ML20138F245
| ML20138F245 | |
| Person / Time | |
|---|---|
| Site: | Oyster Creek |
| Issue date: | 09/13/1985 |
| From: | Wilson R GENERAL PUBLIC UTILITIES CORP. |
| To: | Murley T NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I) |
| References | |
| RFW-85-0610, RFW-85-610, NUDOCS 8510250220 | |
| Download: ML20138F245 (5) | |
Text
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GPU Nuclear NQQIg[
100 Interpace Parkway Parsippany, New Jersey 07054 201 2t>3-6500 TELEX 136-482 Writer s Direct Dial Number.
Septenber 13, 1985 RFU- 05-0610 Dr. T. E. Murley Region I
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Regional Administrator U.S. Nuclear Regulatory Commission 631 Park Avenue King of Prussia, Pa.
19406
Dear Dr. Murley:
Subject:
Oyster Creek Nuclear Generating Station Docket No. 50-219 Higher Variable Damping Value and an Alternate Peak Broadening Technique for Piping System Analysis GPU Nuclear Corporation is proposing to utilize new developments in piping criteria, namely the recent ASME Code Case on damping values (N-411) and spectral shifting (N-397), at OCNG, as described in the attachment to this letter.
These criteria are technically justified and provide a more realistic piping design considering thermal and seismic requirements. Consequently, GPUN will be able to eliminate unnecessary seismic restraints, thereby reducing personnel radiation exposure associated with their surveillance and maintenance.
Section 3.7.1.3 of the Updated FSAR currently indicates that for vital piping systems, the critical damping value is 0.5 percent. The ASME Code Case N-411 recommends a damping criteria of 5 percent for frequencies up to 10Hz, linearly decreasing to 2 percent at 20 Hz, and thereafter held constant at 2 percent.
In addition the code case N-397 allows the broadening of spectral peaks based on a probabilistic approach. Hence the FSAR damping value of 0.5 percent for both OBE and SSE appears to be needlessly conservative.
8510250220 850913 PDR ADOCK 05000219 P
pm t$ e GPU Nuclear is a part of the General Pubhc Utikties System
GPUN has performed a generic 10CFR50.59 evaluation for the impact of these codc cases on the piping system and has determined that there are no unreviewed safety questions.
In addition, if as a result of using ASME Code Cases N-411 and N-397, piping supports are moved, modified or eliminated, the expected increased piping displacements due to greater piping flexibility will i
be checked to assure that they can be accommodated and that there will be no adverse interaction with adjacent structures, components and equipment.
Further GPUN will perform a 10CFR50.59 evaluation of the effect of ASME Code Cases N-411 and N-397, for the individual support, to determine that there are no unreviewed safety questions prior to its modification. GPUN plans to update the FSAR to reflect these changes.
This submittal is provided for information only.
i Very truly yours, i
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R.F. Wilson Vice President l
i Technical Functions i
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i Attachment l
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cc: Mr. John A. Zowlinski, Chief j
Operating Reactor Branch No. 5 1
U. S. Nuclear Regulatory Comnission
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Washington, D. C. 20555 l
l NRC Resident inspector
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Oyster Creek Nuclear Generating Station i
Forked River, N. J.
08731 J. Donohew U.S. Nuclear Regulatory Commission 1
7920 Norfolk Avenue Bethesda, Md. 20014 l
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ATTACHMENT REVISED CRITERIA FOR_ SEISMIC ANALYSIS OF j
P! PING SYSTEMS -- OYSTER CREEK NUCLEAR GENERATING STATION t
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j In recent years, a good deal of attention has been focused on ways to increase the capacity factors of nuclear power plants. One area of research has been piping system design. GPUN believes that reduction in the use of seismic j
restraints would have a positive impact on plant availability, specifically:
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--Fewer unplanned outages due to increased system fleutbility j
--Reduced snubber Inservice inspection activities
--Reduced need for plant access for maintenance
--Reduced personnel exposure to radiation Within the industry, research efforts using considerable test data have included l
examination of more refined methods of analysis to demonstrate seismic l
i qualification of flexible piping systems.
The following new criteria have been
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i accepted by the ASME in Code Case N-397 and N-411.
They will be applied to both
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ANSI $31.1 and ASME Section !!!, Olvision 1, Class I, 2, and 3 piping, j
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A) Spectral Shifting --ASME Code Case N-397 i
i This technique seeks to remove some of the conversion introduced by the peak t
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broadening criteria of Reg. Guide 1.122 by using a probabilistic approach.
In i
the particular case where there, is mors than one piping frequency located within the frequency range of a widened spectrum peak, the floor spectrum curve may be more realistically applied in accordance with the following criterton.
I Based on the fact that the actual natural frequency of the structure can assume 1
only one single value within the frequency range defined by fl 0.15frang I
3 not a j
j of the peak spectral value.
Therefore, the selsmic analysis of a piping system i
using the broadened floor design response spetra may be accomplished by the 3
following alternative:
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Determine the natural frequencies (f.)n of the piping system to be quallfled.
2.
Consider all piping natural frequencies in the interval
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f3 - 0.15f 1(f.)n af + 0.15 f 3
3 3
f where f is the frequency of mastmum acceleration in the 3
j unbroadened spectra, and n. I to K (K 15 the number of natural l
frequencies within the Interval).
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3.
The piping system shall then be evaluated by sequentially performing K +
l 3 analyses using the unbroadened floor design response spectrum and also l
the unbroadened spectrum modified by shifting the frequencies associated i
with each of the spectral values by a factor of +0.15. -0.15, and
((f.).
- f 1/f, where n. I to K.
3 3
4.
The resultants of these separate seismic analyses shall then be
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enveloped to obtain the final resultant desired (pipe stress, support l
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loads, accelerations, etc.).
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If no piping system natural frequencies exist in the interval associated with the maxim 1m acceleration peak, then the interval associated with the next highest peak shall be used in the above procedure.
- 8) Frequency Dependent Damping --ASME Code Case N-411 This Code Case is based on a large body of test data which shows current damping criteria for seismic design of nuclear power plant piping (Regulatory Guide 1.61) is unduly conservative.
The proposed new damping criteria is 5 percent for frequencies up to 10 Hz, linearly decreasing to 2 percent at 20 Hz, and thereafter held constant at 2 percent (See attached Figure 1).
This damping criterlon applies for both operating basis earthquake and safe shutdown earthquake, and are independent of pipe diameter.
Conclusions We believe that the changes proposed by these code cases for higher damping values and for an alternative to peak broadening are more realisitic but still result in a conservative design.
These recommendations have been accepted by the American Society of Mechanical Engineers (ASME) in Code Cases N-397 and N-411 which sets the industry standards.
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Ffoure 1 Oarpfne t'alue for seismic Analysis of pictne (Applicable to both Oct & SSE, Independent of Pipe Olocter) 9 s
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