ML20210C453

Requests Exemption,Per 10CFR50.12(a),from GDC 4 to Apply leak-before-break Concept to Eliminate Postulated Pipe Breaks in RCS Primary Loop from Plant Structural Design Basis.Fee Paid

ML20210C453
Person / Time
Site:	Washington Public Power Supply System
Issue date:	01/30/1987
From:	Sorensen G WASHINGTON PUBLIC POWER SUPPLY SYSTEM
To:	Stolz J Office of Nuclear Reactor Regulation
References
GO1-87-0010, GO1-87-10, NUDOCS 8702090392
Download: ML20210C453 (19)

Text

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WASHINGTON PUBLIC POWER SUPPLY SYSTEM P.O. Box 968

• 3000 George Washington Way

• Richland, Washington 99352 January 30, 1987 Responds to: N/A G01-87-0010 Response Requested: Yes Docket No. 50-460 Director of Nuclear Reactor Regulation Attention: John G. Stolz, Director PWR Project Directorate No. 6 Division of PWR Licensing-B U. S. Nuclear Regulatory Commission Washington, D. C. 20555

Subject:

NUCLEAR PROJECT N0. 1 ELIMINATION OF POSTULATED PIPE BREAKS IN PRIMARY MAIN LOOPS - AN EXEMPTION FROM GENERAL DESIGN CRITERION 4

Reference:

NRC letter from D. M. Crutchfield to L. C. Oakes, dated December 12,1985, " Safety Evaluation of B&W Owners Group Reports Dealing with Elimination of Postulated Pipe Breaks in PWR Primary Main Loops" (GIl-85-0207)

The Supply System hereby requests an exemption, pursuant to 10CFR50.12(a), from General Design Criteria 4 to apply the " Leak-Before-Break" concept to WNP-1 to eliminate postulated pipe breaks in the RCS primary loop from the plant structural design basis.

The Supply System, as a member of the B&W Owners Group, submitted BAW-1847, Revision 1 " Leak-Before-Break Evaluations of Margins Against Full Break for RCS Primary Piping of B&W Designed NSS", and BAW-1889P " Piping Material Properties for Leak-Before-Break Analysis." These B&W generic reports conclude that large breaks will not occur, and that postulated flaws producing detectable leakage exhibit stable growth, thus allow a controlled plant shutdown before any potential exists for catastrophic piping failure. A favorable ruling was made by the Commission (see reference) in the subsequent Safety Evaluation Report of these B&W reports. The reference evaluation concludes that an acceptable basis has been provided to eliminate, as a design basis, the dynamic effects of large rupture in the main loop primary piping of the B&W Owners Group facilities .

(including WNP-1).

B702090392 870130 PDR ADOCK 05000460 A PDR

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Docket 50-460

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. As indicated in Generic Letter 84-04, the staff has accepted the utilization of the " Leak-Before-Break" concept on certain dockets as a means of. obviating- the need to install certain piping / equipment support systems. The attached Exemption Request utilizes such methodology to support the exclusion of dynamic . loss of coolant accident (LOCA) loads from the RCS piping, which will allow the elimination of pipe whip restraints and jet shields, and allow a reduction in the number of hydraulic snubbers restraining the RCS. Attachment 'A' summarizes this Exemption Request. Attachment 'B' summarizes the WNP-1 plant design parameters-which are under the B&W Owners Group umbrella. A safety balance in terms of accidental risk avoidance attributable to protection from dynamic effects of pipe' rupture versus safety gain resulting from a decision not to use such. protection is provided in Attachment 'C'. Note that the estimated cost and safety improvement for the life of the plant are:

Pipe Whip Restraint / Jet Shield Cost Saving: $3.2 Million Reduction in Radiation Exposure: 460 man-rem RCS Hydraulic Snubbers Cost Saving: $1.624 Million Reduction in Radiation Exposure: 218 man-rem The reactor coolant pressure boundary leakage detection system at WNP-1 is designed to conform with the requirements of Regulatory Guide 1.45 and is discussed in detail in Subsection 5.2.5 of the WNP-1 FSAR.

