ML20024D154

Forwards Addl Info Resulting from 830708 Meeting at Structural Mechanics Assoc,Inc Re Severe Accident Risk Assessment.Info Provided to NRC Consultant J Benjamin & Assoc,Inc

ML20024D154
Person / Time
Site:	Limerick
Issue date:	07/27/1983
From:	Bradley E PECO ENERGY CO., (FORMERLY PHILADELPHIA ELECTRIC
To:	Schwencer A Office of Nuclear Reactor Regulation
References
NUDOCS 8308030222
Download: ML20024D154 (30)

Text

_

PHILADELPHIA ELECTRIC COMPANY 2301 M ARKET STREET P.O. BOX 8699 PHILADELPHIA. PA.19101 EDW ARD G. B AU ER. JR.

12151841-4000 vice passessar ano esmanas covass6 3UGENE J. BR ADLEY associais samanat counset July 27, 1983 DONALD BLANMEN RUDOLPH A. CHILLEMI R. C. MIR n H A LL T. H. M ANFM CORN ELL PAUL AUERBACH assistant egnamat covassL cDW ARD J. CULLEN. J R.

Docket Nos. 50-352 THOM AS H. MILLER J R.

50-353 IREME A. McMEMN A assistamt covassh Mr. A. Schwencer, Chief Division of Licensing U. S. Nuclear Regulatory Commission Washington, D. C.

20555

Subject:

Limerick Generating Station, Units 1 & 2 Request for Additional Information

Dear Mr. Schwencer:

As a result of the July 8,1983 meeting at Structural Mechanics Associates, Inc. on the Severe Accident Risk Assessment, additional information was provided to the NRC's consultant (Jack Benjamin and Associates, Inc.).

It consisted of the following enclosed information:

1)

Average Magnitudes and Distances for Seismic Hazard 2)

Coordinates for Piedmont Zone 3)

Structural Mechanics Associates calculations of Earthquake Component Factors 4)

" Comments on Effective Ground Acceleration Estimates" by R. P. Kennedy l

5)

Letter from R. Campbell (SMA) to J. Reed (JB&A) dated l

July 11, 1983.

[

Very truly yours l

l 1

L l

Enclosures Copy to: See Attached Service List

\\

i 8300030222 830727 k(

PDR ADOCK 05000352 A

PDR

O j

e cc:

Judge Lawrence Brenner (w/ enclosure)

Judge Richard F. Cole (w/ enclosure)

Judge Peter A. Morris (w/ enclosure)

Troy B. Conner, Jr., Esq.

(w/ enclosure)

Ann P. Hodgdon (w/o enclosure)

Mr. Frank R. Romano (w/o enclosure)

Mr. Robert L. Anthony (w/o enclosure)

Mr. Marvin I. Lewis (w/o enclosure)

Judith A. Dorsey, Esq.

(w/ enclosure)

Charles W. Elliott, Esq.

(w/ enclosure)

Jacqueline I. Ruttenberg (w/o enclosure)

Thomas Y. Au, Esq.

(w/o enclosure)

Mr. Thomas Gerusky (w/o enclosure)

Director, Pennsylvania Emergency (w/o enclosure)

Management Agency Mr. Steven P. Hershey (w/o enclosure)

Angus Love, Esq.

(w/o enclosure)

Mr. Joseph H. White, III (w/o enclosure)

David Wersan, Esq.

(w/o enclosure)

Robert J. Sugarman, Esq.

(w/o enclosure)

Martha W. Bush, Esq.

(w/o enclosure)

Spence W. Perry, Esq.

(w/o enclosure)

Atomic Safety & Licensing Appeal Board (w/o enclosure)

Atomic Safety & Licensing Board Panel (w/o enclosure)

Docket & Service Section (w/o enclosure)

Robert K. Weatherwax (w/ enclosure) l

~

~

ENCLOSURE 1 LIMERICK SEISMIC HAZARD STUDY AVERAGE MAGNITUDES AND DISTANCES Feak Acceleration,g Setemogenic Zone ab. max 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 0.10 5.8 m

5.2 5.3 5.3 5.4 5.4 5.4 Fiedmont R

26.

19.

16.

15, 14.

13.

6.3 a

5.4 5.5 5.6 5.7 5.8 5.8 5.8 5.9 5.9 R

31.

24.

20.

18.

17.

16.

15.

14.

