ML19322E700
| ML19322E700 | |
| Person / Time | |
|---|---|
| Site: | Davis Besse  |
| Issue date: | 12/07/1979 |
| From: | Crouse R TOLEDO EDISON CO. |
| To: | James Keppler NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III) |
| References | |
| NUDOCS 8004020135 | |
| Download: ML19322E700 (76) | |
Text
i TOLEDO
%mm EDISON Docket No. 50-346 License No. NPF-3 Serial No. 1-109 December 7, 1979 Mr. James G. Keppler Regional Director, Region III Office of Inspection and Enforcement U.S. Nuclear Regulatory Commission 799 Roosevelt Road Glen Ellyn, Illinois 60137
Dear Mr. Keppler:
In accordance with Item 6.a of OI&E Inspection Report No. 50-346/79-23 for the Davis-Besse Nuclear Power Station Unit 1 and our November 5, 1979 letter (Serial No. 1-102) to Mr. G. Fiore111, of your staff, we are submitting our analyses verifying the design of the Davis-Besse Nuc3. -
Power Station Unit 1 pipe whip restraints.
In the attached report s have reanalyzed restraints in one typical reactor coolant system hot a c and cold leg. The analysis methodology is in accordance with Bechtel Power Corporation Topical Report BN-TOP-2, Revision 2, " Design for Pipe Break Effects" approved for use by NRC letter dated June 17, 1974.
The analyses of the specific reactor coolant system pipe whip restraints are complete with the exception of the hot leg upper pipe whip restraints.
All analyses completed verify that the pipe whip restraints are adequately designed using currently accepted assumptions and analytical techniques.
Although the design of the hot leg upper pipe whip restraint meets the commitments made in the Davis-Besse Nuclear Power Station Unit 1 Final Safety Analysis Report (response to Staff Question 3.6.7) a dynamic analysis is continuing on the hot leg upper pipe whip restraints, in accordance with BN-TOP-2, to identify the margin available using current criteria. The results will be submitted to you no later than February 15, 1980.
Yours very truly, f f R. P. Crouse Vice President Nuclear RPC:CLM D
N bj c/6 cc:
i United States Nuclear Regulatory Commission Office of Inspection and Enforcement j
Division of Reactor Operations Inspection THE T Oh SDN b IVIPA EOISON PLAZA 300 MADISON AVENUE TOLEOO, OHIO 43652 80040201$5 L
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Docket No. 50-346 License No. NPF-3 Sarial No. 1-109 December 7, 1979 DAVIS-BESSE NUCLEAR POWER STATION UNIT 1 VERIFICATION STUDY of PIPE WHIP RESTRAINTS on the REACTOR COOLANT SYSTEM 7
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TABLE OF CONTENTS
's Section Page No.
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I.
INTRODUCTION AND
SUMMARY
I-1
1.0 Background
I5 2.0 Summary 1-1 II.
SCOPE, ASSUMPTIONS, AND METHODOLOGY II-l 1.0 Scope II-l 2.0 Assumptions and Methodology II-1 III. HOT LEG PIPE WHIP RESTRAINT SYSTEM 111-1 1.0 Piping System III-l 1.1 Configuration and Properties III-l 1.2 Break Locations III-l 1.3 Desciption of Analysis III-l 2.0 Pipe Whip Restraints III-2 2.1 General III-2 2.2 Description of Analysis III-2 2.3 Description of Pipe Whip Restraints III-2 3.0 Summary of Results III-5 3.1 Pipe Whip Restraint Evaluation III-5 3.2 Cap Evaluation III-7 IV.
COLD LEG PIPE WHIP RESTRAINT SYSTEM IV-1 1.0 Piping System IV-1 1.1 Configuration and Properties IV-1 1.2 Break Locations IV-1 1.3 Description of Analysis IV-1 2.0 Pipe Whip Restraints IV-2 2.1 General IV-2 2.2 Description of Analysis IV-2 2.3 Description of Pipe Whip Restreints IV-3 3.0 Summary of Results IV-5 3.1 Pipe Whip Restraint Evaluation IV-5 3.2 Gap Evaluation IV-7 l
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V.
SUMMARY
AND CONCLUSIONS V-1 i e APPENDICES 1
1 Appendix A - Allowable Stresses for Elastic Behavior Appendix B - Effect of Varying the Theoretical Design Gap 1
t Appendix C - References 4
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LIST OF TABLES Table No.
Title 9*
III-1 Summary of Results for the RCS
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Hot Leg Pipe Whip Restraints III-2 Comparison of Prior Loads and New Loads for the RCS Hot Leg Pipe Whip Restraints IV-1 Summary of Results for the RCS Cold Leg Pipe Whip Restraints IV-2 Comparison of Prior Loads and New Loads for the RCS Cold Leg Pipe Whip Restraints i
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e LIST OF FIGURES Figure No.
Title II-1 RCS Piping and Pipe Whip Restraints Plan II-2 RCSPipingandPipeWhipRestraintsElevation5 111-1 Hot Leg LOCA Pipe Whip Restraint HLR-1 III-2 Hot Leg Pipe Whip Restraint HLR-2 III-3 Hot Leg Pipe Whip Restraint HLR-3 III-4 Hot Leg Pipe Whip Restraint HLR-4 III-5 Hot Leg Upper Pipe Whip Restraints HLR-5 and HLR-6 IV-1 Cold Leg Suction Line Pipe Whip Restraint CLR-1 IV-2 Cold Leg Bumper Pipe Whip Restraint CLR-2 IV-3 RCP LOCA Pipe Whip Restraint CLR-3 IV-4 RCP LOCA Pipe Whip Restraint CLR-4 IV-5 Cold Leg Discharge Line Pipe Whip Restraint CLR-5 IV-6 Cold Leg LOCA Pipe Whip Restraint CLR-6 B-1 Energy Balance for Varying the Gap O
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I.
INTRODUCTION AND
SUMMARY
c.
1.0 Background
1.1 In June 1979 the Nuclear Regulatory Commission (NRC) received an allegation that the steam generator supports s'.
the Davis-Besse Nuclear Powe'r Station Unit I were underdesigned by severa. orders of magnitude. This allegation was investigated by the NRC Office of Inspection and Enforcement,"" Region III at the Davis-Besse site on June 20-22, 1979, at the offices of Bechtel Power Corporation on July 2, 1979, and at the offices of Babcock & Wilcox on July 3, 1979. Based on these inspections, there was no apparent basis for the allegation.
Subsequent to these inspections, the allegator who desires to remain anonymous, informed the NRC that the problem was related to the walls to which the steam generator supports were attached along with the placement and design of the reactor coolant system hot leg supports. This further allegation was investi-gated by Region III at the offices of Bechtel Power Corporation on August 14 and 15, 1979. During this inspection, potential inconsistencies between commitments and design procedures used in the design of the reactor coolant system pipe whip restraints were identified.
A meeting was held at the NRC of fices in Bethesda, Maryland on September 7, 1979, to review and discuss the NRC's findings during their investigation of the allegation. At this meeting, it became apparent that confusion over the design of the reactor coolant system pipe whip restraints had resulted from an attempt to compare a 1971 design and design calculations with current day criteria and analytical techniques. To alleviate the NRC's concerns, Toledo Edison committed to verify the a(aquacy of the reactor coolant system pipe whip restraints using currently accepted criteria and analytical techniques.
1.2 This report presents our verification study of the reactor coolant system pipe whip restraint design. Verification of design for the hot leg upper pipe whip restraints has not yet been completed and will be submitted in a supplemental report by February 15, 1980.
Section II of this report presents the design criteria and analytical methods used in the analysis; Sections III and IV present a detailed review of the hot and coje leg pipe whip restraint system; and Section V presents.the conclusions that are drawn from this report.
2.0 Summary 2.1 The results of the verification study, completed thus far, show that, using present day design criteria and analytical techniques, the Davis-Besse Nuclear Power Station Unit I reactor coolant system pipe whip restraints are adequate to ensure performance of their intended function during a Loss of Coolant Accident. Although the verification of the hot leg upper pipe whip restraints has not been completed, analyses performed to date have veri-fled that they do compiv with the commitments made in the Davis-Besse Nuclear Power Station Unit 1 Final Safety Analysis Report (Reference 1) [ response to NRC Staff question 3.6.7, (10/4/74)].
