ML20042G988

Rev 0 to Interim Operability Criteria (Ioc) Criteria for Performing Safety Analysis for Interim Operability of Piping.

ML20042G988
Person / Time
Site:	Fort Calhoun
Issue date:	05/08/1990
From:	Gambhir S, Morrell C, Phelps R OMAHA PUBLIC POWER DISTRICT
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ML20042G987	List: ML20042G986 ML20042G988
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Download: ML20042G988 (21)

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, k OMAHA PUBLIC F0WER DISTRICT j Fort Calhoun Unit 1 Docket 50-285 3

INTERIMOPERABILITYCRITERIA(IOC)

L CRITERIA FOR PERFORMING SAFETY ANALYSIS FOR INTERIM OPERABILITY OF PIPING l Rev. O  !

May 3. 1990 Prepared By: N bun

• 6- Date: 5/3/90 '

Reviewed By: b c)L . h E . Date: 5 /8 /90 Approved By: d 4 W M d A(.[d*1 Date: MMfe i C. G. Morrell V Acting Manager - Mechanical Engineering Production Engineering Division

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Manager - Design Engineering Nuclear Production Engineering Division k

S. K.' Gambhir Division Manager i Production Engineering Division ._.

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TABLE OF CONTENTS l '

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1.0 INTRODUCTION

& SCOPE. . . . . . . . . . . . . . . I j 2.0 CRITERIA . . . . . . . . . . . . . . . . . . . . 1

3.0 REFERENCES

. . . . . . . . . . . . . . . . . , . . 9 P

4.0 ATTACHMENT

OPPD Position Paper Regarding the Seismic Capability of Welded Steel Piping, R. E. Lewis, P. E.  ;

May 3, 1990 t

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. Ic0 INTRODUCTION AND SIDEI

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These criteria are intended to provide the operability determination requirements for piping and associated supports if it is determined that stresses exceed allowables presented in the USAR (Reference 1) and/or design basis piping code (Reference 2). These criteria permit operation for an interim period only. The interim period will be closed by modifications which return the system to i

within USAR allowables.

These criteria are intended to be used to expeditiously perform necessary evaluations to determine interim operability and not to delay appropriate actions.

2.0 CRITERIA 2.1 Piping Operability Criteria The piping analysis shall be in accordance with the load combinations and stress limits defined below. The design loading conditions to be applied in the analysis shall i

include the Safe Shutdown Earthquake. Relaxations in seismic design basis criteria are justified for operability determinations on the basis of experience data as summarized-in Reference 11. (Attached).

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, i The following are the pipe stress criteria for justifying t ,

continued operation of the plant:

SECONDARY (due to normal operating conditions)

Piping code equations governing thermal expansion and thermal anchor motion stresses (due to normal operating loads) shall be satisfied when generically invoking this IOC. Operability for thermal conditions outside code limits must be demonstrated on a case-by-case basis, and the criteria used for that determination discussed with the NRC. j PRIMARY (due to faulted conditions)

(SLP + SWT s 1.0 Sy) 1 (Ref. 9) l (Stp + SWT + SRSS(SSSE + SDYNJ 5 2.0 Sy ) (Ref. 9)

WHERE: SRSS = Square Root Sum of Squares Combination (Ref. 10, 12)  ;

If OBE-SAM stresses exceed design basis allowables, the following must be satisfied for operability:

SECONDARY (stress amplitude due to SSE-SAM)

(SSAMS s 122.5*N 0.2 [ksi)) (Ref. 8, Sect. 2.5.2, p.2-21) l WHERE: N = n/u allowable cycles n = 10 assumed event cycles u - 0.25 event usage factor ksi = Kips per Square Inch ,

NOMENCLATURE St p = Longitudinal Pressure Stress: Pd2 /(D2-d2 )

SWT = Dead Weight Stress: (0.75iM/Z)*

l SSSE = Inertia Stresses Resulting from Safe Shutdown Earthquake (SSE): (0.75iM/Z)

SDYN = Stresses Resulting from Dynamk 'ransient such as Safgty Valve vischarge:

(0.75iM/Z)

SSAMS = Seismic Anchor Motion (SAM) Stress Amplitude due to SSE: (1.0iM/Z)

Sy - Material Yield Stress at Temperature (Ref. 3 Appendices) i

• Note: 0.75*1 but not less than 1.0 L Page 2 l-

p .

