05000440/LER-1993-003
| ML20056D972 | |
| Person / Time | |
|---|---|
| Site: | Perry  |
| Issue date: | 08/13/1993 |
| From: | Gaston R, Stratman R CENTERIOR ENERGY |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| LER-93-003, LER-93-3, PY-CEI-NRR-1683, NUDOCS 9308190108 | |
| Download: ML20056D972 (6) | |
| Event date: | |
|---|---|
| Report date: | |
| 4402093003R00 - NRC Website | |
text
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\ CENTEOl3TD ENERGY PERRY t UCLEAR POWER PLANT Mail Address ,
Po Box 97 Robert A. Stratman 0 PE RRY, OHIO 44081 VICE PRESIDENT - NUCLEAR 0 4 08, (216) 259-3737 1
August 13, 1993 PY-CEI/NRR-1683 L U.S. Nuclear Regulatory Commission Document Control Desk Vashington, D. C. 20555 :
Perry Nuclear Power Plant Docket No. 50-440 >
LER 93-003 Revision 1 ,
Gentlemen:
Enclosed is Revision 1 to Licensee Event Report (LER)93-003 for the Perry Nuclear Power Plant. This revision is submitted to update information ;
regarding repairs to the B Main Steam Line which vere in progress at the time of the previous submittal. Revised sections of the LER are indicated by a revision bar in the right hand margin.
Should you have any questions regarding this issue, please contact Kevin Donovan, Manager - Licensing and Compliance Section at (216) 259-3737 extension 5606.
Sincerely,
/
[ ,g/g/ -
o ert A. Stratman RAS:RVG:ss Enclosure i
cc: NRC Project Manager tGC Resident Inspector Office IBC Region III ,
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" ") Ircal Irak Rate Test Results lhceed Allcwable Prirrary 03ntaintrent Inakage l'or Main St. cam Lines A, B, and D EvtNT nATE (5) LLR NUMELR (6i REPORT tJUMBER (7) OTHER FACILITIES INVOLVED (8) u tu ma nrvooN Acitm N^m tm uUusi a uwH ru vm vm ,,y, wy , utan tu vt^"
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j 01 14 93 L 93 003 01 08 13 93 5 OPERATING THIS REPORT IS SUDMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR 0 (Check one or rnore) (11)
MODE (9) 5 20 402(d) 20 405(c) 50.73(a)(2)(iv) 73,7i(d)
POWER 20 405(a)(1)(i) 50.36(t)(1) X 50 73(a)(2)(v) 73.71(c)
LEVEL (10) 0 20 405fa)(1)(n) 50 36(c)(2) 50.73(a)(2)(vii) OTHER 20 40$(a)(1)6u) X 5013(a)(2)6) 50 73(a)(2)(viii)(A) N'*W
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LICENSEE CONTACT f OR THIS LER (12) eaur, Tt tt mONL teUVBtH poduce Aees CWe}
Ron W. Gaston, Carpliance Engineer, Ext. 5004 (216) 259-3737 COMPLETE ONE LINE FOR EACH COMPONENT F ALLURE DESCRIBED IN THIS REPORT (13) !
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COMMW( NT MANUS ACTUFO C.AUSE SYSTI M COMPO'ENT MANUFACTUlG 0 SB ISV A585 Y SUPPLEMENTAL REPORT EXPECTED (14) EXPECTED MONTH l OAY W vi s SUDMtSSION I
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ABST AACT (Lmt to 1403 f. paces, i e., appiomimately 15 single spaced typewntten lines) (16)
During the period January 13 - 14, 1993, Local Leak Rate Testing (LLRT) of the fcur Main Steam Line (MSL) penetrations was performed to satisfy a previous commitment regarding mid-cycle testing. Three of the four (A, B, and D) MSLs tested vere found to have leakage in excess of the Technical Specification limit of 25 standard cubic feet per hour (sefh).
At approximately 1100 on January 12, while raising reactor vessel level for normal shutdown evolutions, water was noted leaking from the lagging at the bottom of the inboard Main Steam Isolation Valves (MSIVs). It was subsequently determined that the six MSIVs which were modified during the last refueling outage (RF03) had indications of leakage around the body to bonnet flange. The primary cause of the valve leakage was attributed to gasket relaxation which resulted from insufficient tensioning of the' bonnet flange studs during reassembly of the valves in RF03, combined with non-optimally sized gaskets being installed. MSIV seat leakage was identified after replacing the gaskets in the MSIVs which had previously experienced flange leakage.