14 5.0**

5.1**

5.0 m

Tectonic Zones R

25.

21.

5.5 a

4.9 4.9 4.9 4.9 Crustal R

40.

24.

17.

14 Blocks 6.0 m

5.3 5.3 5.3 5.3 5.3 5.2 5.2 R

51.

42.

36.

32.

29.

27, 26.

6.8 m

5.7 5.9 5.9 6.0 6.1 6.2 6.2 6.2 6.3 6.3 DecoI tement R

55.

40.

32.

28.

25.

22.

21.

19.

18.

17.

m to average body-wave magnitude. R is everage distance in km.

The average magnitude has contributions from en adjacent zone with "b. mat = 6.5.

l l

ENCLOSURE 2 LIMERICK SEISMIC HAZARD STUDY COORDINATES FOR PIEDMONT ZONE Long. (W)

Lat.(N)

Long. (W)

Lat.(N)

~712.00 -

36.7,0

~77.50 36.50 S0.80 36.80 77.50 36.90 79.40 37.40 77.40 37.70 78.70 38.20 77.40 38.30 77.60 39.50 77.30 39.,00 77.60 39.80 74.40 39.50 76.40 40.30 76.30 39.50 75.60 40.50 75.30 39.80 74.00 41.50 73.60 41.00 73.30 43.30 73.10

-41.10 73.20 44.60 72.00 41.20 72.40 46.10 69.40 41.20 70.30 47.30' 64.80 45.10 69.60 47.90 47 80 47 10

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ENCLOSURE 4 SMA 12901.04R C0!HENTS ON EFFECTIVE GROUND ACCELERATION ESTIPR by R. P. Kennedy February, 1981 1.

INTRODUCTION Structural Mechanics Associates (SM) has estimated fragility curves defining the frequencies of seismic induced failures for structures and components in nuclear generating stations.

These frequency of failure estimates are defined as a function of the effective peak ground acceler-ation level (EPA). The EPA is the ground acceleration level at which a broad frequency content structural response spectrun should be anchored for the purposes of predicting structural damage.

For predicting structure and component damage at sites, Sm has used the median broad f requency content structural response spectrun for appropriate ground media as defined in Reference 1.

Sm has assuned 3 to 5 near-peak response excursions approaching the levels defined by this structural response spectrum anchored to the EPA.

This approach is most applicable when dealing with longer duration ground motions which contain a broad range of frequency contents such as the Taf t recording from the 1952 Kern County, California earthquake (local magnitude ML = 7.2, range from causative fault = 40 km) or the highway test laboratory recording from the 1949 01.ympia, Washington earthquake (ML = 7.0, range = 29 km). For such earthquakes, the EPA to which a broad frequency content response spectrum is anchored and the instrumental peak acceleration (IPA) should be essentially the same.

Such records result in 3 to 5 structural response excursions approaching the levels defined by the structural response spectrum.

1 WM

However, the frequency of strong ground motion in areas of low seismicity will be mostly due to lower magnitude earthquakes (Mg g5.7) and shorter ranges (less than 20 km). Ground motions from such earth-quakes have characteristics like those recorded at the Gilroy Array from tha 1979 Coyote Lake, California earthquake (Mt = 5.7, range = 7 km) or the Melendy Ranch Barn record from the 1972 Bear Valley, California earth-qutke (Mt = 4.7, range = 6 km). These records have narrow fmquency content, and within the majority of the frequency range of interest (2 to 10 Hz) their structural response spectra is seriously overpredicted by the Reference 1 broad frequency content median spectre when this spectrum is anchored at the IPA. Secondly, only a single cycle of strong structural respo~nse occurs from these records because of their limited duration and energy content. Thus, for these records the IPA cannot be used as a basis for predicting the level of structural response which is approached 3 to 5 times during an earthquake. Since structural damage predominately depends upon multiple cycles of strong response, the IPA cannot serve as a good indicator of structural damage for these earthquakes.

In these cases, damage is better described by an EPA which is much less than the IPA. This EPA represents the ground &cceleration for an equivalent long duration record with broad frequency content which causes 3 to 5 response cycles and results in the sane expected damage level as the actual record.

2.

EFFECTIVE DEAK VERSUS INTRLMENTAL PEAV AND SUSTAINED PEAK ACCECERATIONS SM is currently engaged with Woodward-Clyde Consultants in a research program sponsored by the Nuclear Regulatory Comission (IRC) to define effective ground motion parameters useful in predicting structural damage. This section briefly suninarizes some of the tentative findings l

to date.

