ML20209A721

Responds to 861211 Request for Addl Info Re Use of ASME Code Case N-411.Proposed Draft Rev to Fsar,Incorporating Use of Damping Values in Code Case N-411,subj to 14 Conditions, Encl

ML20209A721
Person / Time
Site:	Beaver Valley
Issue date:	01/28/1987
From:	Sieber J DUQUESNE LIGHT CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
NUDOCS 8702030422
Download: ML20209A721 (6)

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'At5 Telephone (412) 393-6000 Nuclear Group ppingport, PA 15077-0004 U. S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555

Reference:

Beaver Valley Power Station, Unit No. 1 Docket No. 50-334, License No. DPR-66 Response to Request for Additional Information Regarding the Use of ASME Code Case N-411 Gentlemen:

In the Request for Additional Information (RAI) dated December 11, 1986, the NRC staff requested a commitment to eight (8) additional conditions regarding the use of ASME Code Case N-411. We have reviewed these conditions and discussed them with Mr. Branner of the NRC staff. Based on these discussions, it is our understanding that the damping values of Code Case N-411 are to be used in their entirety in a given analysis of a system containing piping and components attached to the piping. However, if a specific component is analyzed separately, then the damping values specified in Regulatory Guide 1.61 are to be used. Based on this understanding, we commit to the additional conditions listed in the RAI. As requested, enclosed is a proposed draft revision to the Beaver Valley Unit 1 Updated FSAR incorporating the use of ASME Code Case N-411 subject to fourteen (14) conditions.

With regard to the in-structure response spectra for Beaver Valley Unit 1, we intend to use the amplified response spectra (ARS) based on soil-structure interaction (SSI) as described in Section B.2.1.3 of the Updated FSAR with the damping values specified in ASME Code Case N-411. The methodology used in SSI-ARS was approved by the NRC staff in a letter dated May 25, 1979 and also in the August 8, 1979 Order for termination of the proceedings initiated by the Show Cause Order dated March 13, 1979. As stated in the Updated FSAR, we consider that the SSI-ARS forms the present and future design basis for Beaver Valley Unit 1.

If there are any questions concerning this matter, please contact my office.

Very truly yours,

. D. Sieber Vice President, Nuclear AoD 8702030422 DR 870128 I l p ADOCK 05000334 (

PDR

Beaver Valley Power Station, Unit No. 1 Docket No. 50-334, License No. DPR-66 Response to Request for Additional Information Regarding the Use of ASME Code Case N-411 Page 2 cc: Mr. W. M. Troskoski, Resident Inspector U. S. Nuclear Regulatory Commission Beaver Valley Power Station Shippingport, PA 15077 U. S. Nuclear Regulatory Commission Regional Administrator Region 1 631 Park Avenue King of Prussia, PA 19406 Mr. Peter S. Tam U. S. Nuclear Regulatory Commission Project Directorate No. 2 Division of PWR Licensing - A Washington, DC 20555

- Mail Stop 340 Director, Safety Evaluation & Control Virginia Electric & Power Company P.O. Box 26666 One James River Plaza Richmond, VA 23261

BVPS-1-UPDATED FSAR DRAFT out the piping included in each computer analysis. The stiffness matrix used in each analysis is computed based upon the structural behavior of piping elements in NUPIPE.

The seismic inertial response within each mode is computed as the square root of the sum of squares of the response due to the seismic excitation in each of the three orthogonal directions. The seismic inertial response among modes is computed as the square root of the sum of squares of responses due to each mode computed, except that the responses of all modes within a natural frequency band of 10 percent are added absolutely, and this sum is added by the square root of the sum of squares with the remaining computed nodes. This approach is in full compliance with Regulatory Guide 1.92 entitled

" Combining Modal Responses and Spatial Components in Seismic Response Analysis".

The development of amplified response spectra used in the analysis of piping systems is described in Section B.2.1.3. Damping factors used for seismically designed piping and components are 0.5 percent for the OBE and 1.0 percent for the DBE. Refer to Section B.2.1.12 regarding the use of alternate damping valves in ASME Code Case N-411.

Where a piping system is subjected to more than one amplified response spectrum as when support points are located in different parts of the structure or different structures, the amplified response spectrum which is closest to and higher in elevation than the highest support on the piping system is applied to this system or multi ARS are used simultaneously in the analysis.

Relative seismic structural displacements between the piping supports and anchor points, that is, between floor penetrations and equipment supports at different elevations within a building and between the buildings, are used as inputs of equivalent static boundary displacement conditions in the computations. Relative seismic displacements between the pipe support points at different buildings are always considered to be out of phase in order to obtain the most conservative piping response.

For the analysis effort, the effects of the seismic anchor displacements have been evaluated statically and separately from the inertia effect. Static analysis is performed for each direction of relative displacement and for each earthquake, leading to a total of six evaluations. Internal moments resulting from the three evaluations for each earthquake are combined by SRSS on a component

. level and are then combined with the inertia effects by absolute summation, also on a component level.