The seat leakage vas repaired by machining or lapping of seating surfaces as necessary. Successful LLRTs vere completed on the A, B and D MSLs after repairs.
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Perry Nuclear Pcuer Plant, Unit 1 05000 440 2OF5 i 93 003 01 I. Introduction !
On January 9, 1993 the plant shutdown for a scheduled maintenance outage to ;
investigate a suspected leaking fuel assembly. On January 12, 1993, vater was noted leaking from the flange area on the inboard Main Steam Isolation Valves ;
(MSIVs) [ISV). On January 14, 1993 local leak rate testing confirmed that the l leakage from Main Steam Lines A, B, and D exceeded the acceptance of Technical Specification 3.6.1.2(c). A four-hour NRC notification was made to report each ,
test failure pursuant to the requirements of 10CFR50.72. These events are additionally being reported to satisfy the corresponding requirements of ;
At the time of the local leak rate test the plant was in Operation Condition 5 (Refueling) with the reactor pressure vessel at atmospheric pressure.
II. Description At approximately 1100 on January 12, 1993, while reactor vessel level was being raised for normal shutdown evolutions, vater was noted leaking from the lagging at the bottom of three inboard MSIVs. It was later determined that all six of the MSIVs which vere modified during the last refueling outage (RF03) had indications of leakage in the vicinity of tha body to bonnet flange. Local Leak Rate Testing (LLRT) performed on January 14, 1993 quantified the "as found" leakage rates to be as follovs:
Main Steam Line Leakage Rate MSL A 12.94 SLM or 27.43 scfh MSL B 78.93 SLM or 167.33 scfh MSL C 3.11 SLM or 6.59 scfh MSL D 197.42 SLM or 418.53 sefh As indicated above, the leakage rates for MSL's A, B and D exceeded the Technical Specification limit of 25 standard cubic feet per hour (sefh) or 11.79 standard liters per minute (SLM).
Upon identification of water leakage from the MSIVs on January 12, 1993, a Perry Incident Response Team (IRT) vas formed to investigate potential causes for the leaks. The combined water leakage from the three inboard MSIVs (in the Dryvell) was initially determined to be approximately 1/2 gallon per minute (gpm) vith the reactor vessel at 0 psig. An initial assessment of the insulation in the area of the leaks indicated that the vater marks on the insulation appeared to be from recent rather than past vetting of the insulation. Additionally, the insulation in the vetted areas vas not torn. There was no evidence that any substantial body to bonnet steam leakage occurred during plant operation.
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TEXT m more spece os swee use mtucvw ccenes erNRC fom,3ssa) pn A review of sump levels, temperature data and radiation monitor history was p d performed to attempt to correlate these indications with any trends observed !
during the last operating cycle. The valve leakage from the flange area was ;
assumed to have been negligible during plant operation based on the above observations.
1 Additional testing was performed to estimate the contribution of the body to l bonnet leakage to the total "as-found" leakage for the respective penetrations. l Although the body to bonnet leakage could not be quantified directly, the ;
j testing shoved the flanges to be the primary leakage path for the respective penetrations.
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t III. Cause Analysis The Incident Response Team, referred to previously, evaluated a series of (
j possible causes for the MSIV body to bonnet leakage and MSL penetration LLRT l 2 failures. The potential contributors evaluated included defective gaskets, l
seating surface flavs, and the tensioning pattern used during reassembly of the j 3 affected MSIVs. A troubleshooting plan was developed and implemented to l validate the potential causal factors. l It was determined that the body to bonnet leakage for the affected MSIVs was the :
result of a combination of factors which included incorrect gasket dimensional sizing, an inadequate tensioning procedure used during previous valve [
reassembly, and a lack of metal to metal contact on the valve body to cover ;
plate gap. j A review of the gasket dimensions obtained from existing stock revealed that, ;
allowing for manufactured tolerances, the gaskets used previously may not have !
been optimally sized for their application, potentially resulting in insufficient crush of the gaskets after tensioning. i The retaining nuts for the bonnet flange studs on the MSIVs had been tightened
- using manual torque vrenches prior to the 'nodifications performed on the valves !
l during RF03. During RF03 hydraulically operated tensioners were used to l 4
accomplish this task during post modification valve reassembly. The procedure used at that time for tensioning of the studs did not specify a required number ,
- of tensioning passes to minimize the effects of relaxation; nor did it specify [
that there be no gap present in the flange area after tensioning. These ;
requirements were later determined to be critical for maintaining the sealing ,
3 integrity of the valve body after reassembly. l 4 .
