ML20136J495

Safety Evaluation of Shroud Head Bolt Assembly Failures at Peach Bottom Atomic Station,Unit 3

ML20136J495
Person / Time
Site:	Peach Bottom
Issue date:	12/20/1985
From:	Biglieri N, Legate R, Ranganath S GENERAL ELECTRIC CO.
To:
Shared Package
ML20136J479	List: ML20136J477 ML20136J495
References
DRF-B13-01372, DRF-B13-1372, MDE-292-1285, NUDOCS 8601130408
Download: ML20136J495 (25)

Text

. . . _ . . _ _

c Attachm2nt 1

. Docket No. 50-278

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NDE #292-1285 DRF #313-01372 ,' .

,, SAFETY EVALUATION OF SHROUD HEAD BOLT ASSEMBLY FAILURES AT PEACH BOTTOM ATOMIC POWER STATION .

UNIT 3 December 20, 1985 Approved by: ed tf(/es _esL///4 i R. E. Legate, Td mical Idader

, Reactor Pressure Vessel Design .

Approvid bgt

• MT A /. -- > = T ' A 4.72f N. J. Biglieri Hanspr

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Reactor Desigs h. neering .

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. Approved by: M M * ^ k--

S. Ranganath, Manager .

Structural Analysis Services ,

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Approved byr ref- .

[A. E. Rogers, Manager ,

e Application Engineering Services .

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IMPORTANT NOTICE REGAIDING CONTENTS OF THIS EEPORT .<

r PLEASE READ CAREFULLY v~

This report was prepared by General Electric solely for the use of the Philadelphia Iloctric Company. The information contained in this report is believed by General Electric to be an accurate and true representation of the facts known, obtained, or provided to General Electric at the time this report was prepared.

l The only undertakings of the General Electric Company respecting information in this document are contained in Purchase Order No.

P5240504 and nothing contained in this document shall be construed as changing said purchase order. The use of this information except as

• defined by said purchase order, or for any purpose other than that for 1

which it is intended, is not authorized; and with respect to any such .

~

unauthorized use, neither General Electric Company nor any of the contributors to this document makes any representation or warranty (express or implied) as to the completeness, accuracy, or usefulness of the information contained in this document or that such use of such s .. information may not infringe privately owned rights nor do they assume any responsibility for liability or dandse of any kind which may result from such use of such information. ,'

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TABLE OF Gunannis l

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) 1. INIRODUCTION AND

SUMMARY

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l I 2. DESIGN CONSIDERATIONS 1

3. SAFETY EVALUATION A. STRUCTURAL ANALYSIS CONSIDERATIONS B. POTENTIAL FOR ADDITIONAL P3-3 FAILURES i

I C. LOOSE PARTS CONSIDERATIONS i D. CONCLUSIONS e e

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APPENDIX - STRUCTURAL ANALYSIS SERVICES REPORT t

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SAFETY EVALUATION OF SEROUD EIAD .

BOLT ASSEMBLY FAILURES AT PEACB BOTTOM ATOMIC POWER STATION UNIT 3 .

1. INTRODUCTION AND S199tARY -

During the recent refueling and maintenance outage at Peach Botton -

Atomic Power Station Unit 3 (PB-3) four (of forty eight) shroud head W bolts were found to be broken during shroud head installation. The failed bolts were discovered during bolt tightening when the Reactor Technicians were unable to develop the 50 ft-lbs of torque required by the plant procedure. Subsequent under water TV examination showed that there was a separation in the Alloy 600 rod portion of the bolts in the vicinity of the alignment window (see Figure 1). Metallurgical examination performed a,t,GE-Vallecitos of one of the failed bolt .

sections indicates that the cause of the failure was intergranular stress corrosion cracking (IGSCC) in a crevice region. This is the first known instance where IGSCC has caused the complete failure of a L shroud head bolt. . Evaluations have been performed that conservatively demonstrate that twenty-four (24) shroud head bolts assemblies will more than meet the plant licensing basis. Theplannedinstallat$

' of twenty-four new replacements bolts prior to startup will permit

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continued safe operation of the plant.

