05000410/LER-2009-001

LER-2009-001, Momentary Loss of Control Power to High Pressure Core Spray, Pump Due to Degraded Fuse Block Connection

Docket Number
Event date:	08-23-2009
Report date:	10-22-2009
Reporting criterion:	10 CFR 50.73(a)(2)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident
4102009001R00 - NRC Website

A. PRE-EVENT PLANT CONDITIONS:

Prior to and throughout this event Nine Mile Point Unit 2 (NMP2) was stable at 100% power with no other inoperable systems affecting this event.

B. EVENT:

At 0915 hours0.0106 days <br />0.254 hours <br />0.00151 weeks <br />3.481575e-4 months <br /> on August 23, 2009, with (NMP2) operating at 100% power, the control room received an unexpected annunciator for High Pressure Core Spray (HPCS) Inoperable and a Division 3 Diesel Direct Current Control Power Failure annunciator. Both annunciators cleared one second later. An operator was dispatched to the HPCS (Division 3) switchgear room to investigate. It was determined that the two annunciators were indicative of a DC control power failure in the breaker circuit for the HPCS pump. A review of the prints showed that if the circuit monitoring relay for the HPCS breaker changed state, both annunciators would activate. The relay is normally energized and would only de-energize if the relay failed or power was lost to the circuit. Loss of control power to the HPCS pump breaker would prevent the HPCS pump from starting if high pressure injection were required.

During troubleshooting, a degraded connection was found between the removable and stationary parts of the HPCS breaker CLOSE fuse block. The contact gap for one of the receiver connections internal to the stationary section of the CLOSE fuse block was wider than the other 3 receiver connections. At 1715 hours0.0198 days <br />0.476 hours <br />0.00284 weeks <br />6.525575e-4 months <br />, HPCS was declared inoperable and Technical Specification 3.5.1, Condition B, was entered. Condition B requires NMP2 to immediately verify by administrative means that the Reactor Core Isolation Cooling (RCIC) system is operable when RCIC is required to be operable AND restore the HPCS system to operable status within 14 days. In accordance with Condition B, the RCIC system was verified to be operable. The HPCS circuit was taken out of service and the fuse block connection repaired by readjusting the receiver connection. The circuit was re-energized and the HPCS pump was run. No further annunciators were received and the HPCS system was declared operable at 2046 hours0.0237 days <br />0.568 hours <br />0.00338 weeks <br />7.78503e-4 months <br /> on August 23, 2009.

This event involved the potential loss of safety function of the NMP2 HPCS system for 3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br />, 31 minutes and 1 second. This includes the duration the annunciator was in alarm and the time it took for troubleshooting from 1715 hours0.0198 days <br />0.476 hours <br />0.00284 weeks <br />6.525575e-4 months <br /> to 2046 hours0.0237 days <br />0.568 hours <br />0.00338 weeks <br />7.78503e-4 months <br /> on August 23, 2009. The 8-hour Emergency Notification System notification required by 10 CFR 50.72 (b)(3)(v)(D) was completed on August 23, 2009, at 2152 hours0.0249 days <br />0.598 hours <br />0.00356 weeks <br />8.18836e-4 months <br />.

Throughout the event, NMP2 continued to operate at 100% power. The only equipment affected by the degraded fuse connection was the HPCS pump and its associated breaker. The Division 3 Emergency Switchgear and associated Division 3 Emergency Diesel Generator were unaffected by this failure and were available throughout the event.

There was no impact on Nine Mile Point Unit 1 (NMP1) from this event.

THE EVENT:

There were with no other inoperable components that impacted this event.

D. DATES AND APPROXIMATE TIMES OF MAJOR OCCURRENCES:

August, 23, 2009:

0915 HPCS loss of power annunciators were received in the control room:

091525 HPCS System INOP 091525 BKR102-2 DN/NO CONT PWR ALARM 091526 HPCS System ALMCLR 091526 BKR102-2 DN/NO CONT PWR ALMCLR 1715 Troubleshooting revealed that the contact gap for one of the receiver connections internal to the stationary section of the CLOSE fuse block was wider than the other 3 receiver connections. The HPCS system was declared inoperable per Technical Specification 3.5.1.

2043 The fuse block connection was repaired by readjusting the receiver connection. HPCS was returned to standby and the HPCS pump was declared inoperable, but available.

2046 The HPCS pump was run and then restored to operable status.

E.OTHER SYSTEMS OR SECONDARY FUNCTIONS AFFECTED:

None.

F.METHOD OF DISCOVERY:

The fuse connection degradation was first suspected in the control room due to the two HPCS annunciators activating for 1 second.