A summary of the potential benefits which can be realized specifically from the elimination of these pipe breaks for WNP-1 is provided in Attachment 'D'.

Implementation of the " Leak-Before-Break" concept will therefore be cost effective as well as being technically justifiable. The plant piping, equipment, and structures will become more accessible and inspectable, thereby reducing occupational radiation exposures, costs, and the likelihood of undetected defects. The ultimate objective is to reduce the cost of construction and maintenance, reduce radiation exposure, improve thermal flexibility, reduce outage time, and increase plant safety and reliability.

Your prompt and favorable action on this request will be appreciated. Once the request is approved for application, the applicable criteria will be incorporated into a future FSAR revision.

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Attachments': -A. -

RCS Loop Pipe Break Design Basis Exemption. . ,

-B. WNP-1 Plant Design Parameter used-in Leak-Before-Break '

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Sumary of Benefits from the Elimination bf Primary Loop Pipe-

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Attachment A Sepply System WNP-1 BCS Imop Pipe Break Design Basis Exception Esametion Esemest Persesat to 10 CFE 30.12(a), Supply System hereby applies f or an esemption l from the provisions to 10 CFR Port 50, Appendix A, authorizing alternative pipe break malyses stilised in the structural design of the WNP-1. The requested mesprios is based apos the application of advanced fracture mechanics technology as evaluated in the Babcock & Wilcom Topical Report )

BAN-1847 Rev. 1.

Specifically, Sepply Systes requests the af f=f antion of postulated circum-fer ecial sad longitudinal pipe breaks in the reactor coolant systes primary loop from esasideration in the structural design basis of WWF Unit 1. The  ;

impact es important aspects of implesanting leak-before-break on WNP Unit I has been evalented sad is saamarized in Attachment D. A sa mary list of aff ected pipe ship restraints, jet shields, and saubbers is provided in Attachment D.

The bases for the requested eseaption are se follous:

1. Estasive operacias esperimes has desastrated the integritt of the RCS primary loop including the fact that there has never .been a leakage crack.

, 2. In-shop, pre-service, and in-earvice inspections performed on piping f or ,

! the WMP-1 =4=4=ise the possibility of flaws existing in such piping. The application of advanced fracture mechanics has demonstrated that if such flaws mist, they will not grow to a leakage crack when subjected to the ,

worst case loading conditica over the lif e of the plant. t

3. If one postulates a through-wall crack, large margins against anstable crack estension esist f or FUR primary coolant piping when subjected to the worst case twi=! conditicas over the lif a of the plant.

4. The NEC sponsored research as probabilistic fracture mechanics studies was conducted by Lawrence Livermore National Laboratories (LLNL). These studies (Esf erence A1) confirm that both the probability of leakage (e.g. ,

undetected flaw growth through pipe wall by fatigue) sad probability of Double Ended Gaillotine Break (DEGE) are very. low for B&W plants. And those are n=4a=11y identical to those calculated for the Westinghouse and l Combustion Engineering studies. The results given in Raf erence A2 are thatthebest-escinateleakprobabilitiesforWestinghousesplearsteam -

system (NSS) asin loop piping range from 1.2x10 -8 g, g,3gio e plant yearg the best-estimate DEGB probabilities range from 1x10 to 7x10 per plant year. Sia11arif, the best-estianca leak probg111cias f or _Cpbustica Engineering NSS main loop piping range from 1x10 to 3s10,gper pisat_pr, and the best-estimate DEGB probabilities range from 5x10 to 5x10 per plant year. These results do not aff act core seit probabilities in any significant usy.

Page A-L

5. ' The Esf erence A3 study of probability of indirect Double-Ended Guillotine Break (DgGB) in RCS piping as a consequence of ==fa-ic-induced structural failures for Babcock & Wilcos supplied PWR shows that the o g probe ,7  ;

bility of indirect DgGB uns estianced to range between 6s10 and 1x10 j per year. These results do not aff ect core melt probabilities in any l significant my.

