ML17310B335
| ML17310B335 | |
| Person / Time | |
|---|---|
| Site: | Palo Verde  |
| Issue date: | 06/03/1994 |
| From: | James M. Levine ARIZONA PUBLIC SERVICE CO. (FORMERLY ARIZONA NUCLEAR |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| 102-02995-JML-J, 102-2995-JML-J, NUDOCS 9406090294 | |
| Download: ML17310B335 (28) | |
Text
ACCEI ERATO DOCUMENT DIST VTION SYSTEM
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REGULATORY XNFORMATION DISTRIBUTION SYSTEM (RXDS)
ACCESSION NBR:9406090294 DOC.DATE: 94/06/03 NOTARIZED:
NO DOCKET FACIL:STN-50-530 Palo Verde Nuclear Station, Unit 3, Arizona Publi 05000530 AUTH.NAME AUTHOR AFFXLIATION LEVINE,J.M.
Arizona -Public Service Co.
(formerly Arizona Nuclear Power RECIP.NAME RECXPIENT AFFILIATION I
Document Control Branch (Document Control-Desk)
SUBJECT:
Forwards request for relief from AMSE Section XI,hydrostatic pressure test requirements involving SG 32 in Unit 3.
Description of SG nozzle repair also encl.
DISTRIBDTION CODE:
A047D COPIES RECEIVED:LTR 3 ENCL I SIZE:
TITLE: OR Submittal: Inservice/Testing/Relief from ASME Code GL-8 -04 D
NOTES:Standardized plant.
05000530 A
RECIPIENT ID CODE/NAME PDIV-3 LA TRAN, L INTERNAL: ACRS NRR/DE/EMEB NUDOCS-ABSTRACT OGC/HDS1 RES/DSIR/EIB EXTERNAL EGGG BROWN g B NRC PDR COPXES LTTR ENCL 1
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1 RECIPIENT ID CODE/NAME PDIV-3 PD AEOD/DS P/ROA B NRR/EMCB OC LFDCB REG
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D NOTE TO ALL"RIDS" RECIPIENTS:
PLEASE HELP US TO REDUCE WASTETH CONTACI'HEDOCUMENT CONTROL DESK, ROOM Pl-37 (EXT. 504-2065) TO ELIMINATEYOUR NAME FROM DISTRIBUTION LISTS FOR DOCUMENTS YOU DON'T NEEDI TOTAL NUMBER OF COPIES REQUIRED:
LTTR 22 ENCL 19 4
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JAMES M. LEVINE VICE PRESIDENT NUCLEAR PRODUCTION Arizona Public Service Company PALO VERDE NUCLEAR GENERATING STATION P.O. BOX 52034
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PHOENIX. ARIZONA85072-2034 102-02995-JML/J RP June 3, 1994 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Mail Station P1-37 Washington, D.C. 20555
Dear Sirs:
Subject:
Palo Verde Nuclear Generating Station (PVNGS)
Unit 3 Docket No. STN 50-530 Relief Request from ASME,Section XI Hydrostatic Pressure Test Requirements File: 94-056-026 Enclosed is a request for relief from American Society of Mechanical Engineers (ASME),
Section XI, hydrostatic pressure test requirements involving the steam generator 32 in Unit 3. This relief is necessary for Arizona Public Service Company (APS) to repair the intermediate shell level indication nozzle.
APS proposes that in the case of the nozzle repair, the secondary hydrostatic pressure test consist of an In-Service Leak Test (ISLT) at normal secondary operating pressure in Mode 3, as opposed to the 1.25 times design pressure test currently required by ASME Code IWA-5000/IWC-5222.
Pursuant to 10 CFR 50.55a(a)(3) and 10 CFR 50.55a(f)(5)(iii), APS has determined that conformance to the code would be impractical and result in undue hardship without a compensating increase in the level of quality and safety.
Enclosure 1 contains the relief request from ASME,Section XI hydrostatic pressure test requirements. contains a description of the steam generator nozzle repair.
The nozzle repair is critical path for startup of the unit, therefore, APS respectfully requests that the NRC review and approve this relief request expeditiously.
GQUXj 0 94060902'74 940603 PDR ADOCK 05000530 P
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U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Relief Request from ASME,Section XI Hydrostatic Pressure Test Requirements Page 2 Should you have any questions, please contact Richard A. Bernier at (602) 393-5882.