G.MAJOR OPERATOR ACTION:

An operator was dispatched to the Division 3 switchgear room to investigate the cause of the alarms. After repairs were completed, the HPCS pump was run to verify operability.

H.SAFETY SYSTEM RESPONSES:

There were no safety system responses during this event and none were required.

II. CAUSE OF EVENT:

The cause of this event is omission of relevant information from maintenance procedures.

In February, 1978, General Electric issued a Service Advisory Letter (SAL), SAL 322.1, "Type NEC Fuse Holders 30 Amp and 60 Amp," in order to address the potential for loose fuse holders. NMP1 does not use this type of fuse holder, but NMP2 uses them in the 4.16 kV and 13.8 kV switchgear. The SAL was reviewed by Condition Report (CR) 1998-0790, but one recommendation was not incorporated into the maintenance procedures for high voltage switchgear breakers.

Repeated removal and installation of the close fuses for the HPCS breaker resulted in the contact gap of one of the receiver connections within the stationary fuse block to be wider than it should have been. This caused the removable portion of the fuse block connection to not engage the stationary side properly. Had the adjustments recommended in the SAL been incorporated into the maintenance procedure for the HPCS breaker, the contact gap would have been adjusted at the last performed preventive maintenance evolution.

NMP CR 2009-005044 applies to this LER.

III. ANALYSIS OF THE EVENT:

This event is reportable in accordance with 10 CFR 50.73(a)(2)(v)(D) which states that any event or condition that could have prevented the fulfillment of the safety system function of structures or systems that are needed to mitigate the consequences of an accident is reportable.

The HPCS system circuit issue revealed itself at 0915 hours0.0106 days <br />0.254 hours <br />0.00151 weeks <br />3.481575e-4 months <br /> when the annunciators in the control room activated for one second. The HPCS system was declared inoperable 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> later at 1715 hours0.0198 days <br />0.476 hours <br />0.00284 weeks <br />6.525575e-4 months <br /> when it was determined that the HPCS fuse connection was degraded. The system was declared inoperable, but available, at 2043 when the circuit was re-energized. The HPCS pump was run with no further alarms and at 2046 the HPCS system was declared operable. The HPCS system was inoperable for 3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br /> and 31 minutes.

There were no other systems inoperable and no other system failures related to this event. There were no actual safety consequences for this event. HPCS is designed to provide a high pressure injection source to the reactor when required, including a LOCA (Loss of Coolant Accident). Throughout this event, the reactor was stable at 100% power. Had a LOCA occurred, RCIC (Reactor Core Isolation Cooling) was available as well as all other Emergency Core Cooling Systems (ECCS). Under this scenario, adequate core cooling is ensured by the operability of the redundant and diverse low pressure ECCS injection/spray subsystems in conjunction with the ADS (Automatic Depressurization System). Also the RCIC system would automatically provide makeup water at most reactor operating pressures.

This event resulted in a reduction in the Regulatory Oversight Process (ROP) Mitigating System Performance Index (MSPI) for the High Pressure Core Spray System from -1.8E-07 to -1.7E-07 compared to the Green-to- White threshold value of >1.0E-06. This reduction would not result in entry into the "Increased Regulatory (White) Response Band.

IV. CORRECTIVE ACTIONS:

A. ACTION TAKEN TO RETURN AFFECTED SYSTEMS TO PRE-EVENT NORMAL STATUS:

The CLOSE fuse block stationary and removable connections were adjusted and verified to fit tightly into each other.

B. ACTION TAKEN OR PLANNED TO PREVENT RECURRENCE:

To prevent reoccurrence, the procedures for the 4.16kV and 13.8 kV breaker PMs will be revised to include the fuse block contact gap adjustment.

A. FAILED COMPONENTS:

The CLOSE fuse block stationary contact for HPCS pump breaker was the only failed component and it was repaired.

B. PREVIOUS LERs ON SIMILAR EVENTS:

There have been no previous LERs similar to this event.

C. THE ENERGY INDUSTRY IDENTIFICATION SYSTEM (EllS) COMPONENT FUNCTION IDENTIFIER

AND SYSTEM NAME OF EACH COMPONENT OR SYSTEM REFERRED TO IN THIS LER:

�COMPONENT IEEE 803 � IEEE 805 � PART

COMPONENT IDENTIFIER SYSTEM IDENTIFICATION NUMBER

Fuse Block� FUB� BG 0132A1578001 High Pressure Core Spray Pump� P� BG Division 3 Switchgear� SWGR� BG HPCS Breaker� BKR� BG Diesel Generator� DG� EK RCIC System� N/A� BN ADS System� N/A� N/A ECCS� N/A� BO D.SPECIAL COMMENTS:

None.