Overview of Expanded Materials Degradation Analysis and ...

Light Water Reactor Sustainability R&D Program

Overview of Expanded Materials

Degradation Analysis and Research

Roadmap for Cable and Cable Insulation

J.T. Busby Oak Ridge National Laboratory

D. Mantey

Electric Power Research Institute

MEETING BETWEEN THE U.S. NUCLEAR

REGULATORY COMMISSION STAFF AND

INDUSTRY

TO DISCUSS SUBSEQUENT LICENSE RENEWAL

Cable and Cable Insulation

April 30, 2014

2 © 2014 Electric Power Research Institute, Inc. All rights reserved.

Expectation for Subsequent License Renewal

• Provide “reasonable assurance” that cables will perform

through subsequent license renewal period of operation

• How do you provide reasonable assurance?

– Can EQ qualification extended out to 80 years?

– Can condition monitoring results of lab accelerated aging

be used to develop criteria for “qualified condition”?

• Reasonable assurance is evaluated based on

• Remaining environmental qualified life, or

• Remaining life based on “qualified condition”


Research Roadmap Areas of Focus

• Submergence

• Material Degradation and Harvesting Cable Data

• Assessment of Condition Monitoring Elements

• Improved Lifetime Prediction Models and Accelerated

Aging Studies

• Improved Condition Monitoring/NDE Tools

• Potential Lead Plant Activities

• Cable Rejuvenation


Research Needs for LTO

• Understand degradation issues

– Submergence of medium and low voltage cables

– Research identified issues based on original EQ qualification

• Is natural aging more severe than identified by cables aged in absence of oxygen (diffusion limited oxidation)

• Do cables at low dose rates and temperature degrade faster than at high temperature/high dose (inverse temperature effect)

• Is sequential application of dose and radiation less severe aging technique than if applied simultaneously

• How can you determine remaining useful life

• What condition monitoring or non-destructive evaluation tools are best for cable assessment

• Can cables life be extended through rejuvenation

Given the complexity of the reactor systems and

materials degradation, a prioritization tool for

research was developed

• “Knowing the unknowns” is a difficult problem that must be addressed.

• This is a particularly difficult issue for such a complex and varied material/environment system.

• An organized approach similar to the US NRC’s Proactive Materials Degradation Assessment (PMDA) (NUREG/CR-6923 was employed .

• Together with the U.S. NRC, the LWRS Program is working to expand the initial PMDA activity to encompass broader systems and longer lifetimes

– Core internals and primary piping

– Pressure Vessel

– Concrete

– Cabling Proactive Materials Degradation Assessment Matrix

5

NRC and DOE are investigating issues of reactor

aging beyond 60 years to identify possible

knowledge gaps

Final draft versions were submitted for final approval and publication in December 2013.

6

The cable expert panel included a diverse

background and considerable depth of

experience

• S. Ray (US NRC) • R. Bernstein (SNL) • S. Burnay (J. Knott

Associates) • C. Doutt (US NRC) • K. Gillen (retired) • R. Konnik (Marmon

Innovations) • K. Simmons (PNNL) • G. Toman (EPRI) • Greg Von White (SNL)


Group

7

The cable panel used established PIRT

processes to complete their assessment

• The expert panel assembled a list of common insulation manufacturers, materials, and environments.

• A detailed assessment of modes of degradation and key mechanistic understanding gaps was generated.

• Assessment of level of knowledge, susceptibility, confidence, for each of degradation modes/mechanisms made by each panel member for each of the classes of structures

• Spreadsheet reflecting assessments prepared and utilized to determine mean, median, and standard deviation for each potential degradation mode/component combination

• EMDA matrix figures constructed

8

The cable panel performed PIRT scoring for a

number of environmental cases

9

Several potential knowledge gaps and

recommendations were identified by the expert

panel. (1 of 3)

1. A reassessment may be made to determine the number of circuits and types of cable that are in the high-radiation zones (i.e. 70 Mrad over 80 years (up to 1 Gy/hr) between 45 to 55 °C (113 to 131 °F)).

2. Measurements of the operating temperatures of cables in plant are needed, particularly for those cable groups that are subjected to EQ, to quantify the actual temperatures to which cables are exposed.

10



panel. (2 of 3)

3. If, as expected, environmental information demonstrates that thermal aging is the dominant process for nearly all cables in US NPPs, then it is important that the activation energy for the specific cable materials used, under specific environment, be estimated with increased confidence level.

