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:
ical modeling, and performance-confirmation measures than a facility with significant subsurface contamination that has the potential to exceed national radiation protection standards. The appendix to this guide provides a simple ground water flow and transport model acceptable for estimating offsite tritium activity flux at nuclear power plant sites. It is similar to those found in Interstate Technology & Regulatory Council (ITRC), “Use and Measurement of Mass Flux and Mass Discharge” (Ref. 27), and American Petroleum Institute (API) Publication Number 4730, “Groundwater Remediation Strategies Tool” (Ref. 28). It is intended for use with simple hydrogeologic conditions and geometry such as steady-state flow in homogeneous porous sand layers. The model is provided in a spreadsheet format to facilitate identification of model input and output and is available in ADAMS as Accession No. ML15086A566. In this simple model, a transect area is constructed perpendicular to the general ground water flow direction, and is divided into subareas as determined from the hydrogeologic unit heterogeneity; ground water flow conditions; and monitoring-well data. The total activity flux of the contaminant(s) through the transect cross-section is approximated as the sum over all subareas of the product of the contaminant concentration, the subarea specific discharge, and the flow area (see Equation A3). The model in the appendix is an acceptable approach at a simple site for estimating ground water discharges based on ground water flow and transport. An example of a simple site is one that can be modeled as homogeneous or as a simple layering of homogenous hydrogeologic units where ground water flow can be represented as uniform and steady state. In contrast, a complex site may exhibit features such as highly heterogeneous hydrogeologic units or preferential flow paths. Another feature indicating a complex site is non-uniform or transient ground water flow conditions. This may