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D I S C L AI M E RT h i s r e p o r t w as p r e p ar e d a s a n a c c o u n t o f w o r k s p o n s o r e d b y an a g e n c y o f t h e U n i t e d S t a t e sG o ve r n m e n t . N e i t h e r t h e U n i t e d S t a t e s G o v e r n m e n t n o r an y ag e n c y t he r e o f , n o r a n y o f t h e i re m p l o y e e s , m a ke s a n y w ar r a n t y, e x p r e s s o r i m p l i e d , o r a s s u m e s a n y l e g a l l ia b i l it y o r r e s p o n s i -b i l i t y f o r t h e a c c u r a c y , c o m p l e t e n e s s , o r u s e f u l n e s s o f a n y i n f o r m a ti o n , a p p a r a tu s , p r o d u c t , o rp r o c e s s d i s c l o s e d , o r r e p r e s e n t s t h a t i t s u s e w o u l d n o t i n f r i n g e p r i v a t e l y o w n e d r i g h t s . R e f e r -e n c e h e r e i n t o a n y s p e c i f i c c o m m e r c i a l p r o d u c t , p r o c e s s , o r s e r v ic e b y t r a d e n a m e , t r ad e m a r k,m a n u f a c t u r e r , o r o t h e r w i s e d o e s n o t n e c e s s a r i l y c o n s t i t u t e o r i m p l y i t s e n d o r s e m e n t , r e c o m -m e n d a t i o n , o r f a vo r i n g b y t h e U n i t e d S t a t e s G o v e r n m e n t o r a n y a ge n c y t h e r e o f . T h e v i e w sa n d o p i n i o n s o f a u t h o r s e x p r e s s e d h e r e i n d o n o t n e c e s s a r i l y s t a t e o r r e f l e c t t h o s e o f t h eU n i t e d S t a t e s G o ve r n m e n t o r a n y ag e n c y t h e r e o f .

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PHYSICAL BENCHMARKSAs a logical extension of the analytical benchmarking effort; the deve lop-

ment of physical benchmarks was undert aken. The physical benchmark evalua-tions are used to assess the accuracy and adequacy of the analysis methods andassumptions used in typical piping qualification evaluations In each evalua-tion linear elastic finite element methods ar e used to predict the time his -tory response of a system for which physical test results are availab le. Inthe analytical simu lation the measured excitations of each support point andthe measured damping proper ties ar e used a s input and the acceleration anddisplacement response of piping interior points are predicted as output. Eachevaluation is performed blind in that only the measure d inputs are provided atthe time of analys is. At completio n, the measured response data are mad eavailable and by comparison the accuracy of the predicted results are assessed.

To date physical benchmark evaluations have been completed and reportedfor fou;t piping sy ste ms. Table 1 provid es a description of each of thesewit h a Siinimary of key re su lt s. Figure 1 shows th e extended Z bend c onfi gura -tion, the last evaluation complete d. Figure 2 shows the results for theacceleration of node 21 for this mo del . This figure is typical of the di s-placement and acceleration results developed in each evaluation.

Two more physical benchmark evaluations are scheduled. Both involvelaboratory tests of piping performed under joint NRC-EPRI sponsorship andconducted by ANCO Engineers Inc. The piping in each of these tests is 6 inSCH 40 pipe supported from and excited by four hydraulic actuato rs. The firstconfiguration consist so a mult i bend span between two anch ors. The secondconsists of the first configuration expanded with two branch lines. A rep ort -ing of the results of these benchm arks should be available in 1984.

MULTIPLY SUPPORTED PIPING WITH INDEPENDENT SEISMIC INPUTSNuclear power plant piping must have the capacity to withstand the dyn a-

mic loads associated wit h postulated seismic eve nts . Seismic adequacy is mos tcommonly demonstrated by analysis wi th time history or uniform support motion(URS) methods being currently acceptable evaluation procedures. If the re -sponse spectrum method is used, a separate calculation must be performed toaccount for the loads induced by relative support point or anchor pointmotions. In this case the total piping response is the combination of thedynamic component estimate d by the spectrum method and the seismic anchormovement ( SAM) comp onen t. The Standard Review Plan (SRP, reference 1) pro -vides specific guideline s and requirements for the computation of the dynamic,SAM and total componen ts of res ponse .

