05000410/LER-2013-001

LER-2013-001, Reactor Core Isolation Cooling System Isolation Due to a Temperature Switch Unit Failure

Nine Mile Point Unit 2
Event date:	01-23-2013
Report date:	03-25-2013
Reporting criterion:	10 CFR 50.73(a)(2)(iv)(A), System Actuation 10 CFR 50.73(a)(2)(v), Loss of Safety Function
4102013001R00 - NRC Website

A. PRE-EVENT PLANT CONDITIONS:

Prior to the event, Nine Mile Point Unit 2 (NMP2) was operating at 100 percent rated thermal power, with the High-Pressure Core Spray (HPCS) system out of service for planned surveillance testing.

B. EVENT:

On January 23, 2013 at 15:16, Nine Mile Point Unit 2 (NMP2) was operating at 100 percent power when Reactor Building General Area temperature switch unit 2RHS*TS85A failed, resulting in the generation of an isolation signal which was sent to containment isolation valves in the Reactor Core Isolation Cooling (RCIC) system (Group 10) and the Residual Heat Removal (RHR) system (Group 5). This caused the RCIC system to isolate from the reactor vessel. The Group 5 containment isolation valves were already closed, which is their normal position during power operation. The isolation signal was generated due to the failure of the temperature switch unit. Operators verified the temperature indicated by the thermocouple was below the trip setpoint, and the isolation signal was determined to be invalid.

The failure of the temperature switch unit occurred concurrently with the High Pressure Core Spray (HPCS) system inoperable for planned surveillance testing. When the steam supply isolation valve to the RCIC turbine (2ICS*MOV121) closed due to the temperature switch failure, the RCIC system became inoperable.

With both the RCIC and HPCS systems inoperable, high pressure makeup capability to the reactor core was lost. Technical Specification (TS) 3.5.3 Conditions A and B were entered due to the RCIC and HPCS systems being inoperable. Required Action B.1 requires the unit to be in MODE 3 within 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />, and Required Action B.2 requires reactor steam dome pressure to be less than or equal to 150 psig within 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br />. Technical Specification 3.5.1 Conditions B and D were also entered due to the RCIC and HPCS systems being inoperable. Required Action D.1 requires the unit to be in MODE 3 within 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />, and Required Action D.2 requires the unit to be in MODE 4 within 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br />. TS 3.3.6.1 Condition A was entered for the failure of 2RHS*TS85A. Required Action A.1 requires the channel to be placed in trip within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />. At 15:50, the HPCS system was declared operable following filling and venting of the system, and TS 3.5.1 Conditions B and D and TS 3.5.3 Condition B were exited. At 23:59, 2RHS*TS85A was declared operable following replacement of the failed temperature switch, and TS 3.3.6.1 Condition A was exited. On January 24, 2013 at 01:17, the RCIC system was declared operable after reopening the steam supply isolation valve, and TS 3.5.3 Condition A was exited.

This event did not affect Nine Mile Point Unit 1 (NMP1).

An event notification was made in accordance with 10 CFR 50.72(b)(3)(v)(A) and 10 CFR 50.72(b)(3)(v)(D) for the RCIC system and HPCS system concurrently inoperable on January 23, 2013 at 2203 (Event Number 48696).

EVENT:

Prior to the event, the HPCS system was out of service for planned surveillance testing.

D. DATES AND APPROXIMATE TIMES OF MAJOR OCCURRENCES:

January 23, 2013 15:16 Operators received a high temperature alarm for reactor building general area temperature.

An isolation signal is generated by 2RHS*TS85A and sent to Group 5 and 10 isolation valves.

RCIC system is declared inoperable. TS 3.5.3 Conditions A and B and TS 3.5.1 Conditions B and D are entered for RCIC and HPCS inoperable.

2RHS*TS85A is declared inoperable. TS 3.3.6.1 Condition A is entered for 2RHS*TS85A inoperable.

15:50 HPCS system is declared operable following completion of surveillance testing and filling and venting of the system. TS 3.5.1 Conditions B and D are exited. TS 3.5.3 Condition B is exited.

23:04 Replacement of 2RHS*TS85A is complete.

23:59 2RHS*TS85A is declared operable. TS 3.3.6.1 Condition A is exited.

January 24, 2013 01:17 RCIC system is declared operable after reopening the steam supply isolation valve. TS 3.5.3 Condition A is exited.

E. OTHER SYSTEMS OR SECONDARY FUNCTIONS AFFECTED:

No other systems or functions were affected.

F. METHOD OF DISCOVERY:

On January 23, 2013 at 15:16, Operators received a high temperature alarm for reactor building general area temperature.

G. MAJOR OPERATOR ACTION:

n RCIC system was declared inoperable.

n TS 3.5.3 Conditions A and B were entered for RCIC and HPCS systems inoperable.

n TS 3.5.1 Conditions B and D were entered for RCIC and HPCS systems inoperable.

n 2RHS*TS85A was declared inoperable.

n TS 3.3.6.1 was entered for 2RHS*TS85A inoperable.

H. SAFETY SYSTEM RESPONSES:

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

II. CAUSE OF THE EVENT:

The cause of the temperature switch unit failure was age-related capacitor degradation. The apparent cause of the event is insufficient use of the corrective action program to fully implement a periodic capacitor replacement program for the Riley temperature switches.

Condition reports written in 1997 and 2002 were initiated in response to temperature switch failures and calibration drift respectively. As part of the corrective actions for these CRs, the capacitors were replaced. In 2002, Preventative Maintenance Change Requests (PMCRs) were developed to periodically replace the capacitors in the Riley temperature switches; however, these PM tasks were never implemented, and subsequent capacitor replacements were not performed.

