ML20072K326
| ML20072K326 | |
| Person / Time | |
|---|---|
| Site: | Columbia  |
| Issue date: | 06/24/1983 |
| From: | WASHINGTON PUBLIC POWER SUPPLY SYSTEM |
| To: | NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION V) |
| Shared Package | |
| ML20072K321 | List: |
| References | |
| 10CFR-050.55E, 10CFR-50.55E, NUDOCS 8307060232 | |
| Download: ML20072K326 (2) | |
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Attachment I WASHINGTON PUBLIC POWER SUPPLY SYSTEM NUCLEAR PROJECT NO. 2 DOCKET NO. 50-397 LICENSE NO. CPPR-93 10CFR50.55(e) CONDITION #240 LOSS OF ESF LOADS ON UNDERVOLTAGE TRIP INTERIM REPORT Description of Deficiency On a degraded voltage condition (87.5% of rated voltage) in the critical bus (SM7 or SM8) supplying ESF loads; the second level undervoltage relays are required to trip the source breaker (i.e., startup/ normal or back-up source breaker) and initiate load shedding. The relays are self riset following closing of the alternate source breaker and the voltage on the critical bus returning to normal. However, the design incorporated a seal-in circuit for the 2nd level undervoltage relays. A manual switch was provided to reset the relays following a degraded voltage condition. This resulted in the following:
- 1) An unsuccessful " auto" transfer from the startup/ normal source to back-up source, if the degraded voltage condition existed in the startup/ normal source, and
- 2) ESF load breakers trip circuits being continuously energized until the relays are reset manually.
NOTE:
The tripping of these breakers was initiated by 2nd level undervoltage relays for load shedding.
The diesel will start automatically due to under-voltage condition in the critical bus. The diesel will supply the critical bus following auto-closing of the diesel breaker after a 5-second delay.
However, if a "LOCA" occurs prior to the relays being reset manually then ESF load brcaker anti-pump relay will prevent the breakers from closing.
Once the anti-pump circuits are activated, the circuit breakers will not be able to close back in until the following actions are performed and in the listed order:
- 1) Second level UV relays are manually reset.
- 2) Close signal is stopped. This will reset anti-pump circuit. To stop the close signal, it may be necessary to de-energize the bus (this is true for l
the RHR pumps), but we are in a LOCA condition.
l -
- 3) If bus is de-energized to do step 2, re-energize bus. Timing will start to reclose circuit breakers automatically.
Safety Implication If the situation described above was left uncorrected, it would have caused all division 1 and 2 ESF loads to be unavailable in the case of a degraded voltage condition (87.5% of rated voltage) on busses SM7 and SM8. This situa-tion would have remained unless operator corrective actions were taken.
If the condition occurred within the first 10 minutes following a design basis event, no. operator action is assumed. Therefore, the plant could not be brought to a safe shutdown condition.
830/060232 930624 PDR ADOCK 05000397 8
Corrective Action The Architect Engineer has issued Project Engineering Directive (PED) 218-E-4618 March 3, 1983 to implement corrective action.
PED 218-E-4618 will effect the following changes:
o Delete seal-in circuit for 2nd level undervoltage relays, o Provide a blocking circuit to prevent reclosing of the backup (115V) source breakers when the backup source is supplying the critical bus and an under-voltage condition exists in the backup source.
Upon implementation of PED 218-E-4618 and other associated PED's, the SM7 and SM8 second level undervoltage relays will function as described in Section 8.3.1.1.1 and 8.3.1.2.4.3.2 of the FSAR. This work is currently in progress and is scheduled for completion before fuel load.
We will continue to provide your office with quarterly updates. The next report will be submitted on or before September 21, 1983.
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