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NC STATE UNIVERSITY NUCLEAR ENGINEERIG DEPARTMENT CENTER FOR ENGINEERING APPLICATIONS OF RADIOISOTOPES RADIOACTIVE PARTICLE TRACKING IN PEBBLE BED REACTORS By Prof. R. P. Gardner and Ashraf Shehata A R E C TOPICS Introduction Review of RPT Techniques

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NC STATE UNIVERSITY

NUCLEAR ENGINEERIG DEPARTMENT

CENTER FOR ENGINEERING APPLICATIONS OF RADIOISOTOPES

RADIOACTIVE PARTICLE TRACKING IN PEBBLE BED REACTORS

By

Prof. R. P. Gardner and Ashraf Shehata

A

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TOPICS

  • Introduction

  • Review of RPT Techniques

  • Review of Previous Work on RPT at CEAR

    • The Dual Energy Approach

    • The Nonlinear Inverse Analysis Approach

    • Monte Carlo Simulated Results

    • Experimental Results

  • Introduction To Pebble Bed Reactor

  • Critique on Previous Work

  • An Alternative Approach for RPT

  • A

    R

    E

    C


    INTRODUCTION

    • ORIGIN:Developed Primarily by Chemical

    • Engineers

    • USES:Flow Characterization of Chemical

    • and Mineral Processes

    • EXPECTATIONS:

      • Potential for Benchmarking CFD Calculations

      • Potential for Combining RTD and CFD

      • Potential for Flow Characterization and Mapping of Fuel Pebbles In a Pebble Bed Reactor

      • Potential for Combining Flow Characterization andResidence Time Distribution Calculations

        for optimized Fuel Cycles

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    TOPICS

    • Introduction

    • Review of RPT Techniques

    • Review of Previous Work on RPT at CEAR

      • The Dual Energy Approach

      • Experimental Results

      • The Nonlinear Semi-Empirical Modeling

      • Monte Carlo Simulated Modeling

  • Introduction To Pebble Bed Reactor

  • Critique on Previous Work

  • An Alternative Approach for RPT

  • A

    R

    E

    C


    REVIEW OF PREVIOUS WORK

    • Extensive Review by Larachi, Chaouki, Kennedy, and Dudukovic: Chap.11: RadioactiveParticle Tracking in Multiphase Reactors: Principles and Applications in NON-INVASIVE MONITORING OF MULTIPHASE FLOWS, Elsevier Science, 1996

    • Linearization of Inverse Solution

    • First “full-flow-field” particle velocities in multiphase reactors were by Kondukov et al. (1964), Borlai et al. (1967), and van Velzen et al. (1974)

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    REVIEW OF PREVIOUS WORK

    • University of Illinois System, 1983

    • Florida Atlantic University, 1990

    • Washington University, 1990

    • Ecole Polytechnique of Montreal, 1994

    • Gatt at AAEC Research Establishment, 1977, Flow of Individual Pebbles in Cylindrical Vessels, Nuclear Engineering and Design, 42, 265-275 – missed in review

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    REVIEW OF PREVIOUS WORK

    • CURRENT APPROACHES:

      • Based Primarily on “TOMOGRAPHIC” Imaging, in which an Array of Detectors is Assembled Around the System.

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    REVIEW OF PREVIOUS WORK

    GATT, 1

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    REVIEW OF PREVIOUS WORK

    GATT, 2

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    REVIEW OF PREVIOUS WORK

    GATT, 3

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    TOPICS

    • Introduction

    • Review of RPT Techniques

    • Review of Previous Work on RPT at CEAR

      • The Dual Energy Approach

      • Experimental Results

      • The Nonlinear Semi-Empirical Modeling

      • Monte Carlo Simulated Modeling

  • Introduction To Pebble Bed Reactor

  • Critique on Previous Work

  • An Alternative Approach for RPT

  • A

    R

    E

    C


    PREVIOUS WORK ON RPT at CEAR

    Radioactive Particle Tracking in a Ball Mill

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    PREVIOUS WORK ON RPT at CEAR

