ML20210N385

Requests NRC Approval of Application for Alternative Approach to Postulating Arbitrary Intermediate Pipe Breaks at Facility.Elimination of Arbitrary Intermediate Pipe Breaks Will Not Reduce Level of Plant Safety

ML20210N385
Person / Time
Site:	Limerick
Issue date:	04/25/1986
From:	Kemper J PECO ENERGY CO., (FORMERLY PHILADELPHIA ELECTRIC
To:	Butler W Office of Nuclear Reactor Regulation
References
CON-#286-972 OL, NUDOCS 8605050004
Download: ML20210N385 (18)

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PHILADELPHIA ELECTRIC COMPANY 23O1 M ARKET STREET P.O. BOX 8699 PHILADELPHI A. PA.19101 JOHN 5 KEMPER V IC E-PR E $lD E N T tasamassenn amc astaamcn April 25, 1986 Mr. Walter R. Butler, Director Docket No.: 50-353 BWR Project Directorate #4 Division of Licensing U. S. Nuclear Regulatory Commission Washington, DC 20555

Subject:

Limerick Generating Station Unit 2 Elimination of Arbitrary Intermediate Pipe Breaks File: GOVT l-1 (NRC)

Dear Mr. Butler:

Philadelphia Electric Company proposes to eliminate arbitrary intermediate pipe breaks from the design of Limerick Unit 2.

Arbitrary intermediate breaks (AIB) are those break locations which, based on ASME Code stress analysis, are below the stress limits and the cumulative usage factora 'oecified in the current NRC criteria but were selected to provide a ,-nimum of two breaks between terminal ends.

Current knowledge and experience supports the conclusion that designing for AIB is not justified and that this requirement should be deleted. The NRC Piping Review Committee has recommended deletion of AIB in NUREG-1061 Volume 3, published November 1984. Elimination of AIB offers the opportunity to improve overall plant safety in addition to the benefits due to the deletion of the associated pipe whip restraints and other provisions currently incorporated in plant designs to mitigate the dynamic effects of such breaks. Occupational radiation exposure will be reduced over the life of the unit because of improved access for maintenance and inspection. Piping heat loss at whip restraint locations will also be reduced.

Philadelphia Electric Company therefore requests NFC approval for the application of the following alternative approach to postulating AIB on Limerick Unit 2:

1. AIB in high energy piping systems will be eliminated from the design basis when the following criteria are satisfied:

a. For all piping systems, the stress criteria in Limerick FSAR Section 3.6.2 are not exceeded.

b. For Class 1 piping systems, the usage factors in Limerick FSAR Section 3.6.2 are not exceeded. j\(pD B605050004 DR 860425 l ADOCK 05000353 1 PDR

These criteria provide sufficient protection against pipe breaks at Limerick Unit 2 as discussed in Attachment A.

2. Where AIB no longer need to be postulated, the associated dynamic effects (pipe whip, jet impingement and compartment pressurization loads) can be excluded from the design basis.

This justifies the elimination of pipe whip restraints and jet impingement barriers cu rently provided to mitigate those dynamic effects.

i For environmental qualificatfor. of equipment and structural design of compartments or enclosures traversed by high energy piping systems, breaks will continue to be postulated in accordance with the present project criteria, i.e. in each compartment or enclosure traversed by the high energy piping system, non-mechanistic breaks are postulated to establish environmental consequences. Therefore, elimination of the AIB will not change the existing environmental or structural criteria for any structure, system or component.

Specific technical concerns associated with provisions for minimizing stress corrosion cracking in high energy lines, for minimizing the effects of thermal and vibration induced piping fatigue, and for minimizing water / steam hammer effects are addressed in Attachments C, D, and E, respectively.

The application of the proposed criteria changes will result in the deletion of approximately 40 break locations and 36 pipe whip restraints. The number of pipe breaks (terminal end and intermediate) currently postulated for Limerick Unit 2 are summarized in Attachment B which also identifies the estimated number of pipe breaks and pipe whip restraints in each system to be eliminated from the design through application of the proposed alternate criteria.

Based on current design information, PECo estimates that elimination of AIB will save nearly a million dollars (present day) in analysis, design, fabrication and installation of associated pipe whip restraints. Although further-Tavings will be realized from a reduction in the scope of jet impingement analysis and in the number of required jet impingement barriers, this cost component has not been estimated. Approval of this proposal will also result in fewer inspections and less maintenance and in a man-rem dose reduction over the 40 year unit life, resulting in an additional operational cost savings.