For the purpose of predicting elastic response of structures in the amplified acceleration fmquency range (2 to 10 Hz), median broad

-frequency content response spectra such as those from Reference 1 are com accurately anchored to an EPA defined by:

T lciec 2

w nummme

-m

- - - -+ + - - -

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-nv-,,n.----

p----

--y--wt-*w-4 pr

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A 1.25

• A3F (1)

=

E rather than the IPA. The quahtity A3F represents the third-highest acceleration peak of a filtered acceleration time-history record.

The filter should be chosen to pass all frequency content below about 8 Hz and filter-out all frequency content above about 9 Hz. The quantity A 3F corresponds closely with what Nuttli (Reference 2) has defined as sustained peak acceleration.

Therefore, Equation 1 together with Nuttli's definition of sus-tained acceleration can be used to define an EPA (A ) to be used to E

estimate elastic response of a structure within the 2 to 10 Hz frequency range. However, elastic response is not a good measure of damage. Based upon current work, two ground motion time histories with the same spectral acceleration values at the structure's natural frequency can lead to vastly different nonlinear response or damage for the same structure For instance, one can compare (Reference 3) the maximum nonlinear model.

response (damage) from the Melendy Ranch Barn record (Magnitude 4.7) with that computed from the Taft record (Magnitude 7.2).

It is found that the Melendy Ranch Barn record must be scaled to produce spectral accelerations between 1 and 2 g's at the structural natural frequency to produce the same level of damage as a 0.59 spectral acceleration from the Taft record.

Thus, for Melendy Ranch, the spectral acceleration must be two to four times as great as for Taft to produce the same level of structural damage.

Similar conclusions are reached for the Coyote Lake records (Magnitude 5.7) versus the Olympia record (Magnitude 7.0) or Taft. Thus, for obtaining an EPA corresponding to a given level of structural damage, 1

Equation (1) should be modified, as follows:

1.25 4

A l

D F

• Ap (2) 3 The f actor F must be established as a function of ground motion character-istics for a constant level of structural damage. For magnitudes greater than about 7.0 and ranges greater than about 40 km, F can be taken as M

\\

3 w summesma

unity and Equation (1) can be used to predict the EPA corresponding to structural dange. However, with magnitudes less than about 5 and ranges less than about 20 km, F should have a value greater than 2 for predicting structural damage. As a consequence, the EPA (A ) should range from

)

D less than 0.6 to 1.25 times the sustained ground acceleration (A3p)

)

depending upon the earthquake magnitude and hypocentral range with the lower factor being appropriate to low magnitudes (less than about 5.0) and short hypocentral ranges (less than 20 km). The appropriate ratio of A /A37 is strongly influenced by the duration of strong ground motion.

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The SPR fragility curves for nuclear generating stations are best anchored to the damage EPA defined by Equation (2). For sites where strong motion generally results from low magnitude earthquakes, I would judge that the 905 confidence bounds on F are:

1.0 1 F 1 3.0 (3)

Because of the tentative nature of the research conducted to date and the controversy of the subject of EPA versus IPA, I would recomend that F be conservatively selected for use in Equation (2) and that the EPA be defined by:

I4)

Ap=A3F with Nuttli's sustained peak acceleration (Response 2) being used to e

define A3p.

3.

[FPER BOUND CUTOFF ON EFFECTIVE PEAK ACCELERATION The EPA is being used as a measure of damage to structures with a fundamental natural frequency in the 2 to 10 Hz frequency range. The Modified Mercalli Intensity (I

) is also a measure of damage. Although I, is a subjective scale, it probably correlates best to damage of g z ;--

=

4

=

conventional structures which generally have natural frequencies in the 0.3 to 3 Hz range.

Because both EPA and I, are measures of damage capability of ground motion, these two quantities should be closely cor-related with each other. Thus, one should be able to establish upper bounds on the EPA irrespective of frequency of exceedance if upper bounds exist on intensity.

Table 1 describes the earthquake effects (damage) corresponding to each of the I scale levels. These damage descriptions can be used mn to define upper bounds on the EPA corresponding to a given I, level.

Masonry A construction corresponds to earthquake resistant masonry struc-tures designed to the Uniform Building Code in California (Zone 4).

