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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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Introduction To Pebble Bed Reactor Critique on Previous Work An Alternative Approach for RPT

Introduction To Pebble Bed Reactor Critique on Previous Work An Alternative Approach for RPT

Introduction To Pebble Bed Reactor Critique on Previous Work An Alternative Approach for RPT

Introduction To Pebble Bed Reactor Critique on Previous Work An Alternative Approach for RPT

Introduction To Pebble Bed Reactor Critique on Previous Work An Alternative Approach for RPT

Introduction To Pebble Bed Reactor Critique on Previous Work An Alternative Approach for RPT

Introduction To Pebble Bed Reactor Critique on Previous Work An Alternative Approach for RPT

Critique on Previous Work An Alternative Approach for RPT Discussion and Conclusions

Introduction To Pebble Bed Reactor Critique on Previous Work An Alternative Approach for RPT

Introduction To Pebble Bed Reactor Critique on Previous Work An Alternative Approach for RPT

Introduction To Pebble Bed Reactor Critique on Previous Work An Alternative Approach for RPT

Critique on Previous Work An Alternative Approach for RPT Discussion and Conclusions

However, The Technique Has Some Limitations.

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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- 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

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- 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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- 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

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

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- 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

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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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- 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

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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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- 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

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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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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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- 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

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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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- 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

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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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Monte Carlo Simulated Results:

Schematic of a NaI Detector in an Attenuating Column

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Monte Carlo Simulated Results:

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

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Monte Carlo Simulated Results:

Monte Carlo Simulated Vs. Experimental Results

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- 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

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- 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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- 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

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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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- 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

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- 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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- 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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- 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

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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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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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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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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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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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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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d

R

b

W

a

c

e

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S

D

Effect Of Collimator Parameters On Accuracy and Resolution

- Triangles abc and ade
- are similar. Thus;

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d

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b

W

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c

e

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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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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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Implementation Of The Concept

- Precision Manufactured Platform, and Collimators

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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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- 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

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

- The Limited Speed of The Tracker, Particularly in
- The Vertical Direction, Because of the Heavy
- Mechanical Load

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