Environmental QualificationHave we learned from history or are we

doomed to repeat it?

Vincent P. Bacanskas

Director/Chief Engineer

Entergy Nuclear Operations, Inc.

From Theodore Roosevelt

“People don’t care how much you know until they know how much you care.”

Thermal Aging Analysis

• Man lives in 25°C ambient • Man is 27 years old• Activation Energy for man is 1.0 eV• Want to accelerate age man to get to 62

years old (62-27=35 additional years)• Pick aging temperature of 150°C

Use Arrhenius Equation

Rearranging to solve for ta

Solution

• Plug in the numbers and

371.0

8.617 101

423.151

298.15

• So what’s the answer ?

If you do the analysis properly:

27 Year Old 62 Year old

Start with First Principles

• What are we trying to prove with EQ?– To demonstrate with reasonable assurance

that Class 1E equipment for which a qualified life or condition has been established can perform its safety function(s) without experiencing common cause failures before, during, and after applicable design basis events.

• Great bunch of words that mean what exactly?

1. Ieee Std. 323‐2004 Sec 4.1

So what is a Common Cause Failure

• A common cause failure occurs when events are not statistically independent. That is, one event causes multiple systems to fail.

• An example is when all of the pumps for a fire sprinkler system are located in one room. If the room becomes too hot for the pumps to operate, they will all fail at essentially the same time, from one cause (the heat in the room).

1. IEEE Std 323‐2004 Sec. 4.1

So what does EQ really look like?

So what do we consider to prevent common cause failure?

• Temperature stresses• Radiation stresses• Humidity? (NUREG-0588 says NO for

cable)• Steam stresses• Electrical Stresses• Mechanical Stresses

Temperature

• What are some of the effects of temperature that can lead to common mode failure:– Embrittlement– Softening– Cracking– Dielectric Changes

What did we learn in the past?• Accelerated Thermal Aging was developed by the Nuclear Industry

– WRONG!!!!!!!• Accelerated methods have been used for years and years in the

electrical insulation and other industries as the basis for the design of their insulating systems

• AIEE paper by Dakin in the 1940’s (no commercial nukes then!)• IEEE Std. 1- IEEE Standard General Principles for Temperature Limits

in the Rating of Electric Equipment and for the Evaluation of Electrical Insulation

• IEEE Std. 101 IEEE Guide for the Statistical Analysis of Thermal Life test Data

• IEEE Std.117 Standard Test Procedures for Thermal Evaluation of Systems of Insulating Materials for Random Wound AC Electric Machinery

• IEEE Std. 275 IEEE Recommended Practice for Thermal Evaluation of Insulation Systems for Alternating Current Machinery Employing Form-Wound Preinsulated Stator Coils For Machines Rated 6900 V and Below

Today and Going Forward

• Concerns– Activation Energy Value selection– Extrapolation of φ between transition

regions– Oxygen Diffusion Limitations– Humidity not accounted for

Activation Energy Value Selection

• Must be for the material of interest• Must correlate to the property of interest• Must be developed with an approved

methodology• Many sources for values

Sources of Activation Energy Values• EQDB• EPRI Publications• IEEE Dielectric and Electrical Insulating Society

Publications (DEIS)• Polymer Manufacturer Data Sheets (DuPont

DeNemours, ICI America’s, Dow, ExxonMobil)• Jet Propulsion Laboratory Data• Rome Air Development Center (RADC)• CERN (European Organization for Nuclear

Research) Publications• AEA Harwell Publications (England)• JAERI (Japan Atomic Energy Research Institute)• IAEA Publications• SANDIA Publications

EQDB Screen Shot

Critical Resources

Critical Resources

Activation Energy Sources

Recent Operating Experience (CDBI)

• Safety related non-EQ Service Water Motor in pump house.

• Design of insulation system assumes 40°C maximum ambient.

• NRC inspector monitors area and ambient is 45°C.

• NRC asks why is motor operable? • Motor Engineer provides NEMA MG-1data to

NRC.