1-1 l.
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II.
SCOPE, ASSUMPTIONS, AND METHODOLOGY 1.0 Scope 1.1 The scope of the verification study includes all pipe whip restraints on the Reactor Coolant System (RCS) hot and cold legs for the Davis-Besse Nuclear Power Station Unit 1.
For a general arrangement plan and elevation of the RCS piping and pipe whip restraints, see Figures 11-1 and 11-2.
This study was performed to verify that the RCS pipe whip restraint design ip adequate to prevent uncontrolled pipe whip in case of a Loss of Coolant Accident (LOCA).
The design of each pipe whip restrafnt has been evaluated to confirm the followings The plastic behavior of the pipe whip restraint results in deformations and a.
strains within acceptable limits.
b.
Structural components of the pipe whip restraint such as bolts, plates with holes, welds, and embedments remain elastic and do not limit the plastic capacity of the pipe whip restraint.
c.
The concrete walls will sustain locally the loads due to the pipe whip restraint reactions, and the overall design of the walls is unaffected.
20 Assumptions and Methodology 2.1 Pipe whip restraints are located and designed to provide protection for safety-related equipment, structures, and components from the whipping of a high energy pipe due to a LOCA.
Since pipe whip restraints are not in contact with the piping system during normal operation and/or a seismic event, they are designed for only LOCA loads.
2.2 The methodology used in evaluating the RCS pipe whip restraints consisted of two approaches.
The first approach used Bechtel Power Corporation Topical Report BN-TOP-2, a.
Revision 2, " Design for Pipe Break Effects" (Reference 2), approved for use by NkC Letter dated June 17, 1974. This topical report allows pipe whip restraints to be analyzed by using either conservative energy balance techniques or more exact dynamic analysis techniques.
Thepipewhiprestraintsreviewedinthidreportwerefirstanalyzedusing the conservative energy balance techniques.
If this analysis did not provide the desired margin of safety, then a more exact dynamic analysis was performed for the pipe whip restraint.
In the first analysis, conservative energy balance techniques were used to account for the dynamic response of the pipe whip restraint and for the impact of the pipe. Maximum displacements of the pipe whip restraints were calcu-lated according to the principle of energy balance:
Input Energy = Energy Absorbed by the System The energy absorbed by the piping system was included in the analysis. Force-displacement curves for the piping system and for the pipe whip restraints were developed. The energy input to the system by the pipe break thrust force was balanced by the resistance of the piping and pipe whip restraints 11-1
to datsrmins tha maxinua dicplcccuents and losds davalopsd by the pipe whip restraints. The loads developed were used in evaluating the structural components such as bolts, plates with holes, welds, and embedments, to ensure that they remain elastic.
The dynamic analysis of the piping and pipe whip restraint sy, stem was performed using a finite element code available in the public domain. The analysis utilized the pipe whip restraint's force-displacement curves.(elasto-plastic) which were prepared for the energy balance approach. By applying the dynamic force at the postulated break location, a non-linear dynamic time history analysis is performed to determine the peak response of the piping and pipe whip restraint system.
b.
The em ond approach made use of the results of dynamic analyses performed by Babcock & Wilcox to evaluate the RCS pipe whip restraints. Using a dynamic analysis, B&W determined the maximum loads resisted by the Reactor Coolant Pump (RCP) LOCA pipe whip restraints as given in their Specification 3002/NSS-14/1077 (Reference 3).
In addition, B&W recently analyzed the RCS piping for breaks at the reactor vessel nozzle and first elbow on both the hot and cold legs. The results were obtained by dynamic analysis and are contained in B&W Document No. 86-3041-00 (Reference 4).
The loads determined by these dynamic analyses were used to evaluate the design of the pipe whip restraints where applicable. These results were used because of their availability and the more exact nature of a dynamic analysis.
2.3 Using the criteria given in NRC Branch Technical Position MEB 3-1 (Reference 5),
B&W performed an analysis based upon pipe stress to determine the number, loca-tion, and type of pipe breaks postulated to occur on the hot and cold legs of the RCS piping.
The results of this pipe break analysis are contained in B&W Document No. 86-1105779-00 (Reference 6) and are discussed further in Sections III and IV.
The verification study of the pipe whip restraints was based on these postulated breaks.
2.4 When using the energy balance approach, the pipe break thrust force developed doe to a break in the RCS piping was assumed to be applied instantaneously at its maximum value and to remain constant in magnitude with time. The above assumption is conservative based on the actual blowdown of the RCS. The maximum value for pipe break thrust force was assumed to equal 1.26PA, where P is defined as the operating pressure (2185 psig) for thi piping system and A is the internal flow area of the pipe. The value of 1.26 is taken from BN-TOP-2 (Reference 2) for superheated steam treated as an ideal gas escaping from a frictionless pipe. No additional increase in pipe thrust need be included for rebound since the system blowdown forcing function is not a three-step function [See Appendix B of BN-TOP-2 (Reference 2)].
2.5 The evaluation of the RCS hot and cold leg pipe whip restraints was performed in accordance with Procedure No. 7749-C-101, " Criteria for Verification of Pipe Whip Restraints for the Reactor Coolant System for the Toledo Edison Company Davis-Besac Nrelear Power Station Unit 1" (Reference 7) and Appendix A to this report. 4 &c tjastic behavior of the pipe ship restraint, the stress-strain relatic.% fe: thE material was utilized to levelop the force-displacement curve for ri f ftp thip restraint. The allowable strain was limited to 50 percent o; t.i fagin at ultimate tensile stress in accordance with BN-TOP-2 (Referenet 2).
Strwetural components such as bolts, plates with holes, welds, II-2 I
cnd cab 2daants that could limit tha plastic behavior of tha pipe whip rastraint were required to remain elastic in behavior and were checked for the allowable stresses given in Appendix A.
The effect of a gap between the pipe and the pipe whip restraint was included in the analysis. The gaps were based on the theoretical hot position of the pipe. The gaps were calculated using the cold gap shown on the design drawings and the thermal movements of the pipe given in B&W Specification.-3002/NSS-14/1077 (Reference 3).
The effect of variation of the gap from the theor'etical hot position gap was also evaluated and is discussed in Sections III and IV.
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III. HOT LEG PIPE WHIP RESTRAINT SYSTEM 1.0 Piping System 1.1 Configuration and Properties The hot legs of the RCS piping for Davis-Besse Nuclear Power Station Unit I run from the reactor vessel to the top of the steam generators. See Figures 11-1 and II-2 for a general arrangement plan and elevation of the"RCS piping.
The two hot legs on the RCS piping are identical in configuration for LOCA loads. Both hot legs have identical pipe whip restraint systems. The hot leg piping was fabricated to the following:
a.
ASTM A 106, Grade C material b.
Inside diameter of 36 inches c.
Wall thickness of 3-1/8 inches for the straight sections and 4 inches for the elbows.
1.2 Break Locations The pipe whip restraints for the hot leg piping were evaluated based on the following postulated breaks as shown on Figure II-2.
a.
Guillotine break at the reactor vessel nozzle (GB-1) b.
Guillotine break at the first elbow from the reactor vessel on the horizontal portion of the hot leg (GB-2) c.
Guillotine break at the location of hot leg upper pipe whip restraint HLR-6 (GB-3) d.
Guillotine break at the steam generator nozzle (GB-4)
These breaks are postulated to occur in the hot leg piping by B&W in their Document No. 86-1105779-00 (Reference 6) using the criteria given in the NRC Branch Technical Position MEB 3-1 (Reference 5).
1.3 Description of Analysis When performing the energy balance analysis to evaluate the pipe whip restraints, the input energy resisted by the hot leg piping system was taken into account.