4. Inverse temperature effects need to be understood better if semi-crystalline materials, such as some XLPE/XLPO and EPR insulations, are determined from plant assessment (item 1 above) to be exposed to radiation in-plant dose rates that exceed 0.1 Gy/h (10 rad/h). At that level of radiation dose rate, significant degradation may be observed after 60 years for temperatures < 50C (122F).

11



panel. (3 of 3)

5. Little is known regarding the consequences of long-term wetting of both low- and medium-voltage cables. Research in that area would enable safety significance assessments of long-term submerged cables.

6. For loss of coolant accident simulations, this research has identified oxygen concentration in the atmosphere during a loss-of-coolant accident to be important, needing a consideration of this aspect in engineering simulations.

12

Collaborative research is underway to address

these potential knowledge gaps

• Research has been underway to support these gaps for several years

– EPRI/industry projects

– DOE LWRS programs

– International efforts

• Collaborative efforts have been strong among all research partners

• Frequent meetings are held to coordinate and align ongoing research

13


Research Needs for LTO

• Understand degradation issues

– Submergence of medium and low voltage cables

– Research identified issues based on original EQ qualification

• Is natural aging more severe than identified by cables aged in absence of oxygen (diffusion limited oxidation)

• Do cables at low dose rates and temperature degrade faster than at high temperature/high dose (inverse temperature effect)

• Is sequential application of dose and radiation less severe aging technique than if applied simultaneously

• How can you determine remaining useful life

• What condition monitoring or non-destructive evaluation tools are best for cable assessment

• Can cables life be extended through rejuvenation



Submergence

• Condition assessment using 0.1 hertz Tan δ testing

• Submergence qualification research

• Low voltage wet susceptibility research


• Develop field guide for cable harvesting (web-based and

Android/Ipad formats)

• Cable Polymer Handbook

• Medium Voltage Cable Failure Mechanism Research

Degradation Assessment and Cable

Harvesting


• Evaluate effects of aging stressors

– Diffusion Limited Oxidation (DLO)

– Inverse Temperature Effects

– Synergistic effects of radiation and temperature

• Development of qualified condition data

Improved Lifetime Prediction Models


Improved NDE/Condition Monitoring Tools


Member Actions and Cable Rejuvenation

Summary

• While preliminary, the EMDA process identified several potential knowledge gaps for cable and cable insulation. – Cataloguing of materials and environments

– Characterize activation energies and inverse temperature effects

– Long-term wetting

– LOCA performance

• Joint research is underway in these key areas

• Upcoming presentations will provide more detail into these research projects

21

Andrew Mantey Senior Technical Leader-Plant Engineering

Bo Clark

Program Manager – Plant Engineering

Discussion with NRC Division of License Renewal April 30, 2014

Cable Aging Research &

Development

Electrical Cables – the EPRI ‘Journey’

Much research previously conducted

• EPRI began Electrical Cable research in mid-1980’s –Numerous areas of research

• Other non-EPRI entities began even earlier

The research continues……

• Support of member implementation of cable aging management programs

• Support of Subsequent License Renewal (SLR) needs

Significant data available, particularly on thermal and radiation aging effects

What you will hear from EPRI today…..

• EPRI Cable Program Goals and Objectives

• Our on-going research

• Submergence research

• Efforts to develop methodologies for ‘Determination of Remaining Useful Life’

Cable Program Goals and Objectives

• Support on-going member aging management program implementation and LTO strategic needs:

– via Cable Users Group

– Collection, evaluation of tan δ test data (on-going)

– Cable failure mechanism identification

– Submergence

• Address concerns for medium voltage cable

• Determine susceptibility of low voltage cable to wet degradation

• Provide methodology for members to provide “reasonable assurance” of cable reliability through subsequent license renewal

EPRI Research Areas of Focus

• Apply existing research

• Address submergence concerns

• Evaluate material degradation and harvesting cable

• Improved lifetime prediction models and accelerated aging studies

• Improved condition monitoring/NDE tools

• Potential lead plant/member activities

Apply Existing Cable Research

Research Area Subject EPRI Report

Cable Aging Management Aging management program guidance

1020804, 1021629, 3002000557

Cable Testing Test applicability matrix: Tan Delta test evaluation:

1022969 1025262

MV Cable Failure Mechanism Research

Evaluation of wet aging of various MV cable types

1018777,1021069, 1022965, 1024894, 300200554

Life cycle management End of life guide for MV cable and accessories

1025259

Cable LTO Research In-containment radiation and temperature data

3002000816

•Cable research has been on-going at EPRI since the mid-1980’s (first low and later medium voltage cables)

