ML20042E687

LER 90-007-01:on 900228,determined That Several Supports Would Be Overloaded During Seismic Event on Nonsafety Related & safety-related Main Steam Piping.Caused by Design Deficiency.Piping Supports modified.W/900423 Ltr

ML20042E687
Person / Time
Site:	Fort Calhoun
Issue date:	04/23/1990
From:	Gates W, Van Sant B OMAHA PUBLIC POWER DISTRICT
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-90-007, LER-90-7, LIC-90-0343, LIC-90-343, NUDOCS 9004300274
Download: ML20042E687 (6)

Text

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Omaha Public Power Dirtrkt 444 South 16th Street MaH Omaha Nebraska 68102-2247 402/636-2000 April 23, 1990 LIC-90-0343 4.

U. S. Nuclear Regulatory Commission Attn Document Control Desk Mail Station P1-137 Washington, DC 20555

Reference:

1. Docket No. 50-285

. 2. Licensee Event Report 90-07, March 30, 1990 (LIC 90-253)

) Centlement

Subject:

Licensee Event Report 90-07, Revision 1 for the Fort Calhoun Station Please find attached Licensee Event Report 90-07, Revision 1 dated April 23, 1990. This revision is being submitted per requirements of 10 CFR 50.7.'J(a)(2)(ii)(B)andascommittedintheoriginalLER. Changes are denoted by vertical lines in the margins.  ;

If you should have any questions, please contact me, s Sincerely, ,

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W. G. Gates #1 i Division Man ger l Nuclear Operations WGG/ tem  !

l Attachment l c: R. D. Martin, NRC Regional Administrator l

A. Bournia, NRC Project Manager '

P. H. Harrell, NRC Senior Resident Inspector INPO Records Center  !

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A seismic analysis of the Main Feedwater and Main Steam piping outside containment has shown that several supports would be overloaded during a seismic event on the non-safety related portion of the feedwater piping (classifiedasSeismicClassI),andonboththenon-safetyrelatedandsafety

, related Main Steam p ping. An evaluation was performed to determine what i effect overloading t ese supports would have on the piping system, i conservatively assuming a gross failure of the overloaded su) ports. Design l basis support and piping allowables would be exceeded in bot 1 systems, and l stresses in the Feedwater piping could be postulated to result in a previously unanalyzed High Energy Line Break. Investigation of the problem revealed that the design deficiency has existed since plant construction.

l The corrective actions include modification to the piping sup) orts, l implementation of a Safety Analysis for Operability, establisiment of design criteria for the Seismic Class II piping and the Turbine Building spectra, and restoration of the systems to updated design basis conditions.

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designates certain piping as Seismic Class 1. The piping so designated must be i designed to withstand the effects of a " Design Basis Earthquake" per the

, criteria established in Appendix F of the USAR. The design basis document for l Main Feedwater defines design code for the piping in the Auxiliary Building as l UnitedStatesofAmericaStandard(USAS)831.7fromthecontainmentpenetration l l to the isolation valve and USAS B31.1 for the remainder of the piping in the Auxiliary and Turbine Buildings. Appendix F Section F.1.3.d.3 of the USAR s)ecifically defines the feedwater piping in the Auxiliary Building upstream of '

tie isolation valves as Seismic Class II and the pi)ing downstream of the isolation valve as Class I. A recent records searci performed by Omaha Public l Power District (OPPD), however, has found licensing correspondence that defines i all the feedwater piping in the Auxiliary Building as Seismic Class I. l Appendix *M" of the USAR defines what piping outside of containment is high ,

energy and how it has been analyzed. The Main Feedwater and Main Steam piping aro defined as high energy and were analyzed for High Energy Line Break (HELB) considerations. ,

OPPD created a new analysis of the feedwater piping and supports as part of the design basis reconstitution effort and document update for a temporary modification (TM-89-M-019). This analysis was based on the USAR definition of the feedwater piping upstream of the isolation valves as being Seismic Class .

II. The temporary modification installed a su) port at the feedwater regulating valve during 1989. The recent reanalysis of t1e piping and supports for the  ;

temporary modification wos The reanalysis revealed loads on several " performed to current class II" supports that standards.

eveeed their design

• capacity. Follow up work was initated to demonstrate that the failure of these  !

class II supports would not impact the safety function the feedwater piping.

It was determined that the resultant increase in pipe stress due to the elimination of these supports from the stress analysis created an unanalyzed t high energ this time,y whichline break revealed location. A designcorrespondence the licensing basis search was also performed defining all the at feedwater piping in the Auxiliary Building as Seismic Class I.

At 1130, on February 28, 1990, thepipingandsu)portsweredetermined.tobe =

outside the plant design basis as specified in tie licensing correspondence defining the piping and supports as Seismic Class I. Additionally, the piping i and supports were determined to be outside the design basis as specified in the USAR Appendix M for high energy line break locations. At this time the plant was in a planned shutdown for a refueling outage and the system was not required for operation. Subse pursuant to 10CFR 50.72(b)(2)(quently i). a "four hour" report was made to the NRC I

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FurtherreviewidentifiedasimilarconcernontheMainSteam(MS) system '

piping because of similarity to the Main Feedwater piping. The primary loadings on the MS system would be a combination of Design Baris Earthquake and >

relief valve discharge forces. Engineering evaluation confirmed that the MS I

pipe stress and support allowables were outside the USAR Appendix F design ,

basis. However, no unbounded HELB postulations for the MS system were  :

identified. A determination of reportability was made on March 22, 1990 while ,

the plant was still shutdown for a refueling outage in Mode 5. A "fcur hour" I notificationwasmadetoNRCpursuantto10CFR50.72(b)(2)(1).  ;

j The configuration of the Main Feedwater and Main Steam piping and supports in the Auxiliary Building has not been significantly changed from original construction. Although the ort inal Architect / Engineer (A/E) had seismically analyzed the piping in the Auxi tar Building it was done using a static analysismethodanditisunclearwfatcriterlawereusedtoaccountforanchoc movenents and boundary load from the Turbine Building. The Feedwater and Main -

Steam piping systems were reanalyzed by a different contracted engineering firm as part of the HELB work performed for Appendix M of the USAR. It appears that the scope of this work was limited to predicting pipe break locations only and did not include qualification of the supports for tne resultant loads. As part of the 79-02 and 79-14 work, the existing isometrics and sup) ort drawings were ,

reviewed against as-built conditions. OPPD concluded that t1ere was sufficient agreement between as-built and as-designed to indicate the piping was properly constructed and no reanalysis was required.