Force-displacement curves for the piping system were developed. For the postu-lated guillotine breaks in the hot leg, the pipe was assumed to cantilever from either the steam generator or the reactor vessel. A unit load was applied at the break location in the direction of the pipe break thrust force and the resultant displacements and moments were calculated. The load required to form a plastic hinge at the reactor vessel or steam generator, causing the pipe to yield, was determined. The displacement at the load point was i
calculated. With these values, the force-displacement curves for the pipe were generated.
The area under the force-displacement curve (pipe resistance energy) was utilized to balance the energy input into the system by the pipe break thrust force.
I III-1 l
The plastic behavior of the RCS piping was evaluated using the minimum yield strength, at the operating temperature, as given in Appendix I to the ASME Boiler and Pressure Vessel Code,Section III, Division 1, Appendices (Reference 8).
A 10 percent increase in the minimum yield strength was used to determine the plastic moment of the pipe in accordance with BN-TOP-2 (Reference 2).
2.0 Pipe Whip Restraints 2.1 General Both hot legs of the RCS piping are provided with identical pipe whip restraint systems to resist pipe whip due to a LOCA. The pipe whip restraints on the hot legs are as follows:
a.
Hot leg LOCA pipe whip restraint HLR-1 b.
Hot leg pipe whip restraint HLR-2 c.
Hot leg pipe whip restraint HLR-3 d.
Hot leg pipe whip restraint HLR-4 e.
Hot leg upper pipe whip restraints HLR-5 and HLR-6 These pipe whip restraints for a typical hot leg are located in plan and in elevation on Figures II-l and II-2.
2.2 Description of Analysis In order to evaluate the hot leg pipe whip restraints for a LOCA, force-displacement curves for each of the pipe whip restraints were developed.
The general purpose computer program ANSYS was used to develop these curves. A finite element model of each of the pipe whip restraints was developed. Repre-sentative manufacturer data for the stress-strain relationship of the pipe whip restraint material (ASTM A 516, Grade 70 steel) was used as input to the analysis.
For a force in the direction of each principle axis of the pipe whip restraint, the relationship betweep, force and displacement for elasto/ plastic behavior was obtained.
The curves resulting from the above described analysis were then utilized to determine the pipe whip restraint loads and displacements for the postulated pipe breaka. Using BN-TOP-2 (Reference 2) energy balance methodology, the area under these curves, in addition to the pipe resistance, balances the energy input to the system by the pipe break thrust force.
B&W utilized these curves in their dynamic analysis to obtain the results contained in B6W Document No. 86-3041-00 (Reference 4) as shown in Table III-l of this report.
2.3 Description of Pipe Whip Restraints The following provides a brief discussion of the pipe whip restraint location, configuration, materials, controlling break location, and method of analysis utilized for each of the hot leg pipe whip restraints.
III-2
c.
Hot Leg LOCA Pip 2 Whip Restraint HLR-1 The hot leg LOCA pipe whip restraint HLR-1 is located on the hot leg between the reactor vessel and the first elbow from the reactor vessel.
The configuration of the pipe whip restraint is similar to a wagon wheel, as shown in Figure III-1.
It is comprised of two circular rings which are connected by plates spaced radially at 30-degree intervals to form the spokes of the wheel.
The pipe whip restraint was fabricated in three equal 120-degree sections and assembled by bolting the sections together with ASTM A 490 bolts. The inner ring completely encircles the hot leg pipe while the outer ring is fully embedded in the primary shield wall using headed studs. The pipe whip restraint is fabricated from ASTM A 516, grade 70 steel plates which are connected with full penetration welds.
The gaps between the pipe and the pipe whip restraint were obtained by shim bars located at each of the spoke plates.
The design of hot leg LOCA pipe whip restraint HLR-1 is controlled by a guillotine break at the reactor vessel nozzle.
B&W performed a dynamic analysis for a break at this location. The force-displacement curves for the pipe whip restraint developed as discussed in paragraph 2.2 were utilized in the B&W analysis. The resulting loads to pipe whip re-straint HLR-1 for this postulated break are shown in Table III-1. These loads, obtained from B&W, were the basis for the evaluation of the pipe whip restraint.
b.
Hot Leg Pipe Whip Restraint HLR-2 Hot leg pipe whip restraint HLR-2 is located on the hot leg at the first elbow from the reactor vessel.
It is attached to a base plate ambedded in the primary shield wall. For location of the pipe whip restraint in plan and in elevation, see Figures II-l att II-2.
The pipe whip restraint is comprised of two separate components.
The first component is a strap located at the center of the elbow and intersecting the primary shield wall at an angle of 45-degrees. The strap consists of two plates which are bent to form extended semi-circles and are connected by spacer plates, as shown in Figure III-2.
The strap is connected with ASTM A 490 bolts to a pinned anchorage assembly which is welded to the base plate. As designed, the strap component of pipe whip restraint HLR-2 resists loads away from the wall in the direction of the strap. Shim bars were provided which were fitted to the specified gaps. Pins used in the anchorage assembly for the strap conform to ASTM A 193 Grade B7.
The second component of pipe whip restraint HLR-2 consists of a circular ring which completely encompasses the hot leg pipe.
It is located just above the first elbow on the vertical portion of the hot leg.
The ring is attached to a stiffened built-up section which cantilevers from the base plate. Shim bars are provided and installed to the gaps specified on the design drawings. The entire pipe whip restraint, including the base plate, is fabricated from ASTM A 516, Grade 70 steel plates.
The base plate is embedded in the primary shield wall using ASTM A 540, Grade B23, Class 3 rods.
III-3
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The design of this pipe whip restraint is controlled by a guillotine break at the first elbow from the reactor vessel on the horizontal portion of the hot leg.
For a break at this location, the loads used to evaluate the two components of pipe whip restraint HLR-2 were taken f rom B&W Document No. 86-3041-00 (Reference 4) and are shown in Table 111-1.
B&W obtained these loads using a dynamic analysis and the force-displacement curves for the pipe whip restraint developed as discussed in Paragraph 2.2.
c.
Hot Leg Pipe Whip Restraint HLR-3 Hot leg pipe whip restraint HLR-3 is located at approximately the midpoint of the straight, vertical portion of the hot leg.
The configuration of the pipe whip restraint is shown in Figure III-3.
It is comprised of a circular ring which completely surrounds the hot leg pipe. The ring is welded to a built-up section which cantilevers from a base plate embedded in the secondary shield wall.
The base plate is embedded in the wall by ASTM A 540, Grade B23, Class 3 rods.
The pipe whip restraint is fabricated from ASTM A 516, Grade 70 steel plates which are connected with full penetration welds.
For horizontal displacement parallel to the secondary shield wall, shim bars are installed and adjusted to provide the required gaps. For horizontal displacement perpendicular to the secondary shield wall, no shim bars are provided.
The pipe and pipe whip restraint are installed within specified tolerances to conform to the gaps shown on the design drawings.
Pipe Whip Restraint HLR-3 is not required to resist any of the postulated pipe breaks in the hot leg piping.
d.
Hot Leg Pipe Whip Restraint HLR-4 Hot leg pipe whip restraint HLR-4 is located at the top of the straight, vertical portion of the hot leg positioned just below the pipe elbow.
See Figures II-l and II-2 for the pipe whip restraint location in plan and in elevation.
In configuration, this pipe whip restraint is almost i
identical to the ring component for pipe whip restraint HLR-2.
It consists 4
of a circular ring which is identical to the one used in the ring component for pipe whip restraint HLR-2.
Likewise, the circular ring is connected to a built-up section which cantilevers fr,om a base plate embedded in the secondary shield wall. The only difference in the built-up section is that the distance from the wall to the center of the ring is less for pipe whip restraint HLR-4 than for pipe whip restraint HLR-2. The base plate is embedded in the wall with ASTM A 540, Grade B23, Class 3 rods.
)
Shim bars are provided and installed to obtain the required gaps.
The pipe whip restraint, including base plate, is fabricated from ASTM A 516, j
Grade 70 steel plates and connected by full penetration welds. Figure III-4 i
shows the configuration of the pipe whip restraint.
Pipe whip restraint HLR-4 is not required to prevent pipe whip for any of the postulated hot leg pipe breaks.
e.
