatory_guide
Title: Assessment of Abnormal Radionuclide Discharges in Ground Water to the Unrestricted Area at Nuclear Power Plant Sites Appendix-Simple Ground Water Model for Estimating Offsite Tritium Activity Flux + HISTORY - HISTORY 12/2015 – DG-4025-Proposed New Guide
Source: NRC Regulatory Guide Division 4
Source URL: https://www.nrc.gov/docs/ML1523/ML15237A388.pdf
Revision Date: 2023-06
Chapter: 
Section ID: RG-4.25
CFR Part: 
CFR Title: 

Content:
s at each well location representing the layering at that location – each block will be the thickness of the layer that it represents. If not, discretize the transect to accommodate these variations in hydraulic properties. 5. Select the monitoring wells to be used in estimating the tritium flux into the unrestricted area as close to the site’s boundary as possible given the available data (i.e., geologic borings and monitoring “points” or intervals) 6. Determine, after reviewing the monitoring data, whether there is a basis to vary tritium concentrations with depth within a hydrogeologic unit. If so, further discretize the hydrogeologic unit to accommodate these variations within the hydrogeologic unit layering. If not, no further discretization is warranted. DG-4025, Appendix, Page 2 7. Once the discretization is complete: a. Determine hydraulic properties for each “block” (i.e., subarea in the transect). b. Calculate the specific discharge for each set of hydraulic properties (or each “block”) using the following equation: ݍ௝ൌ െܭ௝ൈ׏݄௝ equation A-1 where ݍ௝ is the specific discharge perpendicular to block ݆, in cubic feet/day per cross- sectional area measured in square feet; ultimately as ft/day ܭ௝ is the hydraulic conductivity for the material in block ݆, ft/day (obtained from site- specific hydraulic tests), and ׏݄௝ is the hydraulic gradient normal to block ݆, ft/ft (dimensionless) (change in hydraulic head over distance to discharge point). c. Calculate the bulk water flux across each block in the discretization using the following equation: Qw୨ൌ q୨ൈA୨ equation A-2 where ܳݓ௝ is the bulk water flux for block ݆, cubic feet/day, and ܣ௝ is the area of block ݆, square ft. d. Determine tritium concentrations for each block and for each time period for which there is a tritium activity measurement. e. Calculate the tritium-activity flux across each block by multiplying the tritium activity concentration