ML20126A067

Snubber Elimination at McGuire Nuclear Station Using Limit Stops, Interim Rept

ML20126A067
Person / Time
Site:	Mcguire, McGuire
Issue date:	12/09/1992
From:	DUKE POWER CO.
To:
Shared Package
ML20126A064	List: ML20126A062 ML20126A067
References
NUDOCS 9212170218
Download: ML20126A067 (13)

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i ATTACHMENT I

SNUBBER ELIMINATION AT MCGUIRE NUCLEAR STATION USING LIMIT STOPS 1

INTERIM REPORT l

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TABLE OF CONTENTS Page No.

1.0 INTRODUCTION

1 2.0 PROGRAM DESCRIPTION 2 2.1 Objectives 2 2.2 Rationale & Benefits 3 2.3 Technical Description 3 2.3.1 Sample Piping 4 2.3.2 Engineering Analyses 4 2.3.3 Hardware Demonstration 6 2.3.4 Conclusions 7 l 3.0 FINAL REPORT 8 j

4.0 CONCLUSION

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5.0 REFERENCES

10 TABLE 1. Characteristics of Sample Piping Problem d

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MCGUIRE SNUBBER ELIMINATION PROGRAM

1.0 INTRODUCTION

Duke Power Company (DPC) has initiated a program that is intended to lead to a substantial reduction in the number of snubbers in use at the McGuire Nuclear Power Plant. This reduction in the number of snubbers will be accomplished by replacing snubbers with Limit Stops manufactured by Grinnell, Inc., under license to Robert L. Cloud & Associates (RLCA),

the original developers. The Electric Power Research Institute (EPRI) contributed partial financial support to the development.

The purpose of this submittal is to present a description of the plan developed by DPC to show the McGuire piping systems remain qualified with Limit Stop pipe supports and to describe the engineering program being conducted in support of the plan. A second submittal will be made at a later time when the engineering program is complete. If the program is successful, the second submittal will contain engineering results that will serve as a basis for changing out snubbers for Limit Stops at McGuire.

This submittal is consistent with verbal information presented by DPC and RLCA to the NRC in a meeting in the White Flint building on June 18, 1992, and fulfills the verbal commitment made at that time to present a written submittal that describes the program.

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2.0 PROGRAM DESCRIPTION 2.1 Objectives The specific objective of the Duke plan is to replace each snubber in the McGuire Plant with a Limit Stop.

This objective was formulated af ter review of dynamic tests on full-scale piping systems that showed the dynamic performance of piping systems under dynamic loads supported by Limi Stops was equivalent or superior to that of piping supported by snubbers (Ref 1,2,3).

In addition, actual experience of piping systems with primitive limit stop seismic supports protected installed power piping in quite severe actual earthquakes.

To support this objective, analytical studies are presently underway to show specifically that the licensing basis for the McGuire Plant is not compromised

by the change-out of snubbers for Limit Stops. In the event that a clear and comprehensive proof of this hypothesis fails to emerge from the analytical studies, a secondary objective has been formulated. The secondary objective is to establish the limitations that exist to the realization of the primary goal, and to formulate criteria that delineate those snubbers that can be changed out for Limit Stops, those snubbers that should be changed f or struts, and those snubbers that should remain. The basis for such criteria, if required, will be the ASME Code and other licensing basis limitations.

In summary, the present program has as a goal the development of analytical support for a complete change-out of snubbers for Limit Stops, or secondarily, the establishment of the limitations of such an approach and development of rules or criteria for a partial change out.

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• 2 ~. 2 Rationale & Benefits i ..

-l i DPC expects to realize significant benefits in each'of i the following areas by changing out snubbers for Limit Stops, j e Safety  !

? e Reliability e ALARA e Cost As regards safety, the Limit Stops are passive devices.

There are no active mechanisms to lock up or otherwise fall and expose the piping to unanticipated loads.

Similarly, corrosion, galling, and other materials-related problems are not anticipated because the Limit Stops are designed with-large clearances to be tolerant of hostile environments and are made from austenitic .

stainless steel.

Concerning reliability, the passive tolerant nature of the Limit Stops are expected to lead- to complete reliability for the devices themselves and concomitantly improved reliability for the systems they are installed-on.

The passive nature, together with the readily visible settings and internal parts of the_ Limit Stops, makes them easily inspectable from a remote distance and also eliminates the need for dismounting and' testing.

Elimination of this function will result in a significant dose reduction.