Hot Leg Upper Pipe Whip Restraints HLR-5 and HLR-6 The hot leg upper pipe whip restraints HLR-5 and HLR-6 are located on the 180-degree pipe section at the top of the hot leg piping. The pipe whip restraints are positioned symmetrically, 45-degrees from the vertical center III-4
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line of the pipa srction as chown in Figures 11-1 and II-2. Each pipe whip rsstroint censiste of a ring menbar which is attachsd to girders spanning between the secondary shield walls.
Figure III-5 shows the configuration of the pipe whip restraints and the supporting structure.
The configuration of each pipe whip restraint is that of a built-up wide flange section curved to conform to the shape of the hot leg pipe's cross section. The pipe whip restraint ring members are welded to base plates which are in turn fastened to the top flanges of the supportin,g girders with ASTM A 490 bolts.
Shim bars are provided on the ring members to allow adjustment for the specified gaps.
Stiffeners are positioned on the pipe whip restraint ring member at each of the shim bar locations.
The supporting structure for pipe whip restraints HLR-5 and HLR-6 consists of two built-up girders spanning horizontally between the secondary shield walls.
In addition, there is a bracing member connected to each girder at the center line of the 180-degree pipe section spanning at a 45-degree angle back to the secondary shield wall closest to the reactor vessel. These built-up girders and bracing members are fabricated to form wide flange sections.
The girders are welded to base plates which are through bolted to the secondary shield walls with ASTM A 490 bolts. Bracing members are connected to base plates embedded in the secondary shield walls with anchor plates.
All members including the pipe whip restraint rings are fabricated from ASTM A 516, Grade 70 steel plates.
The design of pipe whip restraints HLR-5 and HLR-6 is controlled by two of the postulated breaks in the hot leg piping. For a guillotine break at the steam generator nozzle, both pipe whip restraints would be impacted and loaded.
It appears that a guillotine break in the 180-degree pipe section at the location of HLR-6 will be resisted by HLR-5 only.
Due to the com-plexity of this pipe whip restraint (i.e. two independent pipe whip restraints attached to one supporting structure) a dynamic analysis is being performed.
This analysis is in progress and the results will be reported as soon as they are available. Analyses performed on pipe whip restraints HLR-5 and HLR-6 to date, verify that they do comply with the commitments made in the Davis-Besse Nuclear Power Station Unit 1 Final Safety Analysis Report (Reference 1) [ response to NRC Staff question 3.6.7, (10/4/74)). The dynamic analysis will identify the margin available utilizing current criteria.
3.0 Summary of Results 3.1 Pipe Whip Restraint Evaluation Table III-l summarizes the results of the verification study of the hot leg pipe whip restaints. Where applicable, the controlling break location, magni-tude and direction of the load resisted by the pipe whip restraint, displace-ment of the pipe whip restraint in the direction of the load, and the ductility ratio for the maximum strained element are given for each hot leg pipe whip restraint. No data is provided in Table III-1 for pipe whip restraints HLR-3 and HLR-4, since these pipe whip restraints are not required to resist loads from any of the pcstulated pipe breaks. A dynamic analysis is in progress to verify the design adequacy of pipe whip restraints HLR-5 and HLR-6.
The results of the analysis of these pipe whip restraints will be submitted at a later date.
III-5 l
The first step in th2 draign evaluation of the hot leg pipe whip restraints was to verify that deformations and strains resulting from a LOCA are within acceptable limits.
BN-TOP-2 (Reference 2) requires that the strain in the maximum stressed element of a pipe whip restraint be limited to a value equal to 50 percent of the strain at ultimate tensile stress for the pipe whip restraint steel. The findings of the design evaluation are summarized in the following paragraphs.
Pipe whip restraint HLR-1 and the strap component of pipe whip restraint HLR-2 respond elastically to the postulated pipe break loads and are therefore accept-able. The ring component of pipe whip restraint HLR-2 behaves plastically when subjected to the postulated pipe break loads.
Elements of this component are strained beyond the elastic limit for the pipe whip restraint material.
In order to evaluate the effect of the resulting plastic deformations, the strain in the maximum stressed element was determined for the ring.
The maximum strain was then related to the elastic strain to calculate the ductility ratio shown in Table III-1.
Ductility ratio is defined as the ratio of the resulting strain to the strain at the elastic limit. Deformation for the ring component of pipe whip restraint HLR-2 results in a ductility ratio of less than 65.
A ductility ratio of 65 corresponds to a strain equal to 50 percent of the strain at ultimate tensile stress for ASTM A 516, Grade 70 steel plate. Thus, the plastic deformation of the ring component of pipe whip restraint HLR-2 meets the requirements of BN-TOP-2 (Reference 2), and is therefore acceptable.
The next step in the design evaluation of the hot leg pipe whip restraints was to verify that certain structural components do not limit the ability of the pipe whip restraints to react plastically to the postulated pipe break loads.
These components include such items as shear pins, high-strength bolts, rods, headed studs, welds, and plates with holes. For the purpose of the design evaluation, elastic behavior of these components was limited to the allowable stresses given in Appendix A.
A complete check of the hot leg pipe whip re-straints verified that all such components when subjected to the postulated pipe break loads given in Table III-1, conform to the allowable stress requirements of Appendix A.
The last step in the hot leg pipe whip restraint design evaluation was to verify the adequacy of the concrete shield walls for the postulated pipe break loads.
Table III-2 provides a comparison of the prior design loads with the new loads in terms of PA (pressure times area). The results presented in Table III-2 clearly indicate that for every case the new loads are less than the prior design loads.
Therefore, the prior design of the concrete shield walls to which the pipe whip restraints are attached is adequate. Furthermore, calcula-tions verify that the concrete design is locally adequate to support the new pipe whip restraint design loads.
(
III-6 i
3.2 Gap Evaluation The effect of varying the gap was evaluated for the hot leg pipe whip restraints.
For pipe whip restraint HLR-1 the effect of gap varying from the design value is not significant. Shim bars were installed to provide very little gap between the pipe and the pipe whip restraint. The maximum gap physically possible is 3/8 inch while the design gap is 1/4 inch.
Since the resulting d'ctility ratio u
for this pipe whip restraint is less than one, the derivation in Appendix B shows that the pipe whip restraint has sufficient unused strain energy to resist the maximum possible increase in gap.
For pipe whip restraint HLR-2 the effect of gap varying from the design value was similarly evaluated.
For the ring component of this pipe whip restraint, shim bars physically limit the gap to a maximum value of 8-3/4 inches while the design gap is 4 inches. Based on the derivation in Appendix B and the ductility ratio shown in Table III-1, there is adequate unused strain energy to resist the maximum possible increase in gap.
The maximum possible gap for the strap component is 6-1/2 inches based on the physical limitations imposed by the ring component and shim bars located on the strap, while the design gap is 3-1/4 inches. Based on the derivation in Appendix B and the ductility ratio shown in Table III-1, there is adequate unused strain energy to resist the maximum possible increase in gap.
A variation in the gap for pipe whip restraints HLR-3 and HLR-4 has not been evaluated since these pipe whip restraints are not required to resist any of the postulated hot leg pipe breaks. The effect of the gap varying for pipe whip restraints HLR-5 and HLR-6 cannot be evaluated until the analysis is completed for these pipe whip restraints.
III-7 l
l
~
TAPsLE III-1
SUMMARY
OF RESULTS FOR THE RCS HOT LEG PIPE WHIP RESTRAINTS Displacement Maximum Pipe Wh.ip Controll.ing Break New Design New Design Load in Load Ductility Restraint No.
Location Loads Direction Direction Ratio k
Guillotine Break at the P :1248 HLR-1 reactor Wssel nozzle ELEVATIO N P
O.023" less than 1 (GB-1)
P, : B24 (1) k Guillotine Break at first
'f(
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p k
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Su.liotine Break at first P: 6 21
.f, k
HLR-2 elbow frorn the reactor PLAN P
II.
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(ring) wssel.
' Pg = 252 q,
~
( GB-2)
HLR-3 none O
N/A N/A N/A HLR-4 none O
N/A N/A
?
