ML20099B050
| ML20099B050 | |
| Person / Time | |
|---|---|
| Site: | Davis Besse  |
| Issue date: | 07/20/1992 |
| From: | Shelton D ENTERGY OPERATIONS, INC. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| 2067, GL-90-05, GL-90-5, TAC-M84097, NUDOCS 9207300129 | |
| Download: ML20099B050 (11) | |
Text
.
I O
CENTERIOR ENERGY Doned c. shelton 300 Masson Annue Vce Prmdent Nudear Toledo, OH 43652&)01 Davis Besse (419)249 2300 Docket Number 50-346 License Number NPF-3 Serial Number 2067 July 20, 1992 United States Nuclear Regulatory Commission Document Control Desk Vashington, D.C.
20555
Subject:
Request for Relief to Allow Temporary Non-Code Repair of Service Vater Piping in Accordance vith Nuclear Regulatory Commission (NRC) Generic Letter (GL) 90-05 Gentlemen:
The purpose of this letter is to request NRC approval of a temporary non-Code repair of a through-vall leak discovered in Service Water (SV) syster piping at the Davis-Besse Nuclear Power Station, Unit 1 (DBNPS).
Section XI of the American Society of Mechanical Engineers (ASME)
Boiler and Pressure Vessel Code specifies Code-acceptable repair methods for flaws that ex.ceed Code acceptance limits in piping that is in service.
A Code repair of fluved ASME Code piping in accordance vith Section XI, IVA-4000 is required regardless of the operational mode of the plant when the flaw is detected. Toledo Edison has determined that a Code repair is impractical at the present time and requests approval of a temporary non-Code repair in accordance with URC Generic Letter (GL) 90-05.
The throegb-vall leak was discovered during a SV system valk dov on June 26, 1992, in a section of 4" diameter ASMC Section III, Class 3 SV system piping located in the Decay Heat (DH) :ooler room.
The leak is in the same run of approxir.tely 120' of SV piping that has experienced four other through-vall leaks since June 1990. Three of these previous leaks were identified during plant operation and were the subject of previous relief requests for NRC approval of temporary ncn-Code repairs (Serial 1825 dated July 10, 1990, and Serial 1955 dated July 3, 1991) during the last operating cycle.
As these leaks have all occurred in the same run of SV piping, Toledo Edison has concluded that replacement of the affected piping run is the appropriate course of action.
4 5 g 0 00 3 6 04 PDR O
Operahng Compornet (I\\
Cladcoc Et tac Mr ag r we gesan o
. _ - ~.
i---Docket Number 50 346 License Number NP.7-3~
Serial Number-2067
.Page 2 It is noted that-prior to modifications made to the SV system during i
the seventh refueling outage (7RFO), a Code repair and Code required post-repair testing in this section~of SU piping could not be accomplished within the limiting 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> Technical Specification action statement.. Service Water system modifications-implemented during the 7RF0 in 1991 permit taking the affected section of piping out of service during plant operation for a maximum of 30 days. This involves isolating the affected portion of the SV piping by removing spool pieces and installing blind flanges.
Vith t'.e blind flanges installed, SV flov is isolated from one of the two train 2 ECCS room coolers, the DH cooler room cooler and the train 2 hydrogen dilution blover.
In this case, the 30 day hydrogen dilution blover action statement is
-limiting. The one train 2 ECCS. room cooler with SV flow is sufficient to maintain ECCS operability provided SV temperature remains less than 78.5'F. Two ECCS room coolers are required for ECCS operability with the SV temperature exceeding 78.5'F.
The 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> ECCS Action Statement would be immediately invoked if the SV temperature vere to exceed 78.b'F, while the flawed section of piping was isolated using the blind flanges.
Although this ability to isolate the flaved piping for up to 30 days during plant operation exists, there is significant potential during the upcoming summer months that-the SV temperature could increase above the 78.5'F-lim't.
On-July =1, 1992, SV temperature was 71*F cnd had risen three degrees-in the previous week.
Ir previous _ summers, SV temperature has reached approximately 84'F.
