ML20035F139
| ML20035F139 | |
| Person / Time | |
|---|---|
| Site: | Limerick  |
| Issue date: | 04/14/1993 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20035F130 | List: |
| References | |
| NUDOCS 9304200315 | |
| Download: ML20035F139 (3) | |
Text
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'n UNITED STATES 3
-i NUCLEAR REGULATORY COMMISSION i
WASHINGTON. D.C. 20555 l
+
SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO THE INSERVICE INSPECTION PROGRAMS FOR PHILADELPHIA ELECTRIC COMPANY f
f LIMERICK GENERATING STATION. UNITS 1 AND 2 f
i DOCKET NOS. 50-352 AND 50-353 l
l
1.0 INTRODUCTION
In a letter dated October 5,1992, the Philadelphia Electric Company (PEco) l requested approval to perform an alternative inspection program that includes American Society of _ Mechanical Engineers (ASME) Code requirements that have not yet been referenced in 10 CFR 50.55a(b).
The Technical Specifications (TS) for the Limerick Generating Station, Units 1 i
and 2, state that inservice inspection and testing of (ASME) Code Class 1, 2, l
and 3 components shall be performed _in accordance with Section XI of the ASME j
l Boiler and Pressure Vessel Code and applicable Addenda, as required by 10 CFR l
50.55a(g), except where specific written relief has been granted by the Commission, pursuant to 10 CFR 50.55a(g)(6)(1).
Pursuant to 10 CFR 50.55a (a)(3) alternatives to the requirements of paragraph (g) may be used, when j
i authorized by the NRC, if the proposed alternatives would provide an acceptable level of quality and safety, or compliance with the specified requirements would result in hardship or unusual difficulties without a compensating increase in the level of quality and safety.
j Also,10 CFR 50.55a(g)(1)(iv) permits a licensee to meet the requirements set j
forth in subsequent editions of ASME Section XI referenced-in 10 CFR 50.55a(b) i subject to the limitations and modifications listed therein and subject to Commission approval.
Portions of editions or addenda may be used provided that all related requirements of the respective editions or addenda are met.
2.0 CODE CONSIDERATIONS This action applies to all ASME Code Class 1 pressure retaining components, Code Examination Category B-P Item Numbers B15.10 through B15.71 that contain bolted connections.
9304200315 930414 PDR ADOCK 05000352 P.
The ASME Section XI, 1986 Edition, Examination Category B-P, requires a VT-2 visual examination of all Class I components during the performance of the system leakage or hydrostatic pressure test.
The purpose of the VT-2 examination is to detect leakage.
The acceptance standard for dealing with the results of this examination is contained in paragraph IWB-3522. This acceptance standard requires correction of specific relevant conditions, to meet the requirements of IWB-3142 and IWA-5250, prior to continued service.
IWA-5250(a)(2) indicates that i bolting shall be removed, VT-3,f leakage occurs at a bolted connection, the examined for corrosion, and evaluated in accordance with IWA-3100.
3.0 EVALUATION The licensee has requested relief from performing the bolt removal requirement of IWA-5250(a)(2) if leakage occurs at a bolted connection.
The requirement to disassemble the bolted connection solely for the purpose of performing a visual examination of the bolting for corrosion is not always logical.
Bolted connections which experience leakage could have been reworked i
during the current plant or system outage.
If t.ne connection was reworked, all associated bolting, whether original or replaced, would have been visually examined prior to reassembly of the connection. Additionally, this bolting j
material would likely not have been exposed to system service, thereby minimizing the possibilities of corrosion. This position is supported by the 1
ASME Section XI interpretation IN90-023, which was issued on September 10, i
1991.
A portion of the pressure retaining bolting used in Class 1 applications at Limerick Generating Station is made up of stainless steel materials. These materials are not as susceptible to corrosion (wastage) as are carbon or low "IWA-2212 VT-2 Examination (a) VT-2 examination are conducted to detect evidence of leakage from pressure retaining components, with or without leakage collection systems, as required during the conduct of system pressure test.
i (b) VT-2 examinations shall be conducted in accordance witt. IWA-5000. For direct examination, the Table IWA-2210-1 maximum examination distance shall apply to the distance from the eye to the surfaces being examined.
"'IWA-2213 VT-3 Examinations VT-3 examinations are conducted to determine the general mechanical and structural condition of components and their supports by verifying parameters such as clearances, settings, and physical displacements; and to detect discontinuities and imperfections, such as loss of integrity at holted or welded connections, wear, or erosion. VT-3 includes examinations for conditions that could after operability or functional adequacy of snubbers and constant local and spring type supports.
alloy materials. Also, since the normal Class 1 pressure boundary of a BWR facility contains only demineralized water, the chances of severe corrosion are minimal.
While stainless steel boltinn materials are susceptible to stress corrosion cracking under certain conditions, detection of this type of corrosion on the bolting material is difficult using the VT-3 visual examination method.
Therefore, removal and examination of the bolting will have little significance.
Further, if evidence exists which indicates that the leakage found is not a i
preexisting condition and the leakage is stopped, the concern for corrosion of the bolting material is reduced. The cost and added radiation exposure associated with the requirement to disassemble and examine the bolting, along with the inherent need to repeat all or portions of the associated pressure test and the potential impact on plant operations, far outweigh the increase in safety resulting from performance of this examination.
However, if during a Section XI pressure test, the VT-2 examination reveals a relevant condition as listed in IWB-3522, at a Class I bolted connection which has been in service; the entire connection will be visually examined using the VT-1"' method.
This examination will be conducted to determine the overall condition of the connection with respect to corrosion. The examination will be conducted with all bolting in place, under tension.
The results of this examination along with additional relevant factors will be useu to perform an evaluatiot, of the condition of the bolted connection. The additional factors which may be used in the evaluation could include but are not limited to: type of material used for the bolting, the nature of the leak itself, the service age of the bolting material, date of previous visual 3
examination of bolting, scheduled maintenance for the subject joint, results of ISI volumetric examinations, and confirmation of leak stoppage.
If any of the factors used for the evaluation indicates a potential for degradation of the bolting due to corrosion, then one bolt will be removed and VT-1 (not VT-3) examined for corrosion, and evaluated in accordance with IWA-3100.
The bolt selected for removal and examination will be the bolt most likely to be affected by the subject leakage.
When the removed bolt has evidence of degradation, all-the remaining bolting in the connection will be removed, receive a VT-1 examination, and an evaluation in accordance with IWA-3100.
7WA-2211 VT-1 Examination VT-1 examinations are conducted to detect discontinuities and imperfections on the surfaces of components, including such conditions as cracks, wear. corrosion, or erosion.
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