ML20112C632

Forwards Revised Damping Values for Piping Analysis.Rept Details Recent & Extensive Body of Test Data Which Identifies Significant Conservatism in Current Design Basis. Review Requested

ML20112C632
Person / Time
Site:	Vogtle
Issue date:	01/04/1985
From:	Foster D GEORGIA POWER CO.
To:	Adensam E Office of Nuclear Reactor Regulation
References
GN-503, NUDOCS 8501110293
Download: ML20112C632 (9)

Text

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, Georoa Power Company Route 2, Box 299A Waynesboro, Georg a 30830 Telephone 404 554 9961, Est 3360 404 724 8114. Ext 3360 D. O. Fost., Georgia Power Gene anage N*" CW MI""

Vogtle Project January 4, 1985 Director of Nuclear Reactor Regulation File: X7BC35 Attention: Ms. Elinor G. Adensam, Chief Log: GN-503 Licensing Branch #4 Division of Licensing U. S. Nuclear. Regulatory Commission Washington, D.C. 20555 NRC DOCKET NUMBERS 50-424 AND 50-425 CONSTRUCTION PERMIT NUMBERS CPPR-108 AND CPPR-109 V0GTLE ELECTRIC GENERATING PLANT - UNITS 1 AND 2 REVISED DAMPING VALUES FOR PIPING ANALYSIS

Dear Mr. Denton:

Enclosed are five copies of a report detailing the basis for revised damping values for piping analysis at the VEGP. The currently used

' damping values'were developed in the early 1970's. The enclosed report details a more recent and extensive body of test data which identifies significant conservatism in the current design basis. The revised damping values would be of benefit to Georgia Power Company.

In order to maximize the benefits which can be realized, it is

. requested that your staff review the attached report. Should your staff approve the proposed use of the new damping values, Georgia Power Company would implement the new values in the design of Plant Vogtle. The application of these damping values to systems there design is not complete will permit optimization of the systems, keep the number of snubbers to a minimum, and cause the design of the systems to better satisfy normal operating conditions.

If I or any member of my organization can be of assistance to your staff by_providing additional information or clarificaton, please

'do not hesitate to call.

Yours truly 2

D. O. Foster DOF/ JAB /sw xc: List attached.

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I Director of Nuclear Reactor Regulation. File: X7BC35

January 4, 1985 Log: GN-503 Page 2 xc: R. A. Thomas >

. J. A. Bailey G. F..Trowbridge, Esquire-J. E. Joiner, Esquire C. A. Stangler.

L. Fowler.

M.-A. Miller L. T. Gucwa:

r, G.~Bockhold, Jr. ,

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i J USE OF PVRC RECOMENDED DAMPING VALUES FOR ThE j V0GTLE ELECTRIC GENERATING PLANT UNITS 1 AND 2

1.0 INTRODUCTION

The currently used damping values for seismic analysis of piping systems were developed in th'e early 1970's. Since that time, a much larger body of test data has been developed which identifies significant conservatism in the current design basis. The. conservatism inherent in the current seismic analysis damping values, given in Regulatory Guide 1.61 EI3 and Westinghouse O

b topical report WCAP-7921-AR, " Damping Values of Nuclear Power Plant Components"[2], results in a larger number of unnecessary piping system seismic supports. Excessive numbers of supports result in reduced themal flexibility of the supported system during normal operation, which could result in thermal stress induced cracking. Therefore, Georgia Power Company (GPC) has established a revised position on dampirg values for seismic analysis based on the latest test data available, studies performed by the Pressure Vessel Research Council, and ASE Code Case N411 E33 The revised position provides adequate safety margins for earthquake events, while improving thermal flexibility for nomal conditions. The GPC position is described herein, along with a brief summary of the significant benefits to be realized. The technical basis for adopting this position is given in reference 4.

2.0 TECHNICAL POSITION The GPC position on damping values for seismic analysis applies to the primary i

loop piping systems .and to other piping systems. The position is illustrated A in Figure 1 and utilizes for all piping systems analyzed by the response t

- spectra method, the frequency dependent approach established by the Pressure Vessel Research Council (PVRC) Technical Committee on Piping Systems (TCPS). '

, When the time-history integration method is used for piping analysis the damping values in Figure 2 will be retained. The use of the frequency e

dependent damping values for piping analysis is also put forward in the American Society of Mechanical Engineers' ( ASK) approved draft Code Case 411 O

7873Q:1D/102284

i as an alternative to the damping values of non-mandatory Appendix N of Section ,

III of the ASFE Boiler and Pressure Vessel Code. The Appendix N damping  !

values are identical to those of Regulatory Guide 1.61.U The current GPC position on damping is il?ustrated in Figure 2. Comparison of Figures 1 and 2 shows that tha new position provides damping values that are generally equal' to or greater than the previous position. Georgia Power O Company will apply the damping values descrioed in this position and shown in Figure 1 for all piping systems where the design analysis has not been completed. During the as-built reconciliation of all piping systems these damping values will be used if re-analysis is required.