Code case N 411 (Reference 4) allows for increased damping values, independent of pipe diameter, for seismic' analysis. '

Therefore, increased damping values, in accordance with Reference 4, will be acceptable when performing these ,

analyses to meet operability. If the piping analysis stresses exceed the above values, or pipe supports do not meet their operable limits (see Sect. 2.2), then additional

[ < iterative and/or refined analysis of the piping may be performed or modifications made to meet the operability or USAR limits. ,.

The itentive analysis may use the knowledge that a support is not capable of withstanding the loads, and can be removed from the analysis. Where feasible, the actual support stiffness may be included in the iterative analysis, along with other refinements. The Code Case N-411 analysis will be an alternative analysis procedure to that of the original piping seismic design methodology. Analysis employing Code Case N-411 spectra, from Reference 13 & 14, will be performed based upon US NRC Regulatory Guide 1.84, Rev. 26. (Reference 5). The Reguletory Guide specifies that the use of Independent Support Motion (ISM) with N 411 damping be j us'. i fi ed. Referer.ce 7, B.2 (1), p. 74 provides justification. However, the NRC does not currently approve of the use of ISM with N-411. OPPD does not intend to use ISM in the routine application of these criteria.

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2.2 .-Pipe Support and Hanger Operability Criteria i

- As a first step in evaluating the support, a' linear elastic l

analysis method will be used to determine the stress and i

[ forces in the support members. In addition to.the loading in Section 2.1, the support loads must include pipe thermal- j

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loads, results of free end-thermal displacement and anchor .

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p. motion. The stresses and forces calculated for each support 'j

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- member shall be compared with the following' criteria.  :{

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(seepages 58)

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. A. Supplemental. Steel (Ref. 3 Appendix F) j n:  :

p-Tension- Ft = 1.2 Sy but j l

,,0.7 SU

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Bendina j 1'

Plates, bars & doubly symmetrical members-Bent about their minor axis- l Fb = 1.5 Sy i Compact sections & rectangular tubing- '

[ Bent about their minor axis: .

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Fb = 1,32 Sy  ;

I' others.  ;

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l Fb = 1.2 Sy  !

Shear Fy = 0.72 Sy but .-

1 0.42 Sg Comoression 2 Fa=0.667ttE/(Kl/r)2 but iFt Combined Stress. For axial compression and bending or axial tension and bending, use AISC Chapter 5, Section1.6,'(Ref.-6),exceptuseabove allowables, c

Fillet Weld Stress Fw = 0.42 SV (OI weld material)

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Ft Allowable Tensile Stress 3 ^

[.r (b - Allowable Bending Stress n.

.w f Fy - Allowable Shear Stress y

F - Allowable Axial Compressive Stress-1 .

g> Fw = Allowable Fillet Weld Shear Stress 4' Sy-- Specified Minimum Yield Stress at Temperature

'SU = Specified Minimum Tensile Stress at Temperature w .

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B. Anchor Bolts Use Factor of Safety of 2 against ultirate tension and shear values (Reference 9).

C. Snubbers Hydraulic: Load 1 manufacturers faulted load rating.

Movement 5 total travel D. Springs Load within catalog range without bottoming out E. All Remaining Catalog items The maximum of the following:

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1. Manufacturer's published faulted load rating. I

2. When faulted allowables are not given and the factor of safety is specified in the catalog for the normal operating allowable, a design allowable shall be scaled  :

to a safety factor of 2. Alternatively, the normal i operation allowable may be increased by a factor of 2.

3. When test data is available, the design allowable shall t .

, have a safety factor of 2.

4. For a simple component item where an analysis can be

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performed, the allowable shall be evaluated the same as for supplemental steel.

If a support fails using the linear elastic method, then a -

more refined analysis may be performed such as using plastic analysis techniques or the restraint may deleted from the i piping analysis model if iterative analysis are performed per Sect. 2.1. Plastic analysis will follow the design rules of ASME Section III, Appendix F, (Ref 3). In lieu of analysis, the support may be modified to meet operability or USAR i limits.

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3. Eff.[BEliC15:

1. Fort Calhoun Unit 1 Updated Final Safety Analysis Report. l NRC Docket No. 50-285

2. USAS B31.7 1968 Draft Nuclear Power Piping Code.

3. American Society of Mechanical Engineers, Boiler and Pressure Vessel Codes,Section III, 1986 Edition, (NRC endorsed per 10 -

CFR50.55a(b)(1), March-31,1989).

