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Recent Advancements in Harsh Environment Fiber Optic Sensors: An Enabling Technology for Emerging Nuclear Power Applications
Presented at the International Atomic Energy Agency Meeting Knoxville, TN
By

Robert S. Fielder
Of

Luna Innovations, Incorporated Co-authors: Roger Duncan and Matthew Palmer June 28th, 2005
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Directed Energy Target Failure Sensors

Introduction
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The purpose of this paper is to highlight recent development of extreme environment fiber optic sensors. Substantial advancements have been made which have demonstrated the capability of fiber optic sensors to operate in high-radiation and hightemperature environments. Additional areas for continued development will also be covered.

Recent Advancements in Harsh Environment Fiber Optic Sensors: An Enabling Technology for Emerging Nuclear Power Applications

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Outline
 Introduction to fiber optic sensors  Radiation Testing of Fiber Bragg Grating Sensors  Radiation Testing of Hybrid Pressure-Temperature Sensors  Radiation Testing of Optical Fiber  High-Temperature Testing of Fiber Bragg Grating Temperature Sensors  High-Temperature Testing of EFPI-based Pressure Sensors  High-Temperature Testing of Optical Fiber  Conclusions and Future Development

Recent Advancements in Harsh Environment Fiber Optic Sensors: An Enabling Technology for Emerging Nuclear Power Applications

www.lunainnovations.com

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Introduction to Fiber Optic Sensors

Advantages of Fiber Optic Sensors  Extremely Small Size  Low mass  Immune to EMI  Long cable leads (km lengths)  High accuracy and sensitivity  High-temperature resistance  Radiation hard  Self diagnostics / sensor health monitoring

Recent Advancements in Harsh Environment Fiber Optic Sensors: An Enabling Technology for Emerging Nuclear Power Applications

www.lunainnovations.com

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Fiber Bragg Grating Sensors, Theory of Operation

Recent Advancements in Harsh Environment Fiber Optic Sensors: An Enabling Technology for Emerging Nuclear Power Applications

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Extrinsic Fabry-Perot Interferometer (EFPI) Sensors, Theory of Operation
(A)
Broadband Source

Principles of Operation
(C) Diaphragm
Sensor

Optical fiber

R2 P R1

Signal Processing

Pressure Sensor

Intensity

Sensor chip Optical fiber R2 J R1
 60 m gap  120 m gap

Temperature Sensor (D)

(B)

Data contained within the fringe pattern enables sensor self-diagnostics
Recent Advancements in Harsh Environment Fiber Optic Sensors: An Enabling Technology for Emerging Nuclear Power Applications

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Outline
 Introduction to fiber optic sensors  Radiation Testing of Fiber Bragg Grating Sensors  Radiation Testing of Hybrid Pressure-Temperature Sensors  Radiation Testing of Optical Fiber  High-Temperature Testing of Fiber Bragg Grating Temperature Sensors  High-Temperature Testing of EFPI-based Pressure Sensors  High-Temperature Testing of Optical Fiber  Conclusions and Future Development

Recent Advancements in Harsh Environment Fiber Optic Sensors: An Enabling Technology for Emerging Nuclear Power Applications

www.lunainnovations.com

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Combined Neutron and Gamma Survivability Testing of FBG Sensors
Executive Summary of Results

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Long-term (2 months) continuous exposure, in-core Demonstrated FBG survivability in extremely high radiation environment (2x1019cm-2 (Neutron, >1MeV) and 8.7x108 Gy (8.7x1010 Rad) gamma)

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Identified optimal fiber composition for radiation resistance.

Recent Advancements in Harsh Environment Fiber Optic Sensors: An Enabling Technology for Emerging Nuclear Power Applications

www.lunainnovations.com

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Combined Neutron and Gamma Survivability Testing of FBG Sensors
Experimental Design and Setup
Experimental Goals  Surveyed existing literature to design broad-spectrum experiment  Duplicated virtually all reported measurements, except Raman scattering  Exceeded highest exposure levels by 2000x  Tremendous effort to assemble complex experiment within very short window of opportunity Measurements  FBG wavelength shift  Fiber attenuation at 1310/1550nm  Fiber attenuation between 10001600nm  FBG reflectivity (relative)  Temperature (via thermocouples) Variables  Total neutron and gamma dose  Neutron and gamma dose rate  Fiber composition (4)  FBG reflectivity (3)  Over 500 FBGs tested

Recent Advancements in Harsh Environment Fiber Optic Sensors: An Enabling Technology for Emerging Nuclear Power Applications