The application of advanced fracture mechanics technology has demonstrated that small flaws or leakage cracks (postulated or real) will reasin stable and will be detected either by ia-service inspection or by leakage soaitoring systems laag before such flaws can grow to critical sizes which otherwise .

could lead to large break areas such as the double-ended rupture of the largest pipe of the Besctor Coelaat Systaa. To date, use of this advanced fractue ==ah==f as technology has best limited by the definition of a IDCA in Appendix A to 10CFE Part 50 as including postulated double-ended ruptures of piging, regardless of the associated probability. Application of the IACA definitica without regard to this adv meed technology to large diameter thick-walled piping, such as the primary aaalaat pipes of a F91, imposes a severe penalty in tarus of cost and occupational esposure because of the anssive pipe ship restraints, jet shields, and supports it requires which must be removed for in-service inspection. This penalty is areasonable because ,

these pipec do not have a' history of failing or cracking and are i aa=== natively designed. Accordingly, for design purposes associated with .

protection against d7mmic eff ects, Supply System requests this esemption from the regulations to eliminate the need to postulate cirenaf erential and longitudinal pipe breaks.

Implementation of the exemption will have the following eff ects on the structural design for WWF Dait 1

1. Eliminate the need to postulate circeferential and longitudinal pipe breaks in the BCS primary loop (hot leg and cold les piping).

l 2. Eliminate the need for associated pipe ship restraints and jet shields in l the RCS primary loop and eliminate the requirement to design f or the structural effects associated with RCS primary loop pipe breaks including jet impingement.

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3. Banovel or eliminatica of snubbers or support devices especially installed to resist combined earthquake and 1.0CA loads or specific load cases such as asyanscric bloudous or jet impingement. -

4. Eliminate ther need to. consider dynamic effects and loading conditions associa'ted with previously postulated primary loop pipe breaks. These aff acts include bloudoue loads, jet imping ment loads, reactor cavity and subcompartment pressurization, and pipe rupture generated missiles (insulation, support, etc.).

The amenption would not eliminate pipe breaks in the RCS primary loop as a design basis f or the f allowing:

1. Containment design l 2. Sizing of Energency Core Cooling System 3.. Tavironmental qualification of equipment Page A-2 1

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As stated above, Supply Systes requests that the esemption authorize, with l respect to the planc structural design basis, the eliminacion of pipe breaks  !

in the ECS primary loop. The use of advanced fraccure mechanics permits a deterministic evaluacios of the stability of poeculated flaws / leakage cracks in piping as sa alternative to the currenc mandace of overly conservative poeculacions of piping ruptures. The requesced exemption is, thus, consistent with the provisions of foocuoca 1 to 10 C71 Part 50, Appendix A, which refers to che development of "further decails relating to t.he type, size and  ;

oriescation of poeculated breaks in specific componenes of the reactor coolanc pressure boundary."

Esferences:

A1. NBC letter from D.M. Crucchfield to L.C. Oakes " Safety Evaluacion of B&W Owners Group Reports Dealing with Elimination of Poeculated Pipe Breaks in PUE Primary Main Loope" deced December 12, 1985.

12. T. Lo, R.E. Woo, G.S. Holman and C.E. Chou, "Tailure Probabilities o'f PWE Emaccoe Coolanc Loop Piping" ASME PYP Conference; June 17-21, 1984, l

San Antonic, Teams.

A3. M.E. Ravindra,1.D. Campbell, T.E. Eipp and 1.U. Suas ; " Probability of Pipe Failure in the Reactor Coolant Loops of Babcock is Wilcox PWE Plants" NUREC/CE-4290 volume 2; July 1985.