There is no intention on the part of GPC to mix the criteria of R.b.1.61 with the criteria of Code Case 411 for a given piping analysis. Further, as part of the integrated GPC piping analysis /as-built reconciliation program, GPC will assure that piping displacements and clearances are acceptable.

3.0 BENEFITS In an effort to investigate the overall effects of the damping values presented in Section 2.0, a number of independent studies are cited in Reference 4 for typical piping systems which assess the potential benefits resulting from use of the frequency-dependent damping values for the seismic ,

analysis of piping. The overall conclusions of these studies are that the use of the PVRC frequency-dependent damping values results in reduced piping responses and a reduction in the number of rigid supports and snubbers.

Independent studies perfomed by Westinghouse also support this conclusion.

The recomrmnded application of these damping values to systems where design is V not complete will permit optimization of the systems, keep the number of snabbers to a minimum, and cause the design of the systems to better satisfy nomal operating conditions. For systens that are past the design phase, the use of these damping values in the as-built reconciliation phase will limit p(/ the' number of changes in the design.

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7873Q:1D/102484

4.0 CONCLUSION

The above discussion demonstrates the benefits that can be achieved by application of the damping values in Figure 1 while retaining adequate seismic safety margins. Georgia Power Company recommends the use of these values for seismic response spectra piping analysis on Vogtle Electric Generating Station Unt'ts 1 and 2.

5.0 REFERENCES

1. " Damping Values for Seismic Design of Nuclear Power Plants, USNRC Regulatory Guide 1.61, October,1973.

2. " Damping Values of Nuclear Power Plant Components," WCAP-7921-AR, May, 1974.

3. Code Case N-411 " Alternative Damping Values for Seismic Analysis of Piping Section III, Division I, Class 1, 2, and 3," Annex 84-371 American Society of Mechanical Engineers Boiler and Pressure Vessel Code.

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4. Westinghouse letter NS-EPR-84-2955, E. P. Rahe, Jr. to James P. Knight,

USNRC,

Subject:

Use of Frequency Dependen Damping Values," dated:

August 16, 1984.

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. FIGURE 1 Georgia Power Company Position on Seismic Damping Values' 4

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Code Case N-Ell Alternative Damping Values for Scis=ic Analysis ci P:. ping Secticn 1:1, Div.ision 1 Class 1,2, ana 3. .

Question:

What alternatives to the damping values given in Table N-313 0-1, Appendix N,Section II Oi'Jisicn 1-are accc tabic for use in seismic analysis of Class 1,2, and 3 pip n:? .

.Feply:

It is che c;inien of the C0==ittee thr.t for Secticn : !,

Oi'visien 1, Class 1,2, and 3 construction, the damp ng value fer seismic analysis cf piping shown in Figure 1 may he used as an alternar:.ve to these given 1n Table N-123 0-1, Append:.x N.  !

'The damping value in Figure 1 is applicable to both OEI and SSE, and is independent of pipe dianeter.

This Code Case number shall be shosn in the documentation for this analysis and en the Code Data Report.

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Water Reactor NshwischnologDe Westin$Nuge Electric Corporation Divisions ,,35 ,

' PmsbwghPeseytvanis15230 August 16, 1984 NS-EPR-84-2955 I

l Mr. James P. Knight, Assistant Director O Components and Structures Engineering Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Washington, D.C. 20014

Subject:

Use of Frequency Dependent Damping Values

Dear Mr. Knight:

Over the past several months there has been considerable regulatory, PVRC, and ASE Code activity relative to the use of damping values in piping analysis.

Westinghouse has participated in and followed these developments closely and believes that there is a strong technical basis for the application of higher damping values in all phases of piping analysis. The purpose of this letter O

is to provide justification for the use of higher damping values, define the intended applications for these damping values, and request NRC approval of

.this position. It should be nott.d that the infomation contained herein is intended to supersede the Westinghouse positions on damping values in WCAP-7921-AR, " Damping Values of Wuclear Power Plant Components," and FSAR's currently under NRC review.