The )rimary cause of this condition is attributed to design deficiency: failure l

of tie original A/E to consider loads induced on the piping from the non-seismic portion of the system. Why this was not done cannot be determined due to insufficient documentation of design practices used by the A/E during  ;

original construction.

A factor which impeded earlier discovery of this condition is the conflicting information contained in the USAR. Prior to Bulletins 79-02 and 79-14 and up-until the determination of this event, the design basis of the USAS B31.1 Feedwater piping and supports was considered to be Seismic Class II and non-safety related. This interpretation was based on Appendix F section F.1.3.d.3 which specifically defines the Feedwater piping in the Auxiliary Building upstream of the iseration valves as Seismic Class II. The Seismic ,

l Class II portion of the system had no defined licensing basis.

OPPD contracted an independent consulting firm to determine the impact these '

overloaded supports could have on the safety related Seismic Class I portion of the Feedwater piping. During this review a concern was raised as to the l seismic classification of.the B31.1 portion of the Feedwater piping in the j Auxiliary Building. l l

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Appendix F Section F.2.2.2 of the USAR for Seismic Class I criteria states that j B31.1 piping in the Auxiliary Building " received the same attention with regard ,

to selection of hangers and restraints as the B31.7 piping. Seismic stresses  :

were combined with longitudinal stresses due to pressure, weight, and other  !

sustained loads". These statements are conflicting for the Feedwater pipirg  !

i upstream of the isolation valves. OPPD performed a search of the design basis s i

recordsanddiscoveredthata"USNRCSafetyEvaluation...Regarding(theSeismic) from Postulated Ruptures of Noncategory I i Potential for Flooding,he Systems" acknowledged t Feedwater piping in the Auxiliary Building as being .

i Seismic Class I. This seismic design requirement for the B31.1 feedwater piping in the Auxiliary Building made the overloaded supports a reportable condition since they are now outside the Seismic Class I design basis defined  !

. in Appendix F of the USAR. t OPPD requested the independent consulting firm to continue the analysis of the  !

piping to determine the impact of the support failures on the system. The  ;

contractor's approach was to perform the piping analysis and review support .

capacities to determine what supports exceeded operability criteria. These j supports were removed from the model and the analysis was rerun. After several i l iterations it was determined that, although some of the supports still exceeded i their design capacity, they would not fail, and the piping would not exceed i operability limits. However, at this wint the threshold stress for consideration of High Energy Line Breac (HELB) criteria was exceeded in a ,

location not previously analyzed in USAR Appendix M, Section M.3.2/ Attachment ,

B. Attachment B of Appendix M defines the break locations previously I considered in the USAR. +

The Feedwater piping is routed out of the Containment Building through the  !

Auxiliary Building and ends in the Turbine Building. The seismic class II i piping in the Turbine Building must be seismically analyzed to determine the loads transmitted back to the Seismic Class I piping and supports in the Auxiliary Building. Seismic analysis of the piping in the Turbine Building will require the use of a response spectra for components located in that building. The Fort Calhoun Station USAR does not contain a response spectra

• for the Turbine Building; however, OPPD has submitted a proposed spectra to the NRC for approval under the Alternate Appendix F submittal. Final resolution of this problem will require NRC acceptance of the Turbine Building spectra. '

It was determined that corrective modifications to all affected Main Feedwater and Main Steam supports could not be accomplished due to the time and resource constraints of the 1990 refueling outage and the lack of an approved design basis for the non safety related Main Steam and Feedwater piping. The following short term corrective actions will therefore be implemented prior to start-up from the outage:

(1)ImplementaSafetyAnalysisforOperability(SAO)forchepipingand supports. The SA0 will establish interim acceptable criteria for plant operation until appropriate long term criteria can be established, j w.c on ma um

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01 1 01 5 or 0l5 Tuten . cs ,new nn (2) Modify (underMR-FC-89-45)thepipingsupportstomeetoperability requirements defined in the SAO, and eliminate any new break locations.

Long term corrective actions include

, (1)ApprovaloftheTurbineBuildingresponsespectrabyHRC. The Turbine

Building spectra is not defined in any licensing basis and has been submitted to the NRC as part of the alternate Appendix F criteria.

3 (2) Clarification of the USAR concerning the seismic design requirements for the Main Feedwater and Main Steam piping outside containment. I (3)Modificationofp(ip)ingsupportsasrequiredtocomplywiththedesignbasis updates noted in 1 and (2) above. This is presently scheduled for the 1991 refueling outage.

(4) Initiate review of seismic classification of systems identified in "USNRC Safety Evaluation...Regarding the Potential for Flooding, from Postulated RupturesofNoncategoryI(Seismic) Systems".

This event is similar to the event reported in LER 90-03 as it describes

, conditions outside design basis due to design deficiencies by the original A/E, Generic corrective actions noted in t1at LER will also apply for this event. LER 89-21 also concerned design deficiencies by contracted companies.

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