L-97-248, Requests Relief from Requirement of ASME Section XI,1989 Edition,Paragraph IWA-5250(a)(2) to Remove All Bolting (Studs) on 4B Reactor Coolant Pump,Iaw 10CFR50.55a(a)(3) (II)
| ML17354A663 | |
| Person / Time | |
|---|---|
| Site: | Turkey Point  |
| Issue date: | 09/24/1997 |
| From: | Hovey R FLORIDA POWER & LIGHT CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| L-97-248, NUDOCS 9709300013 | |
| Download: ML17354A663 (11) | |
Text
CATEGORY j.
REGULAT(
INFORMATION DZSTRISUTIONOLSTEM (RIDE)
SUBJECT:
Forwards requests relief from requirement of ASME Section XI,1989 Edition, Paragraph IWA-5250(a)(2) to remove all bolting (studs-)
on 4B RCP.
DISTRIBUTION CODE: A047D COPIES RECEIVED:LTR ENCL SIZE:
TITLE: OR Submittal: Inservice/Testing/Relief from ASME Code GL-89-04 NOTES:
~7 ACCESSION NBR:9709300013 DOC.DATE: 97/09/24 NOTARIZED: NO DOCKET FACIL:50-250 Turkey Point Plant, Unit 3, Florida Power and Light C 05000250 50-251 Turkey Point Plant, Unit 4, Florida Power and Light C 05000251 AUTH';NAME AUTHOR AFFILIATION HOVEY,R.J.
Florida Power
& Light Co.
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'PAIL.
SEP 34 l997 L-97-248 10 CFR 50.55a U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, D.C. 20555 Re:
Turkey Point Units 3 and 4 Docket Nos. 50-250 and 50-251 Inservice Inspection Program Third Ten Year Summary Relief Request No.19 In accordance with 10 CFR 50.55a(a)(3)(ii), Florida Power and Light Co. (FPL) is requesting relieffrom the requirement ofASME Section XI, 1989 Edition, Paragraph IWA-5250(a)(2), to remove all bolting (studs) on the 4B Reactor Coolant Pump.
As discussed during our telephone conversation of September 22, 1997, attached is ReliefRequest No. 19, Corrective Measures for Leakage at the 4B Reactor Coolant Pump flange.
Should there be any questions concerning this submittal, please contact us.
Very truly yours, J. Hovey Vice President Turkey Point Plant CLM Attachment cc:
L. A. Reyes, Regional Administrator, Region II, USNRC T. P. Johnson, Senior Resident Inspector, USNRC, Turkey Point Plant R. Croteau, Project Manager, NRR, USNRC 9709300013 970924 PDR ADQCK 05000250 P
PDR HNILLL%5llttltttitl%%itgwiI an FPL Group company
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ATTACHMENTTO L-97-248 RELIEF REQUEST NO. 19
I Florida Power Ec Light Company (FPL) began a refueling outage on Turkey Point Unit 4 on September 8, 1997.
Evidence ofleakage was found at the main flange ofthe "4B"Reactor Coolant Pump (RCP) during a routine walkdown ofsystems within the containment building.
This walkdown is required by plant procedures while the unit is in Mode 3. In addition, a VT-2 examination ofthe RCP flange bolting (studs) was performed in Mode 5. The leakage was minor (small boric acid deposits), and the accumulation had just begun touching two studs.
Similar examinations in April, 1997, and in previous refueling outages, did not identify any leakage at this location. The leakage was an emergent issue for this refueling outage.
Two methods ofrepair were identified from vendor recommendations:
1.
Retorque the flange and repair at a subsequent outage, or 2.
Disassemble the pump for gasket replacement.
FPL elected to disassemble the pump to replace the flange gaskets and repair the leak.
Disassembly would also allow a thorough examination ofthe studs as required by Section XI IWA-5250. One ofthe two studs closest to the source ofleakage was removed, and a VT-1 visual examination performed.
The stud showed no evidence ofboric acid attack.
Five additional studs were removed in other areas ofthe flange, to allow for pump disassembly.
VT-1 examination ofthese studs also showed no evidence ofboric acid attack.
The pump material is a 316 stainless steel, and is resistant to boric acid attack.
The stud material is A540, a high strength, high alloy, carbon steel.
The studs are susceptible to boric acid attack, and need to be examined.
The studs are about 30.5 inches long and 3.5 inches in diameter.
About 6 inches ofthe bottom end, and 8 inches ofthe top end ofeach stud is threaded.
About 5 inches ofeach stud is threaded into the flange stud holes in the pump casing.
The remaining portion ofeach stud (approximately 84% ofthe total surface area) is accessible for visual examination.
Relief Re nest No. 19 I.
C m onentldentificati n
Turkey Point Unit 4 "4B" Reactor Coolant Pump Studs II.
Examination Re uirements Rules for Inservice Inspection ofNuclear Power Plant Components, 1989 Edition, IWA-5250(a)(2):
"Ifleakage occurs at a bolted connection, the bolting shall be removed, VT-3 visually examined for corrosion, and evaluated in accordance with IWA-3100....".
d FPL has removed 6 ofthe 24 studs from the 4B RCP main flange, and performed VT-1 visual examinations.
FPL requests relieffrom the requirement to remove the remaining bolting (studs) from the 4B RCP.
FPL proposes to perform the visual examinations ofthe remaining studs while still installed, instead ofremoving them as required by IWA-5250(a)(2).
1V.
i P
iiiF During this emergent outage activity ofreplacing the 4B RCP main flange gaskets, FPL has maintained the unit in a defueled status to avoid performing the repair in a reduced inventory condition. Performing the examinations as required by the 1989 edition ofthe ASMECode is a hardship and presents unusual diAiculties without a compensating increase in the level ofquality and safety.