Based on the information provided above and in the attachments to this letter, it is concluded that the elimination of AIB will not reduce the level of safety or change the operational basis of the plant.

Attachments A through E provide identical information and proposed alternate criteria to what has previously been reviewed by the NRC for Hope Creek and for which relief was granted in a letter from W. R.

l Butler to R. L. Mitti dated September 20, 1985. Hope Creek is a BWR similar in design to Limerick Unit 2.

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_3 In order to achieve the maximum adiantage from the arbitrary break criteria change, we request a decision on this proposal by July 1, 1986. Construction is progressing on 1.imerick Unit 2 and certain pipe whip restraints associated with AIB are scheduled to be installed beginning in July. Without a timely (ecision on this issue the structural support steel for the whip restraints must be erected, thereby reducing the benefits to be renlized by elimination of AIB. If we can be of further assistance, or *.f a meeting with the Staff is deemed beneficial for a final re olution of this matter, please contact us. Following your approval, the necessary FSAR changes will be implemented.

Sincerely, f .W_ ,l.-

RRH/pdO4148603 See Attached Service List

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cc: Troy B. Conner, Jr., Esq. (w/ enclosure)

Ann P. i @ 7, Esq. (w/ enclosure)

Mr. Frank R. Romano (w/ enclosure)

Mr. Robert L. Anthony (w/ enclosure) l Ms. Phyllis Zitzer (w/ enclosure)

! Charles W. Elliot, Esq. (w/ enclosure)

Barry M. Hartman, Esq. (w/ enclosure)

Mr. Thomas Gerusky (w/ enclosure)

Director, Penna. Emergency (w/ enclosure)

Management Agency Angus R. Love, Esq. (w/ enclosure)

David Wersan, Esq. (w/ enclosure) l Robert J. Sugarman, Esq. (w/ enclosure)

Kathryn S. Lewis, Esq. (w/ enclosure) l Spence W. Perry, Esq. (w/ enclosure) day M. Gutierrez, Esq. (w/ enclosure)

Atomic Safety & Licensing (w/ enclosure)

Appeal Board Atomic Safety & Licensing (w/ enclosure)

Board Panel Docket & Service Section (w/ enclosure)

Mr. E. M. Kelly (w/ enclosure)

Mr. Timothy R. S. Campbell (w/ enclosure) i 2

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Attachment A JUSTIFICATION FOR ELIMINATION OF ARBITRARY INTERMEDIATE PIPE BREAKS (AIB)

The following is the Justification for the elimination of arbitrary intermediate pipe breaks and the associated pipe whip restraints and Jet impingement barriers at Limerick Unit 2.

A. Current Criteria The break selection criteria currently enployed by PEco for Limerick Unit 2 are taken from NRC Branch Technical Positions ASB 3-1 and MEB 3-1 of Standard Review Plan 3.6.2 and are described in Section 3.6 of the Final Safety Analysis Report (FSAR). These docunents require that, for ASE Code piping, pipe breaks be considered at terminal ends and at intermediate locations where stresses or cunulative usage factors exceed specified limits. If two Intermediate locations cannot be determined based on the above, i.e. stresses and curulative usage factors are below specified Ilmits, then the two highest stress locations are selected.

B. Postulation of Arbitrary Intermediate Breaks Not Supportable

1. Pipe breaks are postulated to occur at locations where stresses exceed 80% of Code a110wables (Class 1, 2 and 3 piping) or where the ctrulative usage factor exceeds 10% of I

the Code allowable 1.0 (Class 1 piping only). By

, definition, the arbitrary breaks to be eliminated all exhibit stresses and usage factors below these conservative thresholds. Arbitrary Intermediate breaks are often postulated at locations where stresses are well below the ASE Code allowables and within a few percent of the stress levels at other points in the same system. This results in conplicated protective features being provided for specific break locations in the piping system that provide t ittle to enhance overall plant safety. Thus, arbitrary intermediate

! breaks are only postulated to provide additional conservatism in the design. There is no technical JustifIcatIcq for postulating these breaks.