As shown in the attached position paper, Westinghouse plans to use damping values of eight percent (8%) and five percent (51) of critical damping for their primary coolant loop systems for SSE and OBE, respectively. For other piping systems in the Westinghouse scope of design and/or analysis 5% of critical damping is planned for frequencies of from 0 to 10 Hz and 2% for frequencies of 20 hz and above with values decreasing linearly from 5 to 2%

between 10 to 20 Hz.

Adequate justification for adopting this method of applying damping values and the benefits derived therefrom are significant. An assessment of the impact of the new damping values was perfomed by the Lawrence Liversore National

. Laboratory (LLNL) which showed that ample safety margins still exist.

O Additionally, a neber of independent evaluations were perfomed on typical piping systems, including evaluations by Westinghouse, to investigate the overall effects of frequency-dependent damping. All of these evaluations detemined that the application of frequency-dependent damping values results in reduced piping responses, a. reduction in the number of rigid supports -

and/or snubbers and reduced piping loads. This reduction in the neber of i

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Mr. James P. Knight August 16, 1984 NS-EPR-84-2955

supports and snubbers reduces inspection / replacement time and, consequently, personnel radiation exposure while additionally providing greater flexibility to the piping system thereby reducing themal expansion loadings.

This position on damping values for seismic analysis applies to the Westinghouse primary loop piping systems in Westinghouse plants and to other piping systems in Westinghouse scope of design /or analysis. The position i utilizes, for general piping systems, the frequency-dependent approach I L established by the Pressure Vessel Research Council (PVRC) Technical Committee on Piping Systems (TCPS). For Westinghouse primary loop systems, the damping values of 81 and 5% for SSE and OBE loadings respectively, apply to the design

, and/or analysis of the primary equipment supports and the large diameter primary coolant piping. '

This position of applying damping values will apply to all methods of seismic analysis, e.g., time-history, response spectra, etc. It will be applied to all Westinghouse plants for all piping systems, including primary loop piping

. systems in Westinghouse scope of design and/or analysis. Further, Westinghone intends to apply this position to operating plants on a backfit basis if the need arises, during the as-built reconciliation process where preliminary analysis has been completed, and on a forward fit basis for plants

! under construction for new analysis or reanalysis.

1 O Because of ongoing analysis efforts your expeditious review and approval would be appreciated in order to' expedite implementation and maximize the benefits of this position. At your request, Westinghouse would be pleased,to meet with you to discuss this subject further. If you have arty questions, please contact J. J. McInerney of sty staff.

( Very truly yours.

WESTINGICUSE ELECTRIC CORPORATION Nw .

l E. P. Rahe, ., Manager i Nuclear Safe -

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WESTINGHOUSE POSITION ON DMFING VALUES

, FOR' NUCLEAR POWER PLANT PIPING -

-l TABLE OF CONTENTS

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1.0 Introduction 2.0 Technical Position 3.0 Technical Basis - Part 1

- General Piping Systers 4.0 Technical Basis - Part 2

- Westinghouse Primary Coolant Loop Piping Systems -

5.0 Benefits 6.0 Conclusions 7.0 References Table 1 -Typical Seismic Data for Westinghouse Primary Coolant Loop Piping System .

Figure 1 -Westinghouse Position on Seismic Damping Values for i Piping Systems l .

j Figure 2 -Previous Westinghouse Position on Damping Values for

! Piping Systems Figure 3 -Percent of Critical Damping for Westinghouse Primary Loop Systems I ,

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1.0 IlfflKDUCTIDM The currently used damping values for seismic analysis of piping systems were developed in the early 1970's. Since that time, a much larger body of test data has been developed which identifies significant conservatian in the curmnt design basis.The

, conservatism inherent in the current seismic analysis damping values, given in Regulatory Guide 1.61 and Westinghouse topical

.w t WCAP-7921-AR, " Damping Values of Huclear Power Plant Components,[23, results in a large number of unnecessary piping system seismic supports. Excessive mubers of supports result in reduoed therinal flexibility of the supported system during normal operation, W11ch could result in thermal stress induoed cracking. -

Therefore, WesHaem has established a revised position on j damping values for seismic analysis hamad on the latest test data dVailable. The PeVised position proVides Niequate safety M ins for earthquake events, W111e improving thermal flexibility for

.O normal conditions. The Westinghouse position is described herein, along with a brief stamary of the technical basis and a

l. description of the significant benefits to be realized in piping l

systems designed and/or analyzed by Westinghouse. ,

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O 2.0 TEQHIICAL POSITION The Westinh_i== position on damping values for seismic analysis O applies to the Westinghouse primary loop piping systems in I

