ML20237D156

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Summary of 871201 Meeting W/Util Re Status of Thermal Shield Repair at Plant.Util Handout & Attendance List Encl
ML20237D156
Person / Time
Site: Haddam Neck File:Connecticut Yankee Atomic Power Co icon.png
Issue date: 12/15/1987
From: Wang A
Office of Nuclear Reactor Regulation
To:
Office of Nuclear Reactor Regulation
References
NUDOCS 8712230083
Download: ML20237D156 (35)
v • d • e


Text

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['og UNITED STATES

! g NUCLEAR REGULATORY COMMISSION g

nl WASHINGTON, D. C. 20555

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DEC 151967 LICENSEE: Connecticut Yankee Atomic Power Company FACILITY: Haddam Neck Plant

SUBJECT:

SUMMARY

OF DECEMBER 1, 1987 MEETING REGARDING THERMAL l

SHIELD REPAIR '

On December 1, 1987, the NRC met with Connecticut Yankee Atomic Power Company (CYAPCO) to discuss the status of the thermal shield repair at the Haddam Neck Plant. CYAPC0 stated that the bolt failures in the thermal shield occurred as

,a result of high cycle fatigue. Crack propagation was a result of environmental assisted corrosion - fatigue. CYAPC0 believes the precursor to this event was the wear at the displacement limiter keys which resulted in increased loads on the six support blocks. Loads on the support blocks increased to a point where fatigue cracks initiated and propagated in the long visible bolts and then the hidden bolts. Loss of these bolts resulted in further wear at the displace-ment limiter keys allowing increased motions between core barrel and thermal shield j damaging three specimen holders.

Three important problem considerations determining the modifications necessary to alleviate this problem were:

1. Supplementary or refurbishing upper displacement limiter assemblies is vital to limit loads on lower support blocks,
2. Long visible bolts are the limiting components in lower blocks, and
3. No evidence was found which suggest mechanisms other than fatigue under normal plant conditions contributed to initiation of bolt failure.

Based on the above CYAPC0 proposed the following repair plan:

1. Remove and replace all 18 accessible bolts and four protruding dowel pins, l 2. Increase preload in replacement bolting to reduce sensitivity to fatigue,
3. Shim the gap between the bottom of the thermal shield and the support block at the 90 location,
4. Install six new tangential displacement limiters at the upper rim of the thermal shield (increases contact area from 12 in2 to 36 in2 and decreases tangential gap from approximately 20 mils at original design to < 10 mils).

Based on the above, CYAPC0 states the updated design is better than the original design.

8712230083 PDRs ADOCW hppR h3 P

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h The NRC noted thre'e" areas of concern:

L .1. Assuming you have environmentally' assisted corrosion - fatigue, why iricrease the preload and use the same material?

l L 2. . Here. torque" values, corrected for wet installation of bolts? and 1 3. Assuming'long bolts fail first,.is there an installation.~that would allow the bolts to~ break free to allow detection?

To improve the detection fer.. possible internal- reactor vessel damage, CYAPCO:is plahning to add 1) an internal vibration monitoring system, 2) a loose parts

. monitoring.systen,3) check neutron fluence for change in flux to' determine-possible motion and 4) perform visual inspections of support system at next' outage.

The NRC stated CYAFC0 appears to be taking ap'propriate action but he will continue to follow this issue. The NRC requested to see the calculations on fatigue of.the keyways and.long' bolts. Attached is the CYAPC0 handout for this meeting and the attendance list.

