ML17254A749
| ML17254A749 | |
| Person / Time | |
|---|---|
| Site: | Ginna  |
| Issue date: | 02/07/1986 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML17254A748 | List: |
| References | |
| NUDOCS 8602130390 | |
| Download: ML17254A749 (5) | |
Text
SAFETY EVALUATION EY THE OFFICE~R OR REEIIERTIOE C MBUSTI N
NG N ERING WEL D SL E
E ME H
OF S
E M
G NER TOR UBE REP IR ROCHS ERG ND LCRC RP TION N
L R
D CKET N
. 50-244 Materials Evaluation The licensee, Rochester Gas and Electric Corporation (RGSE), plans to repair degraded steam generator tubes in their R.
E. Ginna Nuclear Power Plant (REG) by having certain of these degraded tubes sleeved using a method developed by Combustion Engineering (C-E).
The sleeving contractor (C-E) has performed
- extensive corrosion and mechanical testing on the repair method and materials.
Additionally inspection methods have been developed.
This repair method has been
- used, thus far successfully, for repairs at the Swedish Ringhals 2 plant.
. The sleeving installation method proposed incorporates a cylinder of slightly less OD than the steam generator tubing ID.
Means are provided for temporary mechanical support of the sleeve prior to welding.
Tube material is Inconel 690 which rigorous corrosion testing has shown to be superior to the Inconel 600 alloy which was used to manufacture the tubes currently installed in the Ginna steam generators.
Inasmuch as each sleeve is welded at both ends to each tube being sleeved, this process is considered to provide a leak tight repair.
Essentially the process consists of cleaning the tube to be sleeved at the areas of the welds, insertion of the sleeve, expansion in the weld areas, welding and inspection.
Al,l of the above steps are performed remotely.
The sleeves are of thinner wall than the tubes and the installed sleeve does not significantly affect system flow rate.
Furthermore, since the sleeves are relatively short, the heat transfer capability of the steam generator is also not significantly affected.
Even though the ID of the sleeves is less than that of the tubes, inspection by Eddy Current Testing (ECT) is not seriously limited.
pD
, ~0>90,860207 ADO'('5pppp~+ ",,
PDR j
For those sleeves with rejectable welds a satisfactory plugging technique has been developed that would not require sleeve removal for installation of plugs.
Inspection considerations for the sleeve installation have been developed for (a) the welds joining the sleeve to the tube; (b) the tube volume obscured by the sleeve in the overlap area; (c) the sleeve between the welds; and (d) the remainder of the tube which must be inspected through the constriction of the sleeve.
All of the appropriate aspects for inspection of this sleeve installation appear to have been adequately considered.
. Conclusion The staff concludes that the materials engineering concerns relative to the Ginna Steam Generator Tube Sleeving Program have been satisfied and that upon satisfactory performance of this program this method is an acceptable repair alternative to plugging.
Furthermore, inservice inspection of the sleeve, that portion of tube obscured by the sleeve overlap, and the remainder of tubing will be able to be performed.
No restrictions are being placed on the number of sleeves that can be installed in any refueling outage.
- However, as an alternative for the staff to be promptly informed in the event that substantial degradation is observed during any future steam generator inspection, we will require that NRR be notified within 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> in the event that:
1) more than 10 percent of the tubes inspected have indications in excess of 20K, although previously degraded tubes must exhibit at least 10Ã further wall penetration to be included in this calculation, or 2) more than 1 percent of the tubes inspected have indications requiring plugging or sleeving.
As specified in the RGSE letter dated January 29,
- 1986, RGSE will revise the Ginna Inservice Inspection Program to incorporate this notificat'ion requirement.
Mechanical Evaluation Mechanical tests were performed on mockup steam generator tubes containing sleeves and plugs to provide qualified test date describing the basic properties of the completed assemblies.
These tests determined axial load, collapse, burst, and thermal cycling capability.
These tests demonstrated that the load capability of the upper and lower sleeve welds is sufficient to withstand thermally induced stresses in the weld resulting from temperature differential between the sleeve and the tube and the pressure induced stresses resulting from normal operating and postulated accident conditions.
The burst and collapse pressures of the tested sleeve provided substantial margin over the limiting differential pressure.
Mechanical testing indicated that the installed sle'eve will withstand the cyclical loading resulting from power changes in the plant and other transients.
The licensee has performed analyses to demonstrate the structural integrity of the sleeve-tube assemblies and their compliance with design requirements.
The methodology used is in accordance with the ASME Boiler and Pressure Vessel Code,Section III.
An evaluation was performed to NRC Regulatory Guide 1.121 "Bases for Plugging Degraded PWR Steam Generator Tubes."
Based upon the allowable degradation limit calculated and allowing an appropriate margin for inservice inspection uncertainties and growth of degradation between inspections, the 30K plugging limit for steam generator tube sleeves contained in the Ginna Station guality Assurance Manual (referenced in the Inservice Inspection section of the Technical Specifications) is adequate for the Combustion Engineering welded sleeve method.
C-E has provided bases to conclude that a sleeved tube is no more susceptible to vibration than a normal tube.
Fatigue analysis of the upper and lower sleeve weld joint has been performed and shown.to meet ASME Code allowables.,
A comparison of the calculated failure modes and the test data indicate good agreement.
Conclusion Based upon the analytical and experimental evaluations discussed above it is concluded that the welded tube sleeve meets the structural integrity requirements as stipulated by NRC criteria.
Acknowled ments This safety evaluation was prepared by Dave Sellers and Ted Sullivan.
DATED:
February 7, 1986
Distribution:
NRC PDR Local PDR PAD81 r/f G. Lear OELD E. Jordan B. Grimes J. Partlow C. Miller P. Shuttleworth ACRS (10)
R. Ballad T. Sullivan C. Sellers PADS'1 s/f