2. Pipe rupture is recognized in Branch Technical Position KB j 3-1 as being a " rare event which may only occur under unanticipated conditions." This conclusion is supported by extensive operating experience in over 80 operating U. S.

plants and a nuter of similar plants overseas in which no piping failurs are known to have occurred which would j indicate that designing for arbitrary intermediate breaks is necessary.

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3. The additional pipe rupture devices (whip restraints and Jet Igingement barriers) resulting from this additional " layer" of conservatism may actually reduce rather than Igrove plant safety. This has been demonstrated in " Effects of Postulated Event Devices on Nonnal Operation of Piping Systems in Nuclear Power Plants," NUREG/CR-2136, Teledyne Services, 1981. -

C. Reanalysis Burden of Postulatina Arbitrary Intennediate Breaks

! In practice, consideration of these two arbitrary intermediate i breaks is particularly difficult because the locating of the high

! stress points may move several times as the seismic design and analysis of structures and piping develops. The revised MEB 3-1,

, which was included in the July 1981 revision to the Standard Review Plan (NUREG-0800), provides criteria for not having to relocate intermediate break points when highest stress locations

shift as a result of pipirg reanalysis. As a practical matter,

however, these criteria provide little relief, since the burden is on the designer to prove that not postulating breaks at relocated highest stress points does not degrade safety. This may require extensive additional analysis of break / Jet Ig ingement target interactions for the relocated break points and could result in design, fabrication and Installation of i additional pipe whip restraints at the relocated break points and i elimination of previously InstaIIed restraints at abandoned break i points. Early determination of exact break locations is quite important because of all of the secondary effects of the pipe i break to be considered.

D. Benefits of Elimination of Arbitrary Intermediate Breaks The benefits te be realized from the elimination of the arbitrary intermediate break locations center primarily around the elimination of the associated pipe whip restraints and other l structural provisions to mitigate the consequences of these breaks. While a substantial reduction in capital costs for these restraints and structures can be realized Imnediately, there are also significant operational benefits to be realized over the 40 year life of the plant.

Access during plant operation for such activities as maintenance

and inservice inspection is improved due to the elimination of congestion created by these restraints and the supporting

structural steel, and, in some cases, due to the need to remove j some restraints to gain access to welds. In addition to the decrease in maintenance effort, a significant reduction in manrem exposure can be realized through fewer manhours spent in

radiation areas. Also, the need to verify adequate cold and hot l

clearances between pipes and restraints during initial heatup, which requires additional hold points during this already critical startup phase, can be dispensed with.

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Recovery frcyn unusual plant conditions would also be improved by elimination of this congestion. In the event of a radioactive release or spill ir. side the plant, decontamination operations would be much more effective it the ccumlex shapes, represented by the structurai frameworks supporting the restraints, were eliminated. This results in decreasing manrem exposures associated with decontamination and restoration activities.

Similarly, access for control of fires within these areas of the plant would be invroved, especially under low visibility conditions. Substantial overall benefits in these areas would be realized by reducing the ntsrber of whip restraints required.

By design, whip restraints fit closely around the high energy piping with fairly narrow gaps. Consequently these restraints and their supporting steel significantly increase the heat loss to the surrounding environment. Also, because thermal movement of the piping system during startup and shutdown could deform the piping insulation against the fixed whip restraint, the insulation must be cut back in these areas, creating convecting gaps adjacent to the restraint, which also increases the loss and contributes to the tendency of many containments to operate at termeratures near technical specification Ilmits. The elimination of whip restraints associated with arbitrary intermediate breaks would assist in controlling the nonnal environmental temperatures and improve system operational efficiency.

It is concluded that the elimination of arbitrary intermediate breaks is Justified, based on the reasons stated above.

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l Attacluaent B Part 1 Page 1 of 6 l POSTULATED ARBITRARY INTERMEDIATE BREAKS TO BE ELIMINATED ON LIMERICK UNIT 2 r l

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< Estimated i

) Total No. No. of Arbit.

l Pipe of Breaks Intermediate Estim. No. of

' Piping Nom. Currently Breaks to Whip Restraints Piping System Mat'l.