    Top View

    10 cm

    4 cm

    6 cm

    6 cm

    10 cm

    Sources

    Detector 1

    Detector 3

    25.4 cm

    25.5 cm

    5 cm

    5 cm

    Detector 2

    Detector 4

    Four Detectors, Dual Energy RPT Experiment

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    TOPICS

    • Introduction

    • Review of RPT Techniques

    • Review of Previous Work on RPT at CEAR

      • The Dual Energy Approach

      • Experimental Results

      • The Nonlinear Semi-Empirical Modeling

      • Monte Carlo Simulated Modeling

  • Introduction To Pebble Bed Reactor

  • Critique on Previous Work

  • An Alternative Approach for RPT

  • A

    R

    E

    C


    PREVIOUS WORK ON RPT at CEAR

    The Dual Energy Approach

    • A radioactive particle with two “clean” energies is used – Co-60, Sc-46, Na-24

    • Either two SCA’s with a “window” in each or an MCA with two ROI’s can be used for each detector –> doubling the data available from the same number of detectors

    • The additional data can be placed directly into the least-squares analysis

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    TOPICS

    • Introduction

    • Review of RPT Techniques

    • Review of Previous Work on RPT at CEAR

      • The Dual Energy Approach

      • Experimental Results

      • The Nonlinear Semi-Empirical Modeling

      • Monte Carlo Simulated Modeling

  • Introduction To Pebble Bed Reactor

  • Critique on Previous Work

  • An Alternative Approach for RPT

  • A

    R

    E

    C


    PREVIOUS WORK ON RPT at CEAR

    Y

    Detector 4

    X

    Z

    Particle Trajectory

    Radioactive Particle

    Detector 3

    Detector 1

    Detector 2

    Experimental Results:

    Experiment Schematic

    • System Chosen for Study was Ball Mill

    • Four 2” X 2” NaI Detectors were Used

    • A Sparrow 4-channel system with MCA’s was Used

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    PREVIOUS WORK ON RPT at CEAR

    Y

    Detector 4

    X

    Z

    Particle Trajectory

    Radioactive Particle

    Detector 3

    Detector 1

    Detector 2

    Experimental Results:

    Responses For The Four Detectors

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    TOPICS

    • Introduction

    • Review of RPT Techniques

    • Review of Previous Work on RPT at CEAR

      • The Dual Energy Approach

      • Experimental Results

      • The Nonlinear Semi-Empirical Modeling

      • Monte Carlo Simulated Modeling

  • Introduction To Pebble Bed Reactor

  • Critique on Previous Work

  • An Alternative Approach for RPT

  • A

    R

    E

    C


    PREVIOUS WORK ON RPT at CEAR

    Experimental Results:

    Analytical Nonlinear Model

    Where; Ci=total photopeak counts of ith detector,

    ri=distance from tracer to ith detector,

    R=attenuation of mill wall and charge,

    SR=distance traveled in wall and charge,

    D =attenuation in detector,

    SD=distance traveled in detector,

    B = background,

    A = a constant proportional to the source

    intensity.

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    PREVIOUS WORK ON RPT at CEAR

    Experimental Results:

    Measurements Vs. Model

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    PREVIOUS WORK ON RPT at CEAR

    Experimental Results:

    Measurements Vs. Model

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    TOPICS

    • Introduction

    • Review of RPT Techniques

    • Review of Previous Work on RPT at CEAR

      • The Dual Energy Approach

      • Experimental Results

      • The Nonlinear Inverse Analysis Approach

      • Monte Carlo Simulated Results

  • Introduction To Pebble Bed Reactor

  • Critique on Previous Work

  • An Alternative Approach for RPT

  • A

    R

    E

    C


    PREVIOUS WORK ON RPT at CEAR

    Monte Carlo Simulated Results:

    • The Expected Value Approach Was Used

    • One can Force Every Gamma Ray to be Detected so only a few are required

    • Needed Limiting Subtended Angles to Cylinder: Gardner, Choi, Mickael, Yacout, Jin, and Verghese, 1987, Algorithms for Forcing Scattered Radiation to Spherical, Planar Circular, and Right Circular Cylindrical Detectors for Monte Carlo Simulation, Nuclear Science and Engineering, 95, 245-256

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    PREVIOUS WORK ON RPT at CEAR

    Monte Carlo Simulated Results:

    Schematic of a NaI Detector in an Attenuating Column

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    PREVIOUS WORK ON RPT at CEAR

    Monte Carlo Simulated Results:

    Need Limiting Angle !!