. .;,,, 7, 2. DESIGNCONSIDER$TIONS O.' - The shroud head bolt assemblies retain the shroud / shroud head joint ,

(see Figure 2). The shroud head and separator assembly and shroud head

. bolt assemblies are non ASME Code components that have no direct safety ,

related function. These non-safety related components are, however, t connected to or influenced by or could influence components that are r classified as safety related. The design basis for the bolts requires .

appropriate consideration of their intended service conditions. The ASME Code was used for design guidance. During normal plant operation -

the inner rod of the shroud head bolt assembly is loaded in tension to

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approximately 9,000 to 12,000 lbs. The load is developed as a result .

of differential theresi espansion between the outer sleeve (Type 304 stainless steel) and the inner rod (a combination of Type 304 stainless i steel and Alloy 400). Torquing of the bolts to 50 ft-lbs during assembly develops a bolt load of approximately 1700 lbs.  !

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3. SAFETY EVALUATION A.. Structural Analysis Considerations

,, The shroud / shroud head joint is a flanged joint that can be -

assembled remotely. The flanges are pre-loaded by differential thermal expansion between the two major parts of the shroud head ,

bolt assemblies. The joint design provides a load path to reaction 1 cads caused by differential pressure across the shroud head and separator assemblies, as well as loadings that could occur during a seismic event. The licensing basis for PB-3 does not require combining LOCA and seismic loads.

The original design basis assumed a limiting combination of SSE +

steam line break LOCA, although this was not the licensing basis for PB-3. Furthermore, the allowable stresses were based on ASME Code stress limits. Based on this, a joint design with fdrty-eight (48) shroud head bolts was selected. In this safety evaluation to

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determine the .equired number of bolts, the limiting condition for failure (instead o,f,the ASME Code limits) was selected for analytis.

The differential pressure across the shroud head and separator i assembly can be resisted by dead weight of the component and two (2) shroud head bolts during normal operation.

l In addition to the normal bolt retention capability, flanged joint l

design seismic considerations require that in the event of a Safe Shutdown Earthquake (SSE), the shroud head horisontal motion must be restricted to preclude tapact with the in-vessel core spray piping.

Analysis to evaluate this criteria, supported by test results from tests performed by CE, show that fewer than nineteen (19) bolts are ,,

required.

The number of required bolts for the steam line break LOCA (faulted /i p) condition is sin (6). Combining the LOCA and selenic

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l loads increases the required number of bolts to approximately l tver.ty-four (24). -

, gackup calculations are in the Appendix.

e From structural analysis considerations, it is prudent to distribute the planned replacement shroud head bolt assemblies approximately l uniformly.

B. Potential for Additional PB-3 Failures n e failed bolt metallurgical esselnation (to date one side of one of the four failures) showed that the failure was the result of ICSCC over most of the rod cross-section with final ductile tensile failure over a small portion (order of one percent) of the cross-sectional area. E en the crack initiated cannot*be accurately evaluated, but*the final failure probably occurred some time during the operating period following the previous refueling outage.

TWe PS-3 failures are the first known in operating BWRs, even though 4 several plants are signi(icantly older than PB-3. H is,different

, behavior can be rationgfid based on our knowledge of coolant impurity effects en creviced Alloy 600 initiation and growth. He P8-3 water conductivity prior to 1985 was relatively high

(-0.6 95/cm average), compared with most BWR plants. Since the water quality has remarkably improved since early 1985, and since PgCo is committed to maintaining improved water quality, it is s/

highly unlikely that ICSCC will initiate in the 24 new replacement bolts within the nest 18-month cycle or in fact, in the nest several cycles .

Regineering ,judpost, in summary, is that some additional bolt , l failures stabt be espected to occur la the balance of the originally I installed bolts during the nest operating period. It would be very unlikely, heuever, that any gross failures similar to those recently

O discovered would be sustained in the replacement bolts even ever the next several years. -

C.. Loose Parts Considerations

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,, It is probable that the final failures occurred during plant .

j operation under the normal loads, because the installation torquing l loads are auch smaller.  !

None of the four failures resulted in loose parts. In each case, '

the end of the bolt below the observed failure line was held in .,

position by the position alignment pin which is essentially captured ,

by the structure forming the alignment window (See Figure 1). The upper section of the failed shroud head bolt remained in its normal 1 1

position on the shroud head flange brackets as would be expected. l The position alignment pin would not be expected to fail, because l the. load from the captured bolt section (less than 10 lb) results in [

insignificant pin stress. It is concluded that additional.igfled [

, asneeblies will not produce any loose parts. (

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=ggg D. Conclusions j A detailed evaluation of the safety aspects of the PB-3 shroud head l bolt assembly failures was performed. Based on review of structural f analysis and potential ICSCC bolt failure considerations, it has l been demonstrated that the planned installation of twenty-four (24) i replacement shroud head bolt assemblies will more than maintain the l licensing basis design margins required for shroud / shroud head joint l integrity. It was also shown that loose parts free potential bolt failures pose no safety probles.