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4 Recognizing the hardship and negligible benefit ofexamining all bolting each time leakage is discovered during ASME Section XItesting, later editions ofthe Code have changed the required bolting examinations.
This change allows a utilityto judge whether the remaining bolting must be removed for examination.
The process used to remove the studs involves double nutting and placing a high torque impact wrench on the nuts. The task ofremoving the remaining studs increases the prospect ofstud breakage or damage (which would require stud replacement) or stud hole damage.
In addition, the flange sealing surface ofthe pump is exposed to possible damage from the equipment being used to remove the bolts. Ifthe flange surface or stud holes suffer damage, in-situ pump casing repair would be required. Allofthese activities would result in unnecessary radiation exposure.
With the pump impeller in place, greater than 500 mrem has been accumulated by maintenance
personnel in the removal ofone quarter ofthe studs. With the impeller removed, the unshielded area dose rates range from 1200 to 6000 mrem/hr.
With shielding in place, dose rates range from 100 to 1400 mrem/hr. In order to reinstall the studs, the studs and stud holes would need to be cleaned and studs threaded into the pump casing, resulting in additional exposure.
The remaining studs can be examined while still installed. The flange assembly is an open flange design.
The thermal barrier is sandwiched between the main flange and the pump casing flange.
The studs are located outside the gasket area, and the area around the studs is wide enough that a qualified VT-1 visual examiner can perform an adequate examination ofthe remainder ofthe stud while still installed (see the attached pictures). In addition, the thermal barrier willbe removed before the VT-1 visual examination, allowing improved access to the studs.
AllowingFPL to examine the remaining bolts in place would accomplish the intent ofthe Code, which is to determine whether the leakage has caused any corrosion damage to the studs.
V.
Alternative Ex minati ns FPL proposes to perform a VT-1 visual examination on the remaining reactor coolant pump studs while they are still installed. This is deemed reasonable, since preliminary examinations have shown no visible corrosion damage at the interface between the threaded stud and the flange top surface.
Based on the tight thread fit, measurable corrosion damage is not credible in the engaged threaded stud hole without corresponding indication ofdamage at the first exposed threads.
Approximately five inches ofeach stud is threaded into the pump flange
. The remainder ofthe studs (84% ofthe surface area) are accessible for visual examination.
This VT-1 visual examination willbe used as part of the evaluation in order to determine whether the studs are acceptable for continued service or must be removed. Ifboric acid degradation is found on any of the in place studs, that stud willbe evaluated for continued service or replacement.
Footnote 1 ofCode Examination Category B-G-1 allows an examination to be performed while the stud is in place under tension, when the connection is disassembled, or when the stud is removed.
The area where the boric acid accumulation was noted can be observed easily with the flange connection assembled (see the attached pictures). By removing the boric acid accumulation and leaving the stud in place, it is possible to detect boric acid degradation.
Code Examination Category B-G-1, Item No. B6.180 covers the Code requirements for the RCP studs.
The studs are required to be volumetrically examined, and the Code Examination Category does not contain VT-1 acceptance standards.
The other two item numbers in Examination Category B-G-1 applicable to the RCPs have the acceptance criteria listed as IWB-3517. These acceptance criteria give reasonable guidance for VT-1 examinations and are used for other examinations ofCode Category B-G-1. These are the acceptance criteria FPL proposes to use for the VT-1 examination ofthe studs.
FPL willperform a VT-1 visual examination ofthe flange in accordance with the requirements of Code Item No. B6.190 at this time. This willensure no damage is present on the flange seal surface. A volumetric examination ofthe 24 studs willbe performed in accordance with Code requirements during this outage, to insure the integrity ofthe removed studs and the in place studs.
A system leakage test willbe performed afler reassembly ofthe pump.
VI.
Justificati n f r the Graniin fthe Relief Should the Request for Relief be denied, the risk ofdamage resulting from removal ofthe remaining studs is significantly increased; damage to the studs, to the Reactor Coolant Pump flange surface, and the Reactor Coolant Pump casing.
Regardless ofthe risk ofdamage, significant radiation dose willbe expended to accomplish the removal ofthe studs, the cleanup of the holes, and the reinstallation ofthe studs.
Performance ofthe alternative examinations described above willprovide a reasonable assurance ofthe continued integrity ofthe studs.
The six studs removed provide a good sample ofthe total population ofstuds, and includes one ofthe studs most likely to be damaged (based on the location ofthe leak.) The volumetric examination willprovide assurance that no studs were damaged during the removal attempts, and complete the Code required examinations.
Thus an acceptable level ofquality and safety willhave been achieved and public health and safety willnot be endangered by allowing the proposed alternative examination in lieu ofthe Code requirements.
VII.
Attachments Figures 1-4 are scanned photographs ofthe 4B Reactor Coolant Pump studs in place show the minor boric acid accumulation.
These photographs were taken during the initial inspections.
Figure 1 is a closeup ofthe Component Cooling Water (CCW) outlet piping (between studs 10 and 11). Boric acid is visible around and under the piping. The white spot on stud 11 is glare from the camera flash.
Figure 2 is a closeup ofthe boric acid between studs 7 and 8.
Figure 3 is another view ofthe CCW outlet piping. Much ofwhat appears white is flash glare.
Boric acid is visible under the outlet piping.
Figure 4 is a poor quality closeup ofthe boric acid visible between studs 7 and 8.
"FIGURE 1-1" is copied from the RCP vendor manual, and clearly shows the location ofthe casing, the flange, the thermal barrier, and the flange bolts (studs).
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