ML17158B686
| ML17158B686 | |
| Person / Time | |
|---|---|
| Site: | Susquehanna  |
| Issue date: | 06/24/1996 |
| From: | Stolz J NRC (Affiliation Not Assigned) |
| To: | Byram R PENNSYLVANIA POWER & LIGHT CO. |
| References | |
| TAC-M94154, TAC-M94155, NUDOCS 9606280035 | |
| Download: ML17158B686 (7) | |
Text
go-9~'t gune 24, 1996
Dear Mr. Byram:
Pennsylvania Power
& Light Company (PP&L, the licensee) in its submittal dated November 13,
- 1995, requested NRC appr'oval of relief from the inspection scope and frequency of the intergranular stress corrosion cracking (IGSCC) Category C welds (Relief Request RR-12) for Susquehanna Steam Electric Station, Units 1
and 2.
Specifically, PP&L's Relief Request RR-12 proposed to inspect the IGSCC Category C welds in accordance with the scope and frequency of IGSCC Category B welds.
The IGSCC Category C welds at both units were treated by the mechanical stress improvement process (MSIP) during the last two refueling outages.
In accordance with Generic Letter (GL) 88-01, "NRC Position on IGSCC in BWR Austenitic Stainless Steel Piping," January 25,
- 1988, IGSCC Category C welds are welds made of non-resistant stainless steel materials and were stress improved after 2 years of operation.
All IGSCC Category C welds are required to be ultrasonically inspected (UT) within the next two fuel cycles after the stress improvement application followed by 100% inspection every 10 years.
IGSCC Category B welds are welds made of non-resistant stainless steel material and were stress improved within 2 years of operation.
For IGSCC Category B welds, UT is required for all welds every 10 years.
The main reason for inspecting Category C welds more frequently than Category B welds is that cracks could be initiated in the susceptible welds after 2 years of plant operation.
PP&L's relief request for the inspection of IGSCC Category C
welds consists of eliminating the requirement of the UT inspection within the next wo fuel cycles after the application of the stress improvement and a
reduction of the required inspection to only 50X of the welds every 10 years.
PP&L st ted that there are 32 IGSCC Category C welds on Unit 1 and 31 such welds on Unit 2.
Seventeen of these welds on each unit are nozzle-to-safe-end welds.
These nozzle-to-safe-end welds are located in high radiation areas with radiation levels varying from 0.5 to 5.0 R/hr.
All large pipe diameter welds (12 inches and over) were remotely examined using the GE SMART 20QQ ultrasonic system (23 welds on Unit 1 and 24 welds on Unit 2).
The small pipe diameter welds (6 inches and under) were inspected manually.
PP&L's justification for its Relief Request RR-12 is briefly summarized below:
V gp,RI~EGy~
. UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D,C. 2055&0001
+**++
Hr. Robert G.
Byram Senior Vice President-Nuclear Pennsylvania Power and Light Company 2 North Ninth Street Allentown, PA 18101
SUBJECT:
SUS(UEHANNA STEAM ELECTRIC STATION, UNITS 1
AND 2, SECOND INSERVICE INSPECTION INTERVAL PROGRAM - DENIAL OF RELIEF RE(VEST RR-12, NUREG-0313 (TAC NOS.
H94154 AND M94155) 9606280035 960b24 PDR ADOCK 05000387
~~0 O'0'5 HAIL !t"l11/ gP)~ ~pp
I>~>c
R.
Byram l'he inspection extent and schedule prescribed for IGSCC Category C welds in GL 88-01 is considered overly conservative at this time to ensure adequate safety margins and continued structural integrity/reliability, because the inspection techniques, personnel qualification and the confidence level of UT inspections have been substantially improved since the issuance of GL 88-01.
!2)
(4)
The subject Category C welds at both units were inspected once after application of MSIP and several times prior to MSIP.
No IGSCC indications were reported at both units.
In the past 10 years, MSIP was applied to over 1180 welds, and no IGSCC initiation or crack growth has been reported to date.
The proposed inspection relief will save about 75 person-rem over the remaining life of both units. If the most dose-intensive welds were avoided during inspection, the overall savings in radiation exposure will increase to about 146 person-rem.
The corresponding cost savings is approximately 1.5 million dollars.
The staff has reviewed PPLL's Relief Request RR-12 and concludes that the subject relief request is not acceptable at this time for Susquehanna, Units 1
and 2.
The staff's conclusion is based on the following considerations:
The intergranular stress corrosion cracking (IGSCC) is a time-dependent process.
For IGSCC susceptible welds,'its potential for IGSCC to occur is likely to increase with the ageing of the operating plants.
Therefore, it is not prudent to decrease the inspection scope and increase the interval between inspections as plants age.
(2) The quality of UT inspections has been improved significantly with the use of automatic inspection mode.
However, the techniques of inspection and personnel qualification have been focused on the detection of circumferencial cracks
- and, consequently, axially oriented cracks, in many instances, have continued to be missed.
- Recently, a number of deep axial cracks (with some essentially through wall) were found at several stress improved welds.
It is most likely that these axial cracks were missed in earlier inspections prior to stress improvement.
- However, we can not completely rule out the possibility that the subject mitigation technique is not effective in arresting the axial cracks.
The axial cracks would not impact the structural integrity of the welds because their length is limited to the width of a heat affected zone
(<
1 inch);
- however, they can grow in depth and result in reactor coolant leakage, which is not acceptable for safe plant operation.