Sincerely, JMLIJRP/did Enclosures cc:
W. L. Stewart L. J. Callan B. E. Holian K. E. Johnston K. E. Perkins
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ENCLOSURE 1 ASME SECTION XI RELIEF REQUEST HYDROSTATIC PRESSURE TEST
- REQUIREMENTS
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ASME SECTION XI CODE RE UIREMENT After repairs by welding on the ASME Class 2 pressure retaining boundary, a system hydrostatic pressure test shall be performed in, accordance with ASME,Section XI, Code IWA-5000.
IWA-5000/IWC-5222 requires a test pressure of 1.25 times system (design) pressure.
ll PROPOSED ALTERNATIVETESTING APS proposes that in the case of the steam generator nozzle repair, the secondary hydrostatic pressure test consist of an In-Service Leak Test (ISLT) at normal secondary operating pressure in Mode 3, as opposed to the 1.25 times design pressure test currently required for Class 2 components by IWC-5222.
The Mode 3 secondary pressure of approximately 1170 psig is the highest seen on the secondary side during normal operation, when'the Reactor Coolant System (RCS) is at normal operating pressure and normal operating temperature.
As reactor power is increased, the secondary pressure drops until the normal operating pressure of 1060 psig is reached at 100 percent reactor power (970 psig with 10'F Treduction).
BASIS FOR RELIEF The ASME Code Section XI, IWA-5000/IWC-5222 requires that a 1.25 times design pressure/full secondary hydrostatic pressure test be performed as a result of the use of half bead welding on the steam generator shell for the purpose of adding reinforcement.
Per 10 CFR 50.55a(a)(3)...."Proposed alternatives to the requirements of paragraphs (c),
(d), (e), (g), and (h) of this section or portions thereof may be used when authorized by the Director of Nuclear Reactor Regulation.
The applicant must demonstrate that (i) the proposed alternatives would provide an acceptable level of quality or safety, or (ii) compliance with the specified requirements of this section would result in hardship or unusual difficulties without a compensating increase in the level of quality or safety."
The Code'equired 1.25 times design pressure hydrostatic pressure testing for this modification presents undue hardship on APS for the following reasons:
The hydrostatic pressure test must be performed with the Reactor Vessel (RV) defueled due to the testing prerequisites and design and operational limitations.
A 1.25 times design pressure secondary side hydrostatic pressure test will result in test parameters of 1569 to 1620 psig and 120'F (minimum). Due to a reverse secondary to primary pressure differential limitation of 820 psig imposed by the steam generator stress report, the RCS must be maintained at a minimum of 875 psig and 291'F to support the secondary hydrostatic pressure test.
Since the RCS pressure of 875 psig exceeds the design pressure of the Shutdown Cooling Page 1 of 5
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System (SDCS), the SDCS cannot be utilized for decay heat removal.
Since the SDCS cannot be used, Technical Specifications (TS) require two RCS loops and associated steam generators to be operable for, decay heat removal in Mode 4.
This TS requirement cannot be met while hydrostatic pressure testing the secondary side of the steam generators.
Therefore, it is concluded that performance of the secondary hydrostatic pressure test with the reactor fueled is not a viable option.
Section IWA-5214(d) states, "where the system hydrostatic pressure test of (b) above (reference IWC-5222) imposes system conditions which conflict with limitations included in the plant TS, a system inservice test (IWA-5211(c)) at normal operating temperature shall be acceptable in lieu ofthe system hydrostatic test."
A hydrostatic pressure test performed with the reactor defueled results in the following hardships and technical concerns:
(a)
An unwarranted reactor reassembly in that it requires the Reactor Vessel (RV) Head and Upper Guide Structure (UGS) to be placed and tensioned following defueling for performance of the hydrostatic pressure test, then
- removed, then reinstalled and retensioned, following refueling of the reactor.,
(b)
With the reactor defueled, the Reactor Coolant Pumps (RCPs) would be used to raise and maintain temperature of the RCS.
Consequently, this requires reconnecting the power supplies and position indication for each Control Element Drive Mechanism (CEDM), venting of each Control Element Assemblies (CEAs) to be withdrawn up into the UGS during RCP operations.
(c)
Even with the UGS installed, running the RCPs in "precore" configurations places the RCPs at their upper design limit due to additional stresses caused by a lower hP and higher flow as a result of the reactor being defueled.
This would impose stresses on the shafts and impellers (as well as high amps on the motors) that will never be seen during normal or transient operation at PVNGS.