Rev. 01 Page A-3

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Attachment 3 Plant Design Parameters - Laak Bef ore Break Evaluation Supply System WNP-L Supply Syacue, as a manber of the MW Owner's Group submitted BAN-1847, Bevisiain 1, " Leak Bef ore Break Evaluation of Margins Against Fun Break f or ECS Piping of MS Designed MSS," and "3AE-1889P " Piping Material Properties for. Lank-Before-Break Analysis." These reports provide the technical basis for deter =4=4== that a double-ended guinotine break will not occur and that flaws big enough to produce a detectable leakage rate are stable. This i

stability allows for controned plant shntdown before any potential exists for a catastrophic piping failure.

5AN-1847 demonstrates that:

a. A sabetantial sized flaw in the piping would not grow through the wall nor estead significantly in , length during the plant design lif etime.

b. Even if a flaw were to grow through the umil cf the piping, it would open sufficiently to leak many times the mini == detectable leakage race before attending to anywhere oest the . critical crack length.

c. A very'long thre g. J crack (many times longer than the longitudinal or circimiferential crack length that produces a detectable leakage rate) would remain stable under normal operation plus saf a shutdotat earthquake (SSI) loadings.

l These conclusions provide sufficient justification for al t=ination of large postulated breaks from the design basis for the RCS asin loop piping. The approach fallows a defense-in-depth philosophy by showing substantial margin in each of the analytical steps. The evaluation included structural and fracture mechanics analyses using generic bounding data, loads and material properties, for an MW Ouner's Group (MWOG) plants. Supply System as a member of this Cuner's Group is bounded by the conclusion of the B&W evaluation for its WWP Gait 1 plant. The fonowing is a summary of WNP-1 plant parameters, which are enveloped by the B& WOC evaluation.

i 3.1 Design and Operating Conditions The WNP-L is a MW two-loop designed 205 Fuel-Assembly pressurized water l

reactor plant. A general arrangement of the Nuclear Steam System is shown in Figure 5-1.

Internal Pressure 2150 poi used for leak calculations 2250 poi used f or stress and fracture nachanics calculations Systen Temperature 600*y l

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B.2 ECS Primary Piping Sizes Hot Leg 38" Inside Diameter 38.5" Inside Diamecer Unclad 3.125" Wall Thickness Straight Pipe 4.1875" Wall Mickness Elba -Curved Pipe Upper Cold Lag 28" Inside Diameter 28.5" Inside Diameter Unclad 2.375" Well M ickness Straight Pipe 3.125" Wall nickness Elbe-Curved Pipe La er Cold Ng 32" Inside Dismeter 32.5" Inside Diameter Unelad 2.6475" Wall Mickness Straight Pipe 3.625" Wall nickaces Elba-Curved Pipe 5.3 RCS Primary Piping Material Straight Piping Section SA 106 Grade C Elba curved Piping Section SA 516 Grade 70 Safe Ends SA 336 CL-F8 8.4 BCS Primary Pipe Weld Piller Material Me shop and field weld locations are cha n in Figures ~ B-2 to B-4.

Shop Weld: HiMnMo NicrPe E308 E309 E7015 E7018 Pield Weld: E308 E309 E7018 E705-3 (3eunded by ascerials used in B&WOG analysis) 5.5 RCS Primary Piping and Weld Material Properties Me asterial properties in terms of stress-strain, che asterial resistance to fracture (J-E Curve), and J versus cearing modulus (J-T Curve) for the piping base and weld filler material is provided in B&W reports BAW-1847 Revision I and BAW-1889P.

3.6 BCS Primary Piping Structural Loads Me primary piping scacic loads (dead w eight and charmal) and loads

' associated with safe shuedan earthquake (SSE) condicion are cabulated in Table 3-1.

Rev. 01 Page 3-2

B.7 BCS Laskage Detection Systen N resctor coolant pressure boundary leakage detection system is designed to confora with the requirements of Regulatory Guide 1.45 and is discussed in detail in Section 5.2.5 of WEP-L FSAL h leak detection system is capable to detect a leak rate of one gallos per atauce in an hour. h containment suay level sensors and the cour=4=-t airborne radioparticulate and noble gas monitoring systems are qualified Seismic Category I, and will remain functional through the saf a shutdown earthquake.