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    PREVIOUS WORK ON RPT at CEAR

    Monte Carlo Simulated Results:

    Monte Carlo Map of Counting Rates of one Detector VS. Tracer Position

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    PREVIOUS WORK ON RPT at CEAR

    Monte Carlo Simulated Results:

    Monte Carlo Simulated Vs. Experimental Results

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    TOPICS

    • Introduction

    • Introduction To Pebble Bed Reactor

    • Review of Previous Work on RPT

    • Review of Previous Work on RPT at CEAR

      • The Dual Energy Approach

      • Experimental Results

      • Monte Carlo Simulated Results

      • The Nonlinear Inverse Analysis Approach

  • Critique on Previous Work

  • An Alternative Approach for RPT

  • Discussion and Conclusions

  • A

    R

    E

    C


    CRITIQUE ON PREVIOUS WORK

    • Discrepancies Between Measurements and Monte Carlo Modeling:

    • This is Mainly Due to Information Distortion Due to Counting Losses Typical to High CountingRate Systems (Dead Time, Pulse Pileup,..)

    A

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    TOPICS

    • Introduction

    • Review of RPT Techniques

    • Review of Previous Work on RPT at CEAR

      • The Dual Energy Approach

      • Experimental Results

      • The Nonlinear Inverse Analysis Approach

      • Monte Carlo Simulated Results

  • Introduction To Pebble Bed Reactor

  • Critique on Previous Work

  • An Alternative Approach for RPT

  • A

    R

    E

    C


    MODULAR HIGH TEMPERATURE PEBBLE BED RECTOR

    • Helium Cooled

    • “Indirect” Cycle

    • 8 % Enriched Fuel

    • Can be Built in

    • 2 Years

    • Factory Built

    • Site Assembled

    • On-line Refueling

    • Highly Modular

    • (Modules added to meet demand)

    • High Burnup >90,000 Mwd/MT

    • Direct Disposal of High Level Waste

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    MODULAR HIGH TEMPERATURE PEBBLE BED RECTOR

    For A 110 MWe:

    • 360,000 pebbles in core

    • about 3,000 pebbles handled

    • by Fuel Handling System Daily

    • about 350 discarded daily

    • one pebble discharged every

    • 30 seconds

    • average pebble cycles through

    • core 15 times

    • Fuel handling most maintenance-intensive

    • part of plant

    German AVR Pebble Bed Reactor

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    MODULAR HIGH TEMPERATURE PEBBLE BED RECTOR

    TRISO Fuel Particle; (Microsphere)

    • 0.9mm diameter

    • ~ 11,000 in every pebble

    • 109 microspheres in core

    • Fission products retained inside microsphere

    • TRISO acts as a pressure vessel

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    MODULAR HIGH TEMPERATURE PEBBLE BED RECTOR

    International Activities:

    • China - 10 Mwth Pebble Bed - 2000 critical

    • Japan - 40 Mwth Prismatic

    • South Africa - 250 Mwth Pebble Bed- 2003

    • Russia - 330 Mwe - Pu Burner Prismatic 2007

    • Netherlands - small industrial Pebble

    • Germany 300 Mwe Pebble Bed (Shut down)

    • MIT - 250 Mwth - Intermediate Heat Exch.

