ML20237A679
| ML20237A679 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 08/07/1998 |
| From: | Bajestani M TENNESSEE VALLEY AUTHORITY |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| 50-327-95-18, 50-328-95-18, NUDOCS 9808170013 | |
| Download: ML20237A679 (3) | |
Text
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8 Tennessee Valley Authority, Post Office Box 20LN Soddy Daisy, Tennessee 37379-2000 Masoud Bajestani Sde Vice President Sequoyah Nuclear Plant August 7, 1998 U.
S.
Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D. C.
20555 Gentleman:
In the Matter of
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Docket Nos. 50-327 Teanessee Valley Authority
)
50-328 SEQUOYAH NUCLEAR FIANT (SQN) - NRC INSPECTION REPORT 50-327, 50-328/95-18 -- CHANGE OF COMMITMENT IMPLEMENTATION SCHEDUI.E FOR NOTICE OF V7PLATION (NOV) 50-327,328/95-18-01 The purpose of this letter is to provide NRC with a revised implementation schedule for a commitment that was made in response to the subject NOV.
l TVA's response to the NOV dated September 4, 1996, addressed j
actions taken for a condition involving accelerated degradation of Emergency Core Cooling System (ECCS) throttle valves in an accident scenario.
The NOV response contained a commitment to complete a hardware modification for resolution of the degraded condition during the Units 1 and 2 Cycle 9 l
refueling outages.
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TVA is revising the commitment implementation schedule such that the commitment will now read:
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A hardware modification for resolution of the degraded condition will be implemented during the Units 1 and 2 Cycle 10 refueling outages.
,g d
The commitment implementation schedule is being extended one i
j refueling outage cycle to allow additional design work to be performed.
TVA Engineering entered into a contract with Westinghouse Electric Corporation to develop a design change for resolution of the ECCS throttle valve condition on a schedule sufficient to meet Unit 1 Cycle 9 refueling outage 9908170013 990907
- PDR ADOCK 05000327 G
PDR; L
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U.S. Nuclear Regulatory Commission Page 2 Abgust' 7, 1998 requirements.
The design change involves the installation of a pressure reducing orifice upstream'of the ECCS injection line flow balancing valves.
This change is similar to the change implemented at another nuclear plant to address the same condition.
During design verification of the hardware modification, TVA determined that the valve body / seat configuration of the Sequoyah flow balancing valves results in a relatively narrow range of acceptable differential pressures across the valves.
The maximum flow resistance provided by this narrow operating band is in the range of uncertainties associated with the calculation used to size the upstream differential pressure orifices.
Maximization of the orifice pressure drop could result in ECCS flows that do not meet minimum operability requirements.
Minimization of the orifice
' pressure drop could result in valve throttling, which exceeds the range established to ensure 100-day, post loss-of-coolant accident operation.
Westinghouse has recently informed TVA that it is not possible to analytically size an upstream pressure reducing orifice with sufficient certainty to meet minimum and maximum requirements without actual system performance data.
Additionally, Westinghouse does not recommend fabrication and installation of this design for the-Cycle 9 refueling outage.
As a result, additional time is needed to evaluate alternate design options and develop x revised design change for resolution of the ECCS throttle valve condition.
TVA's review of the commitment extension determined that the extension does not adversely impact plant safety.. Interim l
actionLthat was previously taken revised the site procedure j
for activation and operation of the Technical Support Center.
The procedure revision, which require,s evaluation and monitoring of both the centrifugal charging pumps and safety injection pumps, will remain in place until completion of the hardware modification.
The engineering evaluation which i
. identifies the gradual degradation of the balance valves and j
performance detection of'the pumps remains applicable.
Based on' analysis and interim action taken, safety significance of l
the condition is minimal.
i e
2 l
U.S.
Nuclear Regulatory Commission Page 3 August 7, 1998 If you have any questions regarding chis response, please contact me at extension (423) 843-7001 or Pedro Salas at extension (423) 843-7071.
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Sincerely, y
h[ M '
M. Bajes i
cc:
Mr.
R. W. Hernan, Project Manager Nuclear Regulatory Commission
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One White Flint, North 1
11555 Rockville Pike I
Rockville, Maryland 20852-2739 l
NRC Resident Inspector j
Sequoyah Nuclear Plant 2600 Igou Ferry Road Soddy-Daisy, Tennessee 37379-3624 l
Regional Administrator O.S. Nuclear Regulatory Commission Region II Atlanta Federal Center 61 Forsyth Street, SW, Suite 23T85 Atlanta, Georgia 30303-3415 1
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