M $! 29 3 W Alan B.' Hang, Project Itanager Project' Directorate I-4 Division of Reactor Projects I/II

. Attachments:

As stated

-cc: w/ attachments See next page PDI-4 PDI-4 PDI-SM AWang N JStolz 12/10/87 12/it/87 12/)6 /87 i

1

_ ___ __i____ _ . _ _ . - _ - . . - -

Mr. Edward J. Mroczka 1

Connecticut Yankee Atomic Power Company Haddam Neck Plant ec*

Gerald Garfield, Esquire R. M. Kacich, Manager Day, Berry and Howard Ccurselors at Law Generation Facilities Licensirg

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City Place Northeast Utilities Service Company Hartford, Connecticut 06103-3499 Post Office Box 270 Hartford, Connecticut 06141-0270 W. D. Romberg, Vice President D. 0 Nordquist, Director Nuclear Operations Quality Services Department  ;

Northeast Utilities Service Company Northeast Utilities Services Compary Post Office Box 270 Post Office Box 270 Hartford, Connecticut 06141-0270 Hartford, Connecticut 06141-0270 Kevin McCarthy, Director ~ Regional Administrator -

Radiation Control Unit Region I

. Department of Environmental Protection U. S. Nuclear Regulatory Commi:sfon

, State Office Building 621 Park Avenue

. Hartford, Connecticut 06106 King of Prussia, Pennsylvania 1940E

a. -

[ Bradford S. Chase, Under Secretary Energy Division Board of Selectmen Town Hall

  • fice of Policy and Management Haddam, Connecticut 06103 80 Washington Street Hartford, Connecticut 06106 J. T. Shed1csky, Resident Inspector Haddam Neck Plant D. B. Miller, Station Superintendent c/o U. S. Nuclear Regulatory Commissier Haddam Neck Plant Post Office Box 116 RFD f 1 East Haddam Post Office Post Office Box 127E East Haddam, Connecticut 06423 East Hampton, Connecticut 06424

_ G. H. Bouchard, Unit Superintendent '

Haddam Neck Plant RFD # 1 Post Office Box 127E East Hampton, Connecticut 06424

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CONNECTICUT YANKEE THERMAL SHIELD REPAIR STATUS REPORT 5

1 DECEMBER 1, 1987 STEVE VICK NUSCO LICENSING ERIC DEBARBA )

CY STATION SERVICES SUPERINTENDENT CLINT GLADDING NUSCO ENGINEERING SUBHASH CHANDRA NUSCO ENGINEERING

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AGENDA' e

o', INTRODUCTION - STEVE VICKL o OVERVIEW OF RECOVERY EFFORT - ERIC DEBARBA' o DESCRIPTION OF THERMAL SHIELD SUPPORTS -

SUBHASH CHANDRA O DAMAGE ASSESSMENT - SUBHASH CHANDRA o ENGINEERING EVALUATIONS - CLINT GLADDING FAILURE-MECHANISM INVESTIGATIONS INSIGHTS FOR REPAIRS

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o REPAIR PLAN - CLINT GLADDING PHYSICAL MODIFICATIONS SUPPORTING ANALYSES SAFETY ANALYSES MONITORING / INSPECTION

, o SCHEDULE - CLINT GLADDING o CONCLUSIONS - CLINT GLADDING  ;

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OVERVIEW BACKGROUND o DAMAGE TO THERMAL SHIELD SUPPORTS FOUND AUGUST 25

'o IMPLEMENTATION OF PRELIMINARY RECOVERY PLAN SEPTEMBER 4 ADDITIONAL NDE ENGINEERING EVALUATIONS

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METALLURGICAL EXAMINATIONS REPAIR OF KNOWN DAMAGE CONTINGENCY TOOLING DEVELOPMENT o NRC CONFERENCE CALL ON DAMAGE SEPTEMBER 14 o DOWEL PIN AND ACCESSIBLE BOLT '

REPLACEMENT OCTOBER 2 BROKEN ACCESSIBLE BOLTS ADDITIONAL METALLURGICAL EXAMINATIONS o NON-DESTRUCTIVE EXAMINATION RESULTS AVAILABLE OCTOBER 13 BROKEN HIDDEN BOLTS ONE INDICATION IN CORE BARREL o NRC CONFERENCE CALL OF REPAIR STATUS OCTOBER 20 o PRELIMINARY ENGINEERING ANALYSES RESULTS AVAILABLE OCTOBER 23 l

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BASIC FEATURES OF THERMAL SHIELD SUPPORTS l o 6 SUPPORT. BLOCKS AT BOTTOM AT 30 , 90 , 150 ,

210 , 270 ,330 o EACH SUPPORT BLOCK HAS:

TWO 1" BOLTS ANDf0NE 1" DOWEL PIN IN TOP ROW ONE 1" BOLT AND TWO 0.75" DOWEL PINS IN  !