For piping sys tems subjected to multip le independent support motion s thepresent SRP requirements pr ovide a great margi n of safety and lead to pipingdesigns which are inherently s tiff . The high stiffness of these systems com -promise there capacity to absorb th e thermal expansions associated with nor -mal operating conditi ons. In this study alternate procedures to computethe dynamic , SAM and total compon ents of respo nse , based on independentsupport motion (TSM) aIgoritInns,were investigated. The information

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developed supports and provides some basis for a potential relaxation of theSRP requirements.To predict the dynamic component of response a resp onse spectrum method

whic h allows the use of independent spectra sets for each support or group ofsupports was evaluated. In this method a response parameter is predicted asa function of each support group for each mode and each direction of excita-tion. To obtain the total dynamic response a combination over group s, modesand directions must be performed. In this evaluation the square root of thesum of the squares (SRSS) combination over directions and SRSS combinationwith clustering for closely spaced modes were accepted for the combinationover directions and mo des . For the combination over groups algebraic(methods 1 and 2 ) , SRSS (methods 3-8) and absolute (methods 9-14) combinationwer e considered. Further all sequences of performing these combinations wereconsidered. In all fourteen different combination strategies, metho ds 1-14were evaluated for the computation of the dynamic component of response.

To predict the SAM component of response five procedures were evaluated.Four of these were based on the use of absolute p eak support displacementdata . These methods differed in the manner in which the supports were groupedto account for the unknown phasing between supports. The grouping assumptionsconsidered were random phasing (method 2 ) , grouping by global direction (meth-od 3 ) , grouping b y attachment point (method 4) and grouping by elevation(method 5 ) . Within each group support effects wer e summed algebraically.Between groups both SRSS and absolu te summation were considered. The rema in-ing method evaluated (method 1) was based on sampling the support point di s-placement time history record s. Since in this method support point phasinginformation is retained, no grouping assumptio ns were ma de .

To compute the total component of respon se, both SRSS and absolute co m-bination between the dynamic and SAM components wer e considered. The responseparameters computed included pipe displaceme nts, accelerations, support forcesand resultant mome nts . At each stage the predicted response estimates werecompared to response estimates developed using ISM time history methods whichwere assumed to represent the true respo nse. The relative approach of eachpredicted value to th e time history result was expressed as a degree ofexceedance given by Predicted-TH/TH (TH = timehistory ) . Table 2 shows aflow chart depicting the study effort .

The evaluations were performed for five different piping-structure p rob -lems. The salient charact eristic s for each problem ar e summarized in Table 3.To provide a statistical basis to the study the evaluations for two of theprobl ems, the AFW model and the RHR mode l, were performed for thirty-threedifferent seismic events. For these the time history results were providedby an alternate NRC contractor.

All of the computations were performed using the BNL computer cod ePSAFE2,reference 2. This code is a general purpose, linear elastic, finiteelement piping analysis code which was independently developed for the bench-marking purpose . Analysis options include the independent support motiontime history and response spectrum met hods .

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All study results are summarized in tabular form. Each table lists thetime history estimate a s well a s the response estimate for each calculationaloption and parameter st udied. For the two prob lems involving thirty-threeseismic events the pertinent results are summarized in figure form. Figures3 and 4 show these results for resultant momen ts in the RHR problem. Figure3 corresponds to th e dynamic component while Figure A corresponds to the SA Mcomponent. Each figure shows the mean (data point) and + one standarddeviation (line extent) for the parameter over the thirty-three seismicevents. The figures show the results only for those elements which establishthe lower bound of the degree of exceedance (define the minimum level of con -servatism) .

