05000293/LER-2017-012

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LER-2017-002, Start-Up Transformer Degraded Voltage Relay Found Outside Technical Specification Limit
Pilgrim Nuclear Power Station
Event date: 09-13-2017
Report date: 11-13-2017
Reporting criterion: 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications
2932017002R00 - NRC Website
LER 17-012-00 for Pilgrim Nuclear Power Station Regarding Start-Up Transformer Degraded Voltage Relay Found Outside Technical Specification Limit
ML17325A986
Person / Time
Site: Pilgrim Entergy icon.png
Issue date: 11/13/2017
From: Perkins E P
Entergy Nuclear Operations
To:
Document Control Desk, Office of Nuclear Reactor Regulation
References
2.17.076
Download: ML17325A986 (6)


comments regarding burden estimate to the Information Services Branch (T-2 F43), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e-mail to used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

Pilgrim Nuclear Power Station 05000-293 2017 -00

BACKGROUND

The startup transformer supplies power to the station auxiliary power distribution system whenever the main generator is offline. After the main generator has been synchronized to the 345 kV system and has been partially loaded, the auxiliary power distribution system is manually transferred from the start-up transformer (SUT) to the unit AC power source (unit auxiliary transformer [UAT]).

Automatic fast transfer capability is provided in the design to restore the auxiliary power distribution system to its preferred offsite AC power source, the SUT, in the event that the unit AC power source (UAT) is lost for any reason. The diesel generator load shedding logic will also be actuated immediately upon the fast transfer of the safety related buses A5 and A6 to the SUT if a Loss-Of-Coolant-Accident signal is present when the SUT secondary voltage is below the degraded voltage alarm reset setpoint.

The primary function of the 127A-604/1 degraded voltage relays and their settings for the SUT is to ensure a minimum voltage at which the emergency buses can be operated indefinitely to provide their intended safety functions. If voltage drops below that point for a specified time limit, the degraded voltage relays will initiate transfer of the emergency buses from offsite power to the onsite emergency diesel generators.

EVENT DESCRIPTION

During calibration of four SUT Degraded Voltage Relays (ABB model number ITE-27N) after the relays had been removed from the plant, relay 127A-604/1 had an as-found setpoint value outside the Technical Specifications (TS) Table 3.2.B limit of 110.6 plus or minus 0.56 Volts ac (Vac) (110.04 — 111.16). The as- found value was 109.90 Vac. This relay was replaced with a spare relay that was calibrated prior to its installation.

CAUSE OF THE EVENT

The cause of the relay's potential inoperability is still under investigation at this time.

CORRECTIVE ACTIONS

The relay was replaced, restoring the safety function of the SUT degraded voltage relay to initiate transfer of the emergency buses from offsite power to the onsite emergency diesel generators.

comments regarding burden estimate to the Information Services Branch (T-2 F43), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e-mail to used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

Pilgrim Nuclear Power Station 05000-293 2017 - 00

SAFETY CONSEQUENCES

The 127A-604/1 Degraded Voltage Relay As-Found setpoint value was outside the TS limits. However, per calculation PS147 "Degraded Voltage Trip Relays, Revised Voltage Setpoint" the as-found value was within the analytical limits, which indicates that the degraded voltage relay would operate within safety limits albeit outside the TS limits.

Calculation PS147 "Degraded Voltage Trip Relays, Revised Voltage Setpoint" establishes the trip setpoint, analytical limits, and the no adjust limits for the voltage function of the degraded voltage trip relays (127A-504/1,2,3,4 and 127A-604/1,2,3,4). The upper and lower analytical limits are the limit of a measured or calculated variable established by the plant safety analysis to ensure that a safety limit is not exceeded. The as-found value found for this relay was 109.9 Vac which was outside the TS limits.

However, per PS147, the lower analytical limit is 109.75 Vac. Therefore, the as-found value for 127A- 604/1 does not exceed the established safety limit, and the relay is capable of performing its safety function.

There were no public safety, nuclear safety, industrial safety or radiological safety consequences from this event. No actions to reduce the frequency or consequence are necessary.

REPORTABILITY

Pilgrim Nuclear Power Station is submitting this Licensee Event Report (LER) in accordance with 10 CFR 50.73(a)(2)(i)(B) — Any operation or condition that was prohibited by the plant's Technical Specifications.

PREVIOUS EVENTS

A review of PNPS LERs for the past five years did not identify any other LERs that were submitted for the same reason as this submittal.

REFERENCES:

CR-PNP-2017-9211 - 012