ML18043A629
| ML18043A629 | |
| Person / Time | |
|---|---|
| Site: | Palisades  |
| Issue date: | 04/19/1979 |
| From: | Hoffman D CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.) |
| To: | Ziemann D Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 7904250235 | |
| Download: ML18043A629 (16) | |
Text
consumers Power company General Offices: 212 West Michigan Avenue, Jackson, Michigan 49201
- Area Code 517 788-0550 April 19, 1979 Director, Nuclear Reactor Regulation Att Mr Dennis L Ziemann, Chief Operating Reactors Branch No 2 US Nuclear Regulatory Commission Washington, DC 20555 DOCKET 50-255 - LICENSE DPR PALISADES PLANT - SEISMIC CAPABILITY OF PIPING SUPPORTS Attachment I to this letter is ConsU.Iilers Power Company's follow-up response to a conference call with members of the NRC Btaff on April 11, 1979
I.
INTRODUCTION Within the past year, it was determined that an error existed in an Energy Data Systems, Inc (EDS) computer code which was used in the EDS analysis of certain piping systems at the Palisades Plant.
EDS and Bechtel have reviewed these analyses of the affected piping systems.
That review con-cluded that fourteen pipelines were affected by the computer code error.
Bechtel has informed us that many of these piping systems were later re-analyzed as a normal design iteration but there remained five piping systems affected by this problem.
They are as follows:
- 1.
Main Steam, inside (MSI) and outside (MSO)
~ontainment.
- 2.
Feedwater, inside (FWI) and outside (FWO) containment.
- 3.
Shutdown cooling system (scs).
- 4.
Safety Injection Tank 82A to Primary Loop lA (SIT).
- 5.
Pressurizer Surge Line (PSL).
Only the seismic analyses were of concern.
Thermal flexibility and dead-weight analyses were unaffected by the error.
II.
GENERAL ANALYSIS RESULTS Al\\JD RECOMMENDATIONS The seismic analysis employed was based upon the seismic response spectra used for original design.
The spectra are defined in the Palisades Plant FSAR and employ a.l g ground acceleration for the operating basis earth-quake and a.2 g ground acceleration for the safe shutdown earthquake. All loads and stresses are calculated from linear elastic analysis based on normal mode theory.
The safe shutdown earthquake (SSE) responses are twice the operating basis earthquake responses.
A.
ANALYSIS RESULTS
- l. Pipe Stress All piping in the systems meets the requirements of ANSI B3l.l, 1973 Edition.
The MSI, MSO and PSL piping systems meet the more restrictive requirements of ANSI B31.l, 1967 Edition as well.
- 2.
Equipment Nozzles Reactions on equipment nozzles associated with such components as the main turbine, heaters, steam generators, reactor vessel and containment penetrations are all acceptable.
- 3.
Pipe Supports 2
The structural integrity of the pipe supports must be ensured in order that the pipe and nozzle loads are correct.
The reanalysis has identified eight pipe supports which realize an increase in seismic loads that may result in the supports being overstressed per the limits imposed in Appendix A of the Palisades Plant FSAR or that may imply pipe support lift--off.
As a result of the reanalysis results, modifications have been proposed for eight pipe supports for the following three reasons:
- a.
To provide a physical pipe-pipe support restraint so that the boundary conditions to be used for analysis purposes can be clearly defined and just~fied.
- b.
To meet all standards representative of design and con-struction practice and to ensure that the requirements of Appendix A of the FSAR are met.
3
- c.
To establish consistency in relating the present analysis with previous work on the same pipelines with respect to pipe support considerations.
B.
ANALYSIS CONCLUSIONS The analysis performed by Bechtel and EDS has resulted in the Bechtel recommendation that eight pipe supports associated with the systems being analyzed be modified.
These supports are on the main steam inside containment, feedwater inside and outside containment and the shutdown cooling system.
The pipe stresses" and nozzle stresses are accept~ble.
The modifications defined are based upon present information.
Addi-tional analyses are being conducted on the 'shutdown cooling system to ascertain whether any support is needed at the H802 location.
In summary, the modifications can be catalogued ~s follows:
MSI - Modify EB l-H3 and Hl6 to preclude uplift.
FWI - Modify EB9-H35 and H35A to preclude uplift.
SCS - Modify CC9-H802 to accommodate additional loads.
FWO - Replace EB9-H42 with a frame type pipe support.
Replace EB9-H79 hanger rod with larger size.