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High-Radiation Testing
Experimental Setup

Mothworks

Mission Control

Dry Run Cells Installed

Crisis

Logistics

Installation

Ex-Core

Recent Advancements in Harsh Environment Fiber Optic Sensors: An Enabling Technology for Emerging Nuclear Power Applications

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Combined Neutron and Gamma Survivability Testing of FBG Sensors
After two months of continuous exposure, sensors at core centerline showed good survivability

Sample c
5E+05 4E+05

3E+05

2E+05

100000

Sensor 20
0 0 50000 100 0 200
40000

Fiber Bragg grating showing good survivability after exposure for ~1440hrs at fuel centerline (2x1019 cm-2 (neutron) and 8.7x108 Gy (8.7x1010 Rad) gamma

Reflectivity (a. u.)

Sp ec

7.5

tru

5

m

2.5 10

300
30000

400

Sen

sor

12.5

15 17.5

500
20000

20600

10000

0 125

150

175

200

225

250

275

Spectrum (a. u.)

Recent Advancements in Harsh Environment Fiber Optic Sensors: An Enabling Technology for Emerging Nuclear Power Applications

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Outline
 Introduction to fiber optic sensors  Radiation Testing of Fiber Bragg Grating Sensors  Radiation Testing of Hybrid Pressure-Temperature Sensors  Radiation Testing of Optical Fiber  High-Temperature Testing of Fiber Bragg Grating Temperature Sensors  High-Temperature Testing of EFPI-based Pressure Sensors  High-Temperature Testing of Optical Fiber  Conclusions and Future Development

Recent Advancements in Harsh Environment Fiber Optic Sensors: An Enabling Technology for Emerging Nuclear Power Applications

www.lunainnovations.com

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Radiation Testing of Hybrid PressureTemperature Sensors
Hybrid sensors measure P & T simultaneously by measuring the deflection of and the optical path length through a single sapphire diaphragm.

Diaphragm Optical fiber R2 R3 R1 Pressure Sensor

Directly measuring the temperature of the pressure transducer provides a high-level of active temperature compensation.
Recent Advancements in Harsh Environment Fiber Optic Sensors: An Enabling Technology for Emerging Nuclear Power Applications

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Radiation Testing of Hybrid PressureTemperature Sensors
Three sensors exposed to three different levels of neutron dose over a three-day experimental duration at the Ohio State University.
Accumulated Neutron Fluence vs. Time
Key Features:
Accumulated Dose, (n/cm )
2

1.00E+18 1.00E+17 1.00E+16 1.00E+15 1.00E+14 1.00E+13 0 1000 2000 Time, (min) 3000 4000

AIF, Lower Position AIF, Middle Position AIF, Upper Position Beam Port 1, Nearest Core Beam Port 1, Farthest from Core

 Highest Accumulated Neutron Fluence: 6.9x1017 cm-2 At AIF Lower Position

Total neutron fluence obtained by counting co-located gold and cobalt wire dosimeters after completion of test. Energy spectra spanned 0.025ev to 20MeV.
Recent Advancements in Harsh Environment Fiber Optic Sensors: An Enabling Technology for Emerging Nuclear Power Applications

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Radiation Testing of Hybrid PressureTemperature Sensors
Sensor Rad #2 Repeatiblity vs. Experiment Number with Increasing Dose
500.0

400.0

Measured Pressure (psi)

300.0

200.0

100.0

0.0

-100.0 0.0 100.0 200.0 Applied Pressure (psi) Scan 01 Pressure Scan 09 Pressure Scan 02 Pressure Scan 12 Pressure Scan 03 Pressure Scan 15 Pressure Scan 04 Pressure Scan 19 Pressure Scan 06 Pressure Scan 21 Pressure 300.0 400.0

Sensor Rad #2 performed very well during the OSU experiment. All of the pressure calibrations were extremely linear. Offset due to uncompensated temperature effects.
Recent Advancements in Harsh Environment Fiber Optic Sensors: An Enabling Technology for Emerging Nuclear Power Applications

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Active Temperature Compensation Using Hybrid P-T Sensor
Phase Corrected Temperature Variant Calibrations Sensor # Rad2
100.000

Sensor Rad #2 Calibrations After Thermal Correction of Zeros Based on Sapphire Temperature Reading
5

Sensor Pressure Sensitive Air Gap (um)

