ML20206A141
| ML20206A141 | |
| Person / Time | |
|---|---|
| Site: | South Texas  |
| Issue date: | 04/19/1999 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML20206A130 | List: |
| References | |
| NUDOCS 9904280070 | |
| Download: ML20206A141 (5) | |
Text
!~
A CEO p
T-UNITED STATES g
j NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 30006 4 001
%, *****,e SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATEDTO AMENDMENT NOS.107 AND 94 TO FACILITY OPERATING LICENSE NOS. NPF-76 AND NPF-80 STP NUCLEAR OPERATING COMPANY DOCKET NOS. 50-498 AND 50-499 SOUTH TEXAS PROJECT. UNITS 1 AND 2
1.0 INTRODUCTION
By application dated September 30,1998, STP Nuclear Operating Company, et.al., (the licensee) requested changes to the Technical Specifications (TSs) (Appendix A to Facility Operating License Nos. NPF-76 and NPF-80) for the South Texas Project, Units 1 and 2 (STP).
The proposed changes would revise TS Section 3/4.4.5," Steam Generator" Surveillance Requirements. The future installation of the new A94 steam generators at STP necessitates changes to the steam generator tube sample selection and inspection requirements; inservice inspection frequencies; acceptance criter.a; and inspection reporting requirements.
2.0 BACKGROUND
The Westinghouse Model E steam generators will be replaced with Westinghouse Model A94 steam generators. Unit 1 steam generator replacement is scheduled to occur at the end of Cycle 9, currently planned for spring of the year 2000. Unit 2 replacement is scheduled to occur at the end of Cycle 9, currently planned for the year 2002. The A94 steam generators 1
have a number of different design features including a different tubing material, a different tube diameter and thickness, and a different tube support plate design.
The licensee proposes to amend TS Surveillance Requirements (SRs) for Specification 3/4.4.5,
" Steam Generator" to support steam generator replacement. This proposed change limits the applicability of provisions for voltage-based repair criteria and laser welded sleeving to Model E steam generators only (not applicable to the A94 steam generators), and deletes the F*
alternate repair criteria. It also clarifies the inservice inspection schedule as it pertains to replacement steam generators (Model A94). The licensee proposes that this amendment be implemented following replacement of the Unit 1 Model E steam generators with Model A94 steam generators and prior to Unit 1 operation with the A94 steam generators installed.
As discussed above, the A94 steam generators have a number of different design features. As a result of these design differences, the analyses performed for use of voltage-based repair criteria for tube-to-tube support plate intersections, F* alternate repair criteria for tube-to-tubesheet joints, and tube repair by laser-welded sleeving are not applicable to the A94 steam generators.
9904290070 990419 PDR ADOCK 05000498 P
PDR i
4 2
The technical / topical reports and correspondence submitted by the licensee in association with the license amendments for F* alternate repair criteria, the voltage-based repair criteria, and laser-welded sleeving contain various commitments associated witn the implementation of these license amendments. Following steam generator.* placement in each respective unit, these commitments will no longer apply to that unit. The tubing of the fabricated A94 steam generators will be examined by eddy current methods in accordance with ASME Section XI requirements (i.e., preservice inspection will be performed).
Descriotion of Prooosed Chanoes The proposed steam generator tube inspection surveillance-related TS changes (and associated BASES changes) resulting from replacement of the existing Model E steam generators with A94 steam generators are as follows:
SR 4.4.5.2, Steam Generator Tube Sample Selection and Inspection SR 4.4.5.3, inspection Frequencies SR 4.4.5.4, Acceptance Criteria SR 4.4.5.5, Reports BASES for Specification 3/4.4.5, Steam Generators BASES for Specification 3/4.4.6.2, Operational Leakage The proposed changes delete provisions for the F* alternate repair criteria, and make the provisions in the TSs for voltage-based repair criteria and laser-welded sleeving applicable only to Model E steam generators, not to the A94 steam generators. Also, clarification of the TS describing the first inservice inspections is necessary to reflect steam generator replacement.