Westinghouse plants and to other piping systems in Westinghouse scope of design and/or analysis. The position is illustrated in Figure 1 and utilizes for general piping systems, the ft w y dependent approach established b'; the Pressure Vessel Research Council (PVRC) Technical Committee on Piping Systems (TCPS). For ,

Westinghouse primary loop systems, the damping values are 85 and 55 for SSE and OBE loadings, respectively. These values apply to l the design and/or analysis of the primary equipment supports and l . the large diameter primary coolant piping. This position, when f

used in conjunction with the gr1mnd response spectra of Regulatory Guide 1.60 or equivalent spectra, provides ample' safety margins l

in the plant.

O l The current Westine?== position on damping is illustrated in Figtre 2. Comparison of Figures 1 and 2 shous that the new I- position provides damping values that are generally equal to or greater than the previous position. Therefore, the new l Westinghouse position will be applied to all plants in order to ,

I l maximize the benefits fbr reliability, availability, and ingroyed I

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construction schedules. ,

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LD TEGINICAL BASIS - PART 1 '

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l General Piping Systems Westirmp=* oonours with the frequency-dependent damping values i for seismic analysis of nuclear power piping suggested by the Pressure Vessel Reseamh Council (PVRC) Technical Comatittee on Piping Systems (TCPS) and illustrated by curve 3 of Figure 1. The i

frequency-dependent damiping methodology was derived by the TCPS Task Group on Damping Values. Formal publication of this i

methodology is scheduled for late 1984 in the form of a Welding Research Council (WRC) Bulletin. Until the Bulletin is published, i the technical position of the Task Group on Desping Values l regarding application of toe frequency-dependent damping values to .

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nuclear power piping systems can be found in the letters to the l Editor of t2w. Nay,1984 issue of the Journal of Pressure Vessel Technology . 1he Technical Position contained therein is consistent with curve 3 of Figure 1.

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The American Society of Mechanical Engineers (ASE) has approved a l "

l draft Code Case that permits the use of the frequency-dependent damping values for piping analysis as an altenutive to the desping values of non-eandatory Appendix N of Section III of the ASE Boiler and Presswa Yessel (B&PV) Code. The O Appendix N damping values are identical to those of Regulatory

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Guide 1.61. It is expected that the Code Case, tentatively numbered N-411, will obtain final approval from the ASE and be published sometime in December, 1984

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O The WRC Bulletin mentioned above will contain, in addition to the technical position on damping,' an outline of the purpose, scope, and approach used in evaluating the damping data used to formulate the position, as well as a description of the data collection I

methods and sources.

The collected damping data is fnun a wide spectnan of sources, including laboratory and in-plant tests of piping with different sizes, types of supports and types of excitation. The test results are,- for the most part, from piping systems already installed in nuclear power plants, the exceptions being prototype and scale model tests of nuclear piping systems.

The damping data, which varies widely in format and content, required an evaluation process that would result in rational, technically defendable damping value recommendations. A combination of multiple regression analyses and engineering judasent used to assess the damping data showed a strong <

relationship between decreasing frequency and increasing damping, independent of the pipe diameter. .

The PVRC Task Group on damping performed a series of regression 5

t analyses in an attempt to determine the parametem of a piping ,

systar which may contribute significantly to damping. The

, parameters that were examined include the mnber and type of pipe l

supports, the frequency at which the system vibrates, system configuration, presence or absence of insulation, pipe material, i

i and pipe thickness. The goal of the analyses was to aid in l

, developing and examining empirical relationships between the above parameters and damping using the collected data.

1 The results of the series of analyses slowed a strong inverse relationship between frequency and damping. A dirset relationship was shown between the number of supports and desping, Wiile an inverse relationship was shown to exist between mode mnber and damping. For a fixed mode number, the damping increased as the parameter TOT /PD increased. The quantity TOT /PD is an actual ,

numeric value specific to the subject piping system and is defined -

7 as the total number of supports on the excited piping system divided by the relative pipe length (length of pipe divided by the ,

pipe diameter). For a constant value of TOT /PD, damping decreased with increasing mode manber. Pipe diameter was not an important parameter. The effect of support type was indeterminate due to the limitations of the data. ,

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! The use of multiple regression in the evaluation of desping data requires, theoretically, a homogeneous data base moquired from a set of carefully designed tests. The data base used for l performing this analysis was not as rigidly structured. To the 6

f-i extent that the data base is limited, engineering judpent wa applied in selecting, sorting, weighting, adjusting, and manipulating the data. This was done by graphical representation  ;

of the major parameters which affect systen damping values (graphs O of damping values versus each major parameter) with evaluation based on developed judgment. In this way, the major parameters were examiined on a consistant basis and the results of the i regression analysis critically evaluated. 1he dependency of the results on any one variable, as well as the range through W11ch the dependency is reliable, was nadily seen. In this way, the frequency <lependent damping value recommendation was based on mean values from the graphical representation of the test data.