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Table B-1 l -

1 BCS Primary Pipina Loads for Leak-Before Break Evaluatloa Supply System UNF-1 ,

j Dead Weight Thermal and Safe Shutdown Earthquake 14 ads i

Piping B&W Owners WNP-1 B&W Owners WWP-1 B&W Owners WHe-1

] Haminum Maximum Minimum Minimun g Hasimum g) Maximus j Homente Homenta Homenta Homente Asia 1 Asia 1 j

Force Force l Ft. Kips Ft. Kips Pt. Kips Ft.Eipe Kips Kips i

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Stra18 ht 7253 6787 2407 3154 247 817 Curved 3882 3662 916 1018 i

692 603

! Louer Cold Leg (32" ID) l Straisht 2260 2080 1159 1122 475 315 l Curved 2080 2080 1122 1122

• 315 315 i

1 l Upper Cold Leg (28" ID) i Straight 3098 1591 560 914 250 303

! Curved 2823 1591 1246 . 914 1

539 30 3 Notes:

l. The minimum moments are, reported 'at the highest stress location.

) The minimum moments at other locations results in a leak rate of at least 10 gym.

2. The Homent equivalent = ( Applied Homent + 0.5 x Pipe Mean Radius x Geometry Factor x Axial Force) used in the i

tearing stability snalysis. Even though WNP-l axial force is higher than R&WOG, the Homent equivalent is louer.

The axial force in this equation includes the mechanical force as well as the force due to pressure.

The axial force reported above is only due to mechanical loadings.

3. Tabulated maximum forces and moments are due to dead weight, thermal and SSg loading conditions. The minimum moments are due to dead weight and thermal loading conditions.

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4 FIGURE 8-1 '

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Page 8-8

Acc.,h- eC Safety ==1=.re r14=f== tion of Primary Loop Pipe Breaks on WNF-1 Pursusat to 10CFR50.12(a), Supply System believes the requested exemption will not endanger life or property, or the cosmos defense and security, and is in the public interest. The evaluation is performed in terms of public health and occupational accidental risk avoidance attributed to the protection provided for dynamic effects associated with postulated breaks in the RCS primary loop versus the re. duction in Occupational Radiation Exposure (ORE) resulting from a decision not to use such protection. The estimated increase in public accident exposure associated with omitting RCS primary loop pipe whip eq traints, jet shields, and reduction in hydraulic snubbers is only 3.4210 .co 0.38 asa-res for WEF-l. The value-impact assessment for WWF-1 is based on data from B&W Operating Plants Florida Power--Crystal River Unit 3, and Sacramento Numicipal Utility District--Rancho Seco; and work performed by Lawrence Livermore National Laboratory (LLNL) Reference C1. The data for double ended guillotine break used wr.s from LL3L work (Esference C1), the core melt frequency and dose estimates from WASE-1400 and cleanup and decommissioning estimates from NUREG/C1-2800. The safety balance assessment was performed in accordance with guidance provided in NRC Generic Letter 84-04.

The not benefit in avoidance of exposures for WNP Unit I associated with requested exemption is (best estimates) 678 man-rea of occupational exposure over plant life, based on Sapply System studies. This eliminated radiation exposure is related to pipe whip restraint, jet shield and hydraulic snubber inservice inspection, testing, pipe veld inspection, improved personnel access for operation and maintenance. Consequently, the savings ir. exposure by granting the exemption far exceed the potentially small increase in public risk and avoided accident exposure associated with omitting these devices.

Supply System (best) estimates the net cost savings for WNP Unit 1 of $4.824 aillion, as presented in Table C-1. This not benefit does not take benefit of i che cost of coolacement power, which will be needed due to stretchout of plant startup required due to inspection.