•We need to leverage that work and fill identified gaps

Submergence- Medium Voltage Cables

• Goal: Create a cable qualification for cable types not believed to be degraded in wetted environments (submerged or high moisture environments)

• Approach:

– Obtain service-aged brown and “modern” pink ethylene propylene rubber (EPR) cables in long term service, wetted environments

– Apply an accelerated aging protocol (elevated voltage and frequency)

– Through an ongoing qualification determine the useful life of the cable insulation type

Submergence (continued)

• Results to-date:

– Brown EPR 22 year wet service aged cable which has been in accelerated aging protocol for 1¾ years to-date

• No failures under test protocol

• No change in tan δ results

• Breakdown testing will be performed at end of 2 years aging to determine if acceleration has been achieved

• Continue aging remaining cable

• Repeat breakdown testing

• Results expected to be published in 2015-16

Submergence (continued)

• Future work: – Pink EPR cable obtained with ~22 years wetted service

– Will be placed into similar qualification protocol this year

– Results should be available by 2017

Submergence- Low Voltage Cable-Pilot

• Goal: Determine susceptibility of low voltage cables to degradation in wetted conditions (submerged or high relative humidity)

• Approach: – Evaluate commonly found cross-linked polyethylene (XLPE)

and ethylene propylene rubber (EPR) cable types – Follow EM-60 protocol used by cable manufacturer’s for

electrical stability in submerged condition: • 90°C water bath with high salinity(194°F) • Energized (250 Vdc, 277 Vac) • Individual conductors were used only (external jacket of multi-

conductor cable were removed) • Some thermal damage • Some reduced insulation wall (shaved)


• Approach:

– Commonly used in nuclear plants (Rockbestos, BrandRex, Okonite, Boston Insulated Wire)


• Results: – XLPE (Rockbestos, BrandRex) cables shown below had

no electrical failures or noticeable physical changes other than surface discoloration


• Results:

– EPR (Okonite and Boston Insulated Wire)

• Boston Insulated Wire had swelling and separation of chloro-sulfunated polyethylene (Hypalon) jackets from EPR occurred, but EPR insulation layer was in good condition (not swollen)

• Okonite cables had no bulging of jacket/insulation, but some electrical failures of EPR possibly due to errors in shaving to increase voltage stress


BIW EPR conductor removed from tank and associated swelling

Submergence- Low Voltage Cables Follow-up

• No follow-up research is warranted at this time for the XLPE cables (Rockbestos and BrandRex) due to positive results in the pilot study

• Further study is planned for the EPR cables using same cable types, but with configuration typically seen in actual service, i.e. multi-conductor cables with outer protective jacket, no increased voltage stress (shaving) to see effects on cable insulation functionality

• It needs to be seen if the protection of the outer jacket (45 mil thickness) will reduce or preclude insulation damage

Material Degradation and Cable Harvesting

• Cable Harvesting Guide – Provide members (nuclear power plant operators)

methodology to maximize research use of service-aged cables they remove (will be available in late Summer 2014)

• Cable Material Handbook – Knowledge capture of polymer formulations,

degradation mechanisms for cables used in nuclear power plants

• Medium voltage cables will be first (available early 2015), low voltage power, instrument and control to follow

• Appendices to be forensic analysis of harvested, service-aged cable evaluations

Material Degradation and Cable Harvesting

• Medium voltage cable failure mechanism research

– Forensic research on service-aged, wetted cables (submerged and high relative humidity) to determine degradation mechanisms

– Six reports to-date

– Major findings:

• Black EPR/Butyl Rubber low resistance tunnels

• Compact design jacket/shield layer separation

• Insulation defects in dry section of pink EPR

Failure Mechanism Forensic Evaluation:

Perform Tan δ condition monitoring test and evaluate results

Remove and send cable to forensics lab for analysis

Isolate the problem section(s)

Forensic Evaluation (continued)


Pinpoint the problem


Defect Identification


Goal: Develop “qualified condition” methodology and apply to cable types covering approximately 90% of those found in current fleet of US nuclear power plants

Approach: – Review existing research and see if existing data provides

useful information on thermal and thermal and radiation accelerated aging

– Evaluate data for which methods (tensile, elongation at break, indenter, gel, nuclear magnetic resonance, etc.) provide reasonable discrimination of cable aging near end of useful life