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TWO 1" BOLTS IN THE TOP ROW (HIDDEN) o FOUR DISPLACEMENT LIMITERS BELOW THE RIM OF THERMAL SHIELD (0 , 90 , 180 , 270 )

KEY WELDED TO THERMAL SHIELD KEYWAY WELDED TO CORE BARREL KEYWAY ALSO USED AS ALIGNMENT KEYS FOR UPPER CORE SUPPORT PLATE S,PECIMEN HOLDER TUBES

, l 0 TWO TUBES AT EACH OF FOUR LOCATIONS (313.5 , 316.5 , 223.5 , 226.5 ,

133.5 , 136.5 ; 43.5 , 46.5 )

I o LIVE SPECIMENS AT 46.5 , 133.5 , 223.5 ,

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DAMAGE ASSESSMENT o . VISUAL' EXAMINATIONS SUPPORT BLOCKS UPPER DISPLACEMENT LIMITERS SPECIMEN HOLDER TUBES 5

o REMOVAL OF THE ACCESSIBLE BOLTS o UT OF THE SUPPORT BLOCK LOCATIONS FROM ID OF CORE' BARREL TO EXAMINE:

HIDDEN BOLTS DOWEL PINS CORE BARREL M L:.-_-__ - _ - - .

DAMAGE

SUMMARY

THERMAL SHIELD SUPPORT BLOCKS SUPPORT BLOCK LOCATION STATUS 30 o UPPER LEFT BOLT - BROKEN o UPPER RIGHT BOLT - BROKEN o LOWER BOLT - MISSING o GAP BETWEEN SUPPORT BLOCK

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AND CORE BARREL GROOVE o SMALL LINEAR INDICATION AT THE LOWER EDGE OF THE CORE BARREL GROOVE o UPPER DOWEL PIN PROTRUDING o INDICATIONS IN HIDDEN BOLTS 90 o UPPER LEFT BOLT - INTACT

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o UPPER RIGHT BOLT - BROKEN o LOWER BOLT - BROKEN o VERTICAL GAP BETWEEN THERMAL SHIELD AND LEDGE IN SUPPORT BLOCK o UPPER DOWEL PIN PROTRUDING

-o INDICATIONS IN HIDDEN BOLTS 150 o UPPER LEFT BOLT - INTACT o UPPER RIGHT BOLT - INTACT o LOWER BOLT - INTACT o INDICATIONS IN HIDDEN BOLTS

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(con t 'd)

SUPPORT BLOCK i

L LOCATION STATUS i 210 o UPPER LEFT BOLT - BROKEN o UPPER RIGHT BOLT - BROKEN o LOWER BOLT - INTACT o UPPER DOWEL PIN PROTRUDING  :

o INDICATIONS IN HIDDEN BOLTS l

270 o UPPER LEFT BOLT - MISSING j o UPPER RIGHT BOLT - MISSING o LOWER BOLT - INTACT o UPPER DOWEL PIN PROTRUDING o INDICATIONS IN HIDDEN BOLTS 330 o UPPER LEFT BOLT - BROKEN o UPPER RIGHT BOLT - BROKEN o LOWER BOLT - INTACT .

o INDICATIONS IN HIDDEN BOLTS o 8 OUT OF 18 ACCESSIBLE BOLTS BROKEN o 3 OUT OF 18 ACCESSIBLE BOLTS MISSING o 7 OUT OF 18 ACCESSIBLE BOLTS INTACT l o 4 OUT OF 18 DOWEL PINS PROTRUDING o 12 OUT OF 12 HIDDEN BOLTS HAVE INDICATIONS 4 .,.,,,.,t.,...m-. . . . . . - --

/7

DAMAGE

SUMMARY

(cont'd)_ f UPPER DISPLACEMENT LIMITER KEYS o VISUAL EXAMINATION SHOWS DAMAGE AT CONTACT ,

SURFACES (WEAR, IMPACT, ETC.) AT ALL LOCATIONS o TOTAL GAPS RANGE FROM 90 MILS TO 180 MILS (ORIGINAL NOMINAL GAPS APPROX. 20 - 25 MILS)

E SPECIMEN HOLDER TUBES .