Additionally, with removal of pipe whip restraints, jet shields and snubbers, a substantial improvement in the quality of inservice inspection is anticipated. Also, simplified plant designs will result since removal of thase devices will eliminate potential interferences with other plant structures. Reduced ICS heat loss to containment at pipe whip restraint location will result. The risk of ananticipated pipe contact with restraint and jet shield for thermal growth and seismic movement can be avoided. Also, risk of unanticipated locking for hydraulic snubber, and not locking during seismic can be avoided. Thus, the exemption will lead to an overall improvement in plant safety.

With these operational benefits and with a net reduction of radiation exposure of 678 aan-rem, a not safety gain has been demonstrated for WNP Unit 1. Also, ,

a cost saving'of $4.824 million has been shown, and a technical basis for )

elimination of RCS primary loop pipe breaks has been demonstrated. Therefore,  ;

Supply Systes hereby requests NRC approval of an exemption to GDC-4 in order to apply the " leak-before-break" concept to WNP Unic 1 to eliminate postulated l pipe breaks in the RCS primary loop from the plant structural design basis. j 1

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Eaf eremees:

C1 G.S. Bolman and C.K. Chou " Assessment of ValeImpact kesociated with the ritM=mtion of Poeculated Pipe Euptures from the Design Basis for Nuclear Power Pismes" Lawrence Livermore National Laboratory Emport UCID-20397, March 1985.

C2 hdrews, W.3., et al, "Guidettama for Nuclear Power Plant Saf ety Issues Prioritisation Infornation Developeanc" NDREG/C3-2800 (1983).

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Table C-1 l l

Value Impact Samary--Reactor Coolant Piping Supply System WNF-L I

Best Estimate High Estimate Low Estimate l Talues (ann-rea) ,

j Public Health ~4 E-6 -0.244 0 Occupation Esposure (accidental) -3 E-5 -0.136 0 l Occupation Exposure (Ecutina) '

Fipe Whip Restraint / Jet Shield 460 1,578 66 BCS Snubbers 218 435 196 Yalue Total 678 2,013 262 M ($)

Issplementation and Operating Coat Pipe Whip Eastraint/ Jet Shield -3,200K -4,800K -2,880K ECS Snubber -1,624K -3,248K -1,462K Pouer Ee?!E ---- t Coat Benedit not taken in this evahacion offsite Property 1 9K 0 onsite Property 1 2K 0 Impact Total -4,824K -8,037K -4,342K 9

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Atemehment D Samanry of Benefits from the Eininacios of Primary Loop Pipe Breaks on WNP Unic 1 Catesory Benefits l

1. Pisme Design

• e Simplifies plant design by =14=4== tion of potential interf erences with piping, hangers, impulse cubing, etc. ,

e Optimized compartment ventilation.

2. Ealief of congestion 678 asa-res reduction in radiation improving access for esposure over lifa of plant ($4.824 operation, maintenance,. =ttifos cost savings).

and inservice inspection.

3. Reduction in ECS heat loss Not quantitatively assessed.

to containment at uttip Insulation can be installed on piping at i restraint location. current locations of RCS pipe whip restraints.

4. Improvemmat in overall - . Improvement in ISI quality. Elf =fantion plant safety of potential for restricted thermal or (EUEEG/CR-2136) seismic movement.

5. Simplification of analysis Pressurization loadings reduced on associated with dynamic primary shield wall, erane wall, effacts and loading operating floor, and subcompartment conditicas. analysis.

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Table D-1 Summary of Harduare Aff acted by Elimination of Primary Loop Pipe Breaks Supply Systen WWF-1 Compensat/Fiping Syscan Total To Se Removed A. Enactor Coolant Loop r a) Fipe Whip Restraints Hot Legs 8 8 Upper Cold Legs '4 4 Lower Cold Lage 4 4 b) Jet Impingement Barriers ht hy 2 2 Upper Cold Less 8 8 tower Cold fags 4 4

3. Steam Generator Rydraulic Soubbers 8 Min f == 4 l

Maximum 8 C. RC Pump and Motor Hydraulic Saubbers 8 Min 1 == 4 Maximum 8 l Page,D-2 l

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