– Given one and two above, what point can be chosen as an acceptance criteria to ensure functionality post-LOCA without sacrificing too much useful life of the cable (qualified condition)



• Gaps that are identified will be evaluated by obtaining service-aged cables

• Cables will be harvested from plants recently shutdown, decommissioning, or from operating plants

Qualified Condition

• Condition of cable is such that should a design basis accident occur the cable is still capable of allowing the end device it feeds to perform its intended function (50% elongation at break in this example)


• Cables will be evaluated for remaining life using service time and quantitative cable condition as determined using the appropriate test method


• EPRI is investigating actual plant temperatures and radiation levels that cables operate in to determine delta between actual and qualification based dose and temperature conditions (i.e. why do service aged cables that have been evaluated not show signs of DLO, inverse temperature and synergistic effects related degradation) – In-containment cable radiation and temperature data

collection (technical update 3002000816, issued in December, 2013)

– Follow-up research to obtain actual cable specific in-containment data is being planned

– If dose levels are low, thermal aging becomes major aging degradation factor

Improved Condition Monitoring/NDE Tools

• Collaboration with NDE group to identify existing NDE technologies that can be applied to cable

Active Thermography

IR camera

Heat source

Terahertz (THz)

(air)

Fourier Transform Infrared Spectroscopy (FTIR)

Only FTIR Test results to be presented

Dielectric Measurement

Handheld FTIR Technology

Exoscan , Agilent Technologies

Potential Lead Plant/Member Activities

• Fully implement EPRI cable aging management programs (1020804, 1021629, 3002000557)

• Support gathering cable radiation and temperature data

• Establish a submerged cable strategy

• Shift from “qualitative” to “quantitative” evaluation of cables to manage cable aging in accordance with research results for “qualified condition” acceptance criteria and remaining useful life

Summation

• There is a wealth of cable research supporting nuclear power plants that already exist – Applying it in current cable aging management programs is on-

going – Aging management programs required for license renewal and due

to regulatory requirements are developing and need to continue to identify cables in need of aging management (scope)

• Cable aging questions and concerns identified in the EMDA and through operating experience are being evaluated and are being addressed by NRC/DOE/EPRI research roadmap

• Nuclear power plant operators will need to apply this research – A shift in philosophy from mostly qualitative to mostly quantitative

evaluation of cables to manage aging and ensure reliability of cables through plant operation is needed

Together…Shaping the Future of

Electricity

Light Water Reactor Sustainability R&D Program

DOE R&D Project Status & Planning for

Cables

R. Bernstein, M. Celina, E. Redline, and G. Von White III Sandia National Laboratory

L. Fifield, A. Pardini, M. Prowant, P. Ramuhalli, and K. Simmons

Pacific Northwest National Laboratory

J.T. Busby Oak Ridge National Laboratory

MEETING BETWEEN THE U.S. NUCLEAR

REGULATORY COMMISSION STAFF AND INDUSTRY

TO DISCUSS SUBSEQUENT LICENSE RENEWAL


April 30, 2014

The DOE-NE Light Water Reactor Sustainability Program

is supporting subsequent license extension decisions

Vision

• Enable existing nuclear power plants to safely

provide clean and affordable electricity beyond

current license periods (beyond 60 years)

Program Goals

• Develop fundamental scientific basis to understand,

predict, and measure changes in materials as they age

in reactor environments

• Apply this knowledge to develop methods and

technologies that support safe and economical long-

term operation of existing plants

• Research new technologies that enhance plant

performance, economics, and safety

Scope

• Materials Aging and Degradation

• Advanced Instrumentation and Controls

• Risk-Informed Safety Margin Characterization

More information and recent reports are available on

www.inl.gov/lwrs 56

LWRS research in materials aging and

degradation areas provide results in several ways

• Measurements of degradation: High quality data will provide key information for mechanistic studies, but has value to regulators and industry on its own.

• Mechanisms of degradation: Basic research to understand the underlying mechanisms of selected degradation modes will lead to better prediction and mitigation.

• Modeling and simulation: Improved modeling and simulation efforts have great potential in reducing the experimental burden for life extension studies. These methods can help interpolate and extrapolate data trends for extended life.

• Monitoring: While understanding and predicting failures are extremely valuable tools for the management of reactor components, non-destructive monitoring must also be utilized.

• Mitigation strategies: While some forms of degradation have been well-researched, there are few options in mitigating their effects. New technologies may overcome limits of degradation in key components and systems.