95.000

0
90.000
y = -0.0472x + 95.741 R2 = 1

Corrected Delta Air Gap (um)
400

-5

85.000

80.000

-10

75.000

y = -0.0463x + 92.015 2 R =1

-15

70.000 0 50 100 150 200 Pressure (psi) 00 C air gap 150 C air gap 22 C air gap 172 C air gap 50 C air gap Linear (172 C air gap) 100 C air gap Linear (00 C air gap) 250 300 350

-20 0 50 100 150 200 Pressure (psi) 250 300 350 400

00 C air gap

22 C air gap

50 C air gap

100 C air gap

150 C air gap

172 C air gap

Error without temperature correction approximately 17.24% over 172°C Temperature Range. With temperature correction, error was reduced to 1.8% over the same temperature range.
Recent Advancements in Harsh Environment Fiber Optic Sensors: An Enabling Technology for Emerging Nuclear Power Applications

www.lunainnovations.com

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Outline
 Introduction to fiber optic sensors  Radiation Testing of Fiber Bragg Grating Sensors  Radiation Testing of Hybrid Pressure-Temperature Sensors  Radiation Testing of Optical Fiber  High-Temperature Testing of Fiber Bragg Grating Temperature Sensors  High-Temperature Testing of EFPI-based Pressure Sensors  High-Temperature Testing of Optical Fiber  Conclusions and Future Development

Recent Advancements in Harsh Environment Fiber Optic Sensors: An Enabling Technology for Emerging Nuclear Power Applications

www.lunainnovations.com

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High-Radiation Testing of Optical Fiber
Attenuation vs. Wavelength
Fiber Transm ission vs.  Dose 0 0.00  Dose (GRad) 10.00 10 20 30

Relative Loss (dB)

SMF-28 (1310nm) 20.00 30.00 40.00 50.00 60.00 20% Ge-Doped (1310nm) SMF-28 (1550nm)

Optical attenuation vs. total gamma dose for various compositions and wavelengths

Optical attenuation vs. wavelength for various total gamma doses

Conclusion: While OFDR system operated satisfactorily in high-loss region, performance can be optimized by selecting the proper wavelength. Recent Advancements in Harsh Environment Fiber Optic Sensors: An Enabling Technology for Emerging Nuclear Power Applications

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Outline
 Introduction to fiber optic sensors  Radiation Testing of Fiber Bragg Grating Sensors  Radiation Testing of Hybrid Pressure-Temperature Sensors  Radiation Testing of Optical Fiber  High-Temperature Testing of Fiber Bragg Grating Temperature Sensors  High-Temperature Testing of EFPI-based Pressure Sensors  High-Temperature Testing of Optical Fiber  Conclusions and Future Development

Recent Advancements in Harsh Environment Fiber Optic Sensors: An Enabling Technology for Emerging Nuclear Power Applications

www.lunainnovations.com

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Temperature Mapping in SAFE-100 Using Distributed Fiber Bragg Grating Sensor Probe
Temperature Map to 1100ºC

1000 800 600 400 200

Temperature
1000 800 600 400 200 0 15

Run 3
1200 1000

DSS

0

Temp (C)

800 600 400 200 0 0 500 1000 1500 2000 2500 Time (sec)

200 150 100 5 50

Thermocouple

Position 10

Time

Recent Advancements in Harsh Environment Fiber Optic Sensors: An Enabling Technology for Emerging Nuclear Power Applications

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Outline
 Introduction to fiber optic sensors  Radiation Testing of Fiber Bragg Grating Sensors  Radiation Testing of Hybrid Pressure-Temperature Sensors  Radiation Testing of Optical Fiber  High-Temperature Testing of Fiber Bragg Grating Temperature Sensors  High-Temperature Testing of EFPI-based Pressure Sensors  High-Temperature Testing of Optical Fiber  Conclusions and Future Development

Recent Advancements in Harsh Environment Fiber Optic Sensors: An Enabling Technology for Emerging Nuclear Power Applications

www.lunainnovations.com

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High-Temperature Calibration of EFPI-Based Pressure Sensors: Experimental Setup
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Temperature variations profiled prior to experiment Pressure sensing diaphragm and all hightemperature interfaces fully immersed in hot zone Pressure applied using digital pressure controller Temperature at diaphragm: up to 1050°C Maximum test pressure: 500psi All packaging and assembly procedures verified

Recent Advancements in Harsh Environment Fiber Optic Sensors: An Enabling Technology for Emerging Nuclear Power Applications

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Pressure Sensor Calibration: Results
Experimental Results
Temperature at diaphragm: 800°C  Maximum test pressure: 500psi  All packaging and assembly procedures verified
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Gap (  m)