4. American Society of Mechanical Engineers, Boiler and Pressure N

Vessel Codes, Case N-411-1, Dated February 20, 1986.

5. US Nuclear Regulatory Commission Regulatory Guide 1.84, Design and Fabrication Acceptability, ASME Section III, l Division 1, July 1989, Rev. 26-

6. " Manual of Steel Construction", American Institute of Steel

! Construction, Inc., Seventh Edition, 1980.

! 7. " Independent Support Motion (ISM) Method of Modal Spectral 1 \

Analysis", Pressure Vessel Research Committee, Sept. 11, 1989 l

(Draft).

8. Report of the U. S. Nuclear Regulatory Commission Piping Review Committee, NUREG-1061, Volume 2, April 1985.

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9. Palisades Plant Interim Operating Criteria for IE Bulletin  !

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79 14 Reverification Revision 1. Docket 50-255, License  !

DPR-20, November 22, 1989.

[ j 10; Methodology for Combining Dynamic Responses, NUREG 0484, Rev.

1, May 1980.

11. -OPPD Position Paper Regarding the Seismic Capability of-Welded-Steel Piping, R. E. Lewis, May 3, 1990, EA FC 90 42. f i

12. Report of the U.S. Nuclear Regulatory Commission Piping Review Committee, NUREG - 1061, Volume 4, December 1984, Section 1.3, p. 1 2.  ;

13. Generation of In-Structure Response Spectra for Fort Calhoun Unit 1, Volume I, II, & III, January 1989, ES 86-02.

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14. Seismic Analysis of. Fort Calhoun's Unit 1 Turbine Building, .;

-April 1990, ES-86-02, e

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ATTACHMENT TO INTERIM OPERABILITY CRITERIA, REV. O r

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. i EA-TC-90-42 Rev. No. O j Page No. 1  ;

OPPD POSITION PAPER REGARDING l THE j SEISMIC CAPABILITY OF WEIRED _ STEEL PIPING  ;

R.E. Lewis, P.E.

May 3, 1990 I. PURPOSE To document the following

1) That existing seismic design features (of CQE piping at Ft. '

Calhoun) and data obtained from various walkdowns, provide a high l 1evel of confidence that the piping will perform adequately for the design basis earthquake events. I

2) That a significant level of conservatism exists in the design -

basis seismic qualification process for Ft. Calhoun.

3) That welded steel piping systems are inherently rugged seismically.

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4) That various technical and documentation deficiencies, which have been identified in our piping seismic analyses over the ,

years, are insignificant in comparison to the overall seismic '

capacity of the systems. 1

5) That no significant seismic safety concern exists, for welded steel piping systems, at Ft. Calhoun.

II. EXISTING CONDITIONE '

The CQE piping at Ft. Calhoun was originally designt) for seismic loads, using methods less rigorous than current practice but-which were deemed appropriate at the time. Since then, "as-built" -

walkdowns, complete reanalysis (using updated methods) and substantial modifications were performed to reconcile "as-built and  ;

design discrepancies" found during resolution of NRC IEB 79-02 & '

79-14. In addition, we have performed verification walkdowns for the District's Design Basis Reconstitution program, and continued to l

avaluate and resolve various seismic issues in combination with other work requiring reanalysis of piping. Therefore a significant margin '

of seismic capacity has been incorporated into the CQE piping systems as they exist today. ,

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. EA-FC-90-42 '

Rev. No. 0 Page No. 2  !

However, miscellaneous documentation and technical issues, with regard to demonstrating the seismic qualification of CQE piping at -

Ft. Calhoun, have surfaced over the years. Some of the p&st piping design inputs, assumptions and modeling practices are undocumented i and/or inconsistently applied. The basis for many of the " apparent assumptions" are unknown and not supported by historical industry practice. The associated calculations and documentation are deficient by current standards and practices. Calculations which reconcile these deficiencies, often indicate that various piping and/or restraint components are outside the Seismic Class I design basis limits.

Calcu1Ltions and criteria, prepared for the District's Alternate Appendix F Criteria documents (Ref. 9 & 10), demonstrate that '

significant conservatisms exist in the Design Basis seismic inputs when compared to those derived with current practice methods and criteria. Many of the technical deficiencies noted above, are insignificant in comparison to these excess conservatisms.