N/A HLR-6 HLR-5 i
HLR-5 (later) 9 = stater)
( la t er)
(late r >
ELEVAT ION E
HLR-6 (later)
P : (later) 2 IL (iater)
( la ter) p (1) Q is a frictional load applied at the P load location in the direction paroilel to the pipe l
- a 0
TABLE ID - 2 COMPARISON OF PRIOR LOADS AND NEW LOADS FOR THE RCS H OT L EG PI P E WHI P RESTR A'INTS Pipe Whip Prior Design Load-Fp New Design Load kn Restraint Fp Fn Fn g
No HLR - 1 4440*
2.00 1248*
O.56 HLR - 2 g
x
( Strap )
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( Ring )
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1.50 0
N.A.
H LR-4 3330*
1.50 0
N. A.
H LR -5 4710*
2.12 (Later)
(Later)
HLR-6 4710*
2.12 (Later)
(Later)
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IV.
COLD LEG PIPE WHIP RESTRAINT SYSTEM 1.0 Piping System 1.1 Configuration and Properties The cold legs of the RCS piping run from the steam generators to the RCP (suction line) and from the RCP to the reactor vessel (discharge line).
For a general arrangement plan and elevation of the RCS piping, see Figures II-1 and II-2.
There are four cold legs on the RCS piping with each cold leg having the identical pipe whip rastraint system to prevent pipe whip due to a LOCA.
The cold leg piping was fabricated to the following:
a.
ASTM A 106, Grade C material b.
Inside diameter of 28 inches c.
Wall thickness of 2-9/16 inches for the straight sections and 3-3/8 inches for the elbows.
1.2 Break Locations The pipe whip restraints for the cold leg piping system were evaluated based on the following postulated breaks as shown on Figure 11-2.
a.
Guillotine break at the steam generator nozzle (GB-5) b.
Guillotine break at the end of the first elbow from the steam generator (GB-6) c.
Guillotine break at the center of the second elbow from the steam generator on the suction line (GB-7).
d.
Guillotine break at the RCP suction line nozzle (GB-8) e.
Guillotine break at the RCP discharge line nozzle (GB-9) f.
Guillotine break at the first elbow from the RCP on the horizontal portion of the cold leg discharge line (GB-10) g.
Guillotine break at the first elbow from the reactor vessel on the horizontal portion of the cold leg discharge line (GB-11) h.
Guillotine break at the reactor vessel nozzel (GB-12)
These breaks are postulated to occur in the cold leg piping by B&W in their Document No. 86-1105779-00 (Reference 6) using the criteria given in the NRC Branch Technical Position MEB 3-1 (Reference 5).
1.3 Description of Analysis When performing the energy balance analysis to evaluate the pipe whip restraints, the input energy resisted by the cold leg piping system was taken into acccant.
Force-displacement curves for the piping system were developed. For the postulated guillotine breaks in the cold leg, the pipe was assumed to cantilever from either the steam generator or the reactor vessel. A unit load was applied at the IV-1
break location in the direction of the pipe break thrust force and the resultant displacements and moments were calculated.
The load required to form a plastic hinge at the reactor vessel or steam generator causing the pipe to yield was deter-mined. The displacement at the load point was calculated. With these values, the force-displacement curves for the pipe were generated.
The area _under the force-displacement curve (pipe resistance energy) was utilized t) balance the energy input into the system by the pipe break thrust force.
The plastic behavior of the RCS piping was evaluated using the min mum yield strength, at the operating temperature, as given in Appendix I to the ASME Boiler and Pressure Vessel Code,Section III, Division 1 Appendices (Reference 8).
A 10 percent increase in the minimum yield strength was used to determine the plastic moment of the pipe in accordance with BN-TOP-2 (Reference 2).
2.0 Fipe Whip Restraints 2.1 General Each of the four cold legs of the RCS piping is provided with identical pipe whip restraint systems to resist pipe whip due to a LOCA. The pipe whip restraints on each of the cold legs are as follows:
a.
Cold leg suction line pipe whip restraint CLR-1 b.
Cold leg bumper pipe whip restraint CLR-2 c.
RCP LOCA pipe whip restraints CLR-3 and CLR-4 d.
Cold leg discharge line pipe whip restraint CLR-5 e.
Cold leg LOCA pipe whip restraint CLR-6 These pipe whip restraints for a typical cold leg are located in plan and in elevation on Figures 1I-1 and II-2.
2.2 Description of Analysis In order to evaluate the cold leg pipe whip restraints for a LOCA, force-displacement curves for each of the pipe whip' restraints were developed. The general purpose computer program ANSYS was used to develop these curves. A finite element model of each of the pipe whip restraints was developed. Repre-sentative manufacturer data for the stress-strain relationship of the pipe whip restraint material (ASTM A 516, Grade 70 steel) was used as input to the analysis. For a force in the direction of each principle axis of the pipe whip restraint, the relationship between force and displacement for elasto/
plastic bet *vior was obtained.
The curves resulting from the above described analysis were then utilized to determine the pipe whip restraint loads and displacements for the postulated pipe breaks. Using BN-TOP-2 (heference 2) energy balance methodology, the area under these curves, in addition to the pipe resistance, balances the energy input to the system by the pipe break thrust force.
B&W utilized these curves in their dynamic analysis to obtain the results contained in B&W Docu-ment No. 86-3041-00 (Reference 4) as shovn in Table IV-1 of this report.
IV-2 i
I
2.3 Description of Pipe Whip Restraints The following provides a brief discussion of the pipe whip restraint location, configuration, materials, controlling break location, and method of analysis utilized for each of the cold leg pipe whip restraints.
a.
Cold Leg Suction Line Pipe Whip Restraint CLR-1 The cold leg suction line pipe whip restraint CLR-1 is located on the straight portion of the cold leg suction line and is attached to the floor slab at elevation 565'-0".
Pipe whip restraint CLR-1 consists of two pairs of wire rope wrapped symmetrically around the suction pipe as shown in Figure IV-1.
The wire ropes are 3 inch diameter, 6 x 37 Class (WSC), bridge rope manu-factured by Bethlehem Steel Corporation. The wire ropes are attached to a base plate fabricated from ASTM A 516, Grade 70 steel plates and embedded in the floor slab with ASTM A 540, Grade B23, Class 3 rods. A saddle is provided around the pipe to allow the installation of insulation on the pipe and the transfer of load from the pipe to the wire ropes. The wire ropes allow thermal and seismic displacement without engaging the pipe whip restraint.
Pipe whip restraint CLR-1 is not required to resist any of the postulated pipe breaks in the cold leg piping.
b.
Cold Leg Bumper Pipe Whip Restraint CLR-2 The cold leg bumper pipe whip restraint CLR-2 is located at the first elbow from the RCP on the cold leg suction line.
Pipe whip restraint CLR-2 is a bumper-shaped structure which is supported by the floor slab at elevation 565'-0" as shown in Figure IV-2.
It is positioned to resist pipe whip downward towards the floor slab and horizonally in the direction of the RCP parallel to the suction line. Load is transferred from the pipe to the pipe whip restraint by means of a strap attached to the pipe elbow designed to impact the bumper in either the vertical or horizontal direction.
The pipe whip restraint is fabricated from ASTM A 516, grade 70 steel plates.
ASTM A 490 bolts are used to connect the horizontal load resisting portion of the pipe whip restraint to the portion cantilevered from the floor slab.
The bumper !s attached to the floor slab by ASTM A 490 bolts projecting from the slab.
The design of this pipe whip restraint is controlled by two postulated breaks depending on the direction of the load to be resisted. A guillotine break at the RCP suction line nozzle would result in a downward load to the bumper.
A guillotine break at the end of the first elbow from the steam generator would Joad the pipe whip restraint in the horizontal direction.
IV-3
For these postulated break locations, the loads to be resisted by the pipe whip restraint and the resulting displacements were obtained using BN-TOP-2 (Reference 2) energy balance techniques. For each case, the resistance of the pipe acting as a cantilever to the location of the break was included in the analysis to help resist the pipe break thrust force. The results of the energy balance analysis for the postulated pipe breaks are shown in Table IV-1.
c.
