NUREG/CR-0098, Forwards SEP Position Re Consideration of Inelastic Response Using NUREG/CR-0098 Ductility Factor Approach,Providing Addl Guidance Regarding Application of Ductility Methodology

Forwards SEP Position Re Consideration of Inelastic Response Using NUREG/CR-0098 Ductility Factor Approach,Providing Addl Guidance Regarding Application of Ductility Methodology

ML20054K135
Person / Time
Site:	Yankee Rowe
Issue date:	06/23/1982
From:	Caruso R Office of Nuclear Reactor Regulation
To:	Kay J YANKEE ATOMIC ELECTRIC CO.
References
RTR-NUREG-CR-0098, RTR-NUREG-CR-98 LSO5-82-06-087, LSO5-82-6-87, NUDOCS 8207010212
Download: ML20054K135 (6)

Text

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O June 23,1982 Docket flo.50-029 LS05-32 087 Mr. James A. Kay Senior Engineer - Licensing Yankee Atomic Electric Company 1671 Worcester Road Framingham,ttassachusetts 01701

SUBJECT:

SYSTEMATIC EVALUATION PROGRAtt POSITION RE: CONSIDERATION OF INELASTIC RESPONSE USING THE HUREG/CR-0098 DUCTILITY FACTOR APPROACH HUREG/CR-0098, "Developnent of Criteria for Seismic Review of Selected Nuclear Power Plants" by H.11. tiewnark and W. J. Hall describes in general criteria and methods for seismic analysis of structures, systems and components. The application of the !!UREG/CR-0098 general ductility criteria or similar methodologies are being used by some SEP licensees as part of their seismic reanalysis programs. These methods are not defined in detail in NUREG/CR-0098.

After discussions of this ductility methodology with SEP licensees, it has become apparent that additional guidance is required to assure appropriate application of the ductility evaluation concepts. The enclosed staff position provides additional clarification and guidance regarding the use of this methodology, and the justifications that you should provide to support of your application of this methodology.

This staff position has been reviewed by Dr. W. J. Itall and other staff consultants at Lawrence Livemore National Laboratory and is I

consistent with the author's intent and the general guidance in HUREG/

l CR-0098.

l Sincerely, l

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Ralph Caruso, Project Manager 8207010212 820623 Operating Reactors Branch No. 5 g

5 PDR ADOCK 05000029 Division of Licensing 9

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4 DI STRIBUTION Central Files SEPB Reading ECase DEisenhut Docket No.50-029 Glainas LS05-82 JKnight FSchauer SEPB members Mr. James A. Kay Senior Engineer - Licensing Yankee Atomic Electric Company 1671 Worcester Road Framingham, Massachusetts 01701

SUBJECT:

SYSTEMATIC EVALUATION PROGRAM POSITION RE: CONSIDERATION OF INELASTIC RESPONSE USING TIE NUREG/CR-0098 DUCTILITY FACTOR APPROACH NUREG/CR-0098 describes a general seismic design classification for structures, systems and components, and identifies generally acceptable ranges of limited overall inelastic deformations (ductility) for each The criteria for the application of the NUREG/CR-0098 '

classification.

general ductility criteria or similar methodologies are not defined in great detail. Also, it is not clear in NUREG/CR-0098 that any assumed level of ductility must be judified. In addition, NUREG/CR-0098 lacks l

guidance considering the dGermination of the motions to be used to evaluate items supported from systems which are determined to undergo l

limited inelastic binavior when subject to seismic excitation.

After discussions of this ductility methodology with certain licensees, it has became apparent that additional guidance is required to allow for an appropriate application of the ductility evaluation conceptss Therefore, the enclosure to this letter is being forwarded to you to provide additional clarification and guidance regarding the use of this methodology, and the justifications that you must provide in support of your application of this methodology.

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Please contact myself or my staff should you require any additional infonnation.

Sincerely, l

l l

l William T. Russell, Chief Systematic Evaluation Program Branch Division of Licensing SEPB:DL @ 'SEPB:D @

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A Mr., dames A. Kay cc Mr. James E. Tribble, President Yankee Atomic Electric Company 25 Research Drive 4

Westborough, Massachusetts 01581 Chairman Board of Selectmen Town of Rowe Rowe, Massachusetts 0136J Energy Facilities Siting Council 14th Floor One Ashburton Place Boston, Massachusetts 02108 U. S. Environmental Protection Agency Region I Office ATTN:

Regional Radiation Representative JFK Federal Building Boston, Massachusetts 02203 Resident Inspector

- Yankee Rowe Nuclear Power Station c/o U.S. WRC Post Office Box 28 Monroe Bridge," Massachusetts 01350 Ronald C. Haynes, Regional Administrator Nuclear Regulatory Commission, Region I 631 Park Avenue King of Prussia, Pennsylvania 19406 e

E-~~ E i SYSTEMATIC EVALUATION PROGRAM POSITION RE:' CONSIDERATION OF INELASTIC RESPONSE USING TIE NUREG/CR-0098 DUCTILITY FACTOR APPROACH l.

Seismic Design Classification NUREG/CR-0098 describes a general seismic design classifica, tion for structures, systems and components, and identifies g'enerally acceptable "systen ductility" (i.e., limited overall inelastic deformations of structures, piping, equipment, and components) ranges for the various categories. The criferia for classification (NUREG/CR-0098, Table 4) of the various structures, systems and components in the various categories are not defined in. great.'. detail, nor is,it clear' that any assumed level of ductility must be justified. To provide for consistent classifications by all licensees, and to avoid ambiguity:

a) Reliance on " system ductility" is appropriate in o.nly those cases where the particular " system" behavior can be adequately characterized by that of a single-degree-of-freedom-system and where the properties of the system are known.

b) The acceptable limit of " system ductility" which can be relied upon shall be justified based upon the development of a resistance relation-ship (stress or force vs. deformation) for a particular item, identifying the upper limit of acceptable deformation and strength.