Masonry B construction is reinforced and represents well-engineered masonry structures in UBC Zones 0 or 1.

Masonry C construction represents well-constructed unreinforced masonry structures. The SMA methodology

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used to develop the fragility curves for structures and components at sites with low seismicity will predict very substantial damage and/or at least partial collapse of 50% of these masonry structures for 3 to 5 cycles of the following effective peak ground acceleration (EPA,) levels:

Masonry Type 50% Damage EPA Levels (g's)

C 0.25 - 0.3 B

0.4 - 0.5 A

0.6 - 0.8 Thus, very serious damage to a large number of Masonry A, B, and C structures would be predicted by the SMA methodology to correspond to EPA levels of less than 0.8, 0.5, and 0.3 g's, respectively. The SMA methodology for predicting damage levels has been benchmarked against observed damage in past earthquakes in which substantial damage was observed for sustained ground motions corresponding to these levels.

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Based upon the damage descriptions in Table 1, serious damage to at least some Masonry A, 8, and C construction correspond to I, levels X, IX, and VIII, respectively. Comparing the EPA levels defined above for each of these levels of damage, one would estimate that I, of X would correspond to an EPA of 0.6 to 0.8 g's or less, I, of IX corresponds to an EPA of 0.4 to 0.5 g's or less, and I, of VIII corresponds to an EPA of 0.25 to 0.3 g's or less based upon the described da age to masonry construction. Even considering unce'rt'ainty in the correlation between the two descriptors of damage (I and EPA), an upper band must exist nn on EPA for a given I,n level. Otherwise, the two indicators of damage sculd be contradictory.

In my judgenent, an upper bound on EPA can be estimated by assigning the EPA ground motion levels defined above to an intensity value one level lower than that for which a given type of masonry construction damage is considered appropriate. Thus:

Intensity, I, Upper Bound EPA (g's)

IX 0.8 VIII 0.5 VII 0.3 VI 0.2 In my judgement, the EPA values given in this table represent conservative e

upper bounds for the corresponding intensity levels. These EPA levels would result in the prediction of substantially more damage than that fran which the intensity level is defined.

If @per bound intensity levels, I

, are defined for a site, then the EPA levels should also be limited to being below the upper bound levels defined above when the SPM fragility curves are used to predict structure and component damage. Unless these limits to EPA are applied, one would predict substantially more damage than could possibly corres-E~

pond to a -given upper bound intensity level. Even with these limits. I judge that the level of predicted damcge would correspond to at least one intensity level higher than the upper bound intensity level.

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REFERENCES 1.

"A Study of Vertical and Horizontal Earthquake Spectra", IRSH 1255, Nathan M. Newmrk Consulting Engineering Services, prepared for USAEC, April,1973.

2.

Nuttli, O. W., "The Relation of Sustained Maximtsn Grcund Acceleration and Velocity to Earthquake Intensity and Magnitude", Paper S-73-1 published in State-of-the-Art for Assessing Earthquake Hazards in the United States, U. S. Army Engineer Waterways Experiment Station, Vicksburg, Mississippi,1979.

3.

Kennedy, R. P., Short, S. A., Newmark, N. M., "The Response of A Nuclear Power Plant to Near-Field Moderate Magnitude Earthquakes".

Paper K 8/1, to be presented at Sixth International Conference on Structural Mechanics in Reactor Technoloa2, Paris, France, August 17-21, 121.

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g g STRUCTURAL ENCLOSURE 5 mECHRnKS

""""""" R SS O CI A T E S SMA 14302.01 wm

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5160 Birch Street. Newport Beach. Cahf 9266o (714) 833 7552 July 11, 1983 Dr. John Reed J. R. Benjamin and Associates, Inc.

Mountain Bay Plaza 444 Castro Street, Suite 501 Mountain View, California 94041

Dear John:

During the Limerick PRA review meeting on July 8,1983, you raised some questions which I could not answer off the top of my head. The following responses should clear up the issues.

The first question was regarding an apparent inconsistency between the response factors for piping and for valves. These response factors should be the same as valve response is predicated upon piping response.

Initially the piping response factors were developed on the assumption that 1% damping had been used in the original design analysis when in fact 0.5% was specified. The valve response factors were calculated using the correct damping of 0.5%.

The text in the original report draft erroneously tried to explain the difference. A review of the work uncovered the error in the piping response factors and the cal-culations were changed. Unfortunately the text in the report was not properly changed. The response factors for piping on page 5-59 are low and should be the same as those for valves on page 5-60.