Thould the temperature exceed 78.5'F vhile the flawed piping was being replaced, SV flow could not be restored to the second train 2 ECCS room cooler within the 72 hoor ECCS action statement and a plant shutdown vould be required.
Because of the potential for SV_ temperature-increasing above 78.5'F during the remainder of the summer months, Toledo Edison has determined that it is impractical to perform a Code repair to the flawed piping at this time.
t Although-it may be possible_to effect a Code repair in autumn when lake temperature is-declining, Toledo Edison proposes to defer replacement of the flaved piping until no-later than startup from the eighth refueling outage (8RFO).
Current plans call for replacing the affected piping in February 1993, prior to the start of the 8RFO.
Deferment of the piping replacement until February 1993 vill allow adequate time for planning and shop fabrication of replacement sections of piping and fittings, and vill allow the use of the additional manpover arriving on site in support of the 8RFO.
In addition, if unforeseen problems were
-encountered during the pipe replacement, the limiting 30 day action statement vould not expire prior to the beginning of the 8RFO.
The identified SV piping flav has been evaluated using the guidance provided by NRC Generic Letter 90-05, Guidance for Performing Temporary Non-Code' Repair of ASME Code Class 1, 2, and 3 Piping,' dated June 15, 1990, and found to be acceptable for continued operation. Toledo Edison has concluded that the proposed alternative of a non-Code repair provides an acceptable level of quality and sarety.
Docliet Number '50-346
- - f_
_ License Numbar NPF-3_
-Serial 1 Number 2067-
.Page 3 i
Accordingly, Toledo: Edison. requests relief from the requirements of-the ASME Code,-Section XI, Article IVA-4000.'to allow continued. plant operation with a temporary non-Code repair to the affected SU system piping, as provided:by CL 90-05.- The detailed basis for the acceptability of these temporary non-Code repairs to the SV system piping-leak-is attached.
-If you have any. questions regarding this relief request, please call 1
Hr..R. V. Schrauder, Manager - Nuclear Licensing at (419) 249-2366.
Very tru
- yours,
/p e
V A _3 (NS/dle P
Attachment ec:
A.
B.' Davis, Regional Administrator, NRC Region III J. B. tiopkins, -NRC/NRR DB-1 Senior Project Manager U. Levis, NRC Region:III, DB-1 Senior Resident ~ Inspector
- Utility Radiological Safety Board i
u r
s i ::
l
~
(
Decket Number 50-346 License Number NPF-3 Ser!al Number 2067 i
Attachment Page 1 BASIS-FOR-ACCEPTABILITY OF A TEMPORARY NON-CODE
-REPAIR OF THE SERVICE VATER PIPING LEAK Desc~tption of Flav Detection On June 26, 1992, a through-vall leak vas discovered during valk down of the moderate energy service water (SV) system piping. The leak vr.s found in a horizontal run of service water piping 4"-HBC-44 (See P&ID M-041B, F-5, attached)-in the Decay Heat (DH) cooler room. A pipe clamp vith a rubber gasket was used to minimize-the leakage.
Prior to installation of the clamp and gasket, the leak rate at this location was approximately 1.0 to 1.5 gallons per minute.
The affected SV piping _is schedule 40 rated at 150 psi ASME(SA53,= Grade B carbon steel)
Section III, Class 3.
Ultrasonic testing (UT) vas used to characterize the flaw in support of the assessment of structural integrity in accordance with GL 90-05.
Flav Characterization The flav was characterized by ultrasonic testing on June 26, 1992. The flaw is an approximately circular cavity in the pipe vall about 0.4" to 0.5"_in diameter.
Corrosion is the apparent cause of this flav in the service water piping.
The location of the flav is in the same run of apprcximately 120' of SV piping that has experienced four other through-vall leaks since June 1990.
Three of these previous leaks were identified during plant operation and vere the subject of previous relief. requests for NRC approval of temporary non-Code repairs (Serial 1825 dated July 10, 1990, and Serial 1955 dated July 3, 1991) during the last operating cycle. All of the flavs occurred in straight horizontal-runs of piping with the flaws located between the 5 and 7 o' clock. positions. Additionally, there is normally no flow through this run of piping.