An assessment of the impact of the new damping values on the actual seismic safety sergins was performed by Imrence Liversore National laboratory (LLJIL). This study showed that ample safety .

margins will still exist. LLIL performed a series of comparative analyses on three ZIDII Unit #1 piping systems using the PVRC reocamended frequency dependent damping values and the Regulatory Guide 1.61 damping values. These analyses are reported in NUREG/CR-3526,

• Impact of changes in Damping and Sp'ectnan Peak Broadening on the Seismic Response of Piping Systems".[5]

O In Rererence.5, LLNL compared the results from the response spectnmi analyses of the three piping systems and the results from a sulti-eupport realistic time 411 story analysis of the same three piping systems using the Regulatory Guide 1.61 desping values.

.. .7

The purpose of the time-history analysis was to give the best -

estimate of the actual system response for eich no enveloping of support point input motions was performed. The response spectra l

analyses were based on Regulatory Guide 1.60 envelope ground O response spectria.

l The results of the comparisons of the responses are expressed in terms of the mean ratios of the piping responses. The mean ratios of the responses frtet the analyses using the PVRC proposed damping values compared to the time-history analyses range from 1.05 to 4.98. The mean ratios for the responses from the Regulatory Guide 1.61 response spectrtui analyses compared to the time-history analyses range from 1.9 to 7.6.

O It can be concluded that even though the PVRC frequency dependent l damping values reduced seimnic responses of the subject piping -

i systems, there remained ove all an acoeptable degree of conservatism e en compared to realistic time history data.

4.0 TRcHMicAT. RAMTS PART 2 M = tiny mina Primary f*aalant f =a Pinina Syst -

O The percentage of critical damping for Westinghouse primary loop systems has been 45 for S'E and 25 for OEE loadings, respectively (See Figure 2). The basis for these damping values results from l O some actual plant dynamic tests of primary loop systems dich 8 i

i were publiahad in WCAP-7921-4R[2] approximately ten years ago. -

Figure 3 illustrates the results from the report. A very ig ortant aspect in this figure is that for the primary equipment, the percentage of critical damping is almost linearly proportional to the deflection on a log-log scale. Evaluation of the data in Figure 3 shous that, based on the higher levels of calculated response, conservative damping values for the primary loop are 8%  ;

for SSE and 55 for OBE loadings, respectively.

In structural dynamics, it is well known that the energy dissipation in a structure due to eterial and structural types of damping are mainly based on a number of factors: e.g., type and ntamber of , joints / connections in the structre, the structural material, amount of deformation experienced by the structure and type and construction of supports of the structure.

i The Westinghouse designed reactor coolant loop / support systen t

l consists of a reactor vessel, coolant pumps, steam generators, a i.

pressurizer and large diameter primary loop pipes. Many of these i large and heavy oosponents are supported by the combination of l

bearing, bolted and welded types of steel construction. Effnets of slippage and impact between the ocaponents and their supports will i

O dissipation is due to external structural damping which becomes dominant when the excitation acceleration level and velocity are both high. 1 hat is, the loss of energy increases dann the vibration amplitude increases. Martheriere, the primary components 9

i have complex internal stmetures with small clearances between O . -

parts. The impact of the internal atmetures of the various primary components adds to the energy loss when the ocuponent vibrates. These complex components and stmetural support systems will exhibit more energy dissipation than any simply constmeted

piping elements used in the testa d ere PVRC found 55 damping to be appropriate. '

O Another source of damping is the material damping which corresponds to the internal energy JLasipation within the stmetural material at the microscopic boundary. The small damping value currently used (25 and 45) is based mostly on material damping at the low level of excitation. However, when the excitation level becomes so high (such as SSE), that yielding occtrs in the material, then the material damping will increase greatly due to the hysteresis effect. The ASE Code allows local ,

! yielding without gross deformation for the design of components l and their supports under faulted or SSE condition. Therefore, it 1

is , justifiable to have higher damping factors for SSE analysis than OIE analysis.