Diam. Postulated be Deleted to be Deleted _

Inside Containment:

Reactor Mecirculation SA-312 12 10 0 0

! TP-316K SA-312 22 18 5 2 l

. TP-316K SA-312 28 7 0 0 TP-316K Main Steam SA-106 26 44 4 14 Gr. B HPCI Steam Supply SA-106 10 4 2 2 Gr. B t RCIC Steam Supply SA-106 4 2 2 5 i Gr. B SA-106 Gr. B 3 2 0 0 Botes: 1. 316K is a General Electric designation for low carbon ( 0.02%) stainless steel.

2. Based on the Limerick Unit I design.

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Attachment B Part 1 Pege 2 of 6 POSTULATED ARBITRARY INTERMEDIATE BREAKS j

TO BE ELIMINATED ON LIMERICK UNIT 2 i Estimated Total No. No. of Arbit.

l Pipe of Breaks Intermed. Eatim. No. of Nom. Currently Breaks Whfp Restraints Piping System Mat'1. Diam. Postulated to be Deleted to be Deleted i

Inside Containment, Cont'd.:

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! Main Steam Drain SA-106 3 3 2 0 l Gr. B SA-106 Gr. B 2 8 4 0 i

RPV Head Vent SA-106 4 2 1 0 Gr. B SA-106 2 7 2 0 l

i w/SA-312 f TP 316L trans.

RHR Shutdown SA-358 12 8 4 0 Cooling Return TP 316L &

SA-312 i

TP-304 i

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l Attachment B. Part 1 Page 3 of 6

. POSTULATED ARBITRARY INTERMEDIATE BREAKS TO BE ELIMINATED ON LIMERICK UNIT 2 Estimated Total No. No. of Arbit, i

j Pipe of Breaks Intermed. Estim. No. of Piping Nom. Currently Breaks Whip Restraints Piping System Mat'l. 2 Diam. P stdated to be Deleted to be Deleted i

Outside Containment HPCI Steam Supply SA-106 12 4 2 0 Gr. B SA-106 Gr. B 10 2 0 0 RCIC Steam Supply SA-106 6 4 2 4 Gr. B RWCU SA-312, TP-304L 6 )

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SA-312, TP-304L 4 ) 7 2 3 SA-312. TP-304L 3 )

Main Steam SA-106 26 16 8 6

-Gr. B .

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! Attachment B Part 2 Page 4 of 6 i

i l PIPINGSYSTEMSINWHICHPOSTULATEDARBITRARYINTERMEDIA}EBREAKS

ARE NOT CURRENTLY IDENTIFIED ON LIMERICK UNIT 2

Total No.

i Pipe of Breaks

! Piping Nom. Currently Piping System Mat'l.

Diam. Postulated

! Inside Containment:

Feedwater SA-333, Gr. 6 12 12 SA-333, Gr. 6 20 2 SA-333, Gr. 6 24 4 l

SA-333 Gr. 6 4 2 RWCU SA-312 6 7

TP 316L RPV Drain SA-106 2 8 Gr. B SA-312 2 1/2 1 TP 304L SA-312 4 8 l TP 304L ,

Notes: 1. Currently, no arbitrary intermediate breaks have been identified for these systems. If further analysis

, identifies arbitrary break locations in these systems, I PECo intends to eliminate them on the same technical bases.

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I Attachment B, Part 2 Page 5 of 6 i

PIPINGSYSTEMSINWHICHPOSTULATEDARBITRARYINTERMEDIA}EBREAKS ARE NOT CURRENTLY IDENTIFIED ON LIMERICK UNIT 2 l

i Total No.

l Pipe of Breaks Piping Nom. Currently ,

Piping System Mat'l.

Diam. Postulated

! i Inside Containment,

! Cont'd.:

1 Standby Liquid Control SA-312 2 10 TP-316L i

RHR Shutdown Cooling SA-358 20 5 TP-316 &

. SA-312 TP-304 LPCI Injection SA-358TP-316L 12 28 SA-333 Cr. 6 Notes: 1. Currently, no arbitrary intermediate breaks have

been identified for these systems. If further

. analysis identifies arbitrary break locations in

! these systems, PECo intends to eliminate them

) on the same technical bases.

