ML20004F796
| ML20004F796 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 06/12/1981 |
| From: | Mills L TENNESSEE VALLEY AUTHORITY |
| To: | James O'Reilly NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II) |
| References | |
| 10CFR-050.55E, 10CFR-50.55E, NUDOCS 8106220399 | |
| Download: ML20004F796 (2) | |
Text
.
P00R ORIGINAL 400 Chestnut Street Ttwer II June 12, 1981 SQRD-50-328-Gi-13 8
J WI 1 g yggI h g
'S Mr. James P. O'Reilly, Director
'g "4 %'
Office of I tien and Enforcement
.y g/f U.S. Nuclear atcr/ Ccrmissien 4/-
Regicn II - Sui 3100
,/.
101 Marietta Str b
Atlanta, Gecrgia 303
Dear Mr. O'Reilly:
S'.JCCOYAH NUCLEAR PTMr UNIT 2 - FAIIUPE OF THE GENEPATOR SYSTDi TO SUPPLY AEECr: ATE WLTAGE TO ':UE SAFE'IY-FIIATE BOARDS - SOPD-50-329/81 FI?M. P E T We subject deficiency was initially reportM to NPC-OIE Insoector M. ~tcznas on January 5,1991, in accordance with 10 CFR 50.55(e) as NCR's SON SEB 8054 and hm EEE 3009. Interim rernets were subnitted for Sequoyah unit 2 and Watts Bar units 1 and 2 on Februarv 4 and April 3, 1981. W e Watts Bar deficiency O s D-50-390/81-13 and %'BPD-50-393 /81-12) is nce being handled under a separate recort. Enclosad is our 'inal report.
If you have any questions, please get in touch with.D. L. Imbert at FrS 857-2581.
Very truly yours, T3'lE:SEE VALLEY ALTFOPITY L. M. Mills, vanager Nuclear Pequlation and Safety.
Enclosure Mr. Victor Stello, Director (Enclosure), y ec:
V Office of Inspection a.~.3 Enforcement U.S. Nuclear Regulatcry 0:mnission
?bchington, DC 20555
[h S/ 1 8106220399 3
e 6
ENCLOSURE SEUJOYAH NUCLEAR PLANr LHIT 2 FAILURE OF THE GENERATOR SYSTEM 10 SUPPLY ADEQUATE VOLTAGE TO 'IEE SAFETY-RELATED BOARDS SQRD-50-328/81-13 10 CFR 50.55(e)
FINAL REEORT Descriction of Deficiencv When a reactor is tripped autcmatically for reasons other than an electrical fault or generator bearing failure, the min generator is not tripped for 30 seconds. During this time, the turbine stop valves are closed, and the generator is driven as a synchronous motor. We transfer of the safety boards to the preferred offsite supply is also delayed for 30 seconds.
If the gener:ator voltage regulator system failed to oper a within its specified range during this delay period, inadequate voltage could be supplied to the 6900-volt shutdown boards following the unit trip. If this occurred, both trains of essential safety-related equignent supplied by the 6900-volt shutdown boards would be unable to meet the required response times stated in the safety analysis report.
Safety Imolications If the 6900-volt shutdown board was unable to meet the required response times, then it would be impossible to ensure that core cooling, containment integrity, and other
.:al safety features ara maintained.
Corrective Action TVA is in the process of implementing an undercitage protection scheme on the 6.9-kV unit boards that will transfer each board to its alternate (preferred offsite) supply within six cycles should the main generator voltage beccme degraded. S e transfer will only be enabled during the 30-second time delay following a reactor trip and before the min transformer high-side brea'<ers are tripped. Rese changes will be implemented on unit 2 before initial criticality.
Also, in order to ensure adequate starting voltage for motors in the 480V Class 15 ac auxiliary power system during this 30-second period, the voltage on the 6.9-kV shutdown boards during normal operation must be at least 6700 volts. The unit operators will verify that this voltage is' maintained.
. s O
y
- - -,-