ML19276C788

Final Deficiency Rept Re Potential Superheated Steam Conditions Following Main Steam Line Break Outside Containment.Initially Reported on 840809.Deficiency Not Reportable Per 10CFR50.55(e)

ML19276C788
Person / Time
Site:	South Texas
Issue date:	09/28/1984
From:	Oprea G HOUSTON LIGHTING & POWER CO.
To:	Jay Collins NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV)
References
ST-HL-AE-1124, NUDOCS 8410100077
Download: ML19276C788 (6)

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The Light company Houston Lighting & Power P.O. Ilox 1700 Houston, Texas 77001 (713) 22g.921; September 28. 1984 ST-HL-AE-1124 File Number: G12.208 I -

Mr. John T. Collins Regional Administrator, Region IV

$Ogg K Nuclear Regulatory Commission i

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4 611 Ryan Plaza Dr., Suite 1000 - 31984 Arlington, Texas 76012 q

Dear Mr. Collins:

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~ South Texas Project

~ Units 1 & 2 Docket Nos. STN 50-498, 50-499 Superheated Mass / Energy Releases Outside Containment On August 9, 1984, HL&P notified the Nuclear Regulatory Commission of an item concerning superheated steam conditions following a main steam line HL&P indicated that this item was potentially break outside containment.

reportable pur.,sant to 10CFR 50.55(e). Please find attached our final report concerning this deficiency. We have determined that this deficiency is not reportable.

If you should have any questions concerning this item, please contact Mr. Michael E. Powell at (713) 993-1328.

Very tru y yours, f/

pre . .

Executive ce President SMH/mg

Attachment:

Final Report Concerning Superheated Steam Consideration in Main Steam Line Breaks

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ST-HL-AE-1124 Hot.ston Lighting & Power Company File Number: G12.208 Page 2 cc:

Darrell G. Eisenhut. Director Brian E. Berwick, Esquire Division of Licensing Assistant Attorney General for Office of Nuclear Reactor Regulation the State of Texas U.S. Nuclear Regulatory Comission P. O. Box 12548, Capitol Station Washington, DC 20555 Austin, TX 78711 Victor Nerses, Project Manager Lanny Sinkin U.S. Nuclear Regulatory Comission Citizens Concerned About Nuclear Power 7920 Norfolk Avenue 114 W. 7th, Suite 220 Bethesda, MD 20016 Austin, TX 78701 D. P. Tomlinson Robert G. Perlis, Esquire Resident Inspector / South Texas Project Hearing Attorney c/o U.S. Nuclear Regulatory Comission Office of the Executive Legal Director P. O. Box 910 U.S. Nuclear Regulatory Comission Bay City, TX 77414 Washington, DC 20555 M. D. Schwarz, Jr., Esquire Charles Bechhoefer, Esquire Baker & Botts Chairman, Atomic Safety & Licensing Board One Shell Plaza U.S. Nuclear Regulatory Comission Houston, TX 77002 Wasnington, DC 20555 J. R. Newman, Esquire Dr. James C. Lamb, III

'Newman & Holtzinger, P.C. 313 Woodhaven Road 1025 Connecticut Avenue, N.W. Chapel Hill, NC 27514 Washington, DC 20036 Judge Ernest E. Hill Director, Office of Inspection Hill Associates and Enforcement 210 Montego Drive U.S. Nuclear Regulatory Comission Danville, CA 9452E Washington, DC 20555 E. R. Brooks /R. L. Range William S. Jordan, III, Esquire Centr 61 Power & Light Company Harmon, Weiss and Jordan P. O. Box 2121 2001 S Street, N.W.

Corpus Christi, TX 78403 Suite 430 Washington, DC 20009 H. L. Peterson/G. Pokorny City of Austin Citizens for Equitable Utilities, Inc.

P. O. Box 1088 c/o Ms. Peggy Buchorn Austin, TX 78767 Route 1, Box 1684 Brazoria, TX 77422 J. B. Poston/A. vonRosenberg City Public Service Board P. O. Box 1771 San Antonio, TX 78296 Revised 08/10/84

Attachment ST-HL-AE-1124 Page 1 of 4 South Texas Project Units 1 and 2 Final Report Concerning Superheated Steam Consideration in Main Steam Line Breaks I. Summary Recent analyses indicate that the steam generator tube bundles may be uncoveredduringaHighEnergyLineBreak(HELB). The time dependent mass / energy blowdown data previously supplied to the 'outh Texas Project for assessing HELB's did not include the effects of superheated steam due to steam generator tube uncovery. The consequences are that the environmental qualification envelopes of safety-related equipment outside containment may be impacted.

On August 2,1984, the Regulatory Response Group of the Westinghouse Owners Group (WOG) met with the NRC Office of Nuclear Reactor Regulation (NRR) to discuss main steam line breaks and associated superheat effects (due to steam generator tube uncovery) on the environmental qualification of equipment.

On August 9, 1984, pursuant,to 10CFR 50.55(e), Houston Lighting & Power Company (HL&P) notified the NRC Region IV, of the above item concerning superheated steam considerations in MSLB's outside contcinment.

