ML16131A325
| ML16131A325 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 10/29/1990 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML16131A324 | List: |
| References | |
| NUDOCS 9011070363 | |
| Download: ML16131A325 (11) | |
Text
UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION REQUEST FOR RELIEF FROM REGULATORY REQUIREMENTS DUKE POWER COMPANY OCONEE NUCLEAR STATION, UNITS 1, 2, AND 3 DOCKET NOS. 50-269, 50-270 AND 50-287 INTRODUCTION The Technical Specifications for the Oconee Nuclear Station, Units 1, 2 and 3, state that inservice examination of ASME Code Class 1, 2 and 3 components shall be performed in accordance with Section XI of the ASME Boiler and Pressure Vessel Code and applicable Addenda as required by 10 CFR 50.55a(g)(4),
to the extent practicable within the limitations of design, geometry and materials of construction of the components, except where specific written relief has been granted by the Commission pursuant to 10 CFR 50.55a(g)(6)(i).
Pursuant to 10 CFR 50.55a(g)(5), if the licensee determines that conformance with an examination requirement of Section XI of the ASME Code is not practical for its facility, information shall be submitted to the Commission in support of that determination and a request made for relief from the ASME Code requirement.
After evaluation of the determination, pursuant to 10 CFR 50.55a(g)(6)(i),
the Commission may grant relief and may impose alternative requirements that are determined to be authorized by law, will not endanger life or property or the common defense and security, and are otherwise in the public interest, giving due consideration to the burden upon the licensee that could result if the Code requirements were imposed.
In letters dated March 31, 1989, October 13, 1989, December 5 and 8, 1989, March 1, 1990, and May 31, 1990, Duke Power Company (the licensee) requested relief from certain examination requirements of Section XI of the ASME Boiler and Pressure Vessel Code. The relief related to the Second Interval of the Inservice Inspection (ISI) Program for the Oconee Nuclear Station, Units 1, 2 and 3. The relief requests and supporting information are evaluated by the staff in this Safety Evaluation.
2.0 EVALUATION RELIEF REQUEST 89-02 Component - Emergency Feedwater System (EFS) seal injection piping, Units 1, 2 and 3. 2-inch weld at the 2-inch x 1-inch reducing insert.
Code Class -
ISI Class C/Duke Class F Code Requirement - Subparagraph IWA-4400(a) requires a system hydrostatic test to be performed in accordance with Article IWA-5000 after repair by welding.
9 0 1 16 9 0 10 29 DRADOCK 05000269 P
-2 Relief Requested - Relief is requested from the hydrostatic test requirement.
Alternative Examination - Welds will be examined with a liquid penetrant (LP) examination, and a visual testing (VT-2) inspection will be performed at operating temperature and pressure.
Basis for Relief Request - There is no practical way to isolate the affected 2-inch line from the turbine driven emergency feedwater pump and piping upstream. The required hydrostatic test could potentially overpressurize the emergency feedwater pump and upstream piping. Alternate methods of isolation were considered but were thought impractical.
The alternate methods considered were:
- 1) Disconnect and blank flange the discharge piping from the turbine driven emergency feedwater pump. This method was unacceptable because the flanges at the pump are not flexible enough to allow for the insertion of the blank flange.
- 2) Install a manual isolation valve on the discharge side of the turbine driven emergency feedwater pump. This method is unacceptable since an isolation valve of any type would be welded in place and the welds on the non-hydro side of the isolation valve would also require hydrostatic testing.
- 3) Perform a hydrostatic test through the turbine driven emergency feedwater pump to the first isolation valve on the intake side. Piping on the intake side of the pump has a design pressure of only 25 psig. Thus, this would overpressurize the piping on the intake side of the pump.
Evaluation - After repair by welding, the Code requires that a system hydrostatic test be performed in accordance to Article IWA-5000 to assure leak tightness. The alternative examination proposed by the licensee arrives at the same objective by first performing a liquid penetrant examination to ensure no evidence of weld cracks and then, after ascension to power, conducting a VT-2 inspection, to assure no leakage at operating pressure and temperature.