Reactor Coolant Pump LOCA Pipe Whip Restraints CLR-3 and CLR-4 RCP LOCA pipe whip restraints CLR-3 and CLR-4 are located on the RCP as shown in Figures II-1 and 11-2.
Pipe whip restraint CLR-3 consists of horizontal wire rope located at two different elevations on the RCP. Each elevation has a pair of 2-1/8 inch diameter wire ropes wrapped around the RCP and attached to the secondary shield walls. Tne wire ropes are attached to the secondary shield walls such that the resultant of each wire rope intersects the secondary shield wall at a 45-degree angle en opposite sides of the RCP center line as shown in Figure IV-3.
Pipe whip restraint CLR-4 is located to resist upward vertical displacement of the RCP due to a guillo-tine break at the RCP suction line nozzle.
This pipe whip restraint is comprised of two pairs of 2-1/8 inch diameter wire ropes wrapped around the RCP as shown in Figure IV-4.
1 l
The wire ropes for pipe whip restraint CLR-3 are attached to anchorages embedded in the secondary shield walls with ASTM A 540, Grade B23, Class 3 rods.
The wire ropes for pipe whip restraint CLR-4 are connected to anchorages embedded in the floor slab at elevation 565'-0".
The anchorages for pipe whip restraints CLR-3 and CLR-4 are fabricated from ASTM A 516, Grade 70 steel plates connected with full penetration welds.
The wire ropes used in pipe whip restraints CLR-3 and CLR-4 are 2-1/8 inch diameter, 6 x 19 Class (WSC), bridge rope manu-f actured by Bethlehem Steel Corpccation. The wire ropes allow thermal and seismic displacements without engaging the pipe whip restraints.
The design of pipe whip restraint CLR-3 is controlled by a guillotine break at the RCP discharge line nozzle. Pipe whip restraint CLR-4 is governed by a guillotine break at the RCP suction line nozzle.
The maximum loads to these pipe whip restraints are given in B&W Specification 3002/NSS-14/1077 (Reference 3) as shown in Table IV-1.
The wire rope loads given in this document are the result of a dynamic analysis and were the basis for the evaluation of the pipe whip restraints, d.
Cold Leg Discharge Line Pipe Whip Restraint CLR-5 The cold leg discharge line pipe whip restraint CLR-5 is located on the straight portion of the cold leg discharge line and is attached to the haunch._ cortion of the primary shield wall. The configuration of the pipe whip rest.aint is shown in Figure IV-5. It is comprised of a circular ring IV-4
which completely surrounds the pipe. The ring is attached to a stiffened built-up section which cantilevers from a base plate embedded in the wall using ASTM A 540, Grade B23, Class 3 rods. The pipe whip restaint is fabricated from ASTM A 516, Grade 70 steel plates which are connected with full penetration welds. Shim plates were installed at 30-degree intervals radially around the inside of the pipe whip restraint ring.
Final shim plate thicknesses were determined to provide the required gap at all shim locations.
The design of pipe whip restraint CLR-5 is controlled by a guillotine break in the cold leg discharge line at the first elbow from the reactor vessel.
For a break at this location, B&W generated loads to the pipe whip restraint using a dynamic analysis which utilized the force-displacement curve for the pipe whip restraint which was developed using the ANSYS computer code. The loads taken from B&W Docueent No. 86-3041-00 (Reference 4) are shown in Table IV-1.
These loads were the basis for the evaluation of pipe whip restraint CLR-3.
Cold Leg LOCA Pipe Whip Restraint CLR-6 e.
The Cold leg LOCA pipe whip restraint CLR-6 is located between the reactor vessel and the first elbow on the cold leg discharge line and is embedded in the primary shield wall.
Pipe ship restraint CLR-6 is similar in con-figurttion to a wagon wheel, as shown in Figure IV-6.
It is comprised of two circular rings which are connected by plates located radially at 30-degree intervals to form the spokes of the wheel.
The pipe whip restraint is fabricated in three equal 120-degree sections which were then bolted together with ASTM A 490 bolts.
The inner ring completely encompasses the cold leg discharge line pipe and the outer ring is fully embedded in the primary shield wall using headed studs.
The plates used to fabricate the pipe whip restraint conform to ASTM A 516, Grade 70 and are connected with full penetration welds. The gaps between the pipe and the pipe whip restraint were obtained by shim bars located at each of the spoke plates.
The design of this pipe whip restraint is governed by a guillotine break at the reactor vessel nozzle in the cold leg, discharge line.
For a break at this location, the loads used to evaluate the pipe whip restraint were taken f rom B&W Document No. 86-3041-00 (Reference 4) and are shown in Table IV-1.
3.0 Summary of Results 3.1 Pipe Whip Restraint Evaluation A summary of the results obtained for the verification study of the cold leg pipe whip restraints is given in Table IV-1.
For each pipe whip restraint, except as noted below, the controlling break location, magnitude and direction of the load resisted by the pipe whip restraint, displacement of the pipe whip restraint in the direction of the load, and the ductility ratio for the maximum strained element are given. For pipe whip restraints CLR-3 and CLR-4, the IV-5
displacement of the pipe whip restraint and the maximum ductility ratio are not given. The design evaluation of wire rope for these pipe whip restraints is based on an allowable tension limited to 90 percent of the specified minimum breaking strength for the wire rope.
No data is given in Table IV-1 for pipe whip restraint CLR-1, since this pipe whip restriant is not required to resist any of the postulated pipe breaks.
The first step in the design evaluation of the cold leg pipe whip restraints was to verify that the deformations and strains resulting from a LOCA are within acceptable limits.
BN-TOP-2 (Reference 2) requires that the strain in the maximum stressed element of a pipe whip restraint be limited to a value equal to 50 percent of the strain at ultimate tensile stress for the pipe whip restraint steel. The findings of the design evaluation are summarized in the following paragraphs.
Pipe whip restraint CLR-6 responds elastically to the postulated pipe break loads and is therefore acceptable. Pipe whip restraints CLR-2 and CLR-5 behave plastica 11y when subjected to the postulated pipe break loads.
In order to evaluate the effect of the resulting plastic deformations, the strain in the maximum stressed element was determined for each of the pipe whip restraints.
The maximum strains were then related to the elastic strain to calculate the ductility ratios shown in Table lV-1.
Deformations for pipe whip re-straints CLR-2 and CLR-5 result in ductility ratios of less than 65.
A ductility ratio of 65 corresponds to a strain equal to 50 percent of the strain at ultimate tensile stress for ASTM A 516, Grade 70 steel plate. Thus, the plastic deformations of pipe whip restraints CLR-2 and CLR-5 meet the require-ments of BN-TOP-2 (Reference 2) and are therefore acceptable.
For pipe whip restraints CLR-3 and CLR-4, the wire rope was required to respond elastically to the pipe break loads. These pipe whip restraints were evaluated by limiting the allowable wire rope tension to 90 percent of the minimum breaking strength.
In addition, a reduction in the allowable wire rope tension was included to account for the bending stresses developed due to the wrapping of the wire rope around a saddle. The resulting wire rope tensions for these pipe whip restraints, given in Table IV.-1, were less than the allowable tensions determined using the criteria described above. Therefore, the design for pipe whip restraints CLR-3 and CLR-4 is acceptable.
The next step in the design evaluation of cold leg pipe whip restraints was to verify that certain structural components do not limit the ability of the pipe whip restraints to react plastically to the postulated pipe break loads. These components include such items as shear pins, high-strength bolts, rods, headed studs, fitting for wire rope, welds, and plates with holes.
For the purpose of the design evaluation, the elastic behavior of these components, was limited to the allowable stresses given in Appendix A.