O PORTION OF TUBE MISSING AT 223.5 AT THERMAL SHIELD RIM o DAMAGE TO TUBE AT 226.5 o DAMAGE TO TUBE AT 313.5 O

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HADDAM NECK THERMAL SHIELD ISSUE ENGINEERING- EV ALU ATIONS PURPOSE

1) TO IDENTIFY AND EVALUATE POTENTIAL FAILURE MECHANISMS WHAT HAPPENED AND WHY DID IT HAPPEN?

HOW CAN A REOCCURRENCE BE PREVENTED?

2) TO EVALUATE THE ADEQUACY OF POTENTI AL REPAIRS /

UPGRADES, DETERMINE THE NECESSITY FOR ALL SUPPORT ELEMENTS DOWEL PINS HIDDEN BOLTS DISPLACEMENT LIMITERS .

3) WHAT ARE THE SAFETY CONSEQUENCES OF THERMAL SHIELD SUPPORT FAILURE?

STRUCTURAL EFFECTS PERFORMANCE EFFECTS

_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ . _ _ _ _ _ _ _ _ _ . _ _ _ .._n..

FAILURE MECHANISM INVESTIGATIONS EVALUATION OF POSSIBLE FAILURE MODES l o MANY CYCLES OF TEMPORARY LOSS OF PRELOAD THERMAL TRANSIENTS COMBINED WITH FLUCTUATING PRESSURE LOADS o PRELOAD REDUCTION DUE TO BOLT RELAXATION.

STEADY STATE THERMAL GRADIENTS

.- IRRADIATION EFFECTS o

BOLT YIELDING DUE TO THERMAL TRANSIENT (S)

PERMANENT LOSS OF PRELOAD l

0 BOLT CORROSION l

MATERIALS (316 STAINLESS)

IRRADIATION ASSISTED STRESS LEVELS (PRELOAD)

THERMAL EFFECTS (CONCENTRATION OF IMPURITIES)

WATER CHEMISTRY 0 DISPLACEMENT LIMITER KEY WEAR INCREASED LOADS ON SUPPORT BLOCKS o BOLT FATIGUE ,

THERMAL TRANSIENTS FLUCTUATING PRESSURE LOADS o EXTREME LOADING CONDITIONS UNDER UNUSUAL LOADING CONDITIONS

- 3 LOOP OPERATION i EXTENDED COASTDOWN

FAILURE MECHANISM INVESTIGATIONS ANALYSES PERFORMED o THERMAL ANALYSES STEADY STATE WITH GAMMA HEATING TRANSIENTS s

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FAILURE MECHANISM INVESTIGATIONS 4 -

' CONCLUSIONS - FAILURE MECHANISM o IMPACT AT DISPLACEMENT LIMITERS OCCURS IN NOMINAL CONDITION OF SUPPORT SYSTEM' 4

o WEAR OF DISPLACEMENT LIMITER KEYS PROGRESSED DVER TIME 4

O. INCREASED TANGENTIAL GAPS RESULTED IN INCREASED LOADS ON 6 SUPPORT BLOCKS 4

o. LOADS ON SUPPORT BLOCKS INCREASED TO THE POINT WHERE FATIGUE CRACKS INITI ATED AND PROP 0 GATE IN LONG VISIBLE BOLTS 4

o FAILURE OR REDUCTION IN PRELOAD IN LONG VISIBLE BOLTS 'DUE TO CRACK PROP 0GATION LEADS TO INCREASED LOADS ON HIDDEN BOLTS AND CRACK INITI ATION AND' PROP 0GATION IN THEM 4

o REDUCTION IN STIFFNESS OF SUPPORT BLOCKS DUE TO '