Conclusion - We conclude that compliance with the specific requirement of Secticn XI of the ASME Code to hydrostatically test the repair welds in the Emergency Feedwater System seal injection piping is impractical to perform at the Oconee Nuclear Station, Units 1, 2 and 3, in that isolation of the affected line cannot be accomplished without adversely affecting plant equipment. Code compliance would require redesign and replacement of the affected component.
The staff accepts the alternative examination proposed by the licensee to verify the structural integrity of the repair welds. Relief from the Section XI requirement is granted as requested in Relief Request 89-02.
-3 RELIEF REQUEST 89-08 Component -
Flange Stud Holes in Reactor Coolant Pumps 3A2 and 3B1 at Oconee Nuclear Station Unit 3 Code Class - ASME Code Class 1/Duke Class A Code Requirement - Subparagraph IWB-2420(b) requires that if flaw indications are evaluated in accordance with Subparagraph IWB-3122.4 and the component qualifies as acceptable for continued service, the areas containing such flaw indications shall be reexamined during the next three inspection programs listed in the inspection programs of Subarticle IWB-2410.
Alternative Examination - At each refueling outage, the flange joint and surrounding area will be inspected for any accumulation of boric acid or visible stud degradation. If any degradation is noted, actual dimensional checks will be made of the studs. Additionally, when a reactor coolant pump is disassembled for maintenance activities, all stud holes will be inspected as required by the ASME Code. Stud holes will be examined during the third ten-year interval as part of the Inservice Inspection Program.
Basis for Relief Request - During outage 9, and as part of the ten-year Inservice Inspection Program, reportable indications were found in the reactor coolant pump 3A2 and 3B1 stud holes. An engineering evaluation was made which showed that the damaged threads in the stud holes were acceptable for continued operation of the reactor coolant pumps. The evaluation indicated that the pumps were operable with 19 of the 20 studs in place.
The damage to the stud hold threads was determined to be characteristic of damage done during the process of removing the studs. Past experience has shown that it is not practical to remove a single stud without loosening all the studs. Loosening all studs is necessary in order to allow some float in the motor stand and motor so that the stud to be removed will not bind.
However, this would require removal of the pump in order to replace the flexatalic gasket which would result in 25 man-REM of radiation exposure per pump. As such, performance of examinations required by Subarticle IWB-2420 during the next three inspection periods would result in a hardship without a compensating increase in the level of quality and safety.
Evaluation - The alternate examination should minimize the possibility of further damage to the stud hole threads during removal and replacement of the studs.
Subparagraph IWB-2420(b) requires reexaminations to verify operability of the subject studs. Evaluations indicated that the reactor coolant pumps are operable with 19 of 20 studs in place. The results of the evaluation
-4 indicated that even if one of the 20 studs is removed, the remaining 19 studs will still remain below the Code allowable stresses. As such, it is not necessary to take credit for the damaged stud hold. The alternate examinations ensure that further stud degradation is detected and compensatory measures taken. Therefore, the proposed alternate examinations provide an acceptable alternative to the ASME Code Section XI Subparagraph IWB-2420(b) requirement.
Conclusion - We conclude that compliance with the specific requirements of Subparagraph IWB-2420(b) of Section XI of the ASME Code is unnecessary for the Oconee Nuclear Station, Unit 3, and if imposed, would result in high radiation doses and cause hardship without a compensating increase in the level of quality and safety. Pursuant to 10 CFR 50.55a(a)(3)(ii) relief is granted as requested in Relief Request 89-08 and the alternative examination procedure imposed to ensure the integrity of the flange stud holes in reactor coolant pumps 3A2 and 3B1.
-5 RELIEF REQUEST 89-09 Component - Welds for the installation of Valves AS-39 and MS-91 in the Auxiliary Steam and Main Steam Systems, Oconee Nuclear Station, Units 1, 2 and 3.
Code Class - ISI Class C/Duke Class F Code Requirement - Subparagraph IWA-4400(a) requires a system hydrostatic test to be performed in accordance with Article IWA-5000 after repair by welding.
