Near Surface Disposal Systems & Performance Craig H. Benson, - - PowerPoint PPT Presentation

Near Surface Disposal Systems & Performance

Craig H. Benson, University of Wisconsin‐Madison James H. Clarke, Vanderbilt University

Landfill Partnership

• C. Benson & J. Clarke, Leads

Objective :

• Science & technology

relevant to DOE & stakeholders needed to build confidence in on‐site disposal facilities (OSDFs)

• Improve performance,

improve construction &

• perations efficiency,

promote effective monitoring, & lower costs. Relevancy:

• Decommissioning & remediation rely

heavily on OSDFs.

• Cost effective design & construction of

OSDFs significantly affects cost & schedule of projects.

• Achieving stakeholder acceptance

remains a major challenge due to lack

• f confidence.

W A S T E

ACCESS ROAD

Final Cover System Liner System

MONITORING WELLS

Figure courtesy M. Othman, Geosyntec Consultants

Barrier Systems

Liners & covers of natural and synthetic materials

NAS (2009) ‐ knowledge of long‐term performance of waste containment structures as a principle science & technology gap for EM. Credibility gap for stakeholders.

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1 10 100 1000

Engineering Property

Time (years) As‐Built Current Field Research & Experience

? ? ?

Prediction? Analogs?

The Challenge – Confident Design for a Millennium

Strategic Approach

Three Principles, Four Themes

Theme 1. Long‐term field performance ‐ documenting field performance at full scale. Theme 2. Prediction – evaluating & parameterizing barrier models for reliable prediction. Theme 3. Barrier degradation – Defining barrier system degradation & degradation mechanisms. Theme 4. Surface barrier evolution ‐ understanding how surface barriers evolve & developing new approaches to ensure adequate performance. Three Principles:

• Demonstrating efficacy of

current & proposed technology at field scale.

• Understanding processes

& mechanisms that affect long‐term performance

• Evaluating predictive

capability, & enhancing , models as needed to more accurately reflect reality.

Research Thrusts in Theme 1:

Understanding Existing Technology

• State‐of‐the‐art: knowledge base from field

studies of barrier performance.

– Resistive barrier technologies – Water balance barrier technologies

• State‐of‐the‐art: lessons learned from field

studies of cover soil pedogenesis.

• Leachate source terms for LLW disposal

facilities.

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LLW Leachate Database – 1st Available

Temporal Behavior: U and Tc

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1x100 1x101 1x102 1x103 1x104 2 4 6 8 10 12 OSDF ERDF EMWMF ICDF Concentration of Uranium ( µg/L) Time (yr) (a) 1x100 1x101 1x102 1x103 2 4 6 8 10 12 OSDF ERDF EMWMF ICDF Concentration of Technetium (pCi/L) Time (yr) (b)

Research Thrusts in Theme 2

Evaluating & Developing Predictive Capability

• Efficacy of contaminant transport models for

barrier systems.

• Evaluating how input uncertainty/sparseness

affects uncertainty in model predictions.

• Mechanistic description and measurement of

radionuclide sorption & diffusion in barrier systems. Hg disposal/containment?

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9 10 20 30 40 50 50 100 150 200 250 300 350 400

Replicate 1 (depth=60mm) Replicate 2 (depth=60mm) Replicate 3 (depth=60mm) Foose et al. (2002) (depth=60mm) POLLUTE (depth=60mm) Replicate 2 (depth=90mm) Foose et al. (2002) (depth=90mm) POLLUTE (depth=90mm)

Time (days) Concentration (mg/L) (c) TCE

Forward “Class A” predictions using independently measured input parameters (not calibrated)

Composite Barrier Transport Model Validation – Independent Validation

Research Thrusts in Theme 3

Understanding Barrier Degradation

• Geomembrane degradation & life expectancy

in LLW facilities.

• Degradation of bentonite barriers due to ion

exchange, hydration‐exchange kinetics, environmental stress (freezing, drying), concrete contact.

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• Three temps (50, 70, 90 C)
• Three solutions (DI, LLW, and

LLW‐Rad)

• 2 mm HDPE (ERDF, OSDF, OSDC).