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    MODULAR HIGH TEMPERATURE PEBBLE BED RECTOR

    Application Of (RPT) To Pebble Tracking:

    • Excessive Time Spent In Parts Of The Bed Could Result In Severe Irradiation And Thermal Damage To The Pebble

    • The Feasibility Of The Recycling Of Fuel Pebbles In a Pebble Bed Reactor Depends On a satisfactory Pebble Flow Through The Vessel, Its Outlet, and The Pebble Extractor

    • So It Is Important To Know Pebble Pathways And Relative Velocities Through The Bed

    • There Is Need For technique To study the Dynamics Of Pebbles In a Pebble Bed Reactor

    • One Can Track pebbles In a Scaled Prototype

      Pebble Bed Reactor (RPT)

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    TOPICS

    • Introduction

    • Review of RPT Techniques

    • Review of Previous Work on RPT at CEAR

      • The Dual Energy Approach

      • Experimental Results

      • The Nonlinear Inverse Analysis Approach

      • Monte Carlo Simulated Results

  • Introduction To Pebble Bed Reactor

  • Critique on Previous Work

  • An Alternative Approach for RPT

  • A

    R

    E

    C


    CRITIQUE ON PREVIOUS WORK

    • Large Number of Detectors is Needed For Reasonably Accurate Tracking :

    • Due to Inherent uncertainties Associated With Linear/Nonlinear Map Search, As much As Possible Redundant Information is Necessary For Sufficiently Accurate Particle Tracking. Thus a Large Number of Detectors is Needed Depending on the Size of The System To Be Investigated

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    CRITIQUE ON PREVIOUS WORK

    • Expected Modeling Difficulties In Stochastic Heterogeneous Systems, Such As Pebble Bed Reactors.

    • Randomly Distributed Pebbles May Produce Large Amount of Contrast in Attenuation Between Different Particle Positions Corresponding To Same Distance From The Detector In Question, Specially At The Container Wall Region

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    TOPICS

    • Introduction

    • Review of RPT Techniques

    • Review of Previous Work on RPT at CEAR

      • The Dual Energy Approach

      • Experimental Results

      • The Nonlinear Inverse Analysis Approach

      • Monte Carlo Simulated Results

  • Introduction To Pebble Bed Reactor

  • Critique on Previous Work

  • An Alternative Approach for RPT

  • A

    R

    E

    C


    ALTERNATIVE APPROACH FOR RPT

    OBJECTIVES

    • Investigate An Improved RPT Approach to Overcome Current Approach Limitations :

      • Eliminate Information Distortion Due to Counting Losses Typical to High CountingRate Systems (Dead Time, Pulse Pileup,..)

      • Reduce number of Detectors Needed

      • Overcome Modeling Difficulties of Heterogeneous Stochastic Attenuating Media Such as Pebble Bed Reactors

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    ALTERNATIVE APPROACH FOR RPT

    OBJECTIVES

    • Investigate An Improved RPT Approach to Overcome Current Approach Limitations :

      • Eliminate Information Distortion Due to Counting Losses Typical to High CountingRate Systems (Dead Time, Pulse Pileup,..)

      • Reduce number of Detectors Needed

      • Overcome Modeling Difficulties of Heterogeneous Stochastic Attenuating Media Such as Pebble Bed Reactors

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    ALTERNATIVE APPROACH FOR RPT

    Overview of The Concept

    • The Concept is Based on Dynamic Motion Control of a Cluster of Three Very Well CollimatedDetectors

    • The Detectors are Mounted on a Platform Whose Height Can be Varied

    • The Center Detector (With a Horizontal Slit) is Used to Directly Establish the Vertical Position of the Tracer

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    ALTERNATIVE APPROACH FOR RPT

    Overview of The Concept

    • The Two Outer Detectors are Independently Rotated To Align With The Tracer (Line of Sight Position)

    • The Angles 1 and 2 are Instantaneously Recorded Providing The Two Cylindrical Coordinates r and 

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    ALTERNATIVE APPROACH FOR RPT

    Coordinates Determination

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    ALTERNATIVE APPROACH FOR RPT

    Coordinates Determination

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    ALTERNATIVE APPROACH FOR RPT

    Coordinates Determination

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    ALTERNATIVE APPROACH FOR RPT

    Sensitivity of Determined Coordinates To Measured Angles

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    ALTERNATIVE APPROACH FOR RPT

    Detector Response to Particle Position

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    ALTERNATIVE APPROACH FOR RPT

    Detector Response to Particle Position

    • The Accuracy and Resolution of the

    • Particle Positions are determined Primarily

    • by Two Factors:

      • How Well Resolved

    • Detector Response

    • Maximum.