O E23 Nhen ICAP-7921-AR uns prepared in 1974, Westinghouse was less knowledgeable than in 1984 in terms of calculated plant seismic O displacements. 1hrough the ,recent investigations of plant data, l

the calculated seismic displacements have been found to be mach higher than the displacements used in the tests. The range of

' seismic displacements for different plants in the Westinghouse 10

primary loop system is shown in Table 1 and in Figure 3. This displacement data is based on response spectnam analysis results using 25 CEE and 45 SSE damping. The range of measured damping of 0.65 to 5.25 oorresponds to a range of displacements from 0.4 mils i

to'40 mila. 1his includes a single data point from the San Femando earthquake, Wiich gave 3.15 5 damping for 0.033 inch displacement with only 0.018 g's at the ground. In contrast, the design basis for the plants shown have much larger displacements and ground accelerations as show in Table 1. Observing the ranges of displacements in Figure 3, it is clear that damping values higher than currently used will provide more realistic damping in the system. This is mainly due to the fact that a higher level of excitation will yield a higher magnitude of damping as discussed above. The damping values in Table 1 are best estimate values obtained by extrapolation from Figure 3. The range for SSE is 115 to 185, while for OIE it is 7.55 to 175.

Consequently, damping values of 85 SSE and 55 OIE provide a conservative design basis.

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l Other industry publications support the use of higher damping values for equipment. 'In 1978, design basis damping values for SSE of 75 for welded construction and 155 for bolted constmotion were recommended by Nessark and Hall in IRIREG-CR-0098.[6] Iater,

! in 1980, best estimate values of 12 75 OBE and 16.25 SSE were suggested in a paper by J. D. S+Avenson in Ibclear Engineering and Design, Issue 60.

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T O 5.0 IEMEEIIS In an effort to investigate the overall effects of the damping values presented in Section 2.0, a ntaber of independent ,

evaluations are cited for typical piping systes which assess the potential benefits resulting from use of the frequency dependent damping values for the seismic analysis of piping. In addition to LIRL, these assessments have been performed by Duke Power Company, l Tennessee Valley Authority, EG&G Idaho, Incorporated, and General Electric Company. The overall conclusions of these studies are that the use of the PVRC frequency-dependent damping values results in reduced piping responses and a reduction in the number I of rigid supports and sntbbers. Independent work by Westinghouse also confirms this finding.

In addition to the adequate margin and reduction in piping

• responses demonstrated by LIRL in the evaluation of the ZION thit 1 piping systems, (See Section 3 0), it was also shown that the use of the roommsended PVRC frequer.cy-dependent damping values can result in a reduction in the ntaber of supports. For one system analyzed by LUIL, a total of seven out of ten horisontal supports and two out of tre snubbers were eliminated. It was shown that

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l use of the PVRC damping values in this new configuration results l

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in the system meeting the applicable standants while the results -

of using the Regulatory Guide 1.61 damping values are that the l

allowable stresses are not met.

Tennessee Valley Authority performed a rather comprehensive assessment of frequency-dependent damping values 3 The analyses '

were performed using two moderately large piping layouts with the existing support system for both Regulatory Guide 1.61 damping and with PVRC dasping. It was found that rigid support loads were reduced in the range of 0 to 100 percent with an average reduction of about 14 pement. Snubber loads for the OIE were reduced fmm l

9 to 44 percent with an average reduction of 27 percent. For the SSE the average reduction was 7.5 pement. The average reduction in stress for the upset condition was between 10 and 20 percent, l

and for the faulted condition, less than 10 percent.

Duke Power Company made an independent assessment t91 of W damping recommendation by comparing response spectra for a typical reactor building shield wall at one elevation for a constant 1 percent damping and for PVRC desping. Comparison of the resulta V showed significant reductions in the low frequancy (less than 20 HZ) spectral accelerations when the frequency-dependent damping is used. Peak accelerations were reduced by at least a factor of two. This implies that fewer supports would be required to seismically qualify the piping systems.

EG&G Idaho [10] performed a limited investigation to detemine the

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effect of increased damping on three sample piping systems. .

Although these investigations did not address frequency-dependent damping, constant 2 percent and 5 percent damping levels were used for each .of the three optimized systems. The results inManted O that increased damping often, buc not always, reduces the mauber of supports required.

