05000220/LER-2013-001

LER-2013-001, Emergency Condenser 11 High Steam Flow Isolation Instrumentation Loss during Plant Startup

Nine Mile Point Unit 1
Event date:	05-14-2013
Report date:	07-12-2013
Reporting criterion:	10 CFR 50.73(a)(2)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident
Initial Reporting
ENS 49029	10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident
2202013001R00 - NRC Website

A. PRE-EVENT PLANT CONDITIONS:

Prior to the event, Nine Mile Point Unit 1 (NMP1) was conducting a reactor startup from the recently completed refueling outage, with reactor power approximately 3 percent.

B. EVENT:

On May 14, 2013, during reactor startup following the completion of refueling outage N1R22, NMPI experienced both channels of high steam flow instrumentation on the EC System Loop 11 going into a gross fail condition. The channel 12 trip unit associated with transmitter DPT-36-06D went into gross fail and subsequently channel 11 trip unit associated with transmitter DPT-36-06C went into gross fail.

On May 14, 2013 at 1215 EC System Loop 11 was manually isolated in accordance with station operating procedures to comply with Technical Specifications (TS). TS 3.1.3.b was entered requiring EC System Loop 11 to be returned to an operable status within 7-days and the completion of TS surveillance requirement 4.1.3.f.

The transmitter equalizing valves for both transmitters were opened and subsequently closed to equalize the sensing lines static head. When this was done the respective trip unit readouts and voltage output readings returned to normal. Afterward, the voltage readings were monitored for a period of 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> to confirm that the instrument differential pressure remained normal and allowing steam condensation to fill the sensing lines. The EC System Loop 11 high steam flow instruments were declared operable followed by restoration of EC System Loop 11 to a standby condition and declaring it operable.

This event did not affect Nine Mile Point Unit 2.

An event notification was made in accordance with 10 CFR 50.72(b)(3)(v)(D) for the loss of EC Loop 11 isolation capability on high steam flow on May 14, 2013 at 1720 (EN# 49029).

EVENT:

Prior to the event, channel 12 high steam flow instrumentation on the EC System Loop 11 was inoperable.

D. DATES AND APPROXIMATE TIMES OF MAJOR OCCURRENCES:

May 14, 2013 0115 The reactor mode switch is placed in startup 0840 The gross fail set point is reached for EC System Loop 11 channel 12 steam flow differential pressure transmitter DPT-36-06D. TS Table 3.6.2.c note (f) action is entered for one channel less than the required minimum for one trip system, requiring the channel to be placed in a trip condition within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />.

1145 The gross fail setpoint is reached for EC System Loop 11 channel 11 steam flow differential pressure transmitter DPT-36-06C. TS Table 3.6.2.c note (f)ztion is entered for one channel less mmk

H. SAFETY SYSTEM RESPONSES:

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

II. CAUSE OF EVENT:

The cause of the failure of channel 11 and 12 high steam flow instrumentation for EC System Loop 11 is leakage from the shared high pressure sensing line for differential pressure transmitters DPT-36-06C and DPT-36-06D. The apparent cause of the leakage in the transmitter high pressure sensing line is leak by on instrument blowdown valves VLV-36-374 and VLV-89-72.

E. OTHER SYSTEMS OR SECONDARY FUNCTIONS AFFECTED:

No other systems or functions were affected.

F. METHOD OF DISCOVERY:

This event has been entered into the Nine Mile Point Nuclear Station corrective action program as condition report number CR-2013-004347.

Operators initiated TS actions resulting in isolating the EC System Loop 11. Following troubleshooting and execution of a confidence run, EC System Loop 11 high steam flow instrumentation system was declared operable, followed by returning EC System Loop 11 to a standby configuration.

On May 14, 2013 at 1145 the control room received Reactor Protection System Analog Trip System (RPS ATS) trouble light for channel 11.

May 15, 2013 0612 EC System Loop 11 is restored to a standby lineup. The system is declared operable and TS 3.1.3.b is exited.