57

The LWRS program has a diverse set of partners

58

Presentation outline and summary of LWRS

activities in cable and cable insulation aging

• Joint research activities and coordination

• Cable aging and performance studies: SNL

• Development of NDE for cable insulation: PNNL

• Rejuvenation of aged cable insulation: PNNL

• Coordination with stakeholders and partners

59

Building consensus in predictive cable aging with

stakeholders has been a key goal

• A coordination meeting was held between partners (EPRI/NRC/PNNL/SNL) at EPRI in October 2013

• A community teleconference, “Joint LWRS-EPRI LTO Cable R&D Meeting Reconnect” on December 13, 2013

• Joint development of cable aging roadmap • EPRI Cable User Group Meeting in Phoenix (Jan 20 – 24,

2014). – A consensus of the meeting attendees was reached

between EPRI/NRC/PNNL/SNL on the goals of R&D cable aging activities covering predictive models, wear-out aging (field-returned specimens), and CM strategies.

– SNL to host the next group meeting July 9-10, 2014

• Quarterly meetings and coordination calls will continue.

60

Joint R/D roadmaps have been developed for key

research areas

61

Cable Aging and Performance Research

62

• The ultimate goal: Understand current cable insulation material state and

expected performance under extended service conditions to enable decisions for cable requalification or replacement recommendations

• Deliver science-based engineering solutions

• Provide best guidance for aged material state, remaining life and expected performance

• Combine generic engineering tests with best practices from polymer degradation science

• Develop improved (and validated) lifetime predictions models which incorporate known material behaviors

Cable performance research has been established to support closing knowledge gaps

2D Graph 1

Temp-1 [10-3 K-1]

2.2 2.4 2.6 2.8 3.0 3.2 3.4 3.6

Tim

e t

o 1

00

% e

lon

ga

tio

n [

yr]

0.1

1

10

100

140°C 110°C 80°C 50°C 25°C

New cable + accelerated

thermal aging predicts 100 year

lifetime

Plant-harvested cable + wear-out aging predicts 30

year lifetime!

Spatially-Resolved Degradation Models

Lifetime Predictions Material Aging Correlations

Surface vs bulk degradation Loss in tensile properties is used as a failure criterion

63

• Thermal aging only (FY14-15) – Consolidate existing thermal aging data and extent with gap filling data sets where possible

– These aging behaviors are to be compared with wear-out behavior (field returned samples)

– IMPACT: Final report with best estimates for projected residual lifetimes and uncertainties FY15

• Thermal-rad aging of EPR and non-inverse T effect materials (FY15-16) – Review existing data (dose, temperature) for predicted lifetimes


– IMPACT : Final report with best estimates for projected lifetimes and uncertainties FY17

• Thermal-rad aging of XLPO and some EPR inverse T effect materials (FY15-18) – Review existing data and extent with new accelerated aging experiments


– IMPACT : Final report with best estimates for projected lifetimes and uncertainties FY18

Aging experiments, predictive models and

correlations with field returned cable materials will

enable best residual lifetime projections

64

Priorities in FY14 cover several key areas

• Extensive effort by LWRS (with community input: EPRI, NRC, PNNL) to support cable requalification – Understand current cable insulation material state and expected performance

sufficiently well to enable joint decisions with EPRI and NRC for cable requalification or replacement recommendations

• HFIR Cable Samples Analysis Report – Experiments completed. Documentation of studies underway from evaluation

of HFIR field return samples

• Argentinian Silicon Cable Radiation Aging Evaluation Report – Experiments completed. Collaboration with CNEA completed. Drafting final

report

• Analysis of Recent and Historical Data • LICA Experimental Apparatus Radiation Exposure Upgrades • On-going Effort for Acquisition of Field Returned Samples

– Preference is for most common materials in service: • Brandrex XLPO with Hypalon Jacket • Anaconda Durasheath EPR, it may likely also have a Hypalon jacket

65

Accelerated aging has continued on service cable

materials to assess remaining useful life

Anaconda Densheath EPR cables returned from service at HFIR at ORNL (~45 yrs of age, Tavg ~27 °C, RH ~70%). These cables were subjected to further thermal aging to assess remaining tensile properties.