An assessment of the affect of damping on piping was perforimod by General ElectricU U. In this assessment, four clifferent damping cases were examined - Regulatory Guide 1.61 values; constant 3 and 5 percent damping; and the PVRC frequency-dependent reocamendation. The overall conclusion from these studies was that dynamic loads and accelerations with the PVRC l frequency-dependent damping are less than corresporW.ing loads and ecoelerations for Regulatory Guide 1.61 damping.

! Westinghouse U23 has performed a seismic (SSE) reeve]uation of a containment spray system line using the damping values in Section 2.0. The purpose of this analysis was to determine what effect, if any, the new da g ing criteria would have on support loads. No L attaapt was made to reduce the mater of supports or to modify the support arrangement. An essalination of the results~ of the reevaluation showed that support loads were in the range of 19 to l 26 percent lower than support loads from an evaluation using l Regulatory Guide 1.61 damping values. '

l l

A ma# benefit of more realistic desping val == for operating 14 L. - _ . - - _ _ _ . _ _ _ . _ . . _ _ _ . _ - . _ _ _ _ _ _ _ _ . __

plants, plants in the design phase, and plants in the as-built .

reconciliation phase, is the reduction in the nJuber of snebers and rigid supports that would be needed to meet the seismic design requirements. For operating plants, t[11s will improve plant reliability by reducing the potential for sneber malfbnetion during normal operation. Also, it will improve availability and reduce man-rem dosage by shortening the time required for maintenance and inspection of snebers. Plants in the design phase will get the additional benefit of reduced material' costs and shortened construction schedule, while plants in the as-built reconciliation pnase will get the further benefit of less design changes caused by the differences between the design configuration and the field,emnfiguration.

O 6.0 COELUSION The above studies demonstrate the significant benefits that can be achieved by application of the damping values in Section 2.0 '

while retaining adequate seismic safety margins. Westinghouse reocumends the use of these values for piping seismic mulysis on O- both operating and nor> operating plants for all piping systems.

i 7.0 REFEREEES i

1. 8'Demping Values for Seismic Design of Nuclear Power Plants",

USilRC Regulatory Guide 1.61, October,1W3.

s' L. _ _ _ _ _ _ _ _ _ _ _ _ _ _ _15_

i s'

\

.r 1,

2. "Desping Values of Nuclear Power Plant Components", .

WCAP-7921-AR, May, 1974.

! .  ; l

3. " Design Response Spectra for Seismic Design of Nuclear Power OA Plants", USNRC Regulatory Guide 1.60, Revision 1, December, 1973

4. Transactions of the ASME, Journal of Pressare Vessel Technology, Volume 106, May,1984

5. " Impact of Changes in Damping and Spectrun Peak Broadening on the Seismic Response of Piping Systems", S. C. Lu and C. K. Chou for Lawence Livermore National Laboratory, NUREG/CR-3526, UCRL-53491.

6. "Developnent of criteria for Seismic Review of Selected Nuclear Power Plants", N. M. Neteark and W. J. Hall, NUREG/CR-0098, May, 1978.

7. " Structural Damping Values as a Function of Dynamic Response Stress and Deformation hvels", J. V. Stevenson, Nuclear Engineering and Design 60 (1980), 211-237.

t

8. " Independent Assessment of Proposed Daging Values", Tennessee O Valley Authority, Septaaber 29, 1983.

9. "A Review of the PVRC Proposed Damping Change, D. L. Rehn, Duke Power Cospany, October 14, 1983.

16

4 i

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10."A Comparison of Piping Syste Stresses iieflacting Support Optimination Based Upon Varying Response Spectra Desping Values",

S. L. Busch fcr EG&G Idaho, Report No. RE-A A 3-006, February, 1983.

11."Ihe Effect on Response of BE Piping to Both Imr and High Frequency Dynamic Imads then Pipe Damping is Varied", N. Yen for General Electric, April 4,1983.

12.latter RGE-84-566 dated May 24, 1984 from Westinghouse (Heeuwis) to Rochestest Gas & Electric (Hutton).

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O -O O TABLE 1 O O O O .

TYPICAL SEISMIC DATA FOR WESTINGHOUSE. PRIMARY j' ' COOLANT LOOP PlPING SYSTEM d

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! SSE OBE Expected Expected Damping Ground ZPA RCL Risplacement Damping Groured ZPA RCL Displacement from Fig. 3 i Plant - (g) - Range-(in) - from -Fig.3(5) -(g) - Range (in) (5)

A 0.25 .53 to .89 13 to 16 0.13 .33 to .69 10 to 14

! 8 0.12 .68 to .77 14 to 15 0.06 .65 to .66 Approx. 14 i

! C 0.20 .55 to 1.20 13 to 18 0.12 .43 to 1.02 12 to 17 D 0.20 .38 to 1.14 11 to 18 0.09 .13 to .44 7.5 to 12 9

9 s

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1

. I

~

. O Percent of Critical 9 ,.