Replace DBl-53 hanger rod with larger size and reinforce structural steel.
III.
SPECIFIC PIPE SUPPORT DETAILS A.
PIPE SUPPORTS INSIDE CONTAINMENT The five modifications recommended by Bechtel are very simple in
4 terms of material and installation.
For MSI and FWI, the modification is merely to preclude vertical uplift which was not postulated to occur under previous analysis.
The shutdown cooling modification is not complex.
However, more detailed analyses may show that the re-straint can be removed all together.
The operating basis earthquake (OBE) and safe shutdown earthquake (SSE) are standard terminologies.
The Palisades FSAR may refer to the SSE as a design basis accident or a hypothetical seismic load.
The maximum design seismic load is deadweight plus or minus the OBE.
The maximum hypothetical seismic load is deadweight plus or minus the SSE.
- l. Main Steam Inside Containment
. The specific concern focuses around line EBl.
The following dis-cussion refers to pipe supports H-3 and H-l6.
These supports are mirror images of one another.
Therefore, the* following applies to both pipe supports.
DATA DEADWEIGHT LOADS
- 23,000 lb
+ 32,31'7 lb OPERATING BASIS EARTHQUAKE LOADS SAFE SHUTDOWN EARTHQUAKE LOADS
+ 64,634 lb MAXIMUM DESIGN SEISMIC LOADS
+ 9,3l'7 lb 55,31'7 lb MAXIMUM HYPOTHETICAL SEISMIC LOADS
+ 41,634 lb 87,634 lb COMMENTS The design seismic and hypothetical seismic loads both indicate net upward loads for the supports.
Presently, the supports offer
no upward restraint.
An analysis of the pipeline has been con-ducted assuming no upward or downward support at the elbow.
An upward displacement of.047.inches for the OBE and.094 inches for the SSE has been calculated.
The maximum stress calculated for the OBE with no support is 4,687 psi at a nozzle.
ASSESSMENT-5 It is advisable that the potential uplift be restrained.
A modi-fication has been proposed to achieve such a restraint.
The pro-posed upward restraint will add certainty to analysis parameters and provide preciseness to analysis results at this and at other locations on the pipeline.
The deflections which have been cal-culated based upon the present support configuration are judged to be upper bounds.
These dis.placements may result in some slight dynamic pipe stress amplification due to impacting on the one-way support.
However, the displacements are extremely small and are judged to be well within the design margins used to accommodate such uncertainties.
The bounding analyses clearly show that the integrity of this line is maintained in the present configuration.
The modification is proposed and will be implemented during the next refueling outage in order to conform to good design practice.
- 2.
Feed-Water System Inside Containment Of specific interest is line EB9.
The following discussion concerns supports H35 and H35A which are mirror images of one another.
DATA DEADWEIGHT LOAD OPERATING BASIS EARTHQUAKE LOADS SAFE SHUTDOWN EARTHQUAKE LOADS MAXIMUM DESIGN SEISMIC LOADS MAXIMUM HYPOTHETICAL SEISMIC LOADS COMMENTS
+
+
+
3,800 lb 4,920 lb 9,840 lb 1,120 lb 8,720 lb
+
6,o4o lb
- 13,640 lb 6
The design seismic and hypothetical seismic loads both indicate net upward loads for the supports.
The present design has two rods supporting a cross bar to which the pipe is U-bolted.
The trapeze-type arrangement does not ensure that the hanger rods will accom-modate compression from the uplifting load.
Howeyer, these rods can sustain the compressiye seismic loads with no buckling.
Pre-sently, the unidirectional nature of the constraint precludes a precise calculation of pipe or support stress.
ASSESSMENT It is adYisable that the potential pipe uplift be restrained and a modification has been proposed to proyide such a restraint.
Pipe rupture restraints exist on either side_of both hangers of concern.
These restraints are 5' and 2'9" from the hangers on each line.
The clearances between the pipe and restraint are considered to be too large to consider the pipe whip restraints as seismic restraints.
The modification which has been proposed for the two pipe supports is Quite simple.
Work is now in progress to implement the modifications.
The work should be completed within 10 days.
I~
7
- 3.
Shutdown Cooling System Inside Containment The specific concern here is a single lateral support on line cc9.
This support is referred to as H802.
DATA MAXIMUM DESIGN SEISMIC LOADS MAXIMUM HYPOTHETICAL SEISMIC LOADS COMMENTS
+
5,575 lb
- ll,l50 lb This lateral support is acceptable for design seismic loads yet overstressed for hypothetical seismic loads.