In addition, the Steam Generator Tube inspection Report requirements must be similarly revised to make the reporting requirements added for the voltage-based repair criteria applicable to Model E steam generators only. Finally, unrelated to the Replacement Steam Generator Project, an incorrect referenced Specification number is corrected in SR 4.4.5.2.b.3, and a superfluous "and"is deleted from SR 4.4.5.4.a.9. These proposed changes are administrative in nature.
The Bases section for Steam Generators has also been revised, as appropriate, to reflect the above TS changes. In addition, the Bases section for Operational Leakage, that discusses more restrictive operating leakage limits (for existing Model E steam generators), has been revised to specify that even with installation of new A94 steam generators, this more restrictive operating leakage limit will still apply.
In addition, two typographical errors in Bases section 3/4.4.6.2 are being corrected. The words "value" and " values" were inadvertently misspelled by the NRC during the issuance of Amendment 83 (May 22,1996).
j 3.0 EVALUATION The A94 steam generators have several design differences that were made to significantly improve the resistance to, or to eliminate, tube degradation mechanisms experienced by the Model E steam generators. These differences render the analyses which were the basis for the
-)
.. tube support plate voltage-based repair criteria, the F* alternate repair criteria, and laser welded sleeving, not applicable to the A94 steam generators.
The Model E steam generators have tube support plates with drilled tube holes. The A94 steam generators have tube support plates with broached tube holes. The broached tube holes provide for open flow around the tube at the support plate intersections, with three short flat-contact points remaining to provide adequate support for the tube for all design conditions. The Model E steam generator tubes are 0.750" diameter,0.043" thick mill annealed Alloy 600.
(Note: fifteen tubes installed in Unit 2 steam generator "D" are thermally treated Alloy 600).
The A94 steam generators tubes are 11/16" diameter,0.040" thick thermally treated Alloy 690 tubes. The basis for the Unit 1 STP voltage-based repair criteria presumes the tubing diameter, tubing thickness, tubing material and tube-to-tube support plate intersection design used in the Model E steam generators. Generic Letter 95-05, " Voltage Based Repair Criteria for Westinghouse Steam Generator Tubes Affected by Outside Diameter Stress Corrosion Cracking," is specific to Westinghouse steam generators with Alloy 600 tubing material and drilled-hole tube support plates, and therefore does not apply to the A94 steam generators.
Accordingly, the TS changes implemented by Amendment No. 83 to the Unit 1 Operating
- License, which changed the steam generator tube surveillance TSs to implement the voltage-based repair criteria for Unit 1, will not apply after steam generator replacement. Similarly, Amendment No. 83 to the Unit 2 Operating License which implemented a 1-volt voltage-based repair criteria for Unit 2 will not apply after steam generator replacement on Unit 2. Restoring the original TS repair limit for applicability to indications at tube-to-tube support plate intersections after installation of the A94 steam generators is therefore appropriate. Thus, the proposed revisions to TSs 4.4.5.2,4.4.5.4, and 4.4.5.5, to make voltage-based repair applicable to Model E steam generators only are acceptable.
The basis for laser-welded sleeving at STP presumes the tubing diameter, thickness and f
material used in the Model E steam generators. Accordingly, the TS changes implemented by Amendment No. 90 to the Unit 1 Operating License and Amendment 77 to the Unit 3 Operating License, which changed the steam generator tube surveillance TSs to implement the Westinghouse laser-welded sleeving process for both Unit 1 and Unit 2, do not apply after installation of the A94 steam generators. The proposed changes that restore the original TS remedy for defective tubes after installation of the A94 steam generators and make laser-welded sleeving applicable only to Niodel E steam generators are acceptable.
