05000410/LER-2014-002

LER-2014-002, High Pressure Core Spray System Inoperability Due to Inoperable High Pressure Core Spray Diesel Generator

Nine Mile Point Unit 2
Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident
4102014002R00 - NRC Website

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A. PRE-EVENT PLANT CONDITIONS:

Prior to the event, Nine Mile Point Unit 2 (NMP2) was operating at rated reactor power.

B. EVENT:

On February 24, at 0400, the Division III emergency diesel generator (EDG) known as the, "HPCS diesel", was declared inoperable for planned maintenance. Technical Specification (TS) 3.8.1 Condition B was entered with a required action to restore the EDG to operable status within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. Shortly after starting the EDG for post maintenance testing (PMT), Operations observed erratic voltage regulator operation. The EDG was secured at 1621 on February 24 before completing the required post maintenance operability test. On February 27 at 0330, the High Pressure Core Spray System (HPCS) was declared inoperable and the action statement for TS 3.5.1 Condition B was entered. This action prevented the plant from exceeding the TS LCO action statement time limit associated with EDG inoperability. When the HPCS System was declared inoperable, the action statement for TS 3.8.1 Condition B was exited in accordance with a TS 3.8.1 Note which indicates, "Division 3 AC electrical power sources are not required to be OPERABLE when HPCS is inoperable." With implementing this TS provision and entering TS 3.5.1, Condition B, personnel were permitted to continue troubleshooting the EDG hardware malfunction.

The erratic EDG voltage regulator performance was corrected with the replacement of a degraded motor operated potentiometer (MOP) and replacement of degraded R3 and R4 potentiometers on the voltage regulator board. These hardware changes enabled the EDG PMT to conclude satisfactorily on February 27 at 1013.

The reportable condition has been entered into the plant's corrective action program as CR-2014- 001623. Nine Mile Point Unit 1 (NMP1) was unaffected by the declaration of HPCS inoperability at NMP2.

THE EVENT:

The inoperable Division III EDG contributed to this event. The TS time constraint required to address the erratic operation of the EDG voltage regulator led to the declaration of HPCS inoperability.

Nine Mile Point Unit 2 05000410

D. DATES AND APPROXIMATE TIMES OF MAJOR OCCURRENCES:

Date Time Occurrence February 24 0400 Declared Division III EDG inoperable for planned maintenance.

TS 3.8.1, Condition B action statement entered February 24 1621 Secured EDG prior to completion of PMT February 27 0330 Declared HPCS inoperable, entered TS 3.5.1 Condition B.

February 27 1013 Declared Division III EDG operable and HPCS operable February 27 1013 Exited TS 3.5.1, Condition B and 3.8.1, Condition B

E. OTHER SYSTEMS OR SECONDARY FUNCTIONS AFFECTED:

No other systems or secondary functions were affected beyond systems discussed in Section I.B

F. METHOD OF DISCOVERY:

The declaration of the HPCS as inoperable due to the status of EDG PMT was determined as a reportable condition.

G. MAJOR OPERATOR ACTION:

The HPCS was declared inoperable and the action statement for TS 3.5.1, Condition B was entered.

Following this action, TS 3.8.1, Condition B was exited. Completion of successful EDG PMT occurred on February 27 and the plant exited the action statements for TS 3.5.1 and 3.8.1 on February 27 at 1013.

H. SAFETY SYSTEM RESPONSES:

No operational conditions requiring the response of safety systems occurred as a result of this condition.

II. CAUSE OF EVENT:

The cause of event was the erratic operation of the Division III EDG voltage regulator during PMT.

Repairs to address this condition were projected to exceed the 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> TS action statement completion time provided by TS 3.8.1 Condition B. Prior to exceeding this time duration, the HPCS was declared inoperable.

III. ANALYSIS OF THE EVENT:

This event is considered reportable under 10 CFR50.72(b) (3)(v)(D) and 10 CFR50.73(a)(2)(v)(D).

NUREG 1022, Rev. 3 notes the provisions of paragraph 50.73(a)(2)(v)(D) as: "Any event or condition that could have prevented the fulfillment of the safety function of structures or systems that are needed to: (D) Mitigate the consequences of an accident". The HPCS system unplanned inoperability resulted from a decision to prevent the PMT of Division III EDG from exceeding Technical Specification (TS) 3.8.1, Condition B time constraint associated with Division III EDG inoperability.

TS Bases 3.8.1 provides an explanation of TS Note 3.8.1, which permits an exit from TS 3.8.1, Condition B for the inoperable HPCS diesel when the HPCS is declared inoperable. This Note is intended to allow declaring of the HPCS inoperable either in lieu of declaring the HPCS diesel inoperable, or at any time subsequent to entering the TS action statement for the inoperable HPCS diesel. This exception is acceptable since, with the HPCS inoperable and the associated TS action statement entered, the HPCS diesel provides no additional assurance of meeting criteria for Modes 1, 2 and 3.

HPCS is an Emergency Core Cooling System (ECCS) designed to pump water into the reactor vessel over a wide range of pressures. For a small break Loss of Coolant Accident (LOCA) that does not result in rapid reactor depressurization, the system maintains reactor water level and coolant inventory.

For large breaks, the HPCS cools the core by a spray. If the HPCS System were to fail, and RCIC capacity is insufficient to maintain reactor vessel level, the Automatic Depressurization System (ADS) automatically initiates depressurization of the reactor to permit low-pressure ECCS to provide makeup coolant.

The Reactor Core Isolation Cooling (RCIC) system is not part of the ECCS. It is designed to assure that sufficient reactor water inventory is maintained in the reactor vessel to permit adequate core cooling in the event that the reactor is isolated from the main condenser. The RCIC system, like the HPCS, can operate over a large pressure range (165 — 1215 psia). During an accident with the RPV at high pressure, either the HPCS or the RCIC system can be used to provide makeup flow to the reactor.

When the low-pressure ECCS operates in conjunction with the ADS, the effective core cooling capability of the low-pressure ECCS is extended to all break sizes. The low-pressure ECCS consists of the Low-Pressure Core Spray (LPCS) system and the Low-Pressure Coolant Injection (LPCI) system.

The RCIC, ADS, LPCS and the LPCI systems were operable during the event. Based on the above considerations, it has been concluded that the safety significance of this event is low, and the event did not pose a threat to the health and safety of the public or plant personnel.

This event does not affect the NRC Regulatory Oversight Process Indicators.

IV. CORRECTIVE ACTIONS:

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

A defective potentiometer on the Division III EDG voltage regulator was replaced; subsequently the Division III EDG testing was completed satisfactorily. The EDG and HPCS were declared operable at 1013 on February 27, 2014. Action Statements for TS 3.8.1 and 3.5.1 were exited.

B. ACTION TAKEN OR PLANNED TO PREVENT RECURRENCE:

The defective potentiometer on the EDG voltage regulator identified as the cause of the erratic voltage regulator performance during PMT was replaced.

A. FAILED COMPONENTS:

There were no other failed components that contributed to this event.

B. PREVIOUS LERs ON SIMILAR EVENTS:

No previous NMP LERs were identified that document a similar event.

C. THE ENERGY INDUSTRY IDENTIFICATION SYSTEM (EIIS) COMPONENT FUNCTION

COMPONENT

IEEE 803 FUNCTION IEEE 805 SYSTEM

IDENTIFIER IDENTIFICATION

Division III EDG

D. SPECIAL COMMENTS:

None