The present support consists of a lateral bar bolted to gussets which are welded to a plate which is in turn bolted into concrete.
The limiting condi-tion for the support i~ the bearing stress in the gussets.
The bearing stress is calculated to be 76% above yield for the hypothe-tical seismic loads.
It has been informally reported by EDS that pipe stresses and nozzle loads are acceptable without this support.
ASSESSMENT An analysis of the shutdown cooling line is being conducted without the lateral support in place.
As noted, preliminary analysis indi-cates that the support is not necessary.
In addition, an inspection is being conducted of the number of pipe supports at other locations along the line.
There is reason to believe that there are more vertical supports than analysis presently accounts for.
Analysis and as-built inspections are presently being pursued with respect to this line. It is anticipated that the results will indicate that the support is not required and can be removed.
Nonetheless,
8 a modification has been proposed and preparations are being made for its implementation during the next refueling outage.
In the interim, the postulated yielding in the support is not a signifi-cant concern because analyses to date indicate that the support is not required.
B.
PIPE SUPPORT OUTSIDE CONTAINMENT The three feed-water outside containment pipe supports discussed are all in the turbine building and all upstream of the feed-water heaters.
The location of the supports is most easily determined by a review of piping drawing Ml58.
The supports are separated from the contain-ment boundary by a seismic Class l wall.
Pipe whip restraints provide further containment boundary protection far downstream of the pipe supports of concern.
The modifications proposed for these three pipe supports result from safe shutdown earthquake loads only.
No FSAR guidelines are violated based upon the operating basis earthquake.
- l. Feedwater Outside Containment - Line EB9 - Support H-42 DATA DEADWEIGHT LOAD
- 10,IOO lb OPERATING BASIS EARTHQUAKE LOAD
! 10,585 lb_;
+ 21,110 lb.
MAXIMUM DESIGN SEISMIC LOAD
- 21,285 lb MAXIMUM HYPOTHETICAL SEISMIC LOAD
+ 10,410 lb
- 31,810 lb
9 COMMENT The present design of this support is a rod-clamp type of hanger arrangement.
The only concern with respect to good design and construction practice is the stress level in the structural steel under the hypothetical seismic loads.
The stress levels are in a main building structural steel member.
The member supports unknown line loads and nonseismic piping.
In view of the unknowns, some very conservative assumptions have been ma.de in calculating a local flexure stress of 1.27 times yield above pipe support H-42.
ASSESSMENT The hanger support is to be modified to a frame support which will provide a better load distribution in the structural steel. It is noted that a binding stress of 1.27 yield does not result in a.
plastic hinge in an I-beam cross section.
There remains signifi-cant elastic material in the locally stressed area and no signifi-cant local or gross structural deformation will occur.
- 2.
Feedwater Outside Containment - Line EB9 - H73 DATA DEADWEIGHT 6,810 lb
+
4,853 lb OPERATING BASIS EARTHQUAKE LOADS SAFE SHUTDOWN EARTHQUAKE LOADS
+
9,706 lb MAXIMUM DESIGN SEISMIC LOADS
- 11,663 lb MAXIMUM HYPOTHETICAL SEISMIC LOADS
+
2,896 lb
- 16,516 lb
10 COMMENT Increased hypothetical seismic loads have resulted in a small deviation from normal vendor design guidelines with respect to hanger bar tensile stresses.
The vendor designs hanger bars at a tensile stress of 20% of ultimate for operating conditions or 30% of ultimate stress for faulted conditions.
The 16;516 lb load on the 1-1/16 inch diameter hanger bar results in a stress of 18.63 KSI which is 630 psi greater than the 18.0 KSI vendor guide-line.
ASSESSMENT A thicker hanger bar will be used to preserve design margin.
Hanger rod is normally SA-36 which has a yield strength of 36 KSI and significant ductility.
There is no structural concern with respect to the hanger.
- 3.
Feedwater Outside Containment - Line DBl - H53 DATA DEADWEIGHT 4,010 lb OPERATING BASIS EARTHQUAKE LOADS
+
5,767 lb SAFE SHUTDOWN EARTHQUAKE LOADS
! 11,534 lb MAXIMUM DESIGN SEISMIC LOADS
+ 1,757 lb 9,777 lb MAXIMUM HYPOTHETICAL SEISMIC LOADS
+
7,524 lb
- 15,544 lb COMMENT For the downward hypothetical seismic loads, the tensile stress in the hanger rod is 28.2 KSI.