A complete check of the cold leg pipe whip restriants verified that all such components, when subjected to the postulated pipe break loads given in Table IV-1, satisfy the allowable stress requirements of Appendix A.
l 6
4 IV-6 l
l
The Icat step in the cold lag pipe whip restraint design evaluation was to verify the adequacy of the concrete shield walls and floor slabs for the postulated pipe break loads. Table IV-2 provides a comparison of the prior design loads with the new loads in terms of PA (pressure times area). The results presented in Table IV-2 clearly indicate that the new design loads are less than the prior design loads except for one case. The ver,tical down-ward load for cold leg pipe whip restraint CLR-2 indicates an has increase in magnitude. However, this load transfers directly into the floor, slab at elevation 565'-0" which is part of the containment base mat which bears directly on bedrock. The increase in the vertical design load for pipe whip restraint CLR-2 has no affect on the overall design of the elevation 565'-0" floor slab. The prior design of the concrete shield walls and floor slabs to which the pipe whip restraints are attached is adequate.
Further, calculations verify that the concrete design is locally adequate to support the new design loads for the cold leg pipe whip restraints.
3.2 Gap Evaluation The effect of varying the gap was evaluated for the cold leg pipe whip re-straints. Since pipe whip restraint CLR-1 is not required to resist any of the postulated cold leg breaks, a variation in gap for this pipe whip restraint has not been evaluated.
For pipe whip restraint CLR-2 the vertical design gap is conservatively assumed to be 1-7/16 inches. Based on as-built measurements of the cold gap and the theoretical thermal movement of the pipe, the actual vertical hot gap is 1-1/4 inches, which is 3/16 inch less than the design gap.
The actual vertical gap could increase by 1-3/8 inches, greater than the design gap, and still be accept-able based on the ductility ratio given in Table IV-1 and the derivation in Appendix B.
For the horizontal direction the design gap equals 3/4 inch.
As-built cold gap measurements and the theoretical thermal movement of the pipe result in a horizontal hot gap of 13/16 inch, which is 1/16 inch more than the design gap.
The actual horizontal gap could increase by 1 inch, greater than the design gap, and still be acceptable based on the ductility ratio given in Table IV-1 and the derivation in Appendix B.
The gaps for the RCP pipe whip restraints CLR-3 and CLR-4 were established by the procedures given on the design drawings.
The procedures required that the gaps be set, to their design values, af ter the RCP's were installed.
Support conditions for the RCP's do not permit their movement after installa-tion, thus ensuring that there will not be any significant variation between the as-built and design gaps for pipe whip restraints CLR-3 and CLR-4.
For pipe whip restraint CLR-5 shim bars physically limit the gap to a maximum possible value of 8 inches while the design gap is equal'to 3-11/16 inches.
Based on the derivation in Appendix B and the ductility ratio shown in t
l Table IV-1, there is adequate unused strain energy to resist the maximum l
possible increase in gap.
For pipe whip restraint CLR-6 the effect of gap varying from the design value is not significant. Shim bars were installed to provide very little gap between the pipe and the pipe whip restraint. The maximum gap physically possible is 3/8 inch, while the design gap is 1/4 inch. Since the resulting ductility ratio for this pipe whip restraint is less than one, the derivation in Appendix B clearly shows that it has sufficient unused strain energy to resist the maximum possible increase in gap.
IV-7 a
" - - +
TABLE N-1
SUMMARY
OF RESULTS FOR THE RCS COLD LEG PIPE WHIP RESTRAINTS Dis a a xi Pipe Whip Controlling Break New Design New Design Load LoNnt et t Restraint No.
Locatson Loads Direct ron Djrect ion Rat to CLR-1 none O
NiA N/A N /A Guillotine Break at end of first elbow frorn the stcom P :1983k P2 m-m 3
generator.
(GB-6) u CLR-2 ELEVATION l
pq Guillotine Brtok at RCP
]
k suction line nozzle.
P: 2736 0 99" 35.3 2
(GB-8)
J., e, CLR-3 Guillotine Break at RCP k
(upper cables) discharge line nozzle.
,p=st4 PLAN P
N/A N/A (lower cables)
(GB-9)
P=629
_ e - :..,
N/A N/A A
Guillotine Break at RCP C LR-4 suction line nozzle.
P :1880k E_L_EVATION N/A N/A (GB-8)
Guillotine Break at first P : 1725k CLR-5 elbow from the reactor SECT ION O 27" 1
3.0 hIII vessel.
(GB 11)
P, : 69O k
O#
lew N 1 Guillotine Break at the q = 337 (1) q CLR-6 reactor vessei nozzle.
- 7a2k ELEVATION p-(GB 12) 2 k(1)
O.W Im h 1 p2f: 329 (1) P, is a frictional load applied at the P loorf locotton in the direction parallel to the pipe.
TABLE IE-2 COMPARISON OF PRIOR LOADS AND NEW LOAD 5 FOR THE RCS COLD LEG PIPE WHIP RESTRAINTS Pipe Whip Prior Design Load-Fp New Design Load -Fn Restraint Fn No.
Fp Fn prg C LR -1 2020*
1.50 0
N.A.
C L R-2 (Horizontal) 202O*
1 50 1983*
1.47 K
K (Vertical) 2020 1 50 2736 2.03 C LR-3 UpperCatk@
6 2 9 "
N/A 614*
N/A Lo^erCatkd 629*
N/A 629*
N/A C LR-4 1917
N/A.
1880 N/A C LR-5 2020*
1.50 1725*
1.28 l
K K
C LR-6 2720 2.02 1120 0.83 Note:
P = Operating Pressure A= Internal Flow Area (1) Design oods were determined by Bobcock & Wilcox, using a dynamic analys
m W'
CLOSED WIRE ROPE SOCKET
-- lNSU L ATION PROTECTION RING J
(2 E ACH SIDE)
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(2 EA. SIDE)
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(( kl ANCHOR & (TYP FOR 4 RODS PER ROW) bN b
3 SECTION,
d COLD LEG SUCTON LINE PIPE WHIP RhdINAINT CLR-1 I
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' 3 ~ Tf 3 ooM o l I\\.c o 2 - [A) i'- s' -= . = = = HEADED ST U D 3 ( T Y P.) ) } yg OUTER
- A h
- o RING t D [3 s
/ / /*/ G if##I43 / ', lf, (' ' ' "1, ,\\ s Q \\ f "O, E '~~ O 4+ ~ SPOKE {- N ._Y ( T Y P.) INNER ' 1 RING t U g 1 1 1 -E->p --T I 7 ( x j p SHIM BAR N,'- 7 \\ jr (TYP.) BOLT S (T Y P. 3 PL ACES) S ECTIO N M E L E VATIO N FIG U R E IE-6 COLD LEG LOCA PIPE WHIP RESTRAINT CLR-6 I V.
SUMMARY
AND CONCLUSIONS 1.0 The purpose of this study was to verify the adequacy of the design of the RCS hot and cold leg pipe whip restraints. Current criteria and ana)ytical techniques were employed.
Loads resisted by the pipe whip restraints were determined by BN-TOP-2 (Reference 2) or dynamic analysis. The nudber, loca-tion, and type of pipe breaks postulated to occur in the hot and cold piping were determined by B&W using the criteria given in NRC Branch Technical Position MEB 3-1 (Reference 5).
2.0 The design verification of each of the hot and cold leg pipe whip restraints, except the upper pipe whip restraints HLR-5 and HLR-6, was completed based upon the loads resulting from the foregoing described methodology. For the resulting loads, plastic behavior of the pipe whip restraint results in defor-mations and strains within acceptable limits. The structural components of the pipe whip restraints such as bolts, plates with holes, welds, and embedments do not limit the capacity of the pipe whip restraints to values less than required to resist the resulting pipe whip restraint loads. The evaluation shows that the concrete walls and floor slabs which support the hot and cold leg pipe whip restraints will sustain the pipe whip restraint loads. Therefore, the design of all RCS hot and cold leg pipe whip restraints, for which the verification study has been completed, is adequate to protect safety-related equipment, structures and components from pipe whip due to a LOCA.
The analysis to determine the pipe break loads resisted by pipe whip restraints HLR-5 and HLR-6 is still in progress. Upon completion, the results of the design verification for pipe whip restraints HLR-5 and HLR-6 will be submitted as a supplement to this report.
