AGU • Fall 2006 Meeting

Neptune and Company, Inc.

Radioactive Waste Disposal in Radioactive Waste Disposal in Hydrologically-Challenged Environments:Hydrologically-Challenged Environments:

Opportunities for Waste Disposal Opportunities for Waste Disposal Resource OptimizationResource Optimization

John Tauxe, PhD, PE and Paul Black, PhD

http://www.neptuneandco.com/~jtauxe/agu06

AGU • Fall 2006 Meeting

Presentation OutlinePresentation Outline

• introduction of the disposal resource

• identification of exposure mechanisms

• mathematical coupling

• probabilistic analysis

• modeling for regulatory compliance

• modeling for resource optimization

• conclusions

AGU • Fall 2006 Meeting

Nevada Test Site Nevada Test Site as a Waste Disposal Resourceas a Waste Disposal Resource

• remotely sited

• unmatched performance

• permitted operations

• radioactive waste is an insignificant addition to existing contamination from weapons testing

AGU • Fall 2006 Meeting

NTS is in the Basin and Range of NVNTS is in the Basin and Range of NV

Frenchman Flat

Yucca Flat

Area 5 RWMS >Area 5 RWMS >

AGU • Fall 2006 Meeting

Nearly 1000 Tests at Yucca FlatNearly 1000 Tests at Yucca Flat

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The Area 3 RWMSThe Area 3 RWMS

In Yucca Flat

AGU • Fall 2006 Meeting

The Area 5 RWMSThe Area 5 RWMS

In Frenchman Flat

AGU • Fall 2006 Meeting

Mechanisms Controlling Mechanisms Controlling Exposure and Potential DoseExposure and Potential Dose

• radon diffusivity and emanation factor

• ant activity

• cover thickness

environmental fate and transport

human behaviors

• site access and occupancy

• inhalation rate

AGU • Fall 2006 Meeting

Engineering ControlsEngineering Controls

active controls:• signs, fences• security force

passive controls:• site knowledge• cover thickness• barriers

photo copyright George Steinmetz

AGU • Fall 2006 Meeting

Mathematical Coupling of Mathematical Coupling of Modeled ProcessesModeled Processes

Physical processes are modeled as coupled partial differential equations:

radioactive decay and ingrowth

gaseous diffusion

aqueous diffusionaqueous advection

bioturbation

plant uptake and redistributionsoil/water chemical partitioning

air/water partitioning

chemical solubilityatmospheric resuspension

i

jjk

jk

t

ii

jeNN

1)0(1121

)(

CDJ sw ~hnK

vx

CDJ sa ~

b

z

zf

max

11

soilRatm CfQ solaq CC

aqHair CKC

soilplant CCRC

soilw

bdwater CKC

1

AGU • Fall 2006 Meeting

Probabilistic AnalysisProbabilistic Analysis

• modeling parameters are defined stochastically, capturing uncertainty

• Monte Carlo is handled by GoldSim*

• sensitivity analysis performed on results

• sensitive parameters are identified

• value-of-information analysis performed

• revisions through Bayesian updating

*GoldSim is modeling software for probabilistic systems analysis.

AGU • Fall 2006 Meeting

Regulatory Compliance:Regulatory Compliance:A common reason for assessmentA common reason for assessment

• regulations (by EPA, NRC, and DOE) are ultimately concerned with protecting human health by specifying a maximum potential dose or release objective

• performance objectives are assessed through modeling fate and transport and future potential doses to a member of the public or intruder

AGU • Fall 2006 Meeting

Resource Optimization:Resource Optimization:A new reason for assessmentA new reason for assessment

• cost/benefit analysis can help inform candidate waste acceptance and disposal technology and configuration decisions

• takes advantage of attributes of the resource

• optimization can be done only through probabilistic modeling and sensitivity analysis

• ALARA - a decision analysis process to keep doses As Low As Reasonably Achievable

AGU • Fall 2006 Meeting

Optimization of OperationsOptimization of Operations

• design disposal operations to minimize future human health effects

• assess candidate waste streams before they are packaged and shipped

• evaluate closure options and expenses

• minimize long-term maintenance and monitoring costs

AGU • Fall 2006 Meeting

ConclusionsConclusions

• optimization (cost/benefit) is made possible through probabilistic modeling and decision analysis

• extension of decision analysis to other environmental problems...

...CERCLA, RCRA, water resources...

• NTS RWMS: a resource worth saving

http://www.neptuneandco.com/goldsim

AGU • Fall 2006 Meeting