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IV. Safety Analysis ;
i Primary containment integrity ensures that the release of radioactive materials ;
from the containment atmosphere vill be restricted to those leakage paths and !
associated leakage rates at the peak pressure of 11.31 psig assumed in the Perry )
Updated Safety Analysis Report (USAR) accident analysis, thereby limiting the !
site boundary radiation doses to within the limits of 10CFR100. The 11esign )
basis analysis of the leakage resulting from a loss of coolant accident (LOCA), s as presented in the USAR, was re-evaluated to address the effects of the increased leakage from the failed MSL penetrations. The calculated figures from this conservative re-evaluation demonstrated that the resulting whole body and thyroid doses at the site boundary would remain below the 10CFR100 limits of 25 rem and 300 rem respectively. The corresponding calculated Control Room whole body doses also amained vell below the 10CFR50, Appendix A General Design Criteria (GDC) - 19 limit of 5 rem. The Standard Review Plan (NUREG-0800) provides additional NRC guidance for the Control Room inhalation dose limit of 30 rem. The re-calculated inhalation dose value did not exceed Standard Review Plan limits.
Realistic Control Room exposures can be shown to be a factor of 10E(+4) lover than those based on the conservative design basis assumptions. The design basis analysis incorporates the airborne activity associated with fuel damage resulting from a LOCA. For the realistic analysis, the availability of the Emergency Core Cooling Systems to mitigate core damage is assumed in accordance with the guidelines of 10CFR50, Appendix K. Therefore, realistic exposures from a postulated LOCA event vould be significantly below the calculated design limits. Additionally, established plant procedures for protection of Control Room personnel vill ensure that potential exposures are minimized. These factors greatly reduce the safety significance of this event.
V. Similar Events Five previous LERs have been submitted to report MSL penetration leak rate test failures. These events were reported in LERs 87-51, 87-67, 89-06, 90-25 and 92-06. In each of these instances, seat leakage from the MSIVs or leakage from other MSL boundary isolation valves was determined to be the cause. Prior to ;
the third refueling outage (RF03) the majority of the corrective maintenance j performed involved the lapping of seating surfaces. A modification was I performed during RF03 for the six MSIVs in MSLs A, B, and D which had exhibited ;
excessive seat leakage during testing. The respective MSIVs vere successfully i tested following modification and repair. l The recent MSL penetration failures vere primarily attributed to MSIV body to bonnet flange leakage, which had not Dreviously been experienced. l l uRc mu mA rs om 1
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- Perry Nuclear Pcrer Plant, Unit 1 - -
93 003 01 TtxT in m nu. v.w.a. m .aa.m.: ce a we oo, , xn (s n VI. Corrective Actions After disassembly of the B Inboard MSIV during the 1993 Maintenance outage and I replacement of the body to bonnet flange gasket, the valve was reassembled and' l failed retest. Additional corrective actions initiated to restore the integrity l of the valve included machining of the valve seat and lover bore and replacement ;
of the valve poppet. The B outboard MSIV required lapping of the poppet to -
correct seat leakage identified after initial valve disassembly and retest. The !
B MSL achieved a successful LLRT following these repairs.
I To address the concerns involving inadequate tensioning of the flanges, a nev i tensioning procedure was developed and incorporated into the work instructions during the recent troubleshooting and repair of the MSIVs. These instructions -
also included a requirement to ensure metal-to-metal contact on the bonnet ;
flange after tensioning. The revised torquing / tensioning requirements, i including the requirement for metal-to-metal contact, vill be incorporated into ,
the permanent MSIV maintenance instruction.
l The MSIV flange gaskets for the penetrations which failed their LLRT vere }
replaced with Flexitallic, Flexicarb gaskets which vere determined to be ,
superior for the desired application. The purchase specification for replacement gaskets has been revised to ensure that proper dimensions and ;
material properties of the gaskets are maintained. The work instructions vill !
I also be revised to require verification of the gasket groove dimensions to ensure proper gasket fit, j Leakage identified as originating from valve seats was repaired by machining or lapping the seating surfaces as necessary. Body to bonnet flange leakage was ?
corrected through improvements to the stud tensioning instructions and enhanced l gasket selection criteria. The A, B and D Main Steam Line penetrations j achieved acceptable post-maintenance LLRT results. j Energy Industry Identification System Codes are identified in the text as [XX]. ),
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