Regulatory concerns over RCP shaft cracking has imposed a Licensing required shaft vibration monitoring system with associated action statements that require immediate plant shutdown.
To expose these shafts to the excessive "precore" stresses would seem to be in conflict with the intent of the regulatory requirements and is considered an unnecessary hardship upon the RCPs.
(d)
Analysis would. be required on the Resistance Temperature Detectors (RTDs) that protrude into the RCS flow.
Flow-induced stresses on the RTDs were a concern during the precore startup testing. The RTDs would have to be analyzed to determine ifthey could withstand the high flowthat would exist with RCP operation in the defueled condition.
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(e)
All Main Steam Safety Valves (MSSVs) and Atmospheric Dump Valves (ADVs) will have to be removed and replaced with blind flanges (note that ADVblock valves may be used if leaktight).
(f)
Due to the safety concerns and supply considerations of pneumatically pressurizing the main steam lines, the lines from the steam generators in containment to the Main Steam Isolation Valves in the Main Steam Support Structure willbe filled with water for the hydrostatic pressure test. This will require pinning/strengthening of existing supports, as well as additional temporary hangers to support the additional weight.
(g)
All boundary valves must be verified to be leaktight.
(h)
Temporary relief valves will be required on the secondary side as the system will be water solid w'ith minimum temperature requirements of 120'F and heat addition from the RCS.
In summary, the hardships and technical issues resulting from a secondary hydrostatic pressure test are numerous.
The only feasible time to perform this hydrostatic pressure test will be with the reactor defueled.
This will result in up to approximately three weeks delay in critical path time with an estimated lost generation cost to the utility= $ 12M (very conservative).
Imposes unwarranted use and movement of the UGS and RV head.
Imposes undue stress on the RCP shafts.
Imposes the highest and most limitingfatigue cycle that the steam generators will encounter.
The increase in safety or quality afforded by the Code-required hydrostatic pressure testing, above that ofthe proposed alternative, is not commensurate with the above described hardships and expenses.
The proposed alternative ISLT would provide an acceptable level of quality and safety sufficient to demonstrate the integrity of the modification and the intent of the ASME code.
This is based on:
(a)
Regulatory Guide 1.147 and Code Case N-498 allow alternate rules for the ten-year hydrostatic pressure testing for Class 1 and Class 2 systems.
As outlined in the Code
- Case, the Committee considers an acceptable alternative to the hydrostatic pressure test to be an ISLT that is conducted after the system has been pressurized to normal operating pressure for Page 3 of 5
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intent of the Code Case to utilize a system leakage test (IWB-5221) in lieu of the unnecessary challenge of a 1.25 times design pressure hydrostatic pressure test.
It is APS'nderstanding that the ASME Code is pursuing action to modify ISI requirements of Class 2 systems so as to eliminate the hydrostatic pressure testing in lieu of an ISLT and conform to the Class 1
requirements.
The reasoning behind this pursuit is that nothing detrimental has ever been discovered during these hydrostatic pressure tests which in turn imposes the highest and most limiting fatigue cycle that the steam generators can experience.
A hydrostatic pressure test of 1.25 times design pressure places the highest strain that the material willexperience.
The existing stress report's cumulative fatigue usage factors are indicative of this by only allowing ten hydrostatic pressure test cycles in the design life of the component.
The steam generators have been hydrostatic pressure tested in the manufacturer's shop and in the field during construction/startup, which has used up two of these ten cycles.
From the information gathered thus far from the industry, there have been no failures of any of the ten-year, 1.25 times design pressure hydrostatic pressure testing of the secondary side.
Therefore, it would be good engineering practice to limit such testing unless it were shown to be absolutely essential.
The majority of the Class 2 side of the PVNGS steam generators was originally analyzed using Class 1 analytical techniques (NB-3000).
The analysis to support the nozzle repair willbe performed using analytical techniques comparable to the Class 1 analysis, including a detailed fatigue analysis.
Non-Destructive Examination (NDE) requirements will utilize magnetic particle (MT) and ultrasonic examination (UT) of the base metal, and final liquid penetrant (PT) and ultrasonic examination to verify weld reinforcement quality.
The ISLT will demonstrate that the modification is sound through the pressure ranges the nozzles will normally experience during plant operation, as pressure on the secondary side is ultimately controlled through the MSSVs.
