ML19296C382
| ML19296C382 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 02/11/1980 |
| From: | TENNESSEE VALLEY AUTHORITY |
| To: | |
| Shared Package | |
| ML19296C379 | List: |
| References | |
| NUDOCS 8002250730 | |
| Download: ML19296C382 (3) | |
Text
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MM[f<p'A ENCLOSURE f_
N SEQUOYAH NUCLEAR PLANT UNIT 1
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VALVE WEIGHT USED IN PIPING ANALYSIS IS INCORRECT
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- O ADDITIONAL INFORMATION Attachment I lists valves for Sequoyah Nuclear Plant unit I which do not have appropriate seismic qualification and will require construction work.
The lack of seismic qualification does not degrade nuclear safety until the time of the planned initial criticality.
Analysis Before initial criticality, the fuel has no fission product inventory or decay heat.
Hence, a fuel handling accident would not cause a radiological release. The only nuclear safety concern before initial criticality is that criticality could be inadvertently achieved.
If this were to occur; it is possible that the containment boundary would be required.
The valves in the listing are a part of the containment boundary.
Their deficiency in seismic qualification means that the containment boundary cannot be ensured after a seismic event.
One means to accidently achieve criticality before initial criticality is to have an inadvertent boron dilution event.
It is highly unlikely for there to be a seismic event (the only time the valves may not function as required) with a baron dilution unless the dilution could be caused by the seismic event. The f ailure of these valves by rupture or mal-function has been examined and determined not to cause a boron dilution (refer to valve function description in Attachment 1).
The remainder of the plant is designed so that a seismic event will not cause a boron dilu-tion.
If, however, a boron dilution were to occur, the FSAR analysis (Section 15.2.4) for uncontrolled boron dilution concludes that the operator would have greater than 90 minutes to stop the dilution before criticality is achieved.
A second consideration for achieving criticality before planned criticality.
is the uncontrolled control rod bank withdrawal from a subcritical condition.
This event is analyzed in the FSAR (Section 15.2.1).
The conclusion is that the fast rise in neutron flux response is terminated by the negative Doppler Coefficient, the transient terminated by the source range flux trip, and the resulting DNBR is well above the limiting 1.30 value.
Therefore, there is no mechanism for significant fission product buildup or release from the fuel pins.
A final consideration for achieving criticality would be the rupture of a control rod drive mechanism housing with control rod ejection.
This event, of course, cannot occur until heatup and pressurization of the RCS begins.
The rod ejection accident under the conditions of a suberitical, unirradiated core is not specifically analyzed in the FSAR.
However, a worst case ejection accident for end of life, zero power, is analyzed (Section 15.4.6).
Examination of Fi,ure 15.4-7 of the FSAR for this event.shows that the t
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core power average is less than 10- of the rated power after a few seconds. Therefore, the generation of fission products by this worst case is extremely small, and any possible release would be negligible in producing an offsite dose.
Conclusion If a seismic event were to cause failure of the valves before initial criticality, their containment boundary function could not be ensured, but it is not necessary for this function to be available to prevent a radiological release under these circumstances.
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a ATTACRMENT 1 VALVES REQUIRING CONSTRUCTION CHANGES TO MEET SEISMIC REQUIREMENTS TVA Valve Numbers Function of Valves
- FCV-61-97 Ice condenser - glycol inlet to flow cooler FCV-61-96 Ice condenser - glycol inlet to flow cooler FCV-61-110 Ice condenser - glycol outlet from flow cooler FCV-61-122 Ice condenser - glycol outlet from flow cooler FCV-77-127 Station drainage - RB floor drain sump discharge FCV-77-128 Station drainage - RB floor drain sump discharge FCV-31C-223 Chiller water - instrument room coolers FCV-31C-224 FCV-31C-229
- All valves are containment isolation valves
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