Based on the above, it is concluded that for operation of PS-3 at _

full powers

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1. There is no increase in the probability of occurrence or consequences of an accident or malfunction of safety-related -

equipment.

2. There is t.o increase in nhe possibility of an accident or malfuncticn of a different type then analyzed, and .

3. There is no reduction in the margin of safety as defined in the basis for the Technical Specifications.

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VERIFICATION OF ANALYSIS A. ANALYSIS TITLE , _ NEww Nh h, d, ma B. RE)0RT IRMBER M M fMk U- -- 1 -

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E. VERIFIER AND DATE T E CA.osv>="e t i 2.7h F. WHAT TYPE OF ANALYSIS WAS P,IRFORMEDT E. WHAT ARE THE INPUTS FOR THE ANALYSIS AND ARE THEY APPROPRIATE 7 H. WHAT TYPE OF LOADING 15 PRESENT AND 15 IT APPROPRIATE 7 I. ARE THE MATERIALS AND CORRESPONDING MATERIAL PROPERTIES USED. CORRECT AND APPROPRIATE 7 J. WHAT COMPUTER CODE WAS USED FOR THE ANALYSIS AND IS IT APPROPRIATE FOR THE PROBLEM 7 -

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Attcchesnt 2 D:ckst No. 50-278 PHILADELPHIA ELECTRIC COMPANY ,

M CHANICAL ENG1E ERING DIVISION N2 2301 Market Street SAFETY EVALUATICBi FOR T M REPLACEM NT OF TWENTY-POUR SHROUD HEADr BOLT ASSEMBLIES PEACH BOTTOM ATOMIC POWER STATION UNIT 3 MOD REQUEST NO. 1868 i

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SUBJECT:

Peach Bottom Atanic Power Station Unit 3, Replacement of Twenty-four of Forty-eight Shroud Head Bolt ,,

Assenti les.

CONCLUSION: This replacement does not involve any changes to safety '

related ccuponents. It does not involve an unreviewed safety question, and no change to the Technical Specifications la regulred.

DISCUS $10N: This Safety Evaluation and the attached GE Safety Evaluation (Attachment !) address the following aspects '

of the subject replacement:

. Strpetural Analysis Considerations .

. Potent %il for Additional Unit 3 Fallures

. . Loose Parts Considerations During the reassenbly of the Peach 86tTtkrunf t '3 . .

reactor Internals, it was detennined that several of the forty-elght shroud head bolts were failed. A ,  ;

metallurgical analysis perfomed tr/ GE concluded that l the failures occurred as a result of Intergranular -

stress corrosion cracking (IGSCC) which had propagated  !

Into the bolt, and the subsequent tensile failure of a -

l Ilgament of bolt material, Alloy 600. ,

Prior to returning the unit to service, twenty-four,of the forty-eight bolt assenblies will be replaced, including the failed bolts. New bolts of the same design '

and material will be Installed, so that in the final

• l configuration, every other bolt will have been replaced. These bolts are not safety related,.but are  ;

.' connected to, or could Influence safety related ,

conponents.

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During normel operation and during a postulated steam line break LOCA these bolts are designed to hold the shroud head and shroud together. During a postulated Safe Shutdan Earthquake (SSE) they will prevent lateral motion between the shroud head and shroud.

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Although it is possible that some failures could occur in the bolts which have not been replaced it Is unlikely that all of the original remaining twenty-four bolts would fall, and no failures should be expected in the bolts e lch have been replaced, for at least several operating cycles. However, to be conservative this evaluation assunos that only the twenty-four replaced bolts are capable of carrying a load.

The PBAPS shroud head bolt and shroud to shroud head fastening arrangement Is based on a generic GE Design which uses 48 shroud head bolts. GE has verifled that for all BWR's utilizing forty-eight bolts the ASPE Code was used for design guidance and, LOCA and SSE generated loads were conblned. ASPE Code conpliance for these conponents and the occurrence of a sinultaneous LOCA and SSE Is not considered as part of the Ilcensing basis for PBAPS, therefore, the use of forty-eight shroud head bolts is conservative. j GE performed a PSAPS specific shroud head bolt analysis utilizing design basis loads and load conbinations, and l