Microbiological 1y induced corrosion (MIC) is the most probable corrosion mechanism.
Flav Evaluation Results Because of past experience with SV piping through-vall leaks, a bounding flav size of 1" vas evaluated to provide acceptance criteria for ultrasonic testing or radiography.
The bounding flav size was analyzed using tFe "through-vall flaw" approach presented in section C.3.a of Enclosure 1 to NRC Generic Letter 90-05, Guidance for
~
Performing Temporary Non-Code Repair of~ASME Code Class 1, 2, and 3 Piping. The individual maximums of deadweight, pressure, thermal and safe shutdown earthquake (SSE) stresses at any-location in the piping run vere combined to provide a maximum total stress (16,845 psi). This is conservative for any location in the piping run.
Consistent with e
the guidance provided by the NRC Safety Evaluation (Log Number 3303, dated August 20, 1990, TAC No. M77037) of a previous Toledo Edison request for_ approval of a non-Code repair under GL 90-05, the nominal pipe thickness (t
) was substituted for the Code minimuw pipe is0.23N)in*thecurrentevaluation.
thickness (t For 4", Schedule 40 pipe t nom
^
Ducke~t Number 50-346 License Number NPF-3 Serial Number 2067 Attachment Page 2 An assumed 1" flav (a;- 0.5") located anywhere in the affected 4" ksi(in)0gterpiperesultsinastressintensftgfactorof32.6 service v This is less than the 35 ksi(in) acceptance criteria for -ferritic steels cited by GL 90-05.
Since the 0.4" to 0.5" flav size determined by UT is less than the 1" bounding flav evaluated in this pipe run a temporary non-Code repair is acceptable.
Determination-of Impracticality of Repair Toledo Edison has determined that it is impractical to perform a Code repair to the affected piping at the present time.
Prior to modifications made to the SV system during the seventh refueling outage (7RFO), a Code repair and Code required. post-repair testing could not be accomplished within the limiting 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> Technical Specification action statement. -Service Water system modifications implemented during the 7RF0 in 1991 permit taking the affected section of piping out of service during plant operation for a maximum of 30 days. This involves isolating the affected portion of the SV piping using valve SV-257. Closure of SV-257 removes SV flov from both train 2 emergency core cooling system-(ECCS) room coolers, rendering one train of ECCS inoperable and invoking a 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> Technical Specification action statement. This closure of SV-257 permits removal of spool pieces in the affected section of SV piping, allowing the installation of blind flanges. The 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> ECCS action-statement is exited when SV-257 is reopened, restoring SV flov to one of the train 2 ECCS room coolers, and operability of the affected ECCS train. Vith the blind flanges installed,-SV flow is' isolated from the other train 2 ECCS room cooler, the DF cooler room cooler and the train 2 hydrogen dilution blower.
The 30 day hydrogen dilution blover action statement is nov limiting since one. train 2 ECCS room cooler is sufficient to maintain ECCS operability provided SV temperature remains less than 78.5'F. Two ECCS room coolers are-required for ECCS operability with the SV temperature exceeding 78.58F.
The 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> ECCS Action Statement would be immediately invoked if the_SV temperature vere to exceed 78.5'F while the~ flawed tection of piping was isolated using the blind flanges.
'Although this ability to isolate.the flaved piping for up to 30 days during plant operation exists, there is significant potential during the summer months that the SV temperature could-increase abote the 78.5'F limit.
On July 1, 1992,-SV temperature was 71'F and had risen three degrees.in the previous week-.
In previous summers, SV temperatute has reached approximately 84"F. Should the temperature exceed 78.5"F while the flaved piping was being replaced, SV flov;could not be restored to the second train 2 ECCS room cooler within the 72 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> ECCS action statement and a plant-shutdown vould be required.
-Because_of the potential for SV temperature increasing above 78.5"F D
during the remainder.of the summer months, Toledo Edison has determined that it is i",ractical to perform a code repair to the flaved piping at l
this time.
l i~
l L
L
~.