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. EA-FC-90-42 <

Rev. No. O Page No. 3 I

III. EXPECTED PERFORMANCE WITH EXISTING CONDITIONS l

The current and past seismic analysis practices, as they apply to 1 nuclear piping design and qualification, are now known to significantly overpredict seismic failures (Ref. 7: p.136, p.158, p.164; Ref. 8 p.67, p.217, p.220, p.233). The over-conservatisms for piping seismic analysis are three fold: 1) analysis methods 2)  ;

seismic input data and 3) code acceptance criteria.

Analysis methods have been refined over the years, but still I typically calculate seismic responses based on the assumption of linear elastic behaviour, use of response spectra methods, conservative Regulatory Guide 1.92 modal combinations (Raf. 7: p.158, l p.167) and Regulatory Guide 1.61 damping values or lower in lieu of higher empirical values. Pipe stresses calculated by the response spectra method can be 2 to 8 times that resulting from a more exact time history method (Ref. 15, p.6). Actual behaviour of seismically excited piping systems displays significant energy dissipation and is non-linear in nature (Ref. 7 p.134; Ref. 8 p.205, p.229, p.233). j Measured responses are usually much lower than calculated (Ref. 7 p.168; Ref. 8 p.67, p.220, p.229).

In addition, the seismic input Floor Response Spectra (FRS) contain artificial conservatisms in the form of Regulatory Guide 1.122 peak broadening, smoothing and enveloping (Ref. 7: p.134, p.158). The seismic structural analysis process, which is used to derive the

• piping FRS, contains similar conservatisms to the piping analysis process and-therefore compounds the conservatisms. Calculations, performed for the District's Alternate Appendix F Criteria (Ref. 10),

demonstrate that significant conservatisms exist in the Design Basis seismic inputs when compared to those derived with current practice methods and criteria.

The piping code criteria, against which calculated seismic inertia stresses are compared, is known to be unrealistic-and overly conservative (Ref. 7 p.164, p.168; Ref. 8 p.67, p.229, p.233).

Failures modes due to seismic loading have been shown, through testing and industry research programs (Ref. 13 & 14), to be caused by fatigue and ratcheting instead of plastic collapse which is the l

basis for the piping code criteria. Numerous stress reversal cycles (far more than would result from actual earthquakes) are needed to induce failure. The codes, however, treat inertia as a primary stress and limit the stress amplitudes without regard to the limited number of cycles involved.

Therefore the cumulative conservatisms inherent in the seismic qualification process are significant and lead to over-prediction of seismic failures. However, relaxation of these excess conservatisms is not currently permited in our licensing basis.

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EA-FC-90-42 Rev. No. O Page No. 4 The actual earthquake experiences of others, have proven time and again that typical power piping systems are inherently rugged seismically. A significant amount of piping performance experience data has been collected from surveys of at least 29 different earthquakes around the world and from testing recently performed for/by recognized industry organizations. This data demonstrates that -

the rare instances of seismically induced piping failures can be attributed to a limited number of root causes as follows (Ref. 1&

2):

Seismic Anchor Movement (SAM)- insufficient flexibility in piping restrained by different structures or equipment that move rela-tive to each other, can result in breach of pressure boundary and/or restricted flow.

Spatial Interaction (SPI)- inadequate clearance between vulnerable components, like control valves, and other structures or equipment can cause loss of function and/or restricted flow.

Corrosion - excessive thining of the pipe wall, due to corrosion, can result in breach of pressure boundary and/or structural fail-ures.

Non-Welded Joints - screwed fittings are vulnerable to breach of pressure boundary failure due to the stress concentrations and reduced cross section present at the thread roots and bolted flange joints might develope leaks.

Welded steel piping systems, designed to standard industry piping codes (even when not designed seismically), exhibit adequate perfor-mance in earthquakes (with recorded peak ground accelerations as high as 0.9g) with few exceptions (Ref. 1). Piping restraint failures, on these same lines, are not uncommon and provide pressure boundary protection by acting as mechanical fuses to provide additional flexi-bility where needed to accomodate SAM movements (Ref. 2). It can be concluded from the above that good seismic design results from provid-ing the necessary flexibility to accomodate SAM, providing sufficient clearances to prevent SPI, providing allowance for errosion/ corrosion and avoiding the use of non-welded joints. Performing rigorous dynam-ic analysis (which is known to significantly over predict the seismic behavior of piping) and applying arbitrary code stress limits (which are known to be unrealistic and over conservative for seismic loads; Ref. 3, p. 2-17) are not required to achieve adequate margin against seismic induced piping failures and may in fact result'in designs which are less reliable than those for which no seismic design is employed (Ref. 2: R. Cloud, p. 81 & Sect. 5.1.3, p. 84).