. detennined that for normal _100% power operation, two )

shroud head bolts and the weight of the shroud head and steam separators will prevent the shroud head from Ilfting off of the shroud, due to the differential pressure across the shroud head. Six shroud head bolts wl11 prevent the shroud head from Ilfting due to a steam Ilne break LOCA, and nineteen bolts will restrain the shroud head f ran lateral motion during an SSE. The analysts conservatively assumed that no friction is present, and that the shroud guide pins offer no resistance +

to motion. As a further conservatism, GE cabined the LOCA C SSE loads, and determined that twenty-four bolts would adequately restrain the shroud head during a simultaneous LOCA and SSE. Therefore, based on this conservative analysis, it is concluded that twenty-four bolts will satisfy the PSAPS Design Basis requirements.

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4 Based on the corrmon failure location of the failed bolts, and the existence of a crevice at this location, it is expected .that any additional failures due to IGSCC would also occur at this location. Should additional similar failures occur, the bolt asserrbly design is

. such that no loose parts would enter the reactor coolant system. As occurred in the failed bolts, the guide pin in the guide window prevents the broken portion of the bolt

, from being separated from the bolt asserrbly.

No change to the UFSAR is required.

Appendix R criteria have been considered and there is no effect on fire protection features.

10CFR50.59 CHANGES, TESTS AND EXPERIMENTS:

1. A change to the Technical Specification is not required. (None applicable)

2. An unreviewed safety question is not involved.

3. An oppilcation for amendnent to the Nicense is not required.

10CFR50.92 SIGNIFICANT HAZARDS DETERMINATION:

s itsis doncluded that:

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, (1) t,3eIther the probabi1ity of occurrence' nor the consequences of malfunction of equipment Irportant to safety previously evaluated in the safety analysis report will be increased by the t 5

modification. *

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(2) The possibility of an accident or malfunction of a' l r different type than any evaluated previously in the safety analysis report is not created.'s' ,

(3) The margin of safety as defined in the basis for '

the technical specification is not reduced. v .

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Prepared by:_ i . M Date 11. f 73 / 85 Reviewed by: M Date/2/2.[8 Rev ewed by: Aal4 - M Date 11 '24/76 ClyAY Section, Resp 6ris,1ble Engineer

~ lf App by: $$ m Date / L-2 3- W

^

Diviston (B ch or Section Head)

Approved by:  % b).b w Date l? fL4/PI Civil S on (Branch or Section Head)

Approved by Date /E & F Nuc}4ar Section ( anch or Section Head)

WJB/pd12128510 Copy to: E. C. Kistner ,

G. T. Brecht A. R. Lewis M. J. Cooney S. J. Kowalski R. S. Fielschmann, 11 P. K. Pav11 des R..A. Mulford G. A. Hunger G. J. Madsen J. Moskowitz ,

W. J. Mindick ..

W. M. Alden ~

d. K. Davenport P. A. Tutton

d. W. Austin F. W. Polaski R. P. Alejnikov DAC (NG-8)

Flie: RES 15-9 RPV 1

l l

- ~ - ,

. 1 i l 10CFR50.59 SAFETY EVALUATION SLM%RY Modification: 1868 A.' ' '

System: Reactor Vessel Internals B. Description *

. .) . a Replacement of twenty-four of the forty-eight shroud head bolts,'

on Peach Bottom Unit 3. .

C. Reason for Change: ,

During the reassently of the Peach Bottom Unit 3 reactor internals, it was detennined that several of the forty-eight -

shroud head bolts were failed. Prior to returning the unit to . ,

service, twenty-four of the forty-eight bolts will be replaced, '

based on an analysis by General Electric Co. which concluded that twenty-four bolts are adequate. None of the original bolts are .

I assuned to be capable of carrying a load.

D. Sunnary of Safety Evaluation:

(I) Does this modification increase the probability of occurrence or consequences of an accident or malfunction of equipment important to safety as previously evaluated in the Final Safety Analysis Report?

. Answer: No, since twenty-four bolts are more than enough

- ..to carry the Design Basis loads.

9 (11) Does this modification create the possibility of an accident or malfmetion of a different type.chan any evaluated previously in the Final Safety Analysis Report?

~

Answer: No, because the cons'equences of a failure of the replaced bolts is no different than the original bolts, which is accounted for in the plant's design.

(111) Does this modification reduce the margin of safety as defined in the basis for any Technical Specification?

Answer: No, because these bolts are non-safety related, -

, and do not affect the plant's Technical.

Specifications.

f WJB/pd12238502

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