Given the approximate nature of the technique, the maximum allowable " system ductility" should be no greater than one-half of the maximum limit so determined (i.e., application of a safety factor of 2), but not less than 1.

c) The upper limit of " system ductility" th-t is acceptable for any safety related item shall be no greater than 3 (NUREG/CR-0098, Table 4, Class II maximum limit).

2.

Det ermination of " System Ductility" Discussions in' NUREG/CR-0098 indicate that the " system ductility" should be based upon considering the behavior of " subsystems" and members com-prising the " system.". Insufficient details are presented regarding factors which should be considered to detennine acceptable " system ductility" l evels. Therefore:

a) "Systen-ductility" factors should be developed based upon an equivalent elasto-plastic resistance function, developed from the " actual" resistance function.for an item. The " actual" resistance function shall be developed considering load redistributions and added deflec-tions which take place as the various members reach and exceed their elastic limits.

Due consideration must be taken of various modes of possible failure which can lead to rather abrupt degradation of resistance as for example buckling (gross and local), connection failure, or brittle and/or ductile type of rupture failure of elements.

The effects of inelastic cycling on both capacities and stiffness shall be determined and considered.

-2.

b) Localized ductility demands shall be examined for all members and elements comprising the " system" assuming displacement compatibility using the " actual" displacement profile for the item, as determined above, considering the possible effects of gross or local failures as defined in 2(a ) above.

The localized ductilities ma upper bound " system ductility" of 3 as defined in 1(b) y exceed the above, however, the limits must be determined and the acceptability, thereof, justified.

c) It must be demont.trated that the overall response (i.e., overall stress level) of the item considered is at a sufficient level to assure the development of the strengths and deformations employed in the analysis.

3.

Application of Ductility Factors Whether a ductility reduction factor (for forces or accelerations) or a modified response spectrum approach is used in an analysis, the net result is the same, namely, a reduction in the accelerations and forces from those predicted by conventional linear elastic analyses. The development of the ductility reduction factors presented in NUREG/CR-0098 indicates their applicability to broad banded response spectra associated with ground motions.

Their applicability to motions filtered by " system" (e.g., building ) motion (e.g., floor response spectra), or foundation spectra derived from soil / structure interaction analyses has not been adequately demonstrated. Therefore:

a) " System ductility" force and acceleration response reductions for

" systems" excited by broad band response spectra associated with ground motion shall be based on the relationships presented in NUREG/CR-0098, Reference 1, or equivalent when accompanied by verification, b) When ductility reductions for response spectra are employed in situations involving other than broad banded ground response spectra; l

such as floor spectra, or foundation spectra derived from soil /

structure interaction analyses, the amount of reduction in response due to ductility shall be justified using methods similar to, or equivalent to those-used in arriving at NUREG/CR-0098 requirements.

(See, for example, Reference 1. )

It must be emphasized that the use of the ductility procedure requires a knowledge of the input (loading) and the resistance function (load vs. '

defomation).

If the ductility assumed is not achieved, for example, then the reduction assumed in all likelihood is not appropriate. At the other extreme, if the " system" is stiffer than assumed, then the generated inertial forces will be greater than assumed, and the deflections or deformations smaller in all likelihood.

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• 4.

" Subsystem" Response Determination Considering Ductile " System" Response When inelastic behavior is relied upon for the evaluation of a system (e.g., structures and equipment cabinets), the normal practice of evaluating supported piping, equipment and components (subsystems) using response spectra generated,from an elastic analysis of the supporting system may not be conservative. The degree of difference in motions of the supported items will be a function of the amcunt of inelastic behavior of the supporting " system." NUREG/CR-0098 does not present any guidance in this area.

However, this subject is addressed briefly, but not exhaustively in NUREG/CR-ll61, " Recommended Revisions to the Nuclear Regulatory Commission Seismic Design Criteria." Based upon our review of these criteria, where " system ductilities" are relied upon, supported subsystems should be evaluated as follows:

a) Where " system ductilities" less than 1. 3 are relied upon, subsystems shall be evaluated using broadened response spectra derived from an elastic " system" analysis using normal practice, b) Where ductilities greater than 1.3, but less than 2 are relied upon, response spectra shall be derived from both an elastic and a simplified nonlinear " system" analysis. As a minimum, 3 real earthquake time histories, representative of site ground motions, shall be used in such nonlinear analyses unless the fluctuations in the results of these analyses suggest that additional analyses are appropriate.

Supported items shall be evaluated using the envelope of these nonlinear and the conventional elastic analyses, broadened appropriately.

c) Where " system ductilities" between 2 and.3 are relied upon, a detailed nonlinear " system" analysis shall be performed per the criteria in 4(b) above, with supported items being evaluated in the same fashion, namely using a broadened envelope of the nonlinear and conventional elastic analyses spectra.

The above represent only general guidance. There may be special cases where only portions of a " system" undergo inelastic deformations where simplified techniques may not be appropriate as a result of changes in load and stiffness redistributions.

Reference 1:

R. Riddell and N. M. Newmark, " Statistical Analysis of the Response of Nonlinear Systems Subjected to Earthquakes,",

UILU 79-2016, August 1979 (available through NTIS).

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