CRACKED LONG VISIBLE AND HIDDEN BOLTS RESULTS IN CONTINUED WEARING F DISPLACEMENT LIMITERS 4

o- INCREASED RELATIVE MOTIONS BETWEEN CORE BARREL AND THERMAL SHIELD FATIGUES SURVEILLANCE SPECIMEN L HOLDER TUBES

..n _ _ . _ . _ _ _ _ _ . - _ _ - . - . _

  1. .. FAILURE' MECHANISM INVESTIGATIONS INSIGHTS 'FOR REPAIRS i

o -- SUPPLEMENTING OR. REFURBISHING UPPER DISPLACEMENT LIMITER ASSEMBLIES IS VITAL TO LIMIT LOADS ON LOWER' SUPPORT BLOCKS o LONG VISIBLE BOLTS ARE THE LIMITING COMPONENTS IN THE SUPPORT. SYSTEM s

o' NO: EVIDENCE WAS FOUND WHICH SUGGESTS MECHANISMS-OTHER THAN FATIGUE UNDER NORMAL FLOW CONDITIONS

-CONTRIBUTED TO INITIATION OF BOLT FAILURE b

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_.____.___._____.______m__________m____m_______________.________

THERMAL SHIELD REPAIR PLAN o REMOVE AND REPLACE ALL 18 ACCESSIBLE BOLTS AND

.FOUR PROTRUDING DOWEL PINS o ,

INCREASE'PRELOAD IN REPLACEMENT BOLTING TO REDUCE SENSITIVITY TO FATIGUE o SHIM THE GAP BETWEEN THE BOTTOM OF THE THERMAL SHIELD AND THE SUPPORT BLOCK AT THE 9D LOCATION o INSTALL 6 NEW TANGENTIAL DISPLACEMENT LIMITERS AT THE UPPER RIM OF THE THERMAL SHIELD l

o MOVE ACTIVE IRRADIATION SPECIMEN (1 LOCATION)

FROM THE DAMAGED HOLDER TO AN INTACT HOLDER

o. REMOVE DUMMY IRRADIATION SPECIMENS FROM DAMAGED HOLDERS (2 LOCATIONS) l

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THERMAL SHIELD REPAIR PLAN BASIS FOR REPAIRS I

o LOWER SUPPORT BLOCKS SHOWN CAPABLE OF WITHSTANDING CALCULATED LOADS INCREASE IN PRELOAD (BY 50%) HELPS COMPENSATE FOR LACK OF HIDDEN BOLTS ,

PEAK LOADING ON BOLTING ASSUMED TO BE 4 TIMES RMS VALUES FOR ALL CYCLES

~

INSTALLATION OF 6 NEW DISPLACEMENT LIMITERS I REDUCES ALTERNATING LOADS ON SUPPORT BLOCKS j AND LONG VISIBLE BOLTS BELOW LOADS FROM i ORIGINAL DESIGN ACCEPTANCE OF LONG VISIBLE BOLTS BASED UPON UNADJUSTED FATIGUE CURVES o OVERALL SUPPORT SYSTEM FOLLOWING MODIFICATIONS SHOWN BETTER THAN ORIGINAL UNDEGRADED SUPPORT SYSTEM o NEW DISPLACEMENT LIMITER KEYS SHOWN CAPABLE OF WITHSTANDING CALCULATED LOADS DESIGN LOADS GENERATED FROM ENVELOPE OF CALCULATED LOADS AND EXPERIENCE WITH OLD DISPL-ACEMENT LIMITERS (SCALED FAILURE LOAD)

DISPLACEMENT LIMITER DESIGN MEETS INTENT OF CURRENT ASME CODE SUBSECTION NG PROJECTED WEAR RATES ON DISPLACEMENT LIMITER KEYS SLOWER THAN FOR ORIGINAL DESIGN . LONGER PREDICTED i.IFESPAN.

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COMPARISON OF ORIGINAL V/S MODIFIED DESIGN

~-

ORIGINAL DESIGN MODIFIED DESIGN o 4 DISP. LIMITER KEYS; 6 DISP. LIMITER KEYS j CONTACT AREA APPROX. CONTACT AREA APPROX.