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'I Recent testing through programs such as the "EPRI/NRC Piping and Fitting Dynamic Reliability Program" (Ref. 13) have provided the industry with considerable insight into the credible failure mechanisms relative to seismically induced response. This data shows '

that (Ref. 1):

" Sound and uncracked piping is " Fail-Proof" to any conceivable  ;

seismic inertia loads in LWR-type plants (more than 10 times  !

current ASME SSE allowable load levels are required to induce pipe failure)."

"There is a natural mechanism to relieve high seismic elastic calculated pipe stresses, and the mechanism is plastic energy -

dissipation which behaves like increased damping."

"The piping failure mode under super seismic type loading is fatigue and ratcheting, and not static collapse as assumed by the current ASME Code rules."

"The ratchet / fatigue failure condition has no sharply defined stress level at which pipe functionality is lost as in the case <

of a static collapse mode."

" Current ASME Code Allowable Stress Criteria with linear dynamic analysis is a very. conservative and unrealistic measure of pipe failure caused by excessive seismic type loads. (The fatigue criteria of the Code is OK)."

"The research explains why it is not necessary to provide horizon-tal support to piping subjected to seismic loading to protect the pipe from stress collapse. The main benefit from horizontal sup-

port is to prevent excessive pipe displacement."

l " Fatigue and ratcheting damage due to one or two large earth-quakes will generally cause insignificant damage to any reason-ably designed piping system (with or without nuclear standards) ."

In summary, seismic induced stresses in welded steel piping systems is not a credible safety concern provided that no SAM, SPI, errosion/

corrosion or non-Velded joint issues exist. In addition, it has been i

recommended that explicit earthquake design requirements be eliminated, for piping subjected to a SSE-ZPGA less than 0.2g, since no observed piping system failures have been noted for earthquakes of I such low magnitude (Ref. 2, Sect. 5.2.2, p. 85).

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EA-FC-90-42 Rev. No. O Page No. 6 With respect to the Fort Calhoun CQE piping systems, the following is known:

1) The equipment.to which CQE piping is attached and the piping itself, was designed to be seismically rigid,-and was anchored to resist seismic loads. Therefore, relative movement between equipment and piping located in the same building structures, at the same elevation, will be insignificant with respect to inducing SAM loads on piping. Furthermore, the Containment and '

Auxiliary-building structures are founded on a common mat and designed to resist seismic loads. Relative SAM movements between and within these structures is known to be insignificant. Seismic movements between the Auxiliary and Turbine building structures c is significant. The CQE Main Steam and Feedwater piping: routed between these structures has been evaluated for the resultant SAM loads. No otherJCQE piping is presently routed between these two structures. Therefore,Lno generic SAM concerns exist for CQE piping at Ft. Calhoun, t

2) The most vulnerable piping components, from the standpoint of SPI concerns, are valve actuators. The seismic design of CQE piping systems, at Ft. Calhoun, typically provided three way.

seismic restraints on the piping at the location of control valves. In addition, out-of-plane restraints were provided for eccentric valve operator masses. Seismic displacement of the valves into other structures or equipment, is thereby prevented.

In general, the original seismic design of CQE piping provided.

sufficient restraint to acheive rigid response with respect to, the building structures. In addition, modifications were made for IEB 79-02 & 79-14 which provided additional restraints to limit  !

pipe stresses and support loads to within acceptable limits. l' Therefore, interaction with other piping components and adjacent valves is unlikely. '

In addition, we have observed that other structures and/or equipment located near CQE equipment were designed and constructed to prevent SPI.-Field inspections of CQE piping, performed for the District's IEB 79-14 program, evaluated clearances between piping components and surrounding structures (

and equipment to ensure that thermal expansion would not be '

inhibited. Cloarances were also' observed during walkdowns  ;

performed for the Design Basis Reconstitution project. Clearances verc found to be adequate. Further review of SPI, with respect to control valves, will be performed for resolution of NRC USI A-46.

