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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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slide1

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

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slide2

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

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slide3

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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slide4

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

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slide5

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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slide6

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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slide7

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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slide11

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

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slide12

PREVIOUS WORK ON RPT at CEAR

Radioactive Particle Tracking in a Ball Mill

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slide13

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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slide14

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

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C

slide15

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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slide16

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

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slide17

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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slide18

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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slide19

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

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slide20

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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slide21

PREVIOUS WORK ON RPT at CEAR

Experimental Results:

Measurements Vs. Model

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slide22

PREVIOUS WORK ON RPT at CEAR

Experimental Results:

Measurements Vs. Model

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slide23

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

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slide24

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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slide25

PREVIOUS WORK ON RPT at CEAR

Monte Carlo Simulated Results:

Schematic of a NaI Detector in an Attenuating Column

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slide26

PREVIOUS WORK ON RPT at CEAR

Monte Carlo Simulated Results:

Need Limiting Angle !!

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slide27

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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slide28

PREVIOUS WORK ON RPT at CEAR

Monte Carlo Simulated Results:

Monte Carlo Simulated Vs. Experimental Results

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slide29

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

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slide30

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,..)

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slide31

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

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slide32

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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slide33

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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slide34

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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slide35

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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slide36

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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slide37

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

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slide38

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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slide39

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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slide40

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

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slide41

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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slide42

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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slide43

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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slide44

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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slide45

ALTERNATIVE APPROACH FOR RPT

Coordinates Determination

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slide46

ALTERNATIVE APPROACH FOR RPT

Coordinates Determination

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slide47

ALTERNATIVE APPROACH FOR RPT

Coordinates Determination

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slide48

ALTERNATIVE APPROACH FOR RPT

Sensitivity of Determined Coordinates To Measured Angles

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slide49

ALTERNATIVE APPROACH FOR RPT

Detector Response to Particle Position

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slide50

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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slide51

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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slide52

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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slide53

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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slide54

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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slide55

ALTERNATIVE APPROACH FOR RPT

Effect Of Collimator Parameters On Accuracy and Resolution

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slide56

ALTERNATIVE APPROACH FOR RPT

Design Optimization Of Collimator

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slide57

ALTERNATIVE APPROACH FOR RPT

Design Optimization Of Collimator

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slide58

ALTERNATIVE APPROACH FOR RPT

Implementation Of The Concept

  • Precision Manufactured Platform, and Collimators

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slide59

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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slide60

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slide61

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slide62

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

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slide63

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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slide64

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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slide65

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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