Right Answer

• Westinghouse motor supplied safety related• Motor insulation system designed using

methods of IEEE 101 and IEEE 275• Asked Westinghouse to provide Arrhenius curve

for insulation system.• Explained to NRC CDBI Inspector Arrhenius

curve, IEEE 101 and IEEE 275 and the design basis for the insulation system

• Provided motor design, not qualification to the NRC

• Question resolved, no violation or open item

Good Source of Theoretical Aspects of Thermal Aging

Extrapolation of φ Between Transition Regions

Reality?

Oxygen Diffusion Limitations

• Degradation reactions for most materials used requires oxygen

• Thermal aging simulations are performed in air ovens thus oxygen is present

• Factor for consideration with the acceleration rate

• Overall concern is more slanted to oxygen in the LOCA chamber

Humidity Aging

• Need to confine effects to RH and not moisture intrusion

• RG 1.89, R1 infers beyond current state of the art and only talks of seals and barriers

• NUREG-0588, R1 Q&A says “Effects of relative humidity need not be considered in the aging of electrical cable insulation” for Category I

Humidity Aging Results

• Humidity aging is addressed in the development of motor insulation systems

• Humidity aging has been heavily studied for medium voltage cable and above (water treeing) not generally applicable to low voltage

• EQ program should address moisture sealing for required electrical components

• Although not specifically accounted for in aging models, humidity does not present a significant aging mechanism

Leak Path into Solenoid Enclosure

NUREG/CR-6384 Arrhenius Conclusions

RIS 2003-09 EQ of Low Voltage Cables

• For license renewal, a reanalysis (based on the Arrhenius methodology) to extend the life of the cables by using the available margin based on a knowledge of the actual operating environment compared to the qualification environment, coupled with observations of the condition of the cables during walkdowns, was found to be an acceptable approach.

• A combination of condition-monitoring techniques may be needed since no single technique is currently demonstrated to be adequate to detect and locate degradation of I&C cables. Monitoring I&C cable condition could provide the basis for extending cable life.

So what do we have to remember?

• Accurately capture the plant environment design vs reality– For plants with complete design specifications,

many of the environments are more severe than design limits, but some may exceed so check

• Understand the degradation properties of what you are aging-limits of the equipment

• Apply the correct activation energy value – don’t substitute a different value to extend life

if you don’t understand all of the ramifications

What about Radiation?• Aging Effects

– Scission and Cross-linking – Function of integrated dose and dose rate– Can lead to softening or hardening of organics

• Dose Rate Effects– Normal aging – Accident (yes accident dose rate effects)– NUREG/CR-4301 “No evidence exists for dose rate

effects in a nitrogen environment” (Mark I Containment BWRs?)

• Highly Sensitive Materials (Teflon, PVC)• Do you have TLD’s or monitoring by ALARA at your plant?• Issue with Halogens (rapid IGSCC)• Adequacy of Cobalt-60 to simulate the combined radiation

environment (NUREG/CR-5231)

Radiation Dose Accuracy

• NUREG/CR-5231 states in part: “it is concluded that present simulation techniques are a conservative method for simulating LOCA radiation effects and that the practices have probably substantially overstressed both bare and jacketed materials during qualification testing.”

• Did we use this to answer Part 21 on dosimetry at test laboratories?

Synergistic Effects

• Synergism - interaction of discrete agencies (as industrial firms), agents (as drugs), or conditions such that the total effect is greater than the sum of the individual effects– Radiation Aging prior to thermal (practical

considerations)– Dose Rate Effects – sufficiently low (<1

Mrad/h)

Electrical Stresses

• Current loading/cycling• Inductive kick• Cabinet temperature rise• Temperature dissipation via non-safety

cooling• Temperature Rise due to continuous

energization• Encapsulated components

Mechanical Stresses

• What are mechanical stresses?– Operating Cycles for Equipment– Vibration

• Manufacturing standards for many components require cyclic testing including breakers, relays, switches.