300

250

200

150

100

50

0

Te

nsile

Elo

ng

atio

n,

%

102

2 3 4 5 6 7 8 9

103

2 3 4 5 6 7 8 9

104

t, hrs

T, ºC 40 64 80 109 124 138

Measure Tensile Data at Varying Times and Temperatures Superpose Tensile Data and Determine Activation Energy

300

250

200

150

100

50

0

Ten

sile

Elo

nga

tion

, %

10-1

100

101

102

103

104

105

t, hrs, Reference 99 °C

T, ºC aT

40 0.01 64 0.07 80 0.25 109 1.96 124 5.04 138 11.43

Ea ~ 79 kJ/mol

66

• Primary data show decrease in tensile elongation at 138 to 109°C.

• No change observed at 80 to 40°C within 1.2 yrs

• Superposition of the limited 138 to 109°C data yields an Ea = 79 kJ/mol

Accelerated aging has continued on service cable

materials to assess remaining useful life (cont.)

67

While there is some uncertainty in linear behavior at long lifetimes, data suggests that additional remaining lifetime is at least a few decades. Anaconda Densheath EPR cables returned from service at HFIR at ORNL (~45 yrs of age, Tavg ~27 °C, RH ~70%). These cables were subjected to further thermal aging to assess remaining tensile properties.

Projections for linear Arrhenius behavior

The CNEA cables have provided valuable insights

on performance under irradiation

Measure Tensile Data at Varying Doses

A single rad-thermal exposure shows tensile elongation decreasing with dose at 100°C.

Data shown is for silicone rubber cables provided by CNEA in Argentina. Cables were irradiated at ~39 Gy/hr at 100 C. This work directly supports the US-Argentina BEWG.

68

Measure other properties as a Function of Dose

The CNEA cables have provided valuable insights

on performance under irradiation (cont.)

Understanding property correlations, like gel content and solvent uptake factors, can be leveraged for future condition monitoring of cables employed in service!

Data shown is for silicone rubber cables provided by CNEA in Argentina. Cables were irradiated at ~39 Gy/hr at 100 C. This work directly supports the US-Argentina BEWG.

69

Gel content [%]

96.0 96.5 97.0 97.5 98.0 98.5

Te

ns

ile

Elo

ng

ati

on

[%

]

0

20

40

60

80

100

120

140

Solvent uptake factor

1.7 1.8 1.9 2.0 2.1 2.2 2.3

Te

ns

ile

Elo

ng

ati

on

[%

]

0

20

40

60

80

100

120

140

Temp (°C)Brandrex

XLPO

Rockbestos

XLPO, black,

green and red

Anaconda

Durasheeth

EPR

50 O O O

64 O

65 O O

80 O O O

95 O O

99 E E

100 O OE, TS, D, M,

O

109 E, O E, TS, O E, O

110E, TS, D, M,

S, G

124 OE, O, NMRgreen,

TSE, O

125 EE, TS, D, M,

S, G, O

138 OE, O, D, Sgreen,

Ggreen

140 E, TS, D, M

150 O E, TS, O O

151E, D, S, G (all

green)

160 E

An examination of past and present rad-thermal

data is ongoing

• This examination of historical data helps to finalize thermal-oxidative aging work

70

The historical analysis is providing a more

complete set of data under different conditions

71

• This work is providing a consolidation and evaluation previous work for trends and future property cross-correlations.

• The primary focus is on XLPO, plus perhaps one EPR material and supplement with oxidation rates. Others will be considered if priorities evolve.

• This work provides several deliverables over FY14. – Oxidation rate measurements compete with tensile and wear out experiments. XLPO and EPR are

common insulation materials with XLPO and some EPR materials exhibiting IT behavior

– Thorough characterization of the materials, including testing for known potential anomalies NEPO 9 - Brandrex XLPO

Dose [kGy]

10-1 100 101 102 103 104

Te

ns

ile

Elo

ng

ati

on

[%

]

0

50

100

150

200

250

300

350

280 Gy/hr, 27°C

176 Gy/hr, 25°C

36 Gy/hr, 25°C

210 Gy/hr, 22°C (1994)

16.8 Gy/hr, 22°C (1991)

Data for rad-thermal of Brandrex XLPO

Dose rate [Gy/h]

101 102 103 104

DE

D (

e=

10

0%

) [G

y]

8e+4

9e+4

2e+5

3e+5

4e+5

5e+5

6e+5

1.0e+5

22°C 1993

41°C 1993

New 27°C 2013

The gamma-irradiation facility at SNL is being

upgraded to support LTO evaluations

• Upgrade facility to conduct thermal-radiation experiments - provides unique critical ability to simultaneously expose materials to thermal and irradiation environments – Included updated electronics for

irradiation experiments to enhance safety

– Experiments will be more representative of field-aged conditions, resulting in improved models for predictive aging

