PowerPoint Presentation

Pathways of Liquid Effluents inGroundwater and Surface Water(Section 2.4.13 SAR)EXAMPLEPathways of Liquid Effluents inGroundwater and Surface Water(Section 2.4.13 SAR)

FRAMES-2.0 Workshop

U.S. Nuclear Regulatory Commission

Bethesda, Maryland

November 15-16, 2007

Pacific Northwest National Laboratory

Richland, Washington

PurposePurpose

Demonstrate Hierarchical Modeling

SSAR assessment: instantaneous mixing, advection, retardation,decay

Modeling: mass balance, advection, dispersion, retardation, decay

Instantaneous release

Long-term release (20-yr leak)

Explore Conservative Assumptions

Full mixing over the Aquifer Depth

Largest Darcy Velocity

No Dispersion

Problem DescriptionProblem Description(direct quote from SAR)

“Reactor Coolant Storage Tank is postulated to rupture,and 80% of its liquid volume (92 m3) is assumed to bereleased in accordance with Branch Technical Position 11-6…Flow from the rupture is postulated to flood the buildingand migrate past the building containment structure andsump collection system and enter the subsurface at the topof the building slab…(V)ertical downward flow ensues. Apathway is created that would allow the entire 92 m3 toenter the groundwater system instantaneously.”

Problem DefinitionProblem Definition

No vadose zone, aquifer only

Uses known tank concentrations

Instantaneously places 80% (not 100%) of the tank’s mass into only theaquifer’s effective pore space

Uses tank’s total liquid volume to estimate the plan view area ofcontamination

NOT an instantaneous release scenario, which requires mass balancechecks on water and mass flux rates

Mixes contamination over the aquifer depth (conservative?)

Maximum Darcy velocity (noted as conservative)

Advection, Decay, and Retardation Only (noted as conservative)

No Dispersion (noted as conservative)

With Dispersion

Fully Mixed

Upper Aquitard

Upper Aquifer Unit

Plume

Source

River

Upper Aquitard

Source

River

Plume

Upper Aquifer Unit

Fully

Mixed

ModulesModules

Source, Vadose Zone, and Aquifer Transport

FRAMES Constituent Database Selection

Source (User-defined source term) – WFF VadoseZone Module

MEPAS 5.0 Aquifer Module

MEPAS 5.0 River Module

Exposure/Intake/Risk

MEPAS 5.0 Exposure Pathways Module

MEPAS 5.0 Receptor Intakes Module

MEPAS 5.0 Health Impacts Module

Model InputModel Input

Registering anExcel WorksheetRegistering anExcel Worksheet

(separate presentation)

Constituent

Database

“Source-Term” Module

Aquifer Module

River Module

Chronic Exposure

Module

Intake Module

Impacts Module

Output ResultsOutput Results

ConstituentConcentrations inAquifer at River’s Edge

pCi/mL

Years

Comments & InvestigationsComments & Investigations

Modeling provides us with an opportunity to morefully understand the problem. SAR case ignoresmass balance of water flux rate.

Maximum Darcy Velocity is conservative – ReduceSZ Darcy Velocity one order of magnitude

Fully mixed condition is conservative – Increasethe aquifer depth

Check to see if a maximum saturated zoneDarcy velocity is conservative:

Reduce the saturated zone Darcy velocity by anorder of magnitude (i.e., 1/10th)

Reduced by 1/10th

Reduced by 1/10th

Reduced by 1/10th

Reduced by 1/10th

ConstituentConcentrations in Aquiferat River’s Edge at 1/10ththe Darcy Velocity

pCi/mL

Years

Hierarchical Modeling Results

Check to see if fully mixed conditions inthe aquifer is conservative:

Increase the aquifer thickness.

This case was not run, but the modeling canprovide insight on how aquifer depth can impactthe conservative assumption.

Rule-of-Thumb Relationships

Rule-of-Thumb Relationship Definitions

SummarySummary

Many important factors determine whetherscenarios and assumptions are conservative

Interdependencies between parameters

Duration of release

Time of concentration

Water mass balance

Contaminant mass balance