0600 EC System Loop 11 high steam flow instrumentation is declared operable. TS Table 3.6.2.c note (f) actions are exited.

1215 EC System Loop 11 is isolated. TS 3.1.3.b is entered.

1500 Both transmitters were equalized, the readings returned to normal, and gross fail alarms reset.

Monitoring for 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> commenced.

than the required minimum for both trip systems. The action requires tripping one channel within an hour and tripping the remaining channel within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />, or alternatively to take the action of TS 3.6.2.a (3), which requires declaring the affected EC System Loop 11 inoperable and taking the action of TS 3.1.3.b.

III. ANALYSIS OF THE EVENT:

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

There were no actual nuclear safety consequences associated with this event. The event was caused by leakage in the shared high pressure sensing line for differential pressure transmitters, resulting in both channels of high steam flow instrumentation for the EC System Loop 11 being declared inoperable. Although EC System Loop 11 was manually isolated, the conditions satisfying the automatic initiation of the EC System Loop 11 were not present, and no automatic isolation due to high steam flow was required.

The safety function of the EC High Steam Flow instruments (DPT-36-06C and DPT-36-06D) is to isolate EC System Loop 11 in the event of an EC System Loop 11 steam leak. Each of these transmitters monitors steam flow to the EC System Loop 11 and each provides an isolation signal on high steam flow indicative of a line break. Normally, with no steam flow, as is the case with the EC in a standby configuration, the differential pressure seen by the transmitters is approximately zero. The sensing lines are a static column of water from the transmitters to where the instrument lines connect to the steam flow elbow. During normal operation, any minor leakage from the sensing lines is made up from condensation from the steam line to both the low and high pressure sensing lines.

The trip unit gross fail function is a design feature to monitor for an off-normal electronic instrument loop component output. For both of these trip units, the signal at the trip unit was reading low and the gross fail could not be reset. A low output signal is non-conservative in that the high steam flow isolation may not occur when required by design. A low output reading is indicative of a lowered high pressure instrument line water column.

The amount of seat leakage has been evaluated for consideration of impact on containment requirements. The total leakage remains well within the allowable value to meet 10CFR50 Appendix J requirements. The leakage, if internal to the drywell, is monitored as part of the floor drain leak rate criteria, as required by Technical Specifications.

Currently the instrument loops are operable with any minor leakage being maintained by condensing steam as designed. The instruments are calibrated and will perform their isolation function.

Based on the above discussion, it is 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 NMP1 Safety System Functional Failures (SSFF). The SSFF PI will increase from 4 to 5 and remains green. The green to white threshold for this PI is greater than 6. No other NRC performance indicators were impacted by this event.

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IV. CORRECTIVE ACTIONS:

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

1. Transmitters DPT-36-06C and DPT-36-06D were equalized via the equalizing valve and the trip units verified to be reading normally.

2. EC System Loop 11 was returned to a standby lineup.

B. ACTION TAKEN OR PLANNED TO PREVENT RECURRENCE:

1. A drywell walkdown of the high pressure sensing line for differential pressure transmitters DPT-36-06C and DPT-36-06D was performed on July 9, 2013, during the recent planned outage confirming that there are no leaks from the sensing line into the drywell.

2. An interim methodology has been developed and is being implemented to monitor the operability of the transmitters DPT-36-06C and DPT-36-06D instrument loops for times when the instrument is required by TS and there is no reactor steam for instrument line makeup.

3. Replace instrument blowdown valves VLV-36-374 and VLV-89-72 during the next refueling outage at NMPl.

A. FAILED COMPONENTS:

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

B. PREVIOUS LERs ON SIMILAR EVENTS:

There were no previous LERs on similar events.

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

COMPONENT

Reactor Protection System EC System Differential Pressure Transmitter

D. SPECIAL COMMENTS:

None IEEE 803 FUNCTION IEEE 805 SYSTEM

IDENTIFIER

IDENTIFICATION N/A JC