The descriptions on page 5-60 of how the valve response factor differs from the piping response factor should be deleted as there is no difference.

You raised another question regarding the deletion of SRV loading from the generic derivation of piping and pipe support fragilities. The SRV loading was purposely lef t out of the generic derivation to examine the more conservative case.

If the majority of the loading is seismic, the resulting capacity factor is lower than if the majority of the loading is from other sources. For instance:

n - "SRV F

=

c s

SSE 9

Dr. John Re:d J. R. Benjamin and Associates, Inc.

July 11, 1983 Page two where strength factor relative to the SSE F

=

s failure stress o

=

c stress from normal pressure and dead weight load o

=

n stress from SRV load

=

oSRV stress from SSE load o

=

SSE is a greaEer+ portion of code allowable results inCSRV) is at Assuming the sum of ( OSSE + 0 the case where OSSE the lowest valve of Fc.

Likewise for supports, we derive the capacity factor for supports wfiich carry only seismic loading as they are the governing cases.

A third question was raised regarding variability in testing due to use of spectral test methods. The attached pages from NUREG-CR1706 describe the problem and attempt to estimate the uncertainty.

I hope this explanation will clear up these issues.

If you have any further questions please don't hesitate to call.

I will be away for several weeks, but both Ravi Ravindra and Greg Hardy should be available to answer any further questions.

Very truly yours, STRUCTURAL MEC NICS ASSOCIATES, INC.

Robert D. Campbell Project Manager RDC:mw cc: M.E.Co.

i L.

4.4.5 Variability Due to the Use of Soectral Testina Methods In Chapter 3 the use of spectral testing methods versus a power spectral density approach was discussed. Smallwood in Reference 23, stated that it is important that a spectrum not be considered as a suffi-cicnt specification. His study of a large variety of synthesis methods concluded that a different method m y produce significantly different results. SWRI, in Reference 22, perfomed an independent evaluation of test methods and concluded that with current spectrum methods, insuff-

)

cicnt excitation of equipment modes might occur. Ileither reference attengted to quantify the magnitude of the variability that might be experienced.

The problem stems from the fact that a synthesized time-history contains peaks and valleys in acceleration or force and that if a signif-icant valley in the time-history input corresponds to a predominant fre-quency of the equipment being tested, the response may be significantly 1 css than the mathematically anticipated and required response.

A much better approach, as reconmended in Reference 23, is to synthesize a time-history that corresponds to a power spectral density which envelopes the RRS rather than make the direct step from the RRS to

[

the synthesized time-history. This approach tends to smooth out the l

l input time-history, resulting in less chance for an equipment mode to coincide with a significant valley. Most testing laboratories do not, i

however, have this capability.

Quantification of the variability that might result from use of spectral methods could be acconplished by analytical studies that com-pared responses to synthesized time-histories keyed to power spectral densities as opposed to those synthesized directly to match the RRS.

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6 4

4-38

The variability due to the use of spectral test methods is expected to be smaller than that due to instrument and control error and acceleration time-history variation and is considered to be prinitpally a modelling uncertainty in that most of the variability could be eliminated by using more sophisticated test equipment. Without conducting a study to quantify the variability, we would estimate the i 26 range of response g of.11 of which S ~ 0.05 and sy ~ 0.10.

to be within i 255 equating to a S g

1 l

f p

e i

20. Smith, P. D., S. Bug us and O. R. Maslenikov, "LLL/ DOR Seismic Conservatism Program, Part VI, Response to Three Input Components".

UCID-17959 (draft report), Lawrence Livemore Laboratory Ljvermore, California, S ril, 1979.

21. USWtc Regulatory Guide 1.60, " Design Response Spectra for Seismic Design of Nuclear Power Plants".

22. Kana, D. D., and R. W. LeBlanc, "An Evaluation of Seismic QualificationTestsforNuclearPowerPlantsEquipment"(draft) prepared for the USWtc by SWRI, Contract No. AT (49-24)-0372.

23.

" Seminar on Understanding Digital Control and Analysis in Vibration Test Systems", sponsored by Goddard Space Flight Center, Jet Propulsion Laboratory and The Shock and Vibration Information Center, held at Goddard Space Flight Center on 17-18 June, 1975 and at the JPL on 22-23 July, 1975.

'l

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4-45

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