130 140 150 160 170 180 40 50 60 70 80 90 100 Oxidation Induction Time (min) Temperature (oC)

Geomembrane Lifetime Evaluation

Time‐Temperature Superposition

Research Thrusts in Theme 4

Surface Barrier Evolution & Design

• State‐of‐the‐art assessment of cover soil

pedogenesis.

• Design strategies that manage degradation &

ensure adequate performance (e.g., evolutionary covers, surface treatments).

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Resistive Cover Soil Profile

305 mm 150 mm 610 mm 610 mm 915 mm Remaining Cover top layer Bedding layer (Rip-rap only) Frost protection layer Radon barrier Transition layer Tailings

1000 Year Erosion - Vegetated Riprap Cover Semi-Arid Climate

1 m 2 m 3 m 4 m 5 m 6 m 7 m

Rip‐rap surface layer

Coupling Hydrology & Erosion Control for Covers – Design Innovation

Long Term Performance of Contaminant Isolation Systems

Investigators: J.Clarke (Lead), M. Abkowitz, C. Benson,

• D. Kosson and J. Rustick, R. Worthy (graduate students)

Project Objective: The overall goal of this project is the development of methodologies and analytical frameworks concerning performance assessment, design, monitoring, and maintenance of near surface contaminant isolation (CI) systems that will provide reliability, transparency, and traceability; enable risk-informed decision-making; and build confidence in containment approaches. Relevance and Impact to DOE: Technical and economic limitations often require that contamination is isolated

• n-site through the use of engineered barriers (covers

and bottom liners) or excavated and moved to off-site disposal facilities when contaminated sites are remediated and nuclear facilities are decommissioned. Both engineered and institutional controls are needed when contaminated materials and wastes are isolated either in on-site or off-site disposal facilities. Accomplishments

• “Impact of Anthropogenic Climate Change on Near

Surface Disposal Facilities”, R. Worthy,

• M. Abkowitz, C. Benson, J. Clarke, American

Nuclear Society Winter Meeting, November 2011.

• “A Systems Approach to Determining Design

Requirements for Near Surface Disposal”

• J. Rustick, J. Clarke and C. Benson, Invited

Presentation to Washington State Department of Ecology Workshop on Barriers, February, 2012.

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Performance Assessment Components

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• Site Conceptual Models:

– Link sources of contamination to potential receptors through environmental transport pathways and exposure routes

• Performance Evaluation

Scenarios:

– Examine how the disposal facility could evolve over the life‐cycle of the facility

• Event Tree Analysis:

– Can be used to select performance evaluation scenarios

(Figure from the Ph.D. dissertation of Kevin Brown)

Examples of Influential Factors on NSDF Performance

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Taken from INEEL/Ext‐01‐01133, 2001

Examples of Sub‐Components For a Broad Systems Approach

• Design specific considerations:

– Type of engineered barriers to be used

• Waste‐specific considerations:

– Waste form – Waste package

• Site‐specific considerations:

– Climate – Geology – Ecology

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Class A trench in 2008 – Barnwell LLW site

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• Natural and anthropogenic processes are believed to be causing climate

change – rises in temperature – variations in precipitation patterns

• Investigate near surface disposal facility hydrological parameters
• Determine how these parameters influence water balance mechanisms

(e.g., runoff, evapotranspiration (ET), percolation and storage).

• Focusing on the HELP model
• Uranium mill tailings disposal facility in Monticello, Utah

– Average Annual Precipitation = 381 mm – Average Annual Temperature = 7.80°C

The impact of Potential Climate Change and Episodic Events on the Performance of Near Surface Disposal Facilities

• Disposal cell completed in 2000
• Layer 1: Fine‐textured soil and rock

(water storage layer)

• Layer 2: Sand layer (capillary barrier)
• Layer 3: High‐density polyethylene

geomembrane

• Layer 4: Compacted soil liner (radon

barrier)

• Composite design regulated under RCRA

Subtitle C and UMTRCA radon attenuation requirements

The Monticello Site