B.2.1.3 Amplified Response Spectra The NUPIPE computer code uses an amplified response spectra (ARS) based on soil-structure interaction (SSI). The methodology used in SSI-ARS is based upon a layered elastic media model for soil and a lumped mass model for the structure. Analysis using these models involves:

B.2-2

-s-3 BVPS-1-UPDATED FSAR DFAFT TABLE B.1-3 DAMPING FACTORS Type and Condition Percentage of

, Stress Level of Structure of Component Critical. Damping l

1. Low stress, well a. Steel, reinforced 0.5 to 1.0 below propor- concrete; no tional limit. cracking and no Stresses below slipping at joints 0.25 yield point

2. Working stress a. Welded steel, well 2.0

• limited to 0.5 reinforced concrete yield point (with only slight cracking)

b. Reinforced concrete 2.0 (with considerable cracking)

c. Bolted steel 5.0

3. At or just a. Welded steel 5.0 below yield point b. Reinforced concrete 5.0

c. Bolted steel 7.0

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4. Vital piping 0.5 OBE systems 1.0 DBE Total system damping for structures including damping from motion in subgrade is assigned to be 5.0 percent for the Operational Basis Earthquake and 7.0 percent for the Design Basis Earthquake.

Refer to Section B.2.1.12 regarding the use of alternate damping valves in 1GE Code Case N-411.

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BVPS-1-UPDATED FSAR DRAFT B.2.1.12 Use of ASME Code Case N-411 As stated in Section B.2.1.2,, the initial design damping values used at Beaver Valley Power Station Unit No. 1 for seismically designed piping and components are 0.5 percent for the operating-basis earthquake (OBE) and 1.0 percent for the design-basis earthquake (DBE). NUREG 1061, " Report to the USNRC Piping Review Committee" has shown that the use of such low damping values for seismic piping analysis are overly conservative, and recommended the damping values given in ASME Code Case N-411 " Alternate Damping Values for Seismic Analysis of Classes 1, 2 and 3 Piping Sections". These damping values are: five percent below a frequency of 10 Hz; linear reduction from five percent to two percent between 10 Hz and 20 Hz; and two percent above 20 Hz. These damping values would apply for both OBE and DBE cases. The NRC staff has conditionally approved the use of the damping values in ASME Code Case N-411 for piping modifications and future piping stress analyses at Beaver Valley, Unit 1 by letter dated .

The alternate damping values in ASME Code Case N-411 may be used at Beaver Valley, Unit 1 provided the following conditions are met:

1. The alternate damping- criteria of this Code Case will be used for seismic analysis in cases where new piping is added, existing systems are modified, existing systems are re-evaluated for new requirements and where existing numbers of snubbers are to be reduced provided that the response mode frequencies are limited to 33 Hz and below.

2. When these alternate damping values are used, they will be used in a given analysis completely and consistently in which current seismic spectra and procedures are employed.

3. The damping values will be used in seismic analysis using response spectrum methods and not for seismic analysis using time-history analysis methods.

4. When used for reconciliation work or for support optimization of existing designs, the effects of increased motion on existing clearances and on line mounted equipment will be reviewed.

5. The alternate damping values will not be used in seismic analyses of piping systems using supports designed to dissipate energy by yielding or piping in which stress corrosion cracking has occurred.

6. When these alternate damping values are used, the 115 percent peak broadening criteria of Regulatory Guide 1.122,

" Development of Floor Design Response Spectra for Seismic Design of Floor-Supported Equipment or Components" will be used.

BVPS-1-UPDATED FSAR DRAFT B.2.1.12 Use of ASME Code Case N-411 (Continued)

7. When the damping values of Code Case N-411 are used, they will lxe used in their entirety in a given analysis and shall not be a mixture of Regulatory Guide 1.61 criteria and the alternate criteria of this Code case.

8. For equipment other than piping, the damping values specified in Regulatory Guide 1.61, " Damping Values for Seismic Design of Nuclear Power Plants", should be used.

9. The damping values specified in Code Case N-411 may be used only in analyses which assume an upper bound envelope of the individual response spectra for all support locations to calculate maximum inertial responses of multiply-supported items.

10. Where predicted maximum piping displacements using Code Case N-411 criteria exceed the current design calculations by an amount greater than acceptable tolerance levels, a physical verification of the availability of adequate clearance with adjacent structures, equipment and components must be performed. For equipment mounted on piping, such as valves with extended structures, proper account must be taken for both rotation and translation in arriving at the predicted maximum displacement at the extreme ends of the pipe mounted equipment.

11. It must be verified that the operability qualification level of pipe mounted equipment is not exceeded by the predicted response using Code Case N-411.

12. Where the existing design loads of piping supports are exceeded by the new loads predicted by the use of Code Case N-411, it must be verified that the new loads do not exceed the design capacity of the supports.

!- 13. It must be verified that the cumulative effect of the i changes of loads on -piping supports that are in turn l supported by a structural element of a building, such as

walls, slabs, beams and columns does not exceed the load carrying capacity of the affected structural element.

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14. A listing of all applications of Code Case N-411 will be l maintained by engineering and the individual files of pipe stress packages re-analyzed using Code Case N-411 will be

, maintained with its respective Design Change Package (DCP) records.

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