All computations in this effort have been completed. The results areunder review and appear to provide some basis for a relaxation of current de -sign requirements.

REFERENCES1. U.S. Nuclear Regulatory Commissio n, Dynamic Testing and Analysis of

Systems,Components and Equipment , Standard Review Pl an, NUREG-0800,Section 3 .9.2.

Subudhi, M. and Bezler, P., PSAFE2-Piping Analysis Program-User's ManualVersion 1981 , Informal Report, July 1981.

T h i s w o r k w a s p e r f o r m e d u n d e r t h e a u s p i c e s of t h e U . S . N u c l e a r R e g u l a t o r yC o m m i s s i o n W a s h i n g t o n DC 2 0 5 5 5 .

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T a b l e 1P h y s i c a l B e n c h m a r k E v a l u a t i o n s

Sys m S y s t e m De s c r i p t ion I n p u t E x c i t a t i o n Com m e n t s a n d R e s u l t s

Z Bend Pla nar configur ati on of Apipe supported from ande x c i t e d b y t h r e e h y d r a u l i ca c t u a tor s

L a bor a tor y t e s t e d w i t hi n d e p e n d e n t s e i s m i c e x -c i t a t ion s of e a c h a c t u a -t or

R e s u l t s good e x c e p t i nv i c i n i t y of c e n t r a l a c t u a tor .P oor r e s u l t s h e r e a t t r i b u t e dto e x i s t e n c e of a c l e a r a n c eg a p a t c e n t r a l a c t u a t o r

I n d i a n Poi n tR i g i d S t r u tConfi g u r a t ion

Segment of boiler feed sys-tem of shu tdown I ndian P t.U n i t 1 pow e r p l a n t . 8 i n ,8 c h 8 0 p i p e a p p rox . 1 0 0 ft .lon g s u p por t e d w i t h r i g i ds t r u t s

I n s i t u , s n a p b a ck t e s t R e s u l t s poor . Cor r e l a t ionfa i r for m a x i m u m r e s p on s e s ,poor e v e r y w h e r e e l s e . Poorr e s u l t s a t t r i b u t e d t o t h e a p -p rox i m a t i on s u s e d to mod e ls u p poi t s

HDR-UR L Rec irc ula tic n loop of shut-P i p i n g d o w n H e i s s d a m p f r e a c t o r .

4 5 0 a n d 3 5 0 m m p i p i n g w i t htwo pumps and four va lves

I n s i t u e x p los i v e , 5 K gb l a s t i n n e a r f i e l d

R e s u l t s p oor w i t h u n d e r p r e -d i c t ion s of p e a k r e s p on s e s .Poor r e s u l t s a t t r i b u t e d tot h e u s e of l i n e a r a n a l y s i sm e t hod s to mod e l a s y s t e m w i t hs t ron g l y non l i n e a r s u p por te l e m e n t s

E x t e n d e d Z B e n d confi g u r a t ionZ B e n d r e d e s i g n e d to e l i m i n a t e

a l l c l e a r a n c e g a p sL a bor a tor y t e s t e d w i t hi n d e p e n d e n t s e i s m i cexc ita tions of eacha c t u a tor

R e s u l t s f a i r . E s t i m a t e s ofd i s p l a c e m e n t s g ood . E s t i m a t e sof a c c e l e r a t ion s r a n g e d fromgood to poor.

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Table 2. Multiply-Supported Piping System Research Program

Building Structure(s) Responses

Seismic Design Research Programfor Piping Analysis Methods

IndependentResponse SpectrumAnalysis forInertia ResponsesIompare Results DevelopCombinationProcedures

Independent Time HistoryAnalysis of PipingSystemI

Pseudo-StaticResponsesInertiaResponses

Total * Responses

Compare ResultsDevelope CombinationMethod

Combi ne ToForm TotalResponses

Seismic AnchorMovement Anal-sis for Pseudo-Static ResponsesICompare Results Develop SAMMethods

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