ML20046C527

Responds to SGTR Overfill Scenario on STP Simulator.Revised Operating Procedures to Reduce Response Times & Increase Existing Margin to Initiation of Overfill

ML20046C527
Person / Time
Site:	South Texas
Issue date:	08/06/1993
From:	Groth J HOUSTON LIGHTING & POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
ST-HL-AE-4528, TAC-M75099, TAC-M75100, NUDOCS 9308110105
Download: ML20046C527 (4)

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Houston Lighting & Power August 6, 1993 ST-HL-AE-4528 File Nos.: G25 M33.02 10CFR55.59 U. S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, DC 20555 South Texas Project Units 1 and 2 Docket Nos. STN 50-498; STN 50-499 Supplemental Response to Steam Generator Tube Rupture Overfill Scenario (TAC Nos. M75099 and M75100)

Reference:

Correspondence from W. H. Kinsey, Jr. (HL&P) to NRC Document Control Desk, dated December 16, 1992 (ST-HL-AE-4257)

In the referenced letter, Houston Lighting & Power (HL&P) submitted the time elapsed for each of the ten STP operating crews to respond to a steam generator tube rupture (SGTR) overfill scenario on the STP simulator. None of the crews identified and isolated the ruptured steam generator within the time originally assumed in the STP-specific analysis (WCAP-12369). The additional mass that would be added to the faulted steam generator was calculated and it was shown that sufficient margin existed in the WCAP-12369 analysis such that the steam generator would not overfill. Consequently, the acceptance criteria were met. For further assurance, operating procedures were revised to reduce the response times and to increase the existing margin to initiation of overfill. HL&P committed to record the operator response times using the revised operating procedures for all the STP operating crews during the licensed operator requalification cycle ending in August 1993. As described below, HL&P has reconsidered this commitment and believes it is unnecessary.

100051 1R\93-214.001 l Project Manager on Behalf of the Participants in the South Texas Project h 9308110105 930806 PDR ADOCK 05000498 P p] big (,

Houston. Lighting & Power Company ST-ML-AE-4528 South Texas Projet Electric Generating Station File Nos.: G25 M33.02 Page 2

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HL&P is vitally interested in maintaining the integrity of the STP steam generators, such that the probability of steam generator tube leaks or SGTRs is minimized. Additionally, HL&P is dedicated to assuring that, should such an event occur, its operational staff is fully prepared to respond to the transient and to isolate the affected steam generator in the correct manner to prevent an overfill event or potentially contaminated steam discharge to the environment through the steam generator relief valves or Power Operated Relief Valves (PORVs).

To facilitate assuring the integrity of the steam generators, HL&P has an aggressive chemistry control program for the STP units.

Additionally, during the present dual unit outage, all steam generator tubes in both units are being inspected to provide a good baseline for tube integrity.

To assure that the operational staff has the capability to respond to a steam generator tube leak or rupture event, HL&P has incorporated both design features and training into its program to aid the operators. First, the STP main steam lines are designed to withstand an overfill event. Second, both the steam generator relief valves and the PORVs at STP are safety-grade and are maintained highly reliable and operable. Finally, STP has provided its operational staff with focused training on SGTR events, including challenging simulator scenarios and detailed discussions of the assumptions utilized in the safety analysis of these events.

The discussions emphasize the vital nature and sensitivity of the analysis to operator response time. The simulator scenarios include the use of " freezing" the simulator and comparing experienced conditions with analysis expectations. The emphasis during the simulator scenarios is for the operators to successfully execute a controlled response to the training scenario, such that the plant is promptly brought to a safe condition that maximizes public health and safety.

HL&P believes, based on lessons learned from industry events, that the above strategy is the best for preventing SGTR events at STP and for responding to them in the unlikely event that one occurs. Events like the Davis Besse loss of feedwater have demonstrated the consequences of preemptory operator response and the need for a controlled, integrated plant response to transients.

HL&P believes that arbitrarily timing operator response to a particular plant casualty creates an atmosphere that detracts from the operators making an appropriate and controlled response, and tends to push them into a potentially undesirable response in an effort to meet a potentially artificial time restraint.

IR\93-214.001

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Houston Lighting & Power Company ST-HL-AE-4528 South Texas Project Electric Generating Station File Nos.: G25 M33.02 Page 3 Based on the above, HL&P believes that it is not in the best interest of safe operation of the STP units to continue timing of operating crews and is revising its commitment with respect to this issue. HL&P will continue to review the results of its training program to assure that all STP operational crews have the capability to respond to steam generator casualty events, but will discontinue time testing.

If there are any questions regarding this matter, please contact Mr. A. W. Harrison at (512) 972-7298 or me at (512) 972-8664.

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A F. Gr t ice President, Nuclear Generation JTC/sr 9

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n Houston Lightig & Power Company ST-HL-AE-4528 South Texas Projen Electric Generating Station File Nos.: G25 M33.02 Page 4 c:

Regional Administrator, Region IV Rufus S. Scott Nuclear Regulatory Commission Associate General Counsel 611 Ryan Plaza Drive, Suite 400 Houston Lighting & Power Company Arlington, TX 76011 P. O. Box 61867 Houston, TX 77208 Lawrence E. Kokajko Project Manager Institute of Nuclear Power U.S. Nuclear Regulatory Commission Operations - Records Center Washington, DC 20555 13H15 700 Galleria Parkway Atlanta, GA 30339-5957 Senior Resident Inspector c/o U. S. Nuclear Regulatory Dr. Joseph M. Hendrie Commission 50 Bellport Lane P. O. Box 910 Bellport, NY 11713 Bay City, TX 77414 D. K. Lacker J. R. Newman, Esquire Bureau of Radiation Control Newman & Holtzinger, P.C., STE 1000 Texas Department of Health 1615 L Street, N.W. 1100 West 49th Street Washington, DC 20036 Austin, TX 78756-3189 D. E. Ward /T. M. Puckett U.S. Nuclear Regulatory Comm.

Central Power and Light Company Attn: Document Control Desk P. O. Box 2121 Washington, D.C. 20555 Corpus Christi, TX 78403 J. C. Lanier/M. B. Lee City of Austin Electric Utility Department 721 Barton Springs Road Austin, TX 78704 K. J. Fiedler/M. T. Hardt City Public Service P. O. Box 1771 San Antonio, TX 78296 IR\93-214.001