In addition to the UT inspection uncertainties, there is a concern regarding the lack of test data to verify the effectiveness of the process control parameters because most of the sensitivity studies were performed by analytical methods.
The staff also has a concern regarding the potential of a relaxation of compressive residual stresses as a
R.
Byram result of operating loads as well as the anticipated and unanticipated transient loads.
Therefore, it is necessary to continue the monitoring of the subject welds in accordance with the current scope and frequency.
(4) HSIP is a relatively new process developed in the mid-1980s.
In 1988, this process was accepted by the NRC in GL 88-01 as an effective process to mitigate IGSCC.
The majority of applications of HSIP to piping welds in nuclear power plants occurred in the last few years and, therefore, its service experience is limited.
Since the plant life is designed for 40 years, it is'not prudent to reduce the inspection of such welds as proposed by PPEL until more service experience is gained.
(5) The staff believes that a significant saving of the total personnel radiation exposure in performing the subject UT inspection can be achieved by implementing the measures discussed below as"appropriate:
(a)
To apply an effective decontamination process to reduce the radiation level of the piping systems where the UT inspection will be performed.
(b) To apply an effective chemical process to remove the hot spots in the piping systems where the UT inspection will be performed.
(c) To implement an effective hydrogen water chemistry (HWC) program at both units so that the extent of an IGSCC inspection can be cut in half as allowed by GL 88-01.
(d) To implement an effective shielding program so that the radiation level can be significantly reduced in the areas where a
UT inspection will be performed.
(e)
To develop and implement an integrated inservice inspection program so that the personnel radiation exposure associated with the subject inspection can be minimized.
For example, in the inspection of dose intensive nozzle-to-safe-end welds, if it can be scheduled to coincide with the reactor pressure vessel inspection, significant savings in personnel radiation experience could be realized because the effort in opening the shield doors, removing the insulation and the installation of scaffolding will not be duplicated.
Similar schemes can be arranged with other relevant inse} vice inspection and testing programs to minimize the personnel radiation exposure.
(f) To perform automatic or UT inspections on small size piping welds.
This could save some inspection time and personnel radiation exposure.
Based on the above considerations, PPKL's Relief Request RR-12 is denied for Susquehanna, Units 1 and 2.
This completes the work effort for TAC Nos.
H94154 and H94155.
R.
Byram If you have any questions concerning the staff's findings, please contact the project manager, Chester Poslusny at 301-415-1402.
Sincerely, Docket Nos. 50-387/388 cc:
See next page John F. Stolz, Director Project Directorate I-2 Division of Reactor Projects I/II Office of Nuclear Reactor Regulation
Mr. Robert G.
Byram Pennsylvania Power
& Light Company Susquehanna Steam Electric Station, Units 1
& 2 CC:
Jay Silberg, Esq.
- Shaw, Pittman, Potts
& Trowbridge 2300 N Street N.W.
Washington, D.C.
20037 Bryan A. Snapp, Esq.
Assistant Corporate Counsel Pennsylvania Power
& Light Company 2 North Ninth Street Allentown, Pennsylvania 18101 Mr. J.
M. Kenny Licensing Group Supervisor Pennsylvania Power
& Light Company 2 North Ninth Street Allentown, Pennsylvania l8101 Mrs. Maitri Banerjee Senior Resident Inspector U. S. Nuclear Regulatory Commission P.O.
Box 35 Berwick, Pennsylvania 18603-0035 Mr. William P. Dornsife, Director Bureau of Radiation Protection Pennsylvania Department of Environmental Resources P; 0.
Box 8469 Harrisburg, Pennsylvania 17105-8469 Mr. Jesse C. Tilton, III Allegheny Elec. Cooperative, Inc.
212 Locust Street P.O.
Box 1266 Harrisburg, Pennsylvania 17108-1266 Regional Administrator, Region I U.S. Nuclear Regulatory Commission 475 Allendale Road King of Prussia, Pennsylvania 19406 Mr. Harold G. Stanley Vice President-Nuclear Operations Susquehanna Steam Electric Station Pennsylvania Power and Light Company Box 467 Berwick, Pennsylvania 18603 Mr. Herbert D. Woodeshick Special Office of the President Pennsylvania Power and Light Company Rural Route 1,
Box 1797 Berwick, Pennsylvania 18603 George T. Jones Vice President-Nuclear Engineering Pennsylvania Power and Light Company 2 North Ninth Street Allentown, Pennsylvania 18101 Dr. Judith Johnsrud National Energy Committee Sierra Club 433 Orlando Avenue State College, PA 16803 Chairman Board of Supervisors 738 East Third Street
- Berwick, PA 18603
R.
Byram If you have any questions concerning the staff's findings, please contact the project manager, Chester Poslusny at 301-415-1402.
Sincerely, Original signed by:
Docket Nos.
50-387/388 cc:
See next page John F. Stolz, Director Project Directorate I-2 Division of Reactor Projects - I/II Office of Nuclear Reactor Regulation DISTRIBUTION:
Docket File PUBLIC PDI-2 Reading SVarga JZwolinski JStolz CPoslusny MO'Brien OGC GHill(4)
- WDean, EDO
- WPasciak, RGN-I WKoo JStrosnider OFFICE PD PDI-2/P PDI-2 D
NAME M
n CPoslusny:mw JStolz DATE y/
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/96 4 />'//96 OFFICIAL RECORD COPY DOCUMENT NAME:
SU94154.LTR