8 - -

(l)  ;

~

7 -

, 6 ,

5 - - - - - - - - - - - (2) 4 ,

2 .

'(3)

) .

l 10 20 Frequency (HZ)

O (1) Applies to Westinghouse primary coolant loop piping systems for SSE events. -

(2) Applies to Westinghouse primary coolant loop piping systems for OBF events.

(3) Applies to general piping systems.

FIGURE 1: lESTINGHOUSE POSITION ON SEISMIC DMFING VALUES FOR PIPING SYSTEMS

Percent of Critical Da ng 5 -

4 SSE (W) (1) 3 .

SSE (General) (2)

)

O 2 @(M.QBE(M,kW(caaarA1.1 A nar(general) (3) 1 .- - - - - _ _ ._ dbl Gih 3FJr9Agral) a (4) 0 10 20 Frequency (NZ) ,

O ' NOTES: (1) Applies to Westinghouse primary loop and connected

t. ... piping ' systems greater than or equal to 12" diameter for SSE

. event.

(2) Applies to general piping systems with diameter greater than 12" for SSE event.

(3) Applies to general piping systems with diameter greater than 12" for the OBE event; to general piping systems with diameters equal to or less than 12" diameter for the SSE; to Westinghouse primary loop systems greater than or equal to 12" diameter for the OBE event and to Westinghouse systems with diameters less than 12" for SSE event.

!O (4) Applies to general piping systems with diameter equal to or less than 12" for the OBE event; and to Westinghouse sys. tams with diameter less than 12" for OBE.

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> FIGURE 2: PREVIOUS WESTINGHOUSE POSITION ON DAWING

. , . ~ VALUES FOR PIPING SYSTEMS

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DEFLECTION (inches) -

TfPICALRANGEOFCALCULAIED FIGLRE 3: PERCENT OF CRITICAL DANING FOR SEISMIC DEFLECTIONS E STINGHOUSE PRIMUtY LOOP SYSTEMS s

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• sfNITED STATES .

a. . ,

4 NUCLEAR REGULATORY COMMISSION ,.

3 .

9tASMWsGTO8t. D. C. 30655 [f .** ,

e, .

AUG 13 .

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l MEMORANDUM FDR: Christopher 1. Grimes, Chief '

System Evaluation Program Branch Division of Licensing -

FROM: Robert J. Bosnak, Chief Mechanical Engineering Branch Division of Engineering ,

SUB$CT: MEB INPUT'DN TECHNJCAL ISSUE 5 PENDIN BEFORE ASME SWG DN DYNAMIC ANALYSIS As requested in your memo of July 31, 1984, the following represents our input /coments on,each of ,the issues discussed in your memo.

li Damping and Spectral Shifting - This branch.has already been approached by three utilities requesting our-position on the use l of the FVRC developed treatment of damping and spectral shifting

, as alternatives to the guicance in Regulatory Guice 1.61.end t

~ 1.122, respectively. Their use currently was stated to'be .

' restricted to load reconciliation work. Each utility was

' advised tc formally submit a letter request indicattag the j .pipin stems to which the above alternative criteria would l

apply, ney were requested to identify ASME Code Case N-397 or I the Sumer '84 Addenda to the 19E3 Edition for Appendix H ort spectral shifting, and Code Case N-411 for damping. This is-appli. gable only to response spectrum seismic analyses for pipDg. When the alternative damping criteria are used, they O. arfa$o be usred in their entirety, and the fact that R. G.1.61 l

criteria,for an .55E with D')12" above 20 Hz is less gdhrervative. ..

cannot, be vs.ed.- The att.ility must select either R. G.-l 61 o'n - ~

Code Case N-411 Criteria. A mixture of both teria is y . _ *-: '*s.arutcceptablee The utilities were a+so advise o be sure that l

- expected increased piping displacements could e accoemodated.

snd to be aware that the PV amping was an interim position subject to future change. , , . ..

4 - l Dur position the PVRC developed damping and 'spiectral shifting

. would also b pplicable to new construction or'to new or . .

replaced systems at operating plants. The PRC report on Seismic O- Desig6 will make formel recomendations for inclusion of the PVRC revisions within Regulatory Guides and the Standard Review Plan. "

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