In the same vein, the cost of operation with Limit Stops will _ be reduced because the greater reliability eliminates the need-for expensive testing as well as the potential for_ snubber-related pipe failure evaluations and the-consequences associated with radiation exposure.

The Limit Stops require no special- : inspection- beyond normal nuclear safety-related pipe support inspection.

2.3 Technical Description The primary _ objective of the present program is to provide _ evidence that the snubbers;-at' McGuire can be changed-out on a one.for one basis with Limit-Stops with no unacceptable compromises in the licensing basis._ The method to be employed is to_ perform an in depth' analysis of a comprehensive sample of the McGuire piping with both-snubbers and . Limit Stops. Based on the in-depth analysis of- the sample _ piping systems, and on _ previous NRC approval of the GAPPIPE computer-program [Ref. 4,5,6],

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J anubbers in the sample piping systems will'be replaced l with Limit Stops pursuant to- 10CFR50.59 criteria. '

Barring some unusual dynamic characteristics of . - the sample systems, it is anticipated-that the results of the analysis and the -in-situ performance- of the installed -'

Limit Stops.will show the licensing basis.-for the plant remains uncompromised.

2.3.1 Sample Piping' The piping systems chosen-to serve-as the sample-for analysis are listed in Table 1. Four systems' -

have been chosen in order to _have a fully comprehensive. sample .-that contains a : good representation of all the attributes of the McGuire piping. In particular as  : can be seen-from the table, the primary attributes are addressed--by the sample as follows:

Attribute Sample Representation ASME Class 1, _ 2 , 3, and non-safety Pipe Size 3/4" to 24" Pipe Material Stainless _

steel and carbon steel Location Reactor- and. Auxiliary Building Problem Size 65 to 500 Mathematical Nodes Flexibility 1st' Mode frequency from 3.4 to 10.9 Hz

Design Temp 110 F to 650 F l As can be seen the sample will represent the

diversity of the piping in the McGuire plant.

All significant attributes and parameters- are i.- included. Although not -noted- in --the table, Problem number 3 which is an ASME class 1 system

! incudes thermal' transient loadingias well. The program presently underway is based'on the logic that inferences and conclusions - which can be

! drawn' from engineering. analyaes and actual j hardware performance of the' sample problems will

( be applicable to_the plant as a whole, j 2.3.2 Engineering Analyses .j Analytical models of the sample piping problems

[ will be created suitable for analysis with'the GAPPIPE [Ref. 4) computer program. The GAPPIPE program permits dynamic analyses of- piping 4

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systems with all common types of nuclear plant dynamic loading. GAPPIPE has been well correlated with full scale tests and approved by the NRC (Ref. 5 & 6) after in depth review and independent verification by the NRC contractor, Brookhaven National Laboratory.

As a first step in this work, it is planned that the sample problems in the original design configuration will be re-analyzed with GAPPIPE to provide as benchmarks to the design analysis.

The original design analysis was performed with the SUPERPIPE program.

The next step is to perform sufficient analysis ,

to be able to support the overall DPC objective, which is to be able to substitute Limit Stops for snubbers on a one for one basis.

The original piping qualification at McGuire was done using seismic spectra based upon Reg. Guido

1. 61 damping. However, McGuire is a modern plant where ASME Code Case N-411 pipe damping is applicable. It follows that it would be straightforward and permissible to re-analyze the piping using N-411 with an optimized number of seismic support where Limit Stops replace the existing snubbers.

Support optimization is not our objective because this would result in fewer seismic supports in the optimized configuration. Thus the piping l system ends up with less support. Although this is currently an acceptable practice, the overall objective is to enhance or at the very least maintain current design margin.

I It is DPC's preference not to implement a Support optimization program at McGuire, but to l substitute Limit Stops for snubbers at each snubber location and perform no new analysis. In this manner the robustness of the support system will be maintained. It is known from the results of several full scale tests that with this approach the safety of the pipe system will not be compromised [Ref. 1,2,3]. Analyses to support this thesis will be performed on the four sample problems described in Section 2.3.1 herein.

As a minimum, the system with all Limit Stop j supports will be analyzed. This will be done l with both Reg. Guide 1.61 and variable N_411 5

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l damping. The results will be compared to the i design analysis. Other analyses will be performed as necessary.