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l I Attachment B. Part 2 Page 6 of 6

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I PIPINGSYSTEMSINWHICHPOSTULATEDA161TRARYINTERMEDIA}EBREAKS ARE NOT CURRENTLY IDENTIFIED On L!MERICK UNIT 2 1

1 Total No.

Pipe of Breaks l Piping Nom. Currently Piping System Mat'I.

l Diam. Postulated Inside Containment, Cont'd.:

f Core Spray SA-333 12 8 l

l Gr. 6 &

SA-358 TP-316L SA-358 10 6 TP-316L RPV Head Spray SA-312 6 2 TP-316L &

304 &

SA-106 GR. 6 Notes: 1. Currently, no arbitrary intermediate breaks have been identified for these systems. If further analysis identifies arbitrary break locations for these systems, PECo intends to eliminate them on the same technical bases.

RRH/pdO6248505

Attachment C i

PROTECTION OF ARBITRARY BREAK LINES FROM INTERGRANULAR STRESS CORROSION CRACKING i

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I In order for intergranular stress corrosion cracking (IGSCC) to I occur in piping, the following three conditions must exist .

j simultaneously: high tensile stresses, a susceptible material, and a corrosive envirorynent (NUREG-1061). The mitigation method that provides the greatest protection against IGSCC cor'cerns is the use of low carbon stainless steel materials, particularly for those lines l

i that experience temperature over 200F. This low carbon stalniess s steel material does not get sensitized during welding and hence prevents the occurrence of IGSCC.  !

For this reason on LGS Unit 2, all stainless steel pipes inside the containment that will experience termeratures over 200F (including

' the recirculation system) will be low carbon (0.02% max.) 304L/316L/316NG stainless steel. The flued heads and ten valves are 316 SS forgings  ;

, and will be Installed with flowing water heat sink welding to minimize

} the sensitization of the base material and the residual stresses on the

! I.D. of the pipe. No case histories are reported for IGSCC occurrence

In flued heads and valves.

1 Outside the contalrvnent the only Irmortant stainless steel system

! which experiences nonnel operating termeratures over 200F is the RWCU l system. For that reason, all the RWCU piping up to the

non-regenerative heat exchangers will be 304L with 0.02% max. C.

Valves In this portion of the system are 316 forgings and will be l Installed with heat sink welding to minimize the sensitization of the

) base material.

In addition, installation specifications have been reviewed to ensure that grinding the ids is Ilmited and followed by polishing.

This prevents cold worked surfaces that can Init! ate IGSCC cracks.

Furt.ber, all welding procedures limit the heat input tc, below 55 kjoules/In. Automated welding using the latest techniques designed to minimize residual tenslie stresses on the ID is being employed whenever practical.

j Thus, for the piping systems in which arbitrary Intermediate

! breaks are proposed to be eliminated, the piping material is either

not susceptible to IGSCC or measures are being taken to minimize such susceptibility.

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Attactment D PROVISIONS FOR MINIMIZING THE EFFECTS OF THERMAL AND V. BRAT 1ON INDUCED P1 PING FATIGUE As discussed below, for the piping systems in which arbitrary intermediate breaks are proposed to be eliminated, provisions have been made in the design and preoperational/ power ascension testing program for minimizing the effects of thermal and vibration induced piping fatigue.

1 I. GEPERAL FATIGUE DESIGN CONSIDERATIONS For Class 1 lines, fatigue considerations (which include thermal transients) are addressed by the cumulative usage factor (CUF).

In order to ensure that piping will not fait due to fatigue, the ASME Code has set the CUF limit at 1.0. By definition, all arbitrary intermediate break locations have CUFs below 0.1.

For Class 2 and 3 lines, fatigue is considered in the allowable stress range check for thermal expansion stresses. This stress is included in the total stress value used to determine postulated break locations. All arbitrary break locations exhibit stresses less than 80% of the code allowables. If the ntsrber of thermal cycles is expected to be greater than 7,000, then the allowable stresses are further reduced by an amourt dependent on the ntsrter of cycles.

II. THERMAL TRANSIENT FATIGUE DESIGN CONSIDERATIONS (CLASS 2)

The thermal transients identified for the main steam Nuclear Class 1 piping inside contairment are based on temperature fluctuations of the steam at the reactor pressure vessel. These thermal transients are relatively small and will diminish further in severity during the steam flow to outside contairment and would result in negligible fatigue effects for the main steam, HPCI and RCIC outside containment piping.

The RWCU return piping (outside contairment) does not experlerue thermal transients; the flow is from the cleanup treatment.

