ML20207N045
| ML20207N045 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 10/14/1988 |
| From: | Gridley R TENNESSEE VALLEY AUTHORITY |
| To: | NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM) |
| References | |
| NUDOCS 8810180472 | |
| Download: ML20207N045 (4) | |
Text
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i TENNES2EE VALLEY AUTHOPITY CH ATTANOOG A. TENN ESSEE 37401 SN 1578 Lookout Place 00T 141988 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Wa55tngton, D.C.
20555 Gentlemen:
In the Matter of
)
Docket Nos. 50-327 Tennessee Valley Authority
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50-328 SEQUOYAH NUCLEAR PLANT (SQN) UNITS 1 AND 2 - REACTOR COOLANT SYSTEM (RCS)
POSTTRIP C00LD0HN AND SHUTDOHN MARGIN (SDH) FOLLOW-UP
Reference:
TVA letter to NRC dated August 31, 1988, "Sequoyah Nuclear Plant (SQN) Units I and 2 - Reactor Coolant System (RCS) Posttrip Cooldown and Shutdown Margin (SDH)"
The referenced letter stated that TVA was investigating severai different options to resolve the posttrip cooldown being experienced at SQN.
That investigation has been completed, and the plan for resolution implementation is provided in enclosure 1.
Summary statements of the commitments contained in this submittal are in enclosure 2.
If you have any questions, please telephone M. A. Cooper at (615) 870-6549.
Very truly yours, TENNESSEE VALLEY AUTHORIT(
ks/.kN.
f b.Gridley, Manager Nuclear Licensing and Regulatory Affairs Enclosures cc:
See page 2 QD I (
Gs10160472 8s1014 PDR ADOCk O'X40327 P
PDC An Equa: opportunity Employer
-o OCT 141989 U.S. Nuclear Regulatory Commission cc (Enclosures):
Ms. S. C. Black, Assistant Director for Projects TVA Projects Division U.S. Nuclear Regulatory Commission One White Flint, North 11555 Rockville Pike Rockvlile, Maryland 20852 Mr. F. R. McCoy, Assistant Director I
for Inspection Programs TVA Prcjects Division U.S. Nuclear Regulatory Commission Region II 101 Marietta Street, NH, Suite 2900 Atlanta, Georgia 30323 Sequoyah Resident Inspector l'
Sequoyah Nuclear Plant 2600 Igou Ferry Road Soddy Daisy, Tennessee 37379 i
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RCS Cooldown Resolution 3
l The root cause of the posttrip cooldown is the excessive mass loss from the 3
steam generators by the steam dump system and miscellaneous steam leaks.
The RCS overcooling is further aggravated by the refilling of the steam generators by the auxillary feedwater (AFH) system with water from the condensate storage i
tank, which is typically 70 degrees.
TVA has investigat'd several options to reduce the mass loss from the steam l
generators.
This reduction in mass loss following a reactor trip would have a twofold effect.
First, the initial RCS cooldown from at-power conditions t
would be slewed and its magnitude reduced.
Secondly, because less mass would be removed from the ! team generators, the amount of AFH that would be required l
to regain steam generator levels would be reduced, thereby limiting the RCS i
cooldown.
As stated in the referenced letter, TVA has provided the appropriate management attention to ensure that steam leaks, which could contribute to tt.J j
RCS cooldown, are adequately c'antrolled by the existing maintenance program.
1 To further reduce the mass Icss from the steam generators following a reactor
{
trip TVA has investigated various methods to optimize steam dump operation, i
These methods have been analy.'ed by Westinghouse Electric Corporation to j
determine their feasibility and effect on RCS cooldown.
The Westinghouse analysis also included a study of the sensitivity of the RCS cooldown to AFH ficw rate.
Based on detailed review of the Westinghouse analysis, TVA has determined that the following corrective actions will be taken to prevent and/or mitigate the posttrip cooldown:
1.
To prevent evercooling of the steam generators. SQN Emergency Instruction (ES) 0.1, "Reactor Trip Response," will be revised to require that the operator take manual control of the AFH system to reduce AFH flow to the intact steam generators while maintaining at least 440-gallons-per-minute flow or greater than 25-percent narrow range level in at least one steam generator.
This revision to ES-0.1 will be completed and implemented for both units before restart of unit 1.
2.
To limit mass loss from the sti.m generators, TVA will optimize the present RCS average temperature (Tavg) steam dump controls to prevent excessive blowdown of the steam generators following a reactor trip.
Unit 1 modifications will be completed no later than February 28, 1989, and unit 2 modifications will be completed before restart of the unit 2 cycle 3 refueling outage.
In addition to the corrective actions stated above. ES-0.1 continues to require manual boration of the RCS if the Tavg drops below the minimum allowable temperature supplied by Westinghouse, This provision ensures that no safety concern exists as a result of RCS overcooling because of unexpected
- events,
-. 4 List of Commitments 1.
To prevent overcooling of the steam generators. ES-0.1, "Reactor Trip Response," will be revised to require that the operator take manual control of the AFH system to reduce AFH flow to the intact steam generators while maintaining at least 440-gallons-per-minute flow or greator than 25-percent narrow range level in at least one steam generator. This revision to ES-0.1 will be completed and implemented for j
both units before restart of unit 1.
2.
To limit mass loss from the steam generators. TVA will optimize the present RCS Tavg steam dump controls to prevent excessive blowdown of the steam generators following a reactor trip.
Unit I modifications will be completed no later than February 28, 1989, and unit 2 modifications will be completed before restart of the untt 2 cycle 3 refueling outage.
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