The Unit 1 Model E steam generator tube-to-tubesheet joint was accomplished using a full-depth hard roll. The A94 steam generator tube-to-tubesheet joint is accomplished using full-depth hydraulic expansion. This design difference results in lower stresses in the replacement steam generator's expanded tubing and expansion transition which reduces the likelihood of stress corrosion cracking in this area; however, the basis for the F* attemate repair criteria presumes that the tube to-tubesheet joint is a full-depth hard roll. Accordingly, the TS changes implemented by Amendment No. 82 to the Unit 1 Operating License will not apply after steam generator replacement. This proposed TS change will be implemented after replacement of the Unit 1 Model E steam generators with A94 steam generators. Therefore, the proposed changes to TSs 4.4.5.2 and 4.4.5.4 that restore the original TS repair limits for applicability to indications in the tubesheet area for Unit 1 after installation of the A94 steam generators are acceptable.
t
. The plugging / repair lirrits for the A94 steam generators will consist solely of the through-wall criteria and will require that tubes be plugged (not sleeved) when imperfections exceed the plugging limit of 40% of the tube nominal wall thickness. This is the same as the Model E steam generator 40% plugging limit which is currently in the TS. Therefore, no TS change 4
regarding this criteria is being requested. The licensee performed analyses in accordance with the ASME Code and Regulatory Guide 1.121 to substantiate the validity of the 40% plugging limit for A94 steam generators. The original 40% plugging limit should be applied to the A94 steam generators.
As part of the license amendment for the voltage-based repair criteria for Unit 1, and later as part of the license amendment for laser-welded sleeving for Unit 2, the primary-to-secondary leakage limit of TS 3.4.6.2.d was lowered from 500 gpd in any single steam generator (combined leakage limited to 1 gpm or 1440 gpd) to 150 gpd in any single steam generator.
This change was made to provide increased margin (i.e., earlier shutdown) following identification of increasing primary-to-secondary leakage, reducing the likelihood that an occurrence of low level primary-to-secondary leakage might propagate to a tube rupture event.
Although this change was made in association with the implementation of the license amendments for voltage-based repair criteria and laser-welded sleeving on existing Model E steam generators, no change (relaxation) to TS 3.4.6.2.d is requested in this submittal to account for the new A94 steam generators. The licensee proposes to retain the increased i
margin against tube rupture events.
Clarifications to the inspection frequency requirements of SR 4.4.5.3 are proposed. The existing wording of SR 4.4.5.3.a includes a specific one-time inservice inspection interval requirement which is only applicable to the first cycle at the beginning of unit life. Since steam generator replacement is analogous to initial unit start-up as related to the steam generator surveillance, it is appropriate to update the wording here to clearly indicate that the same initial interval requirement applies following steam generator replacement. Further, a note is added I
to clarity that no steam generator inservice inspection will be performed during the steam generator replacement outage. Inspecting the Model E steam generators as they are being removed from the plant would serve little purpose, since the ultimate corrective action for any degradation found is being implemented (i.e., replacement). Inservice inspection of the new A94 steam generators during the replacement outage is not possible, since they will not have been in service. The note will ensure that no confusion exists in the event that more than 24 calendar months pass between the last inservice inspection of the Model E steam generators and the first inservice inspection of the A94 steam generators.
Based on its review, the staff concludes that the proposed changes continue to meet the requirements for safe operation and are acceptable.
4.0 STATE CONSULTATION
in accordance with the Commission's regulations, the Texas State official was notified of the propored issuance of the amendments. The State official had no comments.
5.0 ENVIRONMENTAL CONSIDERATION
The amendments change a requirement with respect to installation or use of a facility component located within the restricted area as defined in 10 CFR Part 20 and change
1 5-surveillance requirements. The Nuclear Regulatory Commission staff has determined that the amendments involve no significant increase in the amounts, and no significant change in the types, of any effluents that may be released offsite, and that there is no significant increase in individual or cumulative occupational radiation exposure. The Commission has previously issued a proposed finding that the amendments involve no significant hazards consideration, and there has been no public comment on such finding (63 FR 59595). Accordingly, the amendment meets the eligibility criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9). Pursuant to 10 CFR 51.22(b) no environmental impact statement or environmental assessment need be prepared in connection with the issuance of the amendments.
6.0 CONCLUSION
The Commission has concluded, based on the considerations discussed above, that: (1) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, (2) such activities will be conducted in compliance with the Commission's regulations, and (3) the issuance of the amendments will not be inimical to the common defense and security or to the health and safety of the public.
Principal Contributors: Marsha Gamberoni Cheryl Beardslee Date: April 19,1999