05000285/LER-1990-007
| ML20056A343 | |
| Person / Time | |
|---|---|
| Site: | Fort Calhoun  |
| Issue date: | 08/01/1990 |
| 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-90-0605, LIC-90-605, NUDOCS 9008070067 | |
| Download: ML20056A343 (6) | |
| Event date: | |
|---|---|
| Report date: | |
| 2852090007R00 - NRC Website | |
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L-Omaha Public Power District p August.1j 1990 444 South 16th Street Mall
- , ;. - LIC-90-0605 Omaha, Nebraska 68102-2247 - '
402/636-2000
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U. S. Nuclear Regulatory Commission Attn Document Control Desk p ' Mail Station P1-137. i
-Washington, DC 20555
References:
- 1. Docket No. 50-285-ls 2. Licensee' Event Report 90-07, March 30,_ 1990-(LIC-90-253)
- 3. Licensee Event Report 90-07, Rev. 1, April 23, 1990_(LIC-90-0343)
- 4. Letter from OPPD (W. G. Gates) to NRC (Document Control Desk) dated July 6, 1990 (LIC-90-0417).
Gentlemen:
Subject:
Licensee Event Report 90-07, Revision 2 for the l_ -Fort Calhoun Station Please find attached Licensee Event Report 90-07, Revision 2 dated July 27, 1990. .In previous-revisions of this. report, erroneous information was inadvertantly provided on.the status of :)
.the Turbine' Building spectra-_ submittal. Appropriate steps, !
including initiation of a Quality Assurance Corrective Action Report, have been taken to prevent recurrence of this problem.
H This" revision provides corrected and updated information-denoted
.by vertical lines in.the margins.
-If you should have any questions, please contact me.
i Sincerely, M d.
W. G.-Gates
' Division Manager 3 Nuclear-Operations
'WGG/tcm Attachment c:' R.-D. Martin, NRC Regional Administrator A.'Bournia, NRC Project Manager R..P. Mullikin, NRC Senior Resident Inspector INPO Records Center American Nuclear Insurers 9008070067 900801 E 6 5124 PDR ADOCK 05000285
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ASSTRACT funer to #d00 aperes e e , speewanneevey Armen senere spece rysevarma Apes / (16l A seismic analysis of the Main Feedwater and Main Steam piping outside containment has shown that several supports would be overloaded during a scismic event on the non-safety related portion of the feedwater piping (classified as Seismic Class I),
and on both the non-safety related and safety related. Main Steam piping. An evaluation.was performed to determine what effect overloading these supports would have on the piping system, conservatively assuming a gross failure of the overloaded supports. Design basis support and piping allowables would be exceeded, and stresses in the Feedwater piping result in the postulation of a previously unanalyzed High Energy Line Breake The corrective _ actions include modification to the piping supports, implementation of a Safety Analysis for Operability, establishment 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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012 012 0F 0 15 iixtw - ., m e w m..,nn The Fort Calhoun Station Unit 1 Updated Safety Analysis Report (USAR) designates certain piping as Seismic Class 1. The piping so designated must be 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 Main Feedwater defines design code for the piping in the Auxiliary Building as United States of America Standard (USAS) B31.7 from the containment penetration 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 specifically defines the feedwater piping in the Auxiliary Building upstream of the isolation valves as Seismic Class II and the piping downstream of the isolation valve as Class I. A recent records search performed by Omaha Public Power District (OPPD), however, has found licensing correspondence that defines all the feedwater piping in the Auxiliary Building as Seismic Class I.
Appendix "M" of the USAR defines what piping outside of containment is high energy and how it has been analyzed. The Main Foodwater and Main Steam piping are 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 support at the feedwater regulating valve during 1989. The recent reanalysis of the piping and supports for the temporary modification was performed to current standards.
The reanalysis revealed loads on several " class II" supports that exceed 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 high energy line break location. A design basis search was also performed at this time, which revealed the licensing correspondence defining all the feedwater piping in the Auxiliary Building as Seismic Class I.
At 1130, on February 28, 1990, the piping and supports were determined to be outside the plant design basis as specified in the licensing correspondence defining the piping and supports as Seismic Class I. Additionally, the piping 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 NRC Form 308A Wi9)
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0l 2 0l 3 OF 0l5 TEXT f# anwe apose er soeuned, we oJetourW N#C Form acid W (1h system was not required for operation. Subsequently a "four hour" report was made to the NRC pursuant to 10CFR 50.72 (b) (2) (1) .