This event was entered into the Nine Mile Point Nuclear Station, LLC (NMPNS) corrective action program as condition report CR-2013-00634.

III. ANALYSIS OF THE EVENT:

This event is reportable in accordance with 10 CFR 50.73(a)(2)(iv)(A), as an automatic actuation of containment isolation valves in more than one system. Containment isolation valves in the RCIC and RHR systems received an isolation signal as a result of the temperature switch unit failure. The event is also reportable in accordance with 10 CFR 50.73(a)(2)(v), as an event that could have prevented the fulfillment of the safety function of structures or systems that are needed to: (A) Shut down the reactor and maintain it in a safe shutdown condition, and (D) Mitigate the consequences of an accident.

There were no actual safety consequences from this event. The event was caused by the failure of temperature switch unit 2RHS*TS85A, resulting in the generation of an isolation signal which was sent to containment isolation valves in the Reactor Core Isolation Cooling (RCIC) system (Group 10) and the Residual Heat Removal (RHR) system (Group 5). This caused the RCIC system to isolate from the reactor vessel. The Group 5 containment isolation valves were already closed, which is their normal position during power operation. The isolation signal was generated due to the failure of the temperature trip unit. Operators verified the temperature indicated by the thermocouple was below the trip setpoint, and the isolation signal was determined to be invalid.

The failure of the temperature switch unit occurred concurrently with the HPCS system inoperable for planned surveillance testing. When the steam supply isolation valve to the RCIC turbine (2ICS*MOV121) closed due to the temperature switch failure, the RCIC system became inoperable. With both the RCIC and HPCS systems inoperable, high pressure makeup capability to the reactor core was lost.

The HPCS system 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 system cools the core by a spray. The 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 system, can operate over a large pressure range (165 — 1215 psia). During an accident with the RPV at high pressure, either the HPCS system or the RCIC system can be used to provide makeup flow to the reactor. If the HPCS system was 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 .NRC FORM 366A U.S. NUCLEAR REGULATORY COMMISSION

CONTINUATION SHEET

makeup coolant. 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 ADS and both the 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 affects the NRC Reactor Oversight Process (ROP) Performance Indicators (PIs) for Unit 2 for Mitigating System Performance Index (MSPI) Heat Removal System and Safety System Functional Failures (SSFF). The unplanned unavailability experienced as a result of the temperature switch unit failure will result in an increase in the MSPI Heat Removal System PI by 0.2E-08, from -1.8E-08 to -1.6E-08, and remains green.

The green to white threshold for the MSPI Heat Removal System PI is 1.0E-06. The SSFF PI will increase by 1, from 1 to 2, and remains green. The green to white threshold for this PI is 6.

IV. CORRECTIVE ACTIONS:

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

1. Temperature switch unit 2RHS*TS85A was replaced.

B. ACTION TAKEN OR PLANNED TO PREVENT RECURRENCE:

1. Develop and implement a maintenance strategy for Riley temperature switch units that will implement new preventative maintenance requirements.

2. Refurbish all temperature switch units of the same model type as the failed unit.

3. NMPNS has implemented Department Corrective Action Review Teams (DCARTs) and a Correct Action Completion Evaluation (CACE) committee to provide reinforcement and oversight of corrective action standards.

A. FAILED COMPONENTS:

Reactor Building General Area temperature switch unit 2RHS*TS85A.

Manufacturer: Riley - Beaird, Inc US Riley Corp Model: 86BPTEF-E

B. PREVIOUS LERs ON SIMILAR EVENTS:

There are no previous LERs that are similar to this event. There are two 60-day telephone notifications that were made for temperature switch unit failures, as described below.

.t Event Number: 48570 On October 12, 2012, NMP2 received a Division I primary containment isolation signal which resulted in the closure of Group 5, 6, and 10 primary containment isolation valves (PCIVs). The Division I isolation signal was generated due to the failure of a temperature switch unit. The Division I and II temperature switch units were both reading within limits when the Division I unit failed. Since the isolation signal was not initiated in response to actual plant conditions or parameters satisfying the requirements for initiation, the isolation signal was determined to be invalid.

Event Number: 47547 On November 7, 2011, NMP2 received a Division II reactor building pipe chase high ambient temperature isolation signal, which resulted in closure of isolation valves in the reactor water cleanup (RWCU) system, the reactor core isolation cooling (RCIC) system, and the residual heat removal (RHR) system (isolation valve Groups 5, 6, 7, and 10). The isolation signal was generated by a new NUS/Scientech ambient temperature indicating switch that had recently been installed as a replacement for the original Riley temperature switch.

Operations personnel confirmed that conditions requiring isolation of the RWCU, RCIC, and RHR systems did not exist, based on a check of the Division 1 reactor building pipe chase high ambient temperature channel and area radiation monitors. Therefore, the isolation signal was determined to be invalid.

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

LER:

COMPONENT IEEE 803 IEEE 805

COMPONENT IDENTIFIER SYSTEM IDENTIFICATION

Temperature Switch TS IJ Reactor Pressure Vessel RPV N/A Capacitor CAP N/A Isolation Valve ISV N/A High-Pressure Coolant Injection System N/A BJ Reactor Core Isolation Cooling System N/A BN Residual Heat Removal System N/A BO Low-Pressure Coolant Injection System N/A BO Low-Pressure Core Spray System N/A BM

D. SPECIAL COMMENTS:

None