Relief Requested - Relief is requested from the hydrostatic test requirement.
Alternative Examination - Welds will be 100% radiographed and VT-2 inspected at operating temperature and pressure. The welds will be hydrostatically tested during the second ten-year interval inservice inspection hydrostatic test of the main steam lines.
Basis for Relief Request - Hydrostatic testing would require filling the Auxiliary Steam System with water. The Auxiliary Steam header cannot be properly drained due to the lack of adequate low point drains in the system.
Water remaining in the Auxiliary Steam header following the required hydrostatic test could potentially damage the Emergency Feedwater pump turbine.
It is determined that the ASME Code Section XI test requirement is impractical to perform at Oconee Nuclear Station, Units 1, 2 and 3.
Evaluation - The specified method of hydrostatic testing verifies that there are no leaks at 1.25 times the design pressure. The alternative examination of 100% radiography of welds assures that no significant flaws are present. The VT-2 inspections show that no leaks are detectable when the system is at operating temperature and pressure. The alternative tests provide an equivalent method to indicate a leak at the higher stress level which is normally verified by the specified method of hydrostatic testing. As such, the proposed alternative examinations provide an acceptable level of quality and safety and will not endanger the health and safety of the public.
Conclusion - We conclude that compliance with the specific requirement of Subparagraph IWA-4400(a) of Section XI to hydrostatically test the welds for the installation of valves AS-39 and MS-91 in the Auxiliary Steam and Main Steam Systems is impractical for the Oconee Nuclear Station, Units 1, 2 and
- 3. Water required for the test could not be drained after testing and could damage equipment. In order to comply with the code, the steam systems would have to be redesigned and modified. The staff accepts the alternative examination proposed by the licensee to ensure the structural integrity of the welds. Relief is granted as requested in Relief Request 89-09 and the alternative testing imposed to ensure no significant flaws are present.
-6 RELIEF REQUEST 89-10 Component - Control Rod Drive Mechanism (CRDM) motor tube to nozzle pressure retaining bolting.
Code Class - ISI Class 1/Duke Class A Code Requirement - Subparagraph IWB-2430(a) requires that an examination performed during any inspection that reveals indications exceeding the allowable indication standards of Article IWB-3000 shall be extended to include an additional number of components within the same examination category approximately equal to the number of components examined initially during the inspection.
Relief Requested - Relief from the requirements of Subparagraph IWB-2430(a) of Section XI of the ASME Code.
Alternative Examination - In each refueling outage, all CRDM flanges will be visually examined for evidence of reactor coolant leakage in compliance with Oconee Nuclear Station response to NRC Generic Letter 88-05 and IE Bulletin 82-02. Corrective action will be taken and will include replacement of all affected bolting.
Inspection of any required additional samples of bolting material during CRDM maintenance not associated with flange leakage will be performed in compliance to the requirements of Subparagraph IWB-2430(a).
Basis for Relief Request - Since December 1980, the CRDMs have been visually examined for RCS leakage during each refueling outage. The visual examination was conducted on Unit 3 at the end of the Cycle 11 refueling outage. Eleven CRDMs showed evidence of RCS leakage. These CRDMs were disassembled and examined for compliance to the requirements of Table IWB-2500-1, Item B7.80. The examination resulted in a radiation exposure of 24 man-REM.
The examination of the 11 CRDMs showed damage exceeding the criteria of Article IWB-3000 on only one nut ring. Damage to this nut ring was specifically due to corrosion resulting from RCS leakage. Subparagraph IWB-2430(a) requires that 11 additional CRDMs be disassembled for examination.
The requirement of Subparagraph IWB-2430(a) was determined to be unnecessary because it will require disassembly and examination of CRDM bolting material not affected by RCS leakage. In addition, disassembly and examination of the additional CRDMs would involve a radiation exposure of approximately 20 to 25 man-REM and increase the outage time by about 15 days.