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. EA-FC-90-42 Rev. No. O Page No. 7-For the CQE Main Steam and Feedwater piping, one instance of potential SPI was noted between a MS Isolation Valve and an adjacent FW seismic restraint structure. The potential SPI results from the significant displacements of the MS line predicted to occur in the event that all lateral seismic restraints would fail (this has been conservatively assumed for purposes of demonstrating operability under worst case conditions). A modification was performed to eliminate that SPI concern (Ref. 11 &-12).

In general, no generic SPI concerns exist for CQE piping systems at Ft. Calhoun. A program is to be implemented in the near future t

for USI A-46 which will provide additional. documentation or corrective actions to support this-conclusion.

s-3).The use of corrosion resistant materials, chemical treatment and current monitoring and replacement programs for controling errosion/ corrosion are judged to eliminate these effects from being a concern with respect to seismic induced failures.

4) All known joints in CQE piping (excluding instrumentation lines) at Ft. Calhoun are either welded or flanged. The flanged joints were spucified to use high strength bolts so that complete failure due to seismic loads is unlikely although some leakage may result. The welded joints recieved inspections as required by the appropriate codes.to ensure quality and critical welds are periodically re-inspected thru the District's ongoing ISI program. Therefore, no generic concern with regard to non-welded or poorly welded joints exists at Ft. Calhoun.

5)' The Fort. Calhoun site SSE-ZPGA was determined to be 0.12g,.

from seismological studies, and conservatively established as 0.17g for design basis. Since these values are less than 0.2g, '

explicit design requirements for seismic loads would seem unwarranted.

IV. CCNCLUSION We conclude that: 1) a significant margin of seismic capacity exists in "as-built" design features of CQE piping at-Ft. Calhoun 2) that the design basis seismic qualification process significantly over-predicts seismic responses 3) that welded steel piping is inherently rugged seismicall 4) that outstanding-technical and documentation deficiencies, yregarding the seismic qualification of CQE piping at Ft. Calhoun, are insignificant in comparison to the demonstrated superior seismic performance of welded steel piping in actual earthquakes 5) and that no generic seismic safety concern exists.with regard to CQE piping at Ft. Calhoun.

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REFERENCE LIST I4 1)' Procedure for Seismic Evaluation and Design of Small Bore Piping '

(NCIG-14), Sept. 29, 1989, EPRI NP-6628, Project Q101-16,17

2) Report of the U.S. Nuclear Regulatory. commission Piping Review Committee, USNRC, NUREG-1061, Vol. 2 ADDENDUM

3) Report of the U.S. Nuclear Regulatory Commissicn Piping Review Committee, USNRC, NUREG-1061, Vol. 2 ,

- 4)-Regulatory Analysis for Resolution of Unresolved Safety Issue A-46,. Seismic Qualification of. Equipment in Operating Plants, USNRC, NUREG-1211

5) Task ~ Actions Plans for Unresolved Safety Issues Related to Nuclear Power Plants, USNRC, NUREG-0649, Rev. 1 6). Generic Implementation Procedure -(GIP) for Seismic Verification of Nuclear Plant Equipment, SQUG, Dec. 1988, Rev. 1

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7) "Recent Advances in Seismic Design of Piping and Components",

Proceedings of the 1985 Pressure Vessels and Piping Conference, PVP-Vol; 98-3

' 8) " Seismic Engineering- Recent Advances in Design, Analysis, Testing tand-Qualification Methods". The 1987 Pressure Vessels and Piping Conference, PVP-Vol. 127 i 9)E" Alternate Seismic Criteria & Methodologies for Fort Calhoun Station", Volumes I & II, July 1988, ES-86-02 ,

10)' " Generation of In-Structure Response Spectra for Fort Calhoun 3

- Unit-1",;Vol. I, II & III, Jan. 1989, ZS-86-02 -t

11) MR-FC-89-45, "Feedwater Supports in Room 81 & Turbine Building" L

12)' MR-FC-90-19, " Main Steam Supports in Room 81 & Turbine Building" 13)-EPRI Report No. RP1543-13, " Piping and Fitting Dynamic Reliability Program", Dec. 1989 3' 14):EPRI Report No. NP-3746, " Dynamic Response of Pressurized Z-Bend Piping Systems Tested Beyond Elastic Limits and with Support Failures", Dec. 1984

15) NUREG/CR-3718, UCID-19722, " Reliability Analysis of Stiff Versus Flexible Piping - Status Report", April 1984

,