• Estimated completion: Spring 2014

72

RAD

Future work will provide a model capability to

predict localization of oxidative damage in a

cable assembly

Surface oxidative degradation is likely under EQ testing IEEE323-1974

• Cable degradation behavior depends on local rates which can differ between surface and bulk depending on aging conditions and oxidation properties/processes

• DLO is the phenomenon which introduces variations in behavior under thermal and rad-thermal conditions

• This also affects measurements of ox-rates and CM approaches

Accelerated rad-thermal conditions, which can apply to NIST/NRC LOCA requalification

Homogeneous aging expected under plant conditions

73

Development of NDE Techniques for Cable and

Cable Insulation

74

DOE’s NDE is built upon a roadmap workshop*

that identified three important R&D targets

• Identify key indicators of aging – Correlate aging with macroscopic material properties

• Advance state-of-the-art NDE methods and develop new/transformational NDE methods – Enable in-situ cable condition measurements

– Collect data from laboratory-aged and fielded cables (Need naturally aged cables to be available!)

• Develop models for predicting remaining useful life based on cable condition measurements – Use cable condition index data from new and aged cables above,

existing databases, and other available/relevant sources

75

*LWRS NDE R&D Roadmap for Determining RUL of Aging Cables in NPPs, Simmons, Hashemian, Ramuhalli, Konnick, Brenchley, Ray, Coble, PNNL-21731, 2012

NDE of cable performance will be based on key

indicators of cable aging

• Chemical Properties – Functional group content (e.g., oxidation, cross-

linking) – Additive/filler content (e.g., loss of antioxidant) – Molecular weight (e.g., chain scission) – Degree of crystallinity

• Physical Properties – Melting point, glass transition temperature – Density – Gas permeation, liquid uptake – Coloration – Refractive index

76

Key indicators of cable aging (continued)

• Mechanical Properties – Stiffness (e.g., cross-linking)

– Strength (e.g., chain scission)

– Percent elongation

– Hardness

– Acoustic velocity

• Electrical Properties as Indicators – Conductivity/resistance (mobility, carrier density)

– Dielectric strength

– Permittivity

77

Example: Key chemical

properties

• Thermal (and irradiative) stressors generate radicals that lead to polymer chain scission, cross-linking and associated formation of new C-O and C=C chemical bonds

• Carbonyl (C=O) index is a measure of extent of oxidation

• Phase transitions indicated chemical bonding and content changes

78

TGA

FTIR

DSC

Temperature (°C) Temperature (°C)

Example: Key electrical properties

79

• Thermal and irradiative stresses lead to chain scission, cross-linking, and formation of new C-O and C=C chemical bonds

• Chemical changes result in changes in charge mobility, polarizability and local variations in electric field strength

• Dielectric permittivity and loss tangent measure the polarizability and relaxation phenomena which are impacted by the changes above

Frequency (GHz)

Rel

ativ

e P

erm

itti

vity

Maximum permittivity (from multiple measurements on two identically aged specimens) plotted

Thermal aging time

Aging time (hours)

Rel

ativ

e P

erm

itti

vity

(at

7

.5 G

Hz)

Thermally aged EPR Cable

A test-bed for cable NDE has been established

• Laboratory-scale test-bed for measurements of electrical properties of degraded cable insulators

– Measurements without disconnecting cable

– Other samples aged and available for developing and evaluating other NDT techniques

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Laboratory scale measurements and tests are

now being performed

• Laboratory-scale test-bed for in-situ electrical measurements on degraded cables

– Data to approximately 1200 hrs

• Laboratory-scale NDE measurements on degraded cable insulation

81 High Applied Load (Drill Press) Low Applied Load (Oscilloscope)

Green is source current Blue is load current

Current Measurements

Baseline

Elastic properties are being examined in

different geometries

• Acoustic velocity (bulk and surface waves)

• Acoustic impedance • Correlation to indenter testing, density

and EAB

82 82

Permittivity is being examined in different

geometries

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• Previous measurements of complex permittivity showed variability due to specimen geometry and thickness

• Quantification of variability and impact of conducting backplane (cable conductor) needed for in-situ measurements – Okonite EPR sheet material – 10 flat, square samples (known geometry) – Sample dimensions: 21.5mm(L) x 21.5mm (W) x 1.6mm(H) – No aging, baseline measurements

Electrical properties have been the focus of

recent efforts

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Single sample

Single sample backed with metal

Single sample stacked to >12mm thickness

Tests are also being conducted in geometries

relevant to service conditions

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Individual Samples Samples Stacked >12mm High

6-9GHz previously investigated bandwidth for cable aging

Variations in individual sample measurements could be due to pressure variations and compression of the foam used to press the samples against the probe, or physical surface variations from sample to sample.