Further review identified a similar concern on the Main Steam (MS) system piping because of similarity to the Main Feedwater piping.
The: primary loadings on the MS system would be a combination of Design Basis Earthquake and relief valve discharge forces. l Engineering evaluation confirmed that the MS 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 j 22, 1990 while the plant was still shutdown for a refueling outage I in Mode S. A "four hour" notification was made to NRC pursuant to 10 CFR 50.72 (b) (2) (1) .
The. configuration of the Main Feedwater and Main Steam piping and I supports in the Auxiliary Building has not been significantly changed from original construction. Although the original
-Architect / Engineer (A/E) had seismically analyzed the piping in the Auxiliary Building, it was done using a static analysis method ;
and it is unclear what criteria were used to account for anchor '
movements and boundary load from the Turbine Building. The j 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
- l. _and did not include qualification of the supports for the l- resultant loads. As part of the 79-02 and 79-14 work, the existing isometrics and support drawings were reviewed against ;
as-built conditions. OPPD concluded that there was sufficient -,
agreement between as-built and as-designed to indicate the piping l was properly constructed and no reanalysis was required.
1 The primary cause of this condition is attributed to design deilriency: failure of the original A/E to consider loads induced '
on the piping from the non-seismic portion of the system. Why l this was not done cannot be determined due to insufficient "
l documentation of design practices used by the A/E during original L 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 j considered to be Seismic Class II and non-safety related. This l Interpretation was based on Appendix F section F.1.3.d.3 which l specifically defines the Feedwater piping in the Auxiliary i Building upstream of the isolation valves as Seismic Class II.
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.The Seismic Class II portion of the system had no defined licensing basis.
OPPD contracted an independent consulting firm to determine the impact those 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 seismic classification of the B31.1 portion of the Feedwater piping in the Auxiliary Building.
Appendix F Section F.2.2.2 of the USAR for Seismic Class I criteria states that 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 Foodwater piping upstream of the isolation valves. OPPD performed a search of the design basis records and discovered that a "USNRC Safety Evaluation...Regarding the Potential for Flooding, from postulated Ruptures of Noncategory I (Seismic) Systems" acknowledged the Feedwater piping in the Auxiliary Building as being 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.
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 supports were removed from the model and the analysis was rerun. After several iterations it was determined that, although some of the supports still exceeded their design capacity, they would not fail, and the piping would not exceed operability limits. However, at this point the threshold stress for consideration of High Energy Line Break (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 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 piping in the "5Irbine Building must be seismically analyzed to determine ' loads transmitted back to the Seismic Class I piping and sucports in the Auxiliary Building.
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0 l2 015 0F 015 texttu . < - N=ci w.mn Seismic analysis of the piping in che Turbine Building will
- require the use of a response spectra for components located in i that building.- The Fort Calhoun Station USAR does not contain a response spectra for the Turbine Building. Seismic response spectra plots for the Turbine Building were submitted to the NRC by OPPD in a letter (LIC-90-0417) dated July 6, 1990. Final resolution-of this problem will require NRC acceptance of the Turbine Building spectra.
It was determined that corrective modifications to all affected l
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 ;
L corrective actions were therefore implemented prior to start-up from the outage:
u (1) Safety Analysis for Operability (SAO) 90-04 for the piping l and supports was approved and implemented. The SAO established interim acceptable criteria for plant operation-until appropriate long term criteria can be established. .
1 (2) Piping supports were modified (under MR-FC-89-45) to meet operability requirements defined in the SAO, and to eliminate potential for any new break locations.
Long term corrective actions include:
g (1) Clarification of the USAR concerning the seismic design I
requirements for the Main'Feedwater and Main Steam piping l
outside containment.
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(2) Modification of piping supports as required to comply with the design basis updates noted above. This is presently scheduled for the 1991 refueling outage.
(3) Initiate review of seismic classification of systems identified in "USNRC Safety Evaluation...Regarding the L Potential for Flooding, from Postulated Ruptures of I Noncategory I (Seismic) Systems".
This event is similar to the event reported in LER 90-03 as it l describes conditions outside design basis due to design
- deficiencies by the original A/E. Generic corrective actions noted in that LER will also apply for this event. LER 89-21 also concerned design deficiencies by contracted companies.
i NRC Fe,m 3e6A (s.89)