Thus, for those Class 2 piping systems for which arbitrary intermediate breaks are proposed to be eliminated, no severe i thermal transients are anticipated.

III. VIBRATION DESIGN CONSIDERATION Piping in Limerick Unit 2 is designed and supported to minimize transient and steady state vibration. Although the piping system vibration tests have not yet been defined, testing will be performed as dtscribed in Section 3.9.2 of the FSAR to ensure that vibration of the piping systems is within allowable levels.

Pipe vibration test acceptance will be based on an allowable 6

stress of less than 0.62 times the design fatigue stress for 10 cycles of vibration. This allowable is less than the pipe material endurance Ilmit, assuring that steady state vibration j will not contribute to the fatigue usage factor during the life of the plant.

IV. PREOPERATIONAL/ POWER ASCENSION TESTitE l

The piping systems in which arbitrary Intermediate breaks are

proposed to be eliminated are all addressed in the properation/ power ascension testing program, i

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a i Attachnent E PROVISIONS FOR MINIMlZING STEAM / WATER HNiiER EFFECTS l

A conprc.hensive, system transient evaluation program has been conducted for Limerick Unit 2. The objective of this program was to qualitatively evaluate various systems for susceptibility to fluid transients - especially those which could lead to water or steam-hamner events, to develop operating cautions to preclude such transients, and to initiate system analyses and/or modifications if deemed necessary.

For each systen evaluated, the system funct.lons and modes of operation, including interfaces with other systems, were reviewed. In defining the operating characteristics of each system, the following kinds of documents typically were consulted: the FSAR, design specifications and data sheets, operations and maintenance instruction manuals, ftsictional control diagrams, process diagrams, piping and inst.runentation drawings, system flow and pressure drop calculations, ccrnponent (ptrip, turbine, etc.) manuals, valve data sheets and -

drawings, piping design specificat.lons, piping Isometric drawings, stress calculations, etc.

The Limerick Unit 2 system transient evaluation also encartpassed a review of operating plant water / steam hanTner experiences related to each system gleaned from NUREGs/CR-2059, /CR-2781, -0927 and -0582::,

information on system performance at Bechtel-designed plants (e.g.

I Peach Bottom, Hatch, MontIcello, Duane Arnold and Susquehanna), GE Service Information Letters, plus results frcm preoperational testing at Limerick Unit 1, when available.

o NUREG/CR-2059, EGG-CAAD-5629, "Compliation of Data Concerning Known and Suspected Water Hanmer Events in Nuclear Power Plants,"

liny 1982.

o N WEG/CR-2781, QUAD-1-82-018, EGG-2203, " Evaluation of Water HaTmer Events in Light Water Reactor Plants," July 1987.

o NUREG-0927 (For Coninents), " Evaluation of Water Hanmer Experience in Nuclear Power Plant," May 1983.

o NUREG-0927, Rev. 1, " Evaluation of Water Hanmer Occurrence in Nuclear Power Plants - Technical Findings Relevant to Unresolved Safety Issue A-1," March 198t+.

NUREG-0582, " Water Hanmer in Nuclear Pc.wer Plants," July 1979.

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Generally, the following kinds of transients were considered for each system evaluated; normal operational transients of pmp start and stop, rapid valve opening or closing, relief valve actuation, plus other anticipated transf ents such as stuck open or shut check valves, condensate formatico; and pwp restart folicwing trip. Through this revlea process the adequacy of the design of the piping and supports was vert fled.

Design provisions to minimize the potential for steam / water hanmer events have been made. They consist of systems which ruintain water solid piping in order to Ilmit water hanmer and slope and drainage provisions in steam lines in order to prevent steam hanmer. The condensate transfer system normally provides a continuous supply of water to the RHR, CS, HPCI, RCIC, and Feedwater Systems. Should the condensate transfer system fall the safeguard piping fill system, which is a safety grade system, is available to provide this continuous water supply. The HPCI arsd RCIC steam lines are sloped to direct ccndensate to drain pots on these lines. These steam lines up to the turbine isolation valves are also preheated by main steam to reduce ccodensate formation and piping thermal stresses.

As discussed in FSAR section 3.9, for the piping systems in which arbitrary intermediate breaks are proposed to be deleted, transients are considered to the extent practical in the design and preoperational/

power ascension testing program.

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