12 IN' 36 IN'

. o INITIAL TANGENTIAL INITIAL TANGENTIAL GAP

^

GAP APPROX. 20 MILS s 10 MILS TOTAL TOTAL o- 3 VISIBLE BOLTS 3 VISIBLE BOLTS 2 HIDDEN BOLTS PER NO HIDDEN BOLTS BLOCK 50% HIGHER PRELOAD o N=2 TS MODE CONTRIBU- N=2, TS MODE BROKEN UP TION TO LOADS OR LOWER BY 6 DISPLACEMENT SUPPORT BLOCKS - HIGH LIMITERS. ITS CONTRI- i BUTION TO TS SUPPORT i BLOCKS - LOWER I CONCLUSION i t

BASED UPON A RELATIVE COMPARISON OF LOADS ON THE SUPPORT BLOCKS AND ALTERNATING STRESSES ON LONG BOLTS, UPDATED DESIGN IS BETTER THAN THE ORIGINAL DESIGN.

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THERMAL SHIELD REPAIR PLAN MONITORING / INSPECTION CONSIDERATIONS 1

1 I

CONCERNS.

1. DETECTION OF DEGRADATION PRIOR TO FAILURE
2. DETECTION OF FAILURE

'5 SOLUTIONS o ADDITIONAL MONITORING INTERNALS VIBRATION MONITORING (IVM) SYSTEM LOOSE PARTS MONITORING SYSTEM (LPMS) o INSPECTIONS CONFIRMATION OF IVM AND LPMS OUTPUTS CONCLUSIONS l

0 INSTALL IVM SYSTEM PRIOR TO START-UP l

0 INSTALL LPMS PRIOR TO START-UP 4

o PERFORM VISUAL INSPECTIONS OF SUPPORT SYSTEM AT NEXT SCHEDULED OUTAGE

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U Y N D R E 0 E N E A T 3 M O S H U E E I U C R L C T T T S B P A A A A E M L L T S F O P L S N

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N C I S A O E P I T E I T T D S L T A N N U L A L E E W I D C M E G E W I R H O N M N H F O S E I C I F I D F T O S D B S G O D R F O 7 Y N O K 8 M E U C N / S O L F N O O 4 L U E O L I / G M A D R I B T 2 N E C E T I 1 I T I H K R D R S S C C E 0 D T O Y Y S O S 9 A R T S H L N A I -

P R B I F R T N M -

E E O O S O V F W T R F M I O 8 O R /G O 8 P . S O N T S F U P G N N 9 N I O T O O 1 O T P I M I K R I T A U T R A N T Y T S MM A O P O N S A I E R E H RW I E L A R R A E T L P U U T E R S P E S I U M N T N W E T O D D O A E E O R I O D E C J R R L - - P S L A H R C U S o o C o o o o f:l I

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. . .. CONCLUSIONS o

PLANNED REFURBISHMENT OF THERMAL SYSTEM WILL BE AN IMPROVEMENT OV UNDEGRADED SUPPORT SYSTEM 5

o IDENTIFICATION OF FAILURE MODE AND COMPONENTS IN SUPPORT SYSTEM ENHA PREVENT DEGRADATION IN THE FUTURE o

ENHANCED MONITORING AND INSPECTION HELP PRECLUDE DEGRADATION AS WELL OF DETECTING FAILURES o

SAFETY ANALYSES PERFORMED DEMONSTRA FAILURE MODES ARE NOT A NUCLEAR SAF .

REQUIRES DETECTABILITY:

LPMS INSTALLATION IVM SYSTEM INSTALLATION l

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i MEETING SUMMA,RY_ DISTRIBUTION 4 -'

fa::Dockit2 N1eES NRC & Local FORs SVarga EEoger-AWang OGC-Bethesda-EJordan JPartlow ACRS(10)

HBClayton fiRC Participants Alan L'arg Tom Snedlosky

-- ~J. Rajan

C.O. Sellers W. H. Koo A

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