ML20245K949
| ML20245K949 | |
| Person / Time | |
|---|---|
| Site: | North Anna  |
| Issue date: | 04/26/1989 |
| From: | Cartwright W VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| 89-281, NUDOCS 8905050219 | |
| Download: ML20245K949 (9) | |
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VIItGINIA ELECTItIC AND PowEIt COMPANY Hic 2rwonn,VIHOINIA 20261 April 26, 1989 W. It.CAuTwusonar VSCE I'uB51 DENT Nuen. nan U.S. Nuclear Regulatory Commission Serial No.89-281 Attn: Document Control Desk NAPS /JDH R5 Washington, D.C. 20555 Docket Nos.
50-338 50-339 License Nos.
NPF-4 NPF-7 Gentlemen:
VIRGINIA ELECTRIC AND POWER COMPANY NORTH ANNA POWER STATION UNITS 1 AND 2 EIfAM GENERATOR TUBE LEAK EVENT INFORMATION On March 29,1989, we met with Mr. L. Engle and others of your staff to discuss the February 25,1989 North Anna Unit 1 steam generator tube leak event.
At that meeting, we presented information regarding the operational and technical aspects of the event.
We described the plant status prior to the event, the sequence of events, the operational and radiological considerations, and our corrective actions. We also discussed the North Anna 2 plug installation history, the plug failure scenario, our action plan to support North Anna Unit 2 restart, a summary of the safety considerations pertaining to the event, and outlined our future plans for North Anna Unit 1 and Surry Power Station.
During that meeting, you requested that we provide additional information regarding our review of procedures utilized in the event response and our assessment of the adequacy of operator training to address that type of event. Subsequently, we were also requested by the NRC North Anna Project Manager to provide a summary describing how we meet the Westinghouse criteria for determining the acceptability f steam generator tube mechanical plugs.
The information regarding our assessment of operating procedures and training is provided in Attachment 1.
The information regarding the criteria for acceptable steam generator tube plugs is provided in.
h0N 890505o219 090426
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As you are aware, we plan to submit a detailed report of the event to you in the near future. Based on the March 29,1989 meeting and our review and actions in response to NRC Information Notice 89-33,
" Potential Failure of Westinghouse Steam Generator Tube Mechanical Plugs," dated March 23,1989, we plan to resume power operations for North Anna Unit 2 following completion of its ongoing refueling outage, currently scheduled to be completed on April 30, 1989.
Please contact us immediately if you have any questions or require additional information.
Very truly yours, soA
. R. Cartwright Attachments cc:
U.S. Nuclear Regulatory Commission 101 Marietta Street, NW Suite 2900 Atlanta, Georgia 30323 Mr. J. L. Caldwell NRC Senior Resident inspector North Anna Power Station L
1
l Assessment of Operating Procedures and Training Summary An assessment of the Abnormal Procedure for large steam generator tube leaks and of operator training to diagnose and mitigate a steam generator tube leak has been conducted. As a result of this assessment, no deficiencies were identified.
However, several enhancements to the abnormal procedure are desirable. These enhancements include adding steps for monitoring / maintaining pressurizer level and alternate actions to provide guidance to the operator in the event a tube leak progresses to a tube rupture.
Procedural steps have been enhanced to include additional methods for identifying the affected steam generator and for taking actions to isolate the secondary system that do not preclude affected steam generator identification.
Furthermore, the procedure has been restructured into the symptom-based dual-column format similar to that found in emergency operating procedures.
The current operator training program, which was upgraded after the 1987 Unit 1 steam generator tube leak event, has been reviewed and found to be acceptable. It should be noted that as part of the normal program, operators have been trained on the February 25,1989 Unit 1 leak.
This training included operator responses, the tube plug failure mechanism, repairs being made to the steam generator, and the revised abnormal procedure.
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Steam Generator Tube Plug Acceptance Criteria j
The North Anna Unit 2 action plan for mechanical plugs made from less than optimum heats of material is comprised of the following elements:
The installation and reliance on tube plugs of optimum heats (i.e., plugs of heats having continuous grain boundaries).
l Water-filled tubes (sentinel plugs).
Analysis demonstrates that a water-filled tube effectively mitigates the potential i
for a tube penetration by a plug projectile.
Remaining-life margins based on microstructure and test data that provides a relative time to significant primary water stress corrosion cracking (PWSCC) effects.
Specifi] ally, 334 mechanical plugs are installed in Unit 2.
These plugs were installed during the three previous refueling outages in 1984,1986 and 1987.
In 1987, following the North Anna Unit 1 tube i
rupture event,118 tubes were plugged by installing a solid mechanical plug in the hot leg and a mechanical plug with a driu d e
hole (designated " sentinel plugs") in the cold leg.
Non-sentinel tubes i
were plugged for various reasons including cold-leg thinning; PWSCC at the expansion transition, U-bends, and support plates; foreign objects; and, anti-vibration bar (AVB) indications.
The heats of concern for North Anna Unit 2 are NX 3962 and NX 3513.
However, because of the lack of row / column traceability, plugs made from heat NX 4523 have also been included to assure that heats identified as less than optimum (i.e., having other than continuous grain boundaries) have been removed. A total of 51 hot-leg plugs were replaced by a heat of material with acceptable microstructure (heat NX 6323).
The following four pages contain tables illustrating the Unit 2 mechanical plug installation history, a mechanical plug repair plan which identifies the location of the hot-leg 51 plugs that have been removed, and a detailed mechanical plug repair plan that explains how the number of 51 plugs was derived, starting from a total number of mechanical plugs in Unit 2 of 334.
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Please note that regarding Unit 2's compliance with the criteria identified in Westinghouse WCAP-12244 (" Steam Generator Tube Plug Integrity Summary Report, April 1989), we confirmed the input data used in the algorithm presented in Appendix C.
We also identified several data points that required correction.
These are installation data and temperature data.
Westinghouse has been notified and has agreed to make the necessary corrections. Our corrective actions are not affected by these discrepancies.
4 Because one of the elements of the action plan is based on relative time to PWSCC, a long term plan must be developed to remove those plugs that will, at some future time, experience PWSCC. To develop this plan, we are evaluating several options.
These include:
replacement with currently available acceptable heats I
replacement with alloy 690 plugs (the current design uses alloy 600) plug-in-a-plug (PIP)
This long-term plan will be developed before the next refueling outage for Unit 2.
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