When HL&P was notified by Westinghcase of a possible unreviewed safety question that could result in an impact on the environmental qualification parameters of equipment outside containment, WestSghouse indicated that potential consequential failures which may occur as a result of superheated steam generation during a HELJ must be evaluated. Westinghouse sensitivity studies performed to date indicate that uncovering of steam generator (SG) tubes and the resulting superheat occurs after safety systems are actuated to mitigate the effects of large breaks. Preliminary evaluations for an ice condenser PWR show that *s a result of the effects of superheat, existing environmental temperatu.es for equipment outside containment were exceeded.

The cause of the deficiency is that the current Westinghouse mass and energy release rate analyses does not consider the effects of steam superheating due to uncovering SG tubes.

The only location for which this condition appears to have any potential consequences is in the 4,olation Valve Cubicle. We have evaluated this item and it is not considered reportable.

Note that Westinghouse has previously stated that this issue is not a concern for breaks inside containment (Reference 1).

II. Description of Deficiency The time cependent mass / energy blowdown data previously supplied to the South Texas project by Westinghouse for essessing the effects of HELB's did not include effects of superheated steam due to steam generator tube uncovery.

The con %quences are that the environmental qualification envelopes of safety-related equipment outside containment may be impacted.

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Attachment ST-HL-AE-1124 Page 2 of 4 III. Corrective Action Because the compartmented isolation valve cubicles limit consequential effects of a break to only one of tne four cubicles and no safety hazard exists, no corrective actions are necessary to assure the safety of plant operations.

IV. Recurrence Control This item is an iso'ated occurrence; no recurrence control is required.

V. Safety Analysis In order to determine whether the postulated release of superheated steam in the Isolation Valve Cubicle (outside containment) constitutes a safety hazard a safety review was made of the following:

1) The systems (both safety and non-safety) that could be exposed to temperatures higher than the equipment is qualified to withstand.

2) The failure mechanisms due to high temperature of equipment, cable, instrumentation, and concrete and the failure effects.

3) The compartmented design of the Isolation Valve Cubicle (IVC).

4) The protection features avaiiable to assure adequate core cooling and safe shutdown.

The bases for the review are as follows-

1) Criteria - The consequential failures of a Main Steam Line Break (MSLB) are to be considered concurrent with a worst case single failure.

2) Criteria - The actual failure modes of components subjected to superheated steam (at a temperature of about 450 F) are to be considered in the evaluation of consequential failures.

3) Westinghouse - Based on Westinghouse evaluation, the assumed failure of Input a second MSIV, in conjunction with loss of offsite power (LOOP) (resulting in two steam generators blowing down) can be accommodated with no effect on safe shutdown or public health and safety given that three (3) Safety Injection trains are availabic providing boration flow.

There are no single failures that could result in loss of an MSIV and a Safety Injection train.

4) Assumption - The superheated steam from a MSLB results in temperatures exceeding the environmental qualification envelope (for temperature) of safety related equipment.

5) Assumption - Westinghouse scoping studies indic:te that for large breaks, down to a size of approximately .86 square feet, MSIV closure occurs before the release of superheat.

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Attachment ST-HL-AE-1124 Page 3 of 4 A sumary of the safety evaluations for the spectrum of Main Steam Line Breaks is provided below:

1) For very small breaks, e.g. around .1 squarc foot, there would be no significant uncovering of steam generator tubes and no significant superheated steam generated.

2) For a small break, around .5 square feet, the time would be extended before Main Steam Isolation occurred. Therefore the possibility exists that steam generator tube uncovery resulting in superheated steam could occur before MSIV isolation. Assuming as a consequence of the superheated conditions the MSIV fails to close and a second MSIV fails open (single failure) the resulting blowdown is still less severe than that determined in the Chapter 15 core integrity analyses (1.4 sq. ft.).

Therefore, no analyzed safety hazard exists.

3) For a large break steam line rupture, Westinghouse sensitivity analyses performed to date indicate that steam generator tube uncovery and the resulting superheat occur after safety systems required to mitigate the effects of the breaks have actuated. Fast acting isolation valves are provided in each main steam line that will fully close within 7 secon'ds after receipt of a closure signal. Therefore, isolation will occur prior to release of superheated steam in the IVC.

The MSIV circuitry is such that the MSIV vent valves are de-energized to close the MSIV. The MSIV is actually closed by large steel springs after the air is vented from the piston actuator. Once closed, the MSIV's would remain closed even in a superheated environment due to the simplicity of the MSIV design and the fact that consequential effects could not cause the solenoid vent valves that are de-energized to reopen the MSIV. The consequences of the MSLB are provided in FSAR Section 15.1.5. No consequential failures of the MSLB could occur that would affect the capability to maintain the unit at safe shutdown conditiens.

It should also be noted that plant safety will not be jeopardized due to high temperature effects on concrete. ACI 349 allows for temperatures up to 650 F in the event of pipe breaks for local areas. (The data available indicates the temperature may peak at 450'F and drop off within a matter of minutes).

Therefore, since the analysis conclusions in the FSAR and Westinghouse Analyses of two steam generators blowing down remain valid, we have determined that the effects of a release of superheated steam in the IVC do not pose a threat to the ability to bring the plant to a safe shutdown and there is no reportable deficiency.

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Attachment ST-HL-AE-1124 Page 4 of 4 References Reference 1) k'estinghouse Owners Group Letter QG-AE-133 dated August 20, 1984 from G. Goering to H. Denton.

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