Also during the downward phase
11 of the same loading, structural steel is stressed to.935 yield.
The upward hypothetical seismic load results in a load which is 2.43 times the buckling load of the 1-inch diameter, 66-inch long rod.
ASSESSMENT A modification has been proposed which adds reinforcing structural steel and a thicker hanger rod.
The structural steel and rod material are normally SA-36.
The 28.2 KSI tensile stress in the hanger rod is still well below yield.
The structural steel stress is below yield also.
Thus, the downward loading causes no signifi-cant problem.
The hanger rod buckling implies that some upward deflection is possible at the H53 location during the hypothetical seismic loading.
This particular hanger is the most remote of the hangers noted in the analysis.
The hanger is on the upstream side of the feed-water heaters from the Class 1 piping and is located well into the turbine building and is separated from the Class 1 piping by a s~ismic wall.
Pipe supports and other equipment connections to the feed-water line will significantly dampen any increased feed-water line oscillation due to a buckled rod.
The remoteness of this hanger from the feed-water line Class 1 boundary precludes the potentially buckled rod from significantly affecting the seismic characteristics of the FSAR Class 1 piping.
In addition, the presence of whip restraints on the downstream side of the Class 1 boundary also limits the transmissibility of deflections due to such a buckled rod.
The modification will be implemented during the next refueling outage.
12 IV.
CONCLUSION A reanalysis of fourteen high energy pipelines at the Palisades Plant has been conducted.
This review was initiated when it was determined that the EDS computer code with which the' original analyses were performed was found to contain an error.
The error affected seismic calculations only.
As a result of the reanalysis, eight pipe supports were found to violate the guidelines of good practice as outlined in the Palisades FSAR and in other industry practice guidelines (MSS-58).
Pipe stress and nozzle stress calculations yielded acceptable results with respect to design requirements.
Modifications for the eight pipe supports have been proposed and procurement of the required materials have been initiated.
The deviations of the pipe supports from FSAR design requirements and good practice guidelines are considered to be minor.
In review, it has been calculated that uplifting of the main steam line off of a one-way vertical support can occur during an SSE.
This uplifting has been bounded by separate calculations and has been shown to be extremely small.
The condition represents an analytical problem yet not a safety concern.
A similar uplifting can occur on two pipe supports on the feed-water line inside containment.
As with the main steam support, the feedwater inside containment pipe'support condition represents a calculational problem and not a safety concern.
The pipe whip restraint clearances have been measured on two of the four whip restraints adjacent to these supports.
Based upon these clearances,
13 the whip restraints cannot be considered seismic restraints.
The modifi-cation associated with these supports is very simple compared with the other proposed modifications. It is anticipated that the proposed modi-fication can be completed within 10 days.
The lateral support on the shutdown cooling system has been identified as requiring modification to withstand SSE loads.
An as-built pipe support inspection is being conducted with respect to that line and additional analyses are being performed.
There is reason to believe that there are more supports in the line than employed in the analysis.
Also, preliminary analysis has shown that the support is unnecessary.
Thus, the support may be found to be acceptable or unnecessary.
In either case, there is no safety concern.
The three supports outside of containment of note are far removed from the containment boundary.
These supports are not Class I systems for any-thing but analytical purposes and such systems (PER FSAR) need not meet SSE criteria.
These supports became Class 1 for analysts purposes only for analytical consistency.
The Class 1 analysis model requires a point of known boundary conditions for termination.
Such a termination point does not exist downstream of the feed-water heaters.
Thus, even the pipe supports outside of containment represent analytical anomalies rather than safety concerns.
Nonetheless, these supports must be considered Class 1 for analysis and procurement to be consistent with prior analyses.
The deficiencies noted for line EB9 (H42 and H73) are very minor.
The
potential hanger rod buckling on line EB1-H53 occurs at the most remote hanger of the three outside of containment.
The distance of the hanger from the containment boundary, the Class 1 wall and the pipe whip re-straints at the Class 1 boundary all constitute reasonable basis to assume that even a potential buckled hanger rod does not constitute a safety concern.
14 Therefore, the proposed modifi~ations will be completed before the end of the next refueling outage.
The modifications will undoubtedly reflect what is learned from the analysis an~ as-built inspection which is being conducted with respect to the shutdown cooling and feedwater inside con-tainment lines.