3F0693-02, Special Rept 93-001,consisting of Details of Number & Extent of SG Tubes Inspected & Plugged in Each once-through Sg.Degradation Mechanism of first-span Indications in OTSG B Caused by pit-like Intergranular Attack
| ML20045B248 | |
| Person / Time | |
|---|---|
| Site: | Crystal River  |
| Issue date: | 06/07/1993 |
| From: | Beard P FLORIDA POWER CORP. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| 3F0693-02, 3F693-2, 93-001, 93-1, NUDOCS 9306170037 | |
| Download: ML20045B248 (2) | |
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Florida Power CORPORATION 2OTll June 7, 1993 3F0693-02 U. S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, DC 20555
Subject:
Special Report 93-001
References:
FPC to NRC letter, 3F0792-02, dated July 10, 1992
Dear Sir:
Reference A, " Eddy Current Testing, Technical Specification Report", provided details of the enhanced inspection performed during Crystal River Unit 3's (CR-3)
Refuel 8. Those details included the number and extent of tubes inspected and identified the number and location of plugged tubes in each Once Through Steam Generator (OTSG), including plugged tubes resulting from a supplemental sample inspection performed in the B OTSG. Additionally, the report contained a list of tubes that were removed from service for metallurgical and chemical examination.
CR-3's Technical Specification (TS) 4.4.5.b requires the complete results of the steam generator tube inservice inspection be submitted to the commission in a special report pursuant to TS 6.9.2 within 12 months following the completion of the inspection. The comprehensive information supplied in Reference A fulfills the data requirements of TS 4.4.5.b for the 12-month report (due to the NRC by June 29, 1993) except for the data relevant to location and percent of wall-thickness penetration for each indication of an imperfection. At the time of the earlier report, we expected the low signal indications (S/Ns) to be distortions of the eddy current signals due to tube deposits and/or background noise. As we informed the staff late last year, we have determined those in the first span are more likely to be very low volume pit-like imperfections.
The required data associated with tubes with imperfections will be supplied to the NRC by July 30, 1993 along with the results of analysis performed in the six tubes pulled from the B steam generator.
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,[ L CRYSTAL RIVER NUCLEAR PLANT: Powerkne Road + P.O. Box 219 + Crystal River, Florida 344234219 + (904) 7954486 A Florida Progress Company 93Ob170037 93ObOy PDR ADDCK 0500 2
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U. S. Nuclear Regulatory Commission 3F0693,
Page 2 The analysis of the pulled tubes was funded through a Tailored Collaboration Agreement between Florida Power Corporation (FPC) and the Electric Power Research Institute (EPRI).
EPRI established a contract with the BWNS Research Division in Lynchburg, Virginia to perform the analysis of the tube samples. The analysis of the tube samples have been completed and the evaluation of the results is near completion.
Preliminary evaluation of the results indicate the degradation mechanism of first span indications in the B OTSG is pit-like intergranular attack.
The pits studied in the analysis presented a thumbnail pattern with an average outside diameter of less than 1/16 inch. These pits appear to be originated by~ an acidic attack of the material at the grain boundaries of the Inconel 600. Burst tests were performed on two tube samples with multiple indications to determine the safety significance of the identified degradation mechanism.
Results of these burst tests demonstrated structural integrity of the tube samples at pressures greater than five times the primary to secondary pressure differential during normal operating conditions (1350 psi). This provides confidence that the pit-like intergranular attack found in the pulled tubes has very little detrimental effect on the pressure boundary of the tubes.
FPC will work with our Project Manager to schedule a meeting to discuss the Refuel 8 tube pull results and plans for Refuel 9 OTSG inspections.
Sincerely,
.Gr P.M.deard,Jr.
Senior Vice President Nuclear Operations PMB/LVC:ff xc:. Regional Administrator, Region 11 NRR Project Manager Senior Resident Inspector
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