      • The Precession and Accuracy of the Physical Dimensions of the Tracking System.

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    ALTERNATIVE APPROACH FOR RPT

    Design Optimization Of Collimator

    Using Monte Carlo Simulation to Optimize the

    Design of the Collimator:

    • Effect of Slit Width

    • Effect of the Slit Depth

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    ALTERNATIVE APPROACH FOR RPT

    d

    R

    b

    W

    a

    c

    e

    R

    S

    D

    Effect Of Collimator Parameters On Accuracy and Resolution

    • Triangles abc and ade

    • are similar. Thus;

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    ALTERNATIVE APPROACH FOR RPT

    d

    R

    b

    W

    a

    c

    e

    R

    S

    D

    Effect Of Collimator Parameters On Accuracy and Resolution

    • ROV is to be Minimized

      • Thus Minimize W, and Maximize D

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    ALTERNATIVE APPROACH FOR RPT

    Effect Of Collimator Parameters On Accuracy and Resolution

    • Collimator 1:

      • W= 3mm, & D= 25.4mm; Thus for S=100mm:

      • ROV= 26.6mm

    • Collimator 2:

      • W= 1mm, & D= 50.8mm; Thus for S= 100mm:

      • ROV= 4.94mm

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    ALTERNATIVE APPROACH FOR RPT

    Effect Of Collimator Parameters On Accuracy and Resolution

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    R

    E

    C


    ALTERNATIVE APPROACH FOR RPT

    Design Optimization Of Collimator

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    R

    E

    C


    ALTERNATIVE APPROACH FOR RPT

    Design Optimization Of Collimator

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    ALTERNATIVE APPROACH FOR RPT

    Implementation Of The Concept

    • Precision Manufactured Platform, and Collimators

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    ALTERNATIVE APPROACH FOR RPT

    Implementation Of The Concept

    • Computer Controlled Micro-Stepping Stepper

      Motors (Up to 0.18 Degrees Per Step).

    • Programmable Automation and Control System

      (National Instruments LabView)

    • Development of a Graphical User Interface (GUI)

      LabView Program, for Experiment Automation,

      Control, and Visualization.

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    TOPICS

    • Introduction

    • Introduction To Pebble Bed Reactor

    • Review of Previous Work on RPT

    • Review of Previous Work on RPT at CEAR

      • The Dual Energy Approach

      • Experimental Results

      • Monte Carlo Simulated Results

      • The Nonlinear Inverse Analysis Approach

  • Critique on Previous Work

  • An Alternative Approach for RPT

  • Discussion and Conclusions

  • A

    R

    E

    C


    DISCUSSION AND CONCLUSIONS

    • The Dual Energy Approach Was Useful As It Uses Additional Already Available Data

    • The Nonlinear Inverse Analysis Approach Gave Much Better Accuracy, Than Monte Carlo Mapping

    • Discrepancies Between Monte Carlo Simulation and Experiment Raised Due to Information Distortions Pertinent to High Counting Rate (Dead Time, and Pulse Pileup)

    • A Simpler And More Efficient Alternative Was Needed Particularly for Tracking Pebbles In A Pebble Bed Reactor Vessel.

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    DISCUSSION AND CONCLUSIONS

    • The Approach Proved to Be Valid In General.

    • The Concept Has Remarkable Advantages Over the Current RPT Techniques;

      • Much Less Number of Detectors Needed For Tracking (Only 3)

      • Only Simple Radiation Detection Needed, Based on Measuring Only The Counting

      • Rate of Each Detector, and Identify Their Maxima. This would avoid

      • Measurement Complications,

      • such as Pulse Pile Up,

      • and Dead Time Losses

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    DISCUSSION AND CONCLUSIONS

    • The Concept Eliminates The Need for Complicated, and Time Consuming Modeling and Computations, and Thus It is Most Ideal for Real Time Online RPT.

  • However, The Technique Has Some Limitations.

    • The Limited Speed of The Tracker, Particularly in

    • The Vertical Direction, Because of the Heavy

    • Mechanical Load

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    Thank You

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