Weld reinforcement/half bead welding will be qualified to ASME Section XI requirements.
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(h)
Note that the NRC is proposing a change to 10 CFR 50.55(a) to approve the 1989 and 1991 Addendas to the 1989 Edition,,and 1992 Edition of ASME Section XI. These Code Editions and Addenda allow exemption from hydrostatic testing after welded repairs on a pressure retaining boundary for component connectioris, piping and associated valves that are NPS 1 and smaller, even if the weld procedure is exempt from post weld heat treatment (IWA04710). If approved, these new rules would be applicable to this repair.
Prior to beginning the nozzle repair, the area of the weld build-up pad for the nozzle and an 18-inch radius from the center of the nozzle was ultrasonically examined to the following acceptance criteria.
Any area, where one or more discontinuities produce a continuous total loss of back reflection accompanied by continuous indications on the same plane that cannot be encompassed within a circle whose diameter is 3 inches or one-half of the plate thickness, whichever is greater, is unacceptable.
In addition, two or more defects smaller than described in the above paragraph shall be unacceptable, unless separated by a minimum distance equal to the greatest diameter of the larger defect or unless they may be collectively encompassed by the circle described above.
From.the above statements and the detailed design analysis performed, the manufacturing and installation techniques for the steam generators for this modification are conservative and comparable to the quality and safety requirements of a Class 1.
system and instills the basis that excessive testing is not required.
Hence, APS believes that the Section XI required hydrostatic pressure test of 1.25 times design pressure is overly conservative, more detrimental than beneficial, and thus an unnecessary challenge to the structural integrity of the steam generator and secondary steam piping systems.
The proposed ISLT will be consistent with the ASME Code Case N-498 and.
will provide the assurance that the modification is structurally sound.
During the next scheduled outage with a planned Mode 5 entry, APS willvisually inspect and PT the nozzle repair area.
In addition, a visual inspection and PT will be conducted at the end of the fuel cycle.
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ENCLOSURE 2 STEAM GENERATOR INTERMEDIATE SHELL'EVEL INDICATIONNOZZLE REPAIR
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A.
~BB d
The affected nozzle in PVNGS Unit 3 is installed in the SG shell by a Category D partial penetration weld in accordance with the requirements of the ASME B&PV Code division 1, class 2 on the ID of the vessel.
The typical configuration of the nozzle is shown in Figure 1.
The cause of the Unit 3 steam generator nozzle leak is considered to be due to inside diameter (ID) weld porosity, which is the same reason for nozzle leakage experienced previously in Unit 2 in 1993.
This porosity was confirmed in Unit 2 by a nozzle ID weld liquid penetrant (PT) test performed by APS since the weld surface was accessible.
The current Unit 3 nozzle weld ID is not accessible for PT test.
Therefore, to provide additional assurance that the nozzle leak was not due to cracking, the nozzle ID bore was PT tested, and the shell UT tested.
The results show no indication of cracking. The results, therefore, provide assurance that the nozzle leak was most likely due to weld porosity caused during fabrication and opening over plant operation to cause a leak path.
In addition to the specific Unit 3 steam generator nozzle NDE, the remaining steam generator carbon steel instrument nozzles were visually examined for leakage and confirmed to be satisfactory.
BB Re Iacement Nozzle Desi n
The replacement design (Figure 2) is in accordance with the Category D partial penetration weld class 2 requirements of the ASME B&PV Code division 1.
Referring to the attached sketch, the pressure boundary weld is being moved to the OD of the SG shell.
The sequence of the installation is as follows:
1.
Cut off existing nozzle flush with shell.
2.
Bore out nozzle to approximately 0.5 inches.
3.
Measure bore diameter.
4.
Machine nozzle to meet 0.020 inch maximum diametrical clearance requirement.
5.
Fit nozzle with approximately 0.125 inch gap from existing nozzle for thermal growth clearance.
6.
Weld deposit an inconel pad approximately 3 inches in diameter and 0.5 inches thick on OD of SG shell.
7.
Post Weld heat treat weld pad.
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8.
NDE pad build up.
9.
Machine J-groove weld preparation in weld pad.
10.
Weld reinforced J-groove weld in pad.
11.
NDE J-groove pad.
12.
Perform ASME Code Section XI pressure test or approved alternative.
C.
Installation Schedule:
June 2, 1994 June 5, 1994 June 6, 1994 Commence Welding of pad.
Release SG to Operations.
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