Evaluation - The staff concurs with the licensee that to disassemble and inspect 11 additional CRDM units not showing RCS leakage damage for the sole purpose of compliance to the ASME Code requirement is an unnecessary requirement for the Oconee Nuclear Station which would result in a hardship due to the radiation exposure to workers, while the proposed alternative would provide an acceptable level of quality and safety by providing adequate assurance of component integrity.
-7 Conclusion - We conclude, from our review of the information submitted in support of Relief Request 89-10, that the requirements of Subparagraph IWB-2430(a) of Section XI of the ASME Code are unnecessary for the Oconee Nuclear Station, Units 1, 2 and 3, in the second ten-year inservice inspection interval.
Relief from the requirements of Subparagraph IWB-2430(a) as requested in Relief Request 89-10 is granted pursuant to 50.55&(a)(3)(ii).
-8 RELIEF REQUEST 89-11 Component - Control Rod Mechanism (CRDM) motor tube to nozzle pressure retaining bolting.
Code Class - ASME Class 1/Duke Class A Code Requirement - Table IWB-2500, Item B7.80, CRD Housing (Bolts, Studs and Nuts) require a VT-1 visual examination when disassembled.
Relief Requested - Relief from the required examination for disassembled CRD Housing parts which are not intended for continuation of service.
Alternative Examination - In each refueling outage, all CRDM flanges will be visually examined for evidence of reactor coolant leakage in compliance with Oconee Nuclear Station response to NRC Generic Letter 88-05 and IE Bulletin 82-02. Corrective action will be made, including replacement of affected bolting.
Inspection of CRD bolting materials not associated with flange leakage will be made in compliance to the requirement of Table IWB-2500, Item B7.80,Section XI of the ASME Code.
Basis for Relief Request - The policy of the Oconee Nuclear Station is to discard CRD bolting material removed from service when exposed to reactor coolant leakage containing boric acid. The discarded CRD bolting material is replaced by new bolting material that has had a preservice examination.
Oconee Nuclear Station has long recognized the potential for degradation of the CRD bolting material resulting from the evaporation of the boric acid solution leaking from the reactor coolant pressure boundary and implemented the policy of discarding the bolting materials when boric acid solution or crystals were discovered in the area of the subject components.
Evaluation - The staff concurs with the licensee that the ASME Code required visual examination of disassembled CRD housing parts not intended for reassembly is an unnecessary requirement for the Oconee Nuclear Station, while the proposed alternative would provide an acceptable level of quality and safety.
Conclusion - We conclude that compliance with the specific requirement of Table IWB-2500, Item B7.80, CRD Housing of Section XI of the ASME Code is an unnecessary requirement for the Oconee Nuclear Station, Units 1, 2 and 3, when the parts are not to be reused. The staff accepts the alternative examination proposed by the licensee to ensure the structural integrity of the CRDM motor tube to nozzle pressure retaining bolting. Pursuant to 10 CFR 50.55a(a)(3)(i),
relief from the Section XI requirement is granted as requested in Relief Request 89-11 and the alternative testing imposed.
-9 RELIEF REQUEST 90-01 Component - Steam Drain (SD) welds 24 and 25 for valve ISD-418 installation.
Code Class -
ISI Class B/Duke Class F Code Requirement - Subparagraph IWA-4400(a) requires a system hydrostatic test to be performed in accordance with Article IWA-5000 after repair by welding.
Relief Requested - Relief is requested from the hydrostatic test requirement.
Alternative Examination - Welds will be examined with a liquid penetrant examination and a VT-2 inspection at operating temperature and pressure.
Basis for Relief Request - It is not possible to isolate the subject welds from the condenser and associated piping for hydrostatic testing without redesign and modification of the system. Filling and pressurizing the condenser and associated piping could result in damage to these components. Therefore, the test requirement is impractical to perform at Oconee Unit 1.
Evaluation - The purpose of the ASME Code required hydrostatic test after repair by welding is to verify structural integrity of the welds at limited pressure above operating design pressure. The alternative examination assures that the welds are free of surface cracks. The VT-2 inspection shows that no leaks are detectable when the system is at operating temperature and pressure. The alternative examination will provide verification of the structural integrity of the welds and is acceptable for replacing the ASME Code required hydrostatic test.
