ML19341C233
| ML19341C233 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 02/23/1981 |
| From: | Mills L TENNESSEE VALLEY AUTHORITY |
| To: | Schwencer A Office of Nuclear Reactor Regulation |
| References | |
| RTR-NUREG-0737, RTR-NUREG-737, TASK-2.E.4.2, TASK-TM NUDOCS 8103020475 | |
| Download: ML19341C233 (2) | |
Text
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TENNESSEE V ALLEY A UTHCRIT
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400 Chestnut Street Tower II February 23, 1981 Director of Nuclear Reactor Regulation Attention:
Mr. A. Schwencer, Chief Licensing Branch No. 2 Division of Licensing U.S. Nuclear Regulatory Commission Washington, DC 20555
Dear Mr. Schwencer:
In the Matter of the Application of
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Docket Nos. 50-327 Tennessee Valley Authority
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50-328 My letters to you dated December 19, 1980, and January 7, 1981, transmitted our response to NUREG-0737 for Sequoyah Nuclear Plant units 1 and 2, respec tively. These submittals contained erroneous information related to item II.E.4.2.5, Containment Pressure Setpoint. Enclosed is a revised response to this item.
If you thave any questions, please get in touch with D. L. Lambert at FTS 157-258).
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7 Very truly yours, TENNESSEE VALLEY AUTHORITY T
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L. M. Mills, Manager Nuclear Regulation and Safety
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ENCLOSURE SEQUOYAH NUCLEAR PLANT a-1 NUREG-0737 REQUIREMENT II.E.4.2.5 CONTAINMENT ISOLATION DEPENDA3ILITY
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CONTAINMENT PRESSURE SETPOINT REVISED RESPONSE The Ssquoyah containment pressure high setpoint is required to be less than or equal to 1.54 psig by Technical Specification 3.3.2.1, " Engineering Safety Feature Actuation System Instrumentation." It is more than 1
- psig above the highest primary containment internal pressurd allowed by Technical Spe,cification 3.6.1.4, " Containment Internal Pressure," however, TVA believes that the present containment pressure high setpoint is adequate. The reasons are stated below.
The containment pressure high channel actuates safety injection, turbine trip, and feedwater isolation. Phase "A" containment isolation is actuated from the safety injection logic. Reducing the containment pressure high setpoint increases the potential not only for inadvertent containment isolation but also inadvertent safety injection and feedwater isolation.
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firtuate. protection is alieady provided to prevent the release of
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radicactive caterials following an accident. Containnent ventilation isolation is initiated by diverse signals, including all safety injection actuation channels including low pressurizer pressure, high gaseous ce particulate activity in containcent, and high activity in _
m the' purge air exhaust. -
The containment pressure high and high-high setpoints and low pressurizer pressure'setpoints are reached almost immediately in large loss of coolant accidents (LOCA). ~Lovering the containment pressure high setpoint will not provide any. additional safety =argin to the accident analyses because of
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'the speed at which the contain=cnt pressure rises for large LOCA's.
Two cases _for small LOCA's are considered: those for which the charging system can maintain re ctor coolant system inventory and those that cannot.
f In the first case, cure uncovery will not occur and the radioactivity l released is limiced to the material contained in the coolant. Containment
. vent' isolation vill occur. The setpoint for the ventilation isolation signals are set to prevent _ releases exceeding 10 CFR Part 20 limits (normal
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- release li=its). Iowering the_ containment pressure high setpoint will
- not provide any significant additional safety margin.
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-In the second case, safety. injection will always occur much sooner than core uncovery. Since phase "A"
isolation occurs on safety injection, radioactivity releases prior to ' isolation are limited to material contained
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in the coolant. Containment vent isolation will occur. Lowering the containment pressure high setpoint will not provide any significant additional.safecy margins.
TVA believes l that ' the present containment pressure hig setpoint of 1.54 e
psig isLadequate. Reduction of this setpoint would provide no significant additional' safety margin.
Instead, it.would increase phe potential for inadvertent contain=ent isolation and ' safety injectiosi.
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