ML17254A302
| ML17254A302 | |
| Person / Time | |
|---|---|
| Site: | Ginna  |
| Issue date: | 04/02/1985 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML17254A300 | List: |
| References | |
| NUDOCS 8504040285 | |
| Download: ML17254A302 (3) | |
Text
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UNITEDSTATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION ROCHESTER GAS AND ELECTRIC CORPORATION R. E.
GINNA NUCLEAR POWER PLANT DOCKET NO. 50-244 TUBESHEET SLEEVING, 1985
1.0 INTRODUCTION
By letter dated February 22, 1985, Rochester Gas and Electric Corporation (RG8E) requested permission to install a limited (but yet undetermined) number of tubesheet sleeves in Ginna's steam generator inlets.
In a letter dated March 18,
- 1985, RGIIIE specified the request to include 65 tubesheet sleeves.
2.0 BACKGROUND
The installation of tubesheet sleeves was approved by the Nuclear Regulatory Commission (NRC) in a Safety Evaluation Report (SER) transmitted to RGIIIE by letter dated June 13, 1983.
This SER limited the number of tubesheet sleeves that could be installed in 1983 to not more than 30, and also prevented the installation of additional tubesheet sleeves after the Spring 1983 outage until the effectiveness of inspection techniques could be demonstrated by RG8E.
During the 1983 outage, 4 tubesheet sleeves were installed in the A
Steam Generator and 24 sleeves were installed in the B Steam Generator.
After the 1983 outage the staff recommended technical areas which should be pursued prior to the 1984 outage so that further enhancements to the data acquisition and analysis of sleeve/tube inspection could potentially be developed.
RGBE was supportive of these recommendations and pursued them.
Improvements were made in the eddy current inspection technique, but there weve still some areas of the tubesheet sleeve/tube combination where detection and siting of defects at the 10%%d level
,Iere not possible.
During the 1984 outage, nine more tubesheet sleeves were installed in the B Steam Generator, as allowed by an NRC SER dated May 9, 1984.
Based upon work performed during the 1984 refueling outage, parent tube flaws located 0.75 inch or qreater above the sleeve were detectable with the annular differential maqnetic bias eddy current probe.
Since that time, the technical evaluation and development of nondestructive examination methods for the purpose of optimizing inspectabi lity of tubesheet sleeves/
tube integrity has continued.
An improvement has been achieved which reduces the area above the tubesheet sl, eve regarding inspectabi lity.
i 8504040285 850402 PDR ADOCK 05000244 P
k al Inspections will now be performed utilizing a standard annular differential coil probe delivered from the cold leg of the steam generator.
This increases the area of acceptable inspection to 0.5 inch above the sleeve end.
Defects are marginally detectable at 0.25 inch above the sleeve end.
Improvements in detecting parent tube flaws in the free span region behind the sleeve have been made by increased gain and probe impedance optimization modifications to the Zetec MIZ-12 Multifrequency Eddy Current System; This has improved the sensitivity by a factor of 2 to 3 enabling standard ASME flow detection.
However, flaws located from the sleeve end through expansion transition are still not detectable.
Although improvements have been made in the eddy current inspection techniques, there are still some areas of the tubesheet sleeve/tube combination where the ability to detect and size defects is limited.
These areas are at the weld transitions and at the upper end of the sleeve.
Use of the above coils will allow 205 through wall defects to be identified.
Larger defects can be seen at some intermediate locations.
Research and development efforts are continuing in the following areas:
A.
B.
The Zetec MIZ-18 Multifrequency Eddy Current System, improving gain by, developing a modification to the system.
Improved Design Multi-array Pancake Coil Probes for above 4he sleeve.
C.
Improved Cross-wound Coil Probes, with optimized magnetic bias by.
Eddy Current Technol ogy Incorporated.
I D.
Improved 3-D Eddy Current Coil Probes, with optimized magnetic bias by Eddy Current Technology Incorporated.
E.
Low Frequency Eddy Current Coil Probes, with optimized magnetic, bias penetration of the eddy current fields for inspecting above the explosive weld but below the sleeve end.
F.
Electromagnetic Acoustic Transducers (EMATs) developed for the inspection of the parent tube above the sleeve and down to and inclui.ing the expansion area of the explosive weld.
3.0 EVALUATION In previous safety evaluations (June 13, 1983 and May 9, 1984), the staff made recoreendations with respect to improvements in the data acquisitioi~
and analysis of steam generator "leeve/tube inspections and the licensee has responded by continually exerting efforts to improve the inspection technique.
In each of the last 2 years the staff has granted permission to sleeve a limited number of tubes during the annual refueling outages.
However, sir,cn these are still limitations on the eddy current inspection techniques, the acceptability of installing additional tubesheet sleeves has been reviewed.
The small number of defects
- ound during eddy current inspection of the steam generator tubes in the 1984 outage indicates that the crevice environment, especially at the elevation of the upper end nf the tubesheet
- sleeves, is enhanced by the licensee's programs of crevice flushing and water chemistry control.
Additionally, recent tube pull analyses have shown that the area 'of the tube at or above the explosive weld has essential Iv no intergranular attack, less than 3C involvement.
Therefore, the probability of experiencing additional degradation in the area of concern is minimal.
Further, the indications that have been seen are well within the crevice, below the explosive joint.
Also, the licensee conducted a corrosion test program with Babcock 5 Wilcox to assess the potential for primary side stress corrosion cracking.
Results of samples removed from the test environment have not indicated any detrimental effects due to the tubesheet sleeve process.
4.0 CONCLUSION
The licensee has continued to make progress in increasing the tube defect detectability of sleeved tubes.
Based upon the staff's previous review and acceptance of the licensee's inspection and installation techniques along with the continued improvement in tube degradation detectability, the staff finds that the installation of up to 65 tubesheet sleeves during the 1985 Spring outage is acceptable.
It is recommended however that RGSE continue to trv and improve eddy current testing detectability
.of tube imperfections.
5.0 ACKNOWLEDGEMENT B. Turovlin and C. Hiller contributed to this Safety Evaluation.
Dated:
April 2-,~1985