'. ~
Docket: Number 50i346:
~
~ License Number NPF-3 Serial Number 2067 Attachment-Page-3 Although it may be possible to effect'a Code repair in autumn when lake temperature'is declining, Toledo Edison proposes to defer replacement of the flaved piping.until no later than startup from the eighth refueling outage (8RFO). ' Current plans call for replacing the affected piping in February 1993, pri;r to the start of the eighth refueling outage (8RFO).
Deferment of the; piping replacement until February-1993 vill allov adequate.timetfor~ planning and shop fabrication of replacement sections of piping and fittings, and vill allow the use of the additional manpower arriving on site in support of the 8RF0.
In addition, if unforeseen problems were encountered during the pipe replacement, the limitic. 30 day action statement vould not expire
_ prior to the beginning of the 8RFO.
Based on the foregoing evaluation of-the flav and continued structural integrity of the affected piping.
Toledo Edison proposes to continue operation with the pipe-clamp and rubber gasket in place to limit leakage until no later than startup from:the 8RF0. The 8RF0 is scheduled to begin on March 1, 1993.
Description and Evaluation'of Temporary Repair The. temporary repair of the piping flaw consists of a pipe clamp and rubber gasket. The clamp does not serve any structural function for this application, and its effect on the piping system is negligible due to the very small additional loading involved.
Systems interactions
-(such as flooding,. spraying water on equipment and loss of system flow) have been evaluated, assuming the absence of the clamp and considering the flav location and area sump capacity, and-found to be negligible.
The components in the DH cooler _ room are spray protected and no adverse effects will be created by water _ spray from.he leak in the service water piping. The leakage through the pipe flav vithout the pipe clamp installed does not spray on any electrical component.
In addition, the pipe clamp has a rubber gasket to seal-the defect area and minimize any leakage.
The potential for flooding of the DH cooler room as a result of the service water leaks has been revieved.
The DH cooler room has two 75
- gallon per minute (gpm) capacity sump pumps. The sump pumps have level switches and associated alarms, and are powered-from an essential bus.
Should the pipe clamp come loose and the' leak rate become severe enough to potentially flood-the room, the level alarms associated with.the sump pumps vill alert the control room.
At the current leak rate of approximately 1.0 - 1.5 gpm without the pipe clamp installed, flooding is not_a' concern.
Should the defects open to the maximum allovable size, the leak-rates vill still'be within the capacity of the sump pumps. Veekly inspections of the pipe clamp and assessment of leakage provide assurance that the pipe clamp is intact and flooding of the rooms is not occurring.
The train 2_ECCS room coolers are supplied from the Number 2 Service Water loop.
Coasequently, the flow rates through these coolers could be affected by the pipe leak.
However, with the non-Code repair in place,-flov through these ECCS room coolers is unaffected by the leak.
At :the current _ leak rate with the non-Code repair removed, the maximum
Docket' Number 50-346 License Number NPF-3 Serial Number 2067-Attachment Page 41
_ flow reduction through any one of these coolers is approximately 1.0 -
1.5 gpm which is acceptable. Veekly= inspection of the non-Code repair
-provides assurance _that the Number 2 Service Vater' loop ECCS room coolers will not have reduced flow.
Augmented Inspections On July 6, 1992, Toledo Edir.on performed augmented ultrasonic (UT)-
examinations at five-other SV piping locations with similar geometry and flow characteristics to the flaw location. - None of' these locations e.nhibited unacceptable indications with a measured vall thickness less-than the Code-required minimum _vall thickness.
A qualitative ~ assessment-of leakage th.sugh the temporary non-Code
' repair to determine any degradation of structural integrity vill be made weekly during'valkdown inspections. An assessment of the
-i integrity of the non-Coos-repair vill be made at least quarterly using RT'or UT.
Concemia Based on-the foregoing, continued operation with the identified service water system flav and temporary non-Code repair is acceptable until startup from the eighth refueling outage.
4 U
~
.q OVERSIZE i
DOCUMENT PAGE PULLED 1
SEE APERTURE CARDS
^
NUMBER OF OVERSIZE PAGES FILMED ON APERTURE CARDS l
7 20Td3 o 3.u APERTURE CARD /HARD COPY AVAILABLE FROM RECORDS AND REPORTS MANAGEMENT BRANCH I
i
-