In this submittal which is only intended to formally advise the NRC that this work- is l underway and why, it has not been deemed advisable to layout a rigid and prescribed menu

! of analyses. It is recognized that as the l dynamic characteristics of the piping systems change with the changes in' support systems, the changes in response will- not necessarily be i

uniform and proportional. Nevertheless the first' goal is to show the one-for-one-snubber - Limit

! Stops change out results in acceptable response.

In the event local anomalies arise and it is l found necessary to retain some snubbers, i suf ficient - investigations will be performed to 1 establish criteria for choosing those snubbers to j retain. Since the original design analysis was based upon certain simplifying assumptions (the

state-of-the-art of 1980) it may for - example i prove useful to perform approximately realistic

or exact analyses that simulate test results. In a this manner comparisons between the response of dif ferent ' configurations. can be made that are i free of the potentially confusing' ef fects of

simplifying assumptions.

2.3.3 Hardware Demonstration

! Once the sample piping problems are analyzed and j the proposed support -design changes are j identified, the next 1 step of the engineering program is to implement the actual hardware L replacement of the existing snubbers with Limit Stops in accordance .with 10CFR50.59 criteria.

l DPC plans to begin installing the new Limit Stops

during the upcoming Unit I refueling outage 1 (March,1993), and will' complete the installation

during the upcoming Unit --2 refueling outage

! (July, 1993).

! It is DPC's intention that these Limit Stops will be monitored and inspected'during and after.the planned outage. The intent is to determine as well- as to demonstrate the actual in-situ

performance of the Limit Stops during normal i plant operation. Results of the inspection will serve as supporting evidence that the licensing basis remains uncompromised.

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2.3.4 conclusion Ultimately a set of engineering results will be developed, supporting DPC snubber elimination objectives as described above.

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i 3.0 FINAL REPORT A final report on the work described herein together with overall DPC plans will be compiled and submitted to the NRC.

A verbal presentation with opportunity for discussion is also planned. The overall intent is to keep the NRC advised of the results and findings of the pilot program J

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4.0 CONCLUSION

This report has presented in a general manner the approach DPC plans to take to eliminate snubbers at McGuire. The engineering program which is presently underway to support the DPC plan has been discussed. Finally, the categories of information to be furnished and method of presentation to the NRC that is planned prior to program implementation has been discussed.

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5.0 REFERENCES

1. M.S. Yang, et.al., " Shaking Table Testing of a Piping System.

' Supported by Seismic-Stops," Vol. K2, pp 769-774,-10th SMIRT -

Conference, Anaheim,-CA, August 14-18,-1989.

2. C.A.-Kot, et.al., " SHAM: High-Level Seismic Tests of Piping at the HDR," Proceedings of the U.S. NRC 16th Water Reactor '

i Safety. Information Meeting, NUREG/CP-0097, Vol. 3,-pp 339-362,

NBS - Gaithersburg, MD, October 24-27, 1988.

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) 3. C. A. Kot, et.al. , "High Level Seismic / Vibrational Tests at the i KDR - An Overview," Proceedings of.the U.S. NRC 19th. Water Reactor Safety Information Meeting, -NUREG/CP-0119, Vol. 3,- pp 4

59-90, NBS - Gaithersburgh, MD, October 28-30, 1991.

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4. GAPPIPE/GAPPOST Computer Program Version 2.3 Users Manual, RLCA/P94/04-92/004, March 1992.

l S. USNRC Safety Evaluation Report, " Implementation of Seismic j Stops at Byron Unit No. 2," May 21, 1990.

6. Letter, Anthony H. Hsia, NRC, to Thomas J. Kovach, CECO, dated

i February 7, 1992,-Docket No. STN50-455.

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4 TABLE'1. CHARACTERISTICS OF SAMPLE PIPING PROBLEM Sample Pipe . Pipe Pipe . Problem Size 1st Mode Design Piping'No. Class Size- Matl. Bldg. Snubbers Nodes Frequency _ Temp. *F i (CPS)

, 1. CA152 3, 8 CS AUX 3 135 10.9 160 Aux. . .

NS*

Feedwater s 2. FW350 2. 6, 8, SS AUX 18 500 3.4 '110, 190,

, Refueling 12, 14, 250, 350 Water & 18, 24 Residual Heat ,

' Removal 4

3. NC203 1, 2 .75, 2, SS R.B.** 19 250 8.3 650 t

-Pressurized 4, ' 6, 4 Spray ';

4. S AS ' 2, NS 1, 2 CS R.B. 4 65 3.5 567 ,

i l Aux. Steam '

i Drain-a i

.- *NON SAFETY ** REACTOR BUILDING i 4

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