3.0 The effect of varying the gap between the pipe and pipe whip restraint shown on the design drawings was investigated and is acceptable based upon the availability of unused strain energy.
e V-1
APPENDIX A Allowable Stresses for Elastic Behavior 1.0 Scope 1.1 The allowable stresses given in this Appendix shall be used tb verify the design of the following items whose behavior is required to remain in the elastic range:
a.
Structural components whose failure could limit the plastic capacity of the pipe whip restraint b.
Wire rope pipe whip restraints c.
Concrete walls and slabs 2.0 Definitions F = minimun yield stress y
Fg = allowable tensile stress F = allowable shear stress y
Fb = allowable bending stress Tb = minimum breaking strength for the wire rope T = allowable tensile force for the wire rope 3.0 Allowable Stresses 3.1 Steel plates and members:
F = 0.9 F g
y F = 0.75 F (On net section at pin holes in eyebars or pin connected g
y plates).
Fb = 0.9 Fy F = F / VS-y y
3.2 Steel bolts and threaded parts:
Stresses shall be limited to 1.6 times the allowable stresses given in Table 1.5.2.1 of the AISC " Specification for the Design, Fabrica-tion and Erection of Structural Steel for Buildings" (Reference 9).
In addition, stresses shall not be allowed to exceed 0.9 times the minimum yield stress of the steel.
A-1
~
3.3 Welds
Weld stresses shall not exceed 1.6 times the allowable stresses given in Table 1.5.3 of supplement No. 3 to the AISC " Specification for the Design.
Fabrication and Erection of Structural Steel for Buildings" (Reference 9).
3.4 Wire rope:
T = 0.9 Tb
3.5 Concrete
Concrete stresses shall not exceed allowables given in ACI 349-76 (Reference
- 10) for unfactored loads utilizing ultimate strength techniques.
e A-2
APPENDIX B Effect of Varying the Theoretical Design Gap During the September 7,1979 meeting of the Toledo Edison Company and the Nuclear Rigulatory Commission there was considerable discussion concerning whether or not os-built measurements existed for the hot position gaps between the RCS piping and pipe whip restraints. The Toledo Edison Company explained that these seasurements do not exist because they would have to be obtained inside the containment while the unit was at power generation.
It was agreed that a review would be made to datermine if a variance between the as-buiJ t gap and design gap could impact the verifi-cction study being performed on the pipe whip restraints.
The following discussion dzmonstrates that depending on the strain levels in a specific pipe whip re-ctraint, the gap can be variea without having an adverse affect on the maximu= load carrying capacity of each pipe whip restraint. How this applies to each specific pipe whip restraint is discussed in the summaries of Sections III and IV.
Energy balance methodology is used to evaluate the affect of varying the theoretical d2 sign gap between the pipe and pipe whip restraint. For an energy balance analysis, the piping and pipe whip restraint system can be represented by the two-dimensional model shown in Figure B-1 (a).
The pipe break thrust force is resisted by two elasto-plastic springs; one spring represents the resistance of the piping while the other represents the pipe whip restraint resistance. before the spring representing the pipe whip restraint can be engaged, the mass must travel through a distance equal to the gap between the pipe and the pipe whip restraint. The elasto-plastic spring functions for the piping and the pipe whip restraint are shown in Fi ures B-1 (c) and (d), respectively.
b Energy balance methodology states that the energy input into the system by the pipe break thrust force must equal the energy resisted by the piping and pipe whip restraint.
The energy input into the system by the pipe break thrust force is shown in Figure B-1 (b).
It is assumed for the purpose of this discussion that the resulting deformation of the mass will cause the pipe and the pipe whip restraint to yield.
This assumption is conservative for this analysis and is consistent with the typical piping and pipe whip restraint behavior. The following equation gives the energy balance solution for the assumed piping and pipe whip restraint behavior:
FA = Rp( A _Yn)+ Rr ( A - Yg.Y_t)
(1) 2 2
Thi terms used in this equation are defined in Figure B-1.
Simply stated, this cquation requires that area 1 shown in Figure B-1 (b) must equal the sum of areas 2 cnd 3 shown in Figures B-1 (c) and (d).
l In Figure B-1 (d), the allowable deformation represents the displacement of the mass l
carresponding to the maximum allowable strain for the pipe whip restraint. Areas 4 cnd 5 shown in Figures B-1 (c) and (d) represent the unused energy-resisting capa-bility of the pipe and pipe whip restraint system. This unused potential energy is cvailable to resist an increase in energy input into the system as a result of a gap lcrger than specified. A decrease in the gap will result in less energy input into the system than used in the analysis, making the analysis performed conservative.
B-1
i Energy balance equation (1) for the system can be rewritten in the following form:
Yg = A - p -
A-Rp (A -
(2)
Rr It can conservatively be assumed that Y and Y are small in comparison to the deforma-The above equation reduces to the fo11o0ing:
r tion.
Yg = A -( F -RD)6 (3)
Rr Equation (3) shows that the allowable variation in gap is proportional to the maxinum cllowable deformation and the actual deformation for a given gap or:
allowable Yg = A allow Yg = allowable ductilitv Yg (4)
A actual ducti ity t
Equation (4) demonstrates that the gap can be increased in direct proportion to the pipe and pipe whip restraint system's unused strain energy without having a detrimen-tel effect on the pipe whip restraint.
For example:
Given: Theoretical design gap = 2 inches Allowable ductility ratio = 50 Ductility ratio for design gap = 20 Then:
Maximum allowable gap =
.iQ X 2 inches = 5 inches 20 9
B-2 l
l-
LEGEND
=y
\\
M = mass Kp NV
\\
K : stif f ness F
M
\\
Mb
\\
Y : displacement pipe ' break thrust force F :
= Yg R : resistance
=
a: resulting displacement (O)
Yg :
p be Ji' pipe and Yp : yield displacement of pipe Yr :
d displacement of l
F yy Aallo.v: maximum allowable 1
displacement AREA 1 \\k
\\
g$
N\\ \\\\\\\\\\\\\\
=,
o Aallow (b) w U
E Yp Z
CL H Rp - \\g3yg\\g\\\\\\/7777j E9 AREA 2 AREA 4
\\\\\\\\\\\\\\
//////
y i.s Aallow.
(
(c)
Yg Yr W
s
\\\\\\\\ W//////
l eb AREA 3N AREA 5 FlGURE B-1
$In
\\\\\\\\\\V/////
ENERGY EALANCE FOR 3
uonow.
VARYING THE GAP
.s APPENDIX C References 1.
Davis-Besse Nuclear Power Station Unit 1 Final Safety Analysis Report 2.
Bechtel Power Corporation, " Design for Pipe Break Effects", Topica,1 Report BN-TOP-2, Revision 2, May, 1974.
3.
Babcock & Wilcox, " Specification 3002/NSS-14/1077 for Reactor Coolant System Foundation and Nozzle Loadings", Rev. 3, October 12, 1977.
4.
Babecek & Wilcox, " Toledo-14 Preak Opening Whip Restraint Loads", Document No. 86-3041-00, March 6, 1979.
5.
Nuclear Regulatory Commission Branch Technical Position MEB 3-1, February 3, 1975.
6.
Babcock & Wilcox, "LOCA Pipe Break Locations for Toledo Edison Davis-Besse Unit 1", Document No. 86-1105779-00, November 1979.
7.
Bechtel Power Corporation, " Criteria for Verification of Pipe Whip Restraints for the Reactor Coolant System for the Toledo Edison Company Davis-Besse Nuclear Power Station Unit 1 Dak Harbor, Ohio", Procedure No. 7749-C-101.
- 8. - ASME Boiler and Pressure Vessel Cod 3,Section III, Division 1 Appendices,1977 Edition.
9.
American Institute of Steel Construction, " Specification for the Design, Fabrica-tion and Erection of Structural Steel for Buildings", February 12, 1969 with Supplement Numbers 1, 2 and 3.
10.
American Concrete Institute, " Code Requirements for Nuclear Safety Related Con-crete Structures", (Ac1 349-76).
f.
C-1 L_
J