• Mil Spec testing for vibration has also been used as a screening method

Looking Forward 10CFR50.69 Implementation

The Process

Categorization

50.69

Safety Related

Non Safety Related

Safety Related

High Safety Significance

g

Non Safety Related

High SafetySignificance

g

Non Safety Related

Low SafetySignificance

Safety Related

Low Safety Significance

RISC 1 RISC 2

RISC 3 RISC 4RISC = Risk Informed Safety Class

Low Risk

High Risk

The Results so far

What you can do with it

EQ Recent Affects on Rule

• 10CFR50.69 RISC-3– Delivering the Nuclear Promise

Activity– Benefits for EQ

• Equipment will stay in EQ program• Will not require EQ qualified equipment • Will require ‘reasonable confidence’

equipment can perform as intended• Will not require Appendix B vendor

NUREG/CR-5313 EQ Risk Scoping Study

• From a PRA perspective and given NRC inspection philosophy, this EQ issue of whether correct accident acceleration techniques have been used is not risk significant.

• The importance of performing simultaneous versus sequential accident simulations of radiation, steam, and chemical spray environments. (NRC EQ research has yet to identify equipment that suffers early loss of function because simultaneous rather than sequential accident simulations were used to qualify the equipment.)

• The importance of including oxygen within the qualification test chamber during accident simulations. (Oxygen within the test chamber has been demonstrated to accelerate accident degradation of polymer materials; however EQ research has not demonstrated an early accident functional performance impact for this issue.)

• The importance of appropriately simulating the beta radiation dose (usually via gamma irradiations). (NRC research suggests that current practices are conservative; moreover, accident sequences of PRA interest do not produce a need to demonstrate long term radiation survivability. )

Some Standards/Testing Issues

• IEEE Std. 382-1980, Sec 5.5.3 “A minimum of 10 percent of the required mechanical wear aging operating cycles shall be performed under load during the aging period”

• SOV Testing (including NRC testing that I did) what was used for a process fluid?

• Why was it used? What impact does it have? Think these things through.

Overall EQ Resources• Equipment Qualification Data Bank (EQDB)

– Library and Material Database• Nuclear Utility Group on Equipment Qualification (NUGEQ)

– Library of EQ related publications• NRC Document Collections Web Page

– Hundreds of Information Notices, Bulletins, NUREGs, etc.• National Technical Information Service (NTIS)

– NUREG’s and other reports not available on NRC site• National Laboratory Web Sites

– SANDIA National Laboratories– Brookhaven National Laboratories

• IEEE Publications & Periodicals (most during 80’s & 90’s)– Don’t limit your knowledge to standards

• EPRI Research Reports

The Authoritative Textbook

Critical Resources

Critical Resources

Critical Resources

Current EQ Pilot Inspections

• Industry Input– Focus on program implementation– Don’t revisit basis issues from the 80’s

• NRC Focus on Ongoing Program– Modified inspection procedure to reflect this

shift in focus– Completed 8 Pilot Inspections

• Commercial Grade Dedication• Use of Operating Experience

Industry Lessons Learned

• Basis must be maintained (License renewal/EPU)

• Owner must be knowledgeable in EQ site design basis

• Owner needs support of other groups to succeed (warehouse, maintenance, operations)

• Resource Intensive Inspection– Lots and lots of documents

requested/reviewed

NRC Focus Areas from Pilots

• Qualification/Dedication of replacement parts• Accuracy of Work Orders to restore

qualification when complete• Storage requirements assumed in qualification

(ANSI Level B storage?)• Periodic maintenance assumed in qualification• Extension of Qualified Life in renewed license

(how did we extend?)• Plant environments matching EQ assumptions• Vendor Bulletin/Informational Notices

Recent Inspection Issues10CFR50.49 Statement of Considerations Issue: The effects of time-dependent variations of relative humidity during normal operation cannot be considered for all equipment. There are no detailed standards for how this type of testing should be performed. Response: The Commission agrees. Humidity variation during normal operation are difficult to predict. It has not been demonstrated that the time-dependent variation in humidity will produce any differences in degradation of electric equipment. The words ''Time-dependent variation of relative" have been deleted from Paragraph 50.49(e)(2). (e)(2) Humidity during design basis accidents must be considered.

Recent Inspection Issues

• 50.55(i) Structures, systems, and components subject to the codes and standards in 10 CFR 50.55a must be designed, fabricated, erected, constructed, tested, and inspected to quality standards commensurate with the importance of the safety function to be performed.

Thank you very much!

Questions?