Gap vs. Pressure at 837 C
117.8 117.6 117.4 117.2 117.0 116.8 116.6 0 20 40 60 Pressure (PSI) 80 100 120

Gap vs. Pressure, 125m x 3.2mm Diameter Alumina
62 61 60 59 58 57 56 55 54 53 0 100 200 y = -0.0148x + 61.202 R2 = 0.9999

Gap, (m)

300

400

500

600

Pressure, (psi)

Static room temperature calibration performed, demonstrating lowhysterisis / high-accuracy
Recent Advancements in Harsh Environment Fiber Optic Sensors: An Enabling Technology for Emerging Nuclear Power Applications

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Outline
 Introduction to fiber optic sensors  Radiation Testing of Fiber Bragg Grating Sensors  Radiation Testing of Hybrid Pressure-Temperature Sensors  Radiation Testing of Optical Fiber  High-Temperature Testing of Fiber Bragg Grating Temperature Sensors  High-Temperature Testing of EFPI-based Pressure Sensors  High-Temperature Testing of Optical Fiber  Conclusions and Future Development

Recent Advancements in Harsh Environment Fiber Optic Sensors: An Enabling Technology for Emerging Nuclear Power Applications

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High-Temperature Testing of Optical Fiber
Loss vs. Time and Temperature, Standard SMF-28 Fiber

SMF-28, Ge-doped 1550nm Fiber
35 30 25 1168C

Loss (dB)

20 15 10 5 0 0 50 100 150 200 250 Time (minutes)
Higher temperatures resulted in higher optical attenuation

1111C

1065C

Recent Advancements in Harsh Environment Fiber Optic Sensors: An Enabling Technology for Emerging Nuclear Power Applications

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Developed Process to Improve Optical Fiber Survivability at High Temperatures
Loss vs. Time at 1065°C, Specialty High-Temperature Fiber

Specialty Singlemode Ge-doped 1550nm fiber heated to 1065C
10 8 6 4 2 0 10:30:00 -2 11:42:00 12:54:00 14:06:00 15:18:00 16:30:00 17:42:00

Loss, dB

Time, (hr)

Specialty fiber demonstrated ability to exceed previous temperature limits

Recent Advancements in Harsh Environment Fiber Optic Sensors: An Enabling Technology for Emerging Nuclear Power Applications

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Temperature-Resistant Fibers Subjected to “Long-Term” Survivability Tests at 1170°C
Loss vs. Time at 1170°C, Specialty High-Temperature Fiber
Specialty Singlemode Ge-doped 1550 nm Fiber

35 30 25 20 15 10 5 0 -5

Loss (dB)

1170 C

0:00:00

12:00:00

24:00:00 Time

36:00:00

48:00:00

Specialty fiber demonstrated increased longevity when heating to very high temperatures

Recent Advancements in Harsh Environment Fiber Optic Sensors: An Enabling Technology for Emerging Nuclear Power Applications

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Conclusions, and Future Development
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Fiber optic sensors are being optimized for use in extremely highradiation and high-temperature environments. Hybrid “smart sensors” will enable a level of active temperature compensation and self diagnostics previously unattainable. Software development required to realize these benefits. FBG sensors, coupled with OFDR technology, have the capability to enable a broad spectrum, highly multiplexed instrumentation system for emerging nuclear power applications where low mass and sensor redundancy is critical. Key areas for continued development include: 1) basic research in radiation-induced loss mechanisms and their mitigation, 2) materials research on high-temperature effects on fiber and their mitigation, 3) development of more robust, production-ready sensors, and 4) development of robust, industrial-qualified fiber optic readout systems. ideas taking flight

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Recent Advancements in Harsh Environment Fiber Optic Sensors: An Enabling Technology for Emerging Nuclear Power Applications

www.lunainnovations.com

Acknowledgements
The work presented here was funded in part through the following contracts:
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NASA Marshal Space Flight Center, Contract No. DCN: 1-2-T4-E0550, TPOC: Melissa Van Dyke • Distributed temperature sensing in SAFE-100 DOE, Contract No. DE-FG02-04ER83991, TPOC: Madeline Feltus • Hybrid P-T sensor development and testing

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NASA Dryden Flight Research Center, Contract No. NAS4-02019, TPOC: Ting Tseng • Early high-temperature pressure sensor work
NASA Glenn Research Center, Contract No.NAS3-02173, TPOC: Wayne Wong • Radiation and high-temperature testing of FBG sensors

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Recent Advancements in Harsh Environment Fiber Optic Sensors: An Enabling Technology for Emerging Nuclear Power Applications

www.lunainnovations.com

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