Conclusion - We conclude that compliance with the specific requirement of Section XI of the ASME Code to hydrostatically test the repair welds in the Steam Drain System is impractical to perform at Oconee Nuclear Station, Unit 1, in that isolation of the affected line from the condenser cannot be accomplished. Code compliance would require redesign and modification of the steam drain system. The staff accepts the alternative examination proposed by the licensee to ensure the structural integrity of the welds made during the installation of valve 1SD-418. Relief from the Section XI hydrostatic test requirement is granted as requested in Relief Request 90-01.
10 RELIEF REQUEST 90-02 Component - Integral Piping Attachment on the Feedwater System (Support No. 03-0-480A-H98)
Code Class - ISI Class 2/Duke Class F Code Requirement - Surface examination (PT/MT) Table IWC-2500-1, Category C-C, Item C3.40,Section XI, 1980 Edition including Winter 1980 Addenda.
Alternative Examination - A visual examination will be performed on the Integral Piping Attachments for Support No. 03-0-480A-H9B meeting the requirements of VT-1 visual examination,Section XI, 1980 Edition, Winter 1980 Addenda. The VT-1 examination will provide assurance of the structural integrity of the Integral Piping Attachments.
Basis for Relief Request - The integral attachments are inaccessible for a Surface Examination because of their physical location inside a wall penetration.
The integral attachments are welded to a 24-inch feedwater pipe that runs through a 36-inch pipe sleeve penetrating the wall at an approximate 450 angle.
Due to the angle, the integral attachments are inside the sleeve at a depth of approximately 12 inches from the near side and 36 inches from far side with a maximum clearance of 5 inches.
Evaluation - The staff reviewed the information submitted by the licensee in support of Relief Request 90-02, and concurs that the Section XI ASME Code requirement for the Surface Examination of the Integral Attachment on the Feedwater System (Support No. 03-0-480A-H9B) is impractical for the Oconee Nuclear Station, Unit 1, given that the components are inaccessible. In order to comply with the Code, redesign and replacement of the affected components would be required.
Conclusion - We conclude that it is impractical for the Oconee Nuclear Station, Unit 1, to perform the Surface Examination of the Integral Attachment on the Feedwater System (Support No. 03-0-480A-H9B) in compliance to the requirements of Section XI, ASME Code, 1980 Edition, Winter 1980 Addenda. Therefore, Relief Request 90-02 is granted as requested. The alternative visual examination will be implemented to assure the structural integrity of the Integrally Welded Piping Attachment in the Feedwater System.
11
'CONCLUSION We conclude, from our evaluation of the determinations made by the Duke Power Company, that certain Section XI ASME Code, 1980 Edition, Winter 1980 Addenda, examination requirements were either impractical to perform at the Oconee Nuclear Station, Units 1, 2 and 3, or compliance would result in the redesign or replacement of the affected components. The licensee requested relief from performing the impractical and/or unnecessary Section XI ASME Code examination requirements. Pursuant to 10 CFR 50.55a(g)(6)(i), relief is granted as requested for Relief Request Nos. 89-02, 89-09, 90-01 and 90-02. Pursuant to 10 CFR 50.55a(a)(3)(i), relief is granted as requested for Relief Request No.
89-11, while relief is granted pursuant to 10 CFR 50.55a(a)(3)(ii) as requested for Relief Request Nos. 89-08 and 89-10. In granting Requests Nos. 89-08, 39-10 and 89-11, the staff has determined that the proposed alternatives provide an acceptable level of quality and safety or that compliance with the code will result in hardship or unusual burden without a compensatory increase in the level of quality and safety. In addition, the alternative examination procedures discussed in the body of this report are imposed in lieu of the Code requirements to ensure the structural integrity of the subject components.
This relief granted is authorized by law and will not endanger life or property or the common defense and security and is otherwise in the public interest given due consideration to the burden that could result if the requirements were imposed on the facility.