NDE development will remain a priority for LWRS

• Complete aging and NDE studies on first set of cables

– In-situ monitoring and measurements

– NDE measurements on aged specimens

• Complete analysis of sensitivity of key indicators to aging effects

– Work with polymer aging SME to use results to define next set of aging experiments

86

New Technologies for Repairing Aging Cables in

Nuclear Power Plants

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Cable rejuvenation may provide an additional

bridging strategy for cable service

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• DOE is performing additional studies on mitigation strategies that may provide an alternative to replacement for non-safety non-EQ related cables.

• The work is being performed in several key stages 1. Proof of Concept Treatment of

Highly Accessible Cable Material

2. Diffusion-based Treatment of Cable Specimens

3. Field Deployable Treatment of Intact Cable

Chemical strategies for cable rejuvenation

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• Combined approaches could be applied.

• Initial work has focused on using plasticizers to recover performance.

Plasticizers Cross-linking Polymerize-able monomer

An Ethylene-Propylene Rubber (EPR)

cable was used for initial tests

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• Okoguard Aerial Jumper “Medium Voltage” Cable 15kV 90°C Rating

• Several hundred dog bone specimens were cut from cable (~5.5mm thick)

Cable rejuvenation through chemical soak

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• Aged specimens

• Room temperature

• Atmospheric Pressure

• Soaked for up to 50 days for kinetics

• Weight change over time determined

• Selected mass uptake values targeted for testing (5%, 10%)

• Results showed improved modulus, but not improved strength or ductility

Future processes will apply a combined approach

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• Initial work with added plasticizers and single-site reactive silane showed improved Tg and modulus, but no improvement in strength or Elongation at Break

• Future work will aim at covalently healing cleaved chains in polymer backbone to restore strength and EAB performance

• Repair of thermally-damaged scissioned bond through the use of energetically favorable chemical reactions will the a high priority

Evolution of Rejuvenation Scheme

Collaboration between stakeholders continues to

be a high priority

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Discussions on joint cable research have been

positive and frequent

• All key stakeholders (DOE, EPRI, NRC, others) have been very active and open in sharing needs, resources, and opportunities for sharing

• Quarterly coordination calls involving all parties are routinely being held with next call being held in June 2014.

• Frequent face-to-face meetings are also being held. – Last meeting was attached to EPRI Cable User’s meeting

– Next proposed meeting is in July at SNL.

• Joint road map development has been a positive and productive activity

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LWRS will be supporting decisions by providing

information in coming years:

• Cable Aging and Performance – Complete report detailing highest priority needs and concerns for future testing of cable

insulation, September 2010 – COMPLETED – Initiate testing on key degradation issues for cabling and cable insulation, November 2010 –

COMPLETED – Acquire relevant plant cable insulation for additional testing, June 2012 – COMPLETED – Initiate predictive modeling capability for cable degradation, November 2014 – Begin benchmarking of cable degradation model, March 2016 – Deliver predictive model for cable degradation, August 2019

• Cable NDE Development – Complete assessment of cable insulation precursors to correlate with performance and NDE

signals, September 2015 – Demonstrate prototype system for NDE of cable insulation in laboratory setting, September

2016 – Demonstrate field testing of prototype system for NDE of cable insulation, March 2017

• Repair Technique Development – Initiate evaluation of possible mitigation techniques for cable insulation degradation, March

2011 – COMPLETED – Complete assessment of cable mitigation strategies, September 2015

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Summary

• Several potential knowledge gaps for cable insulation in the subsequent operating period have been identified. – Assessment of service materials and characterization

of environments – Activation energy determinations – Inverse temperature effects – Long-term wetting – Oxygen effects in LOCA conditions

• Joint research is underway in these key areas • Coordination and cooperation is an important

factor in closing these potential knowledge gaps

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Discussion?

10/22/09 STEP Integration Workshop 1 97

Overview of Expanded Materials Degradation Analysis and ...

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