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LER-2017-001, Manual Reactor Trip Due to Lowering Steam Generator Level Caused by Loss of Flow Regulating Valve Positioner Control
Turkey Point Unit 4
Event date: 9-10-2017
Report date: 11-7-2017
Reporting criterion: 10 CFR 50.73(a)(2)(iv)(A), System Actuation
Initial Reporting
ENS 52960 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation, 10 CFR 50.72(b)(3)(iv)(A), System Actuation
2512017001R00 - NRC Website
LER 17-001-00 for Turkey Point, Unit 4, Regarding Manual Reactor Trip Due to Lowering Steam Generator Level Caused by Loss of Flow Regulating Valve Positioner Control
Person / Time
Site: Turkey Point NextEra Energy icon.png
Issue date: 11/07/2017
From: Summers T
Florida Power & Light Co
Document Control Desk, Office of Nuclear Reactor Regulation
Download: ML17311A666 (3)

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.


The event was initiated by failure of the 4C MFRV. At the time of the event, level in the 4B and 4C SGs was being controlled manually due to positioner issues. The operator controlling SG levels noticed the 4C SG level was not responding as expected to controller inputs. The 4C SG level continued to lower even though the 4C MFRV and its associated bypass valve both were demanded full open. The reactor operator manually tripped the reactor as briefed at the 20% level in the 4C SG.

Troubleshooting identified water intrusion in the 4B and 4C MFRV positioner selector switches (PSS). During troubleshooting, the 4C MFRV PSS was found to have a broken wire weakened by corrosion. The wire appears to have broken when a cover was removed during the troubleshooting.


Safety significance is very low because the unit responded as designed to the trip.


Corrective actions are contained in Condition Report 2224218 and include:

ADDITIONAL INFORMATION: EIIS Codes are shown in the format [IEEE system identifier, component function identifier, second component function identifier (if appropriate)].

FAILED COMPONENTS IDENTIFIED: None PREVIOUS SIMILAR EVENTS: None On September 10, 2017 at approximately

1855 hours
0.0215 days
0.515 hours
0.00307 weeks
7.058275e-4 months

, the Turkey Point Unit 4 reactor [AC, RCT] was manually tripped from 88% power due to lowering level in Steam Generator [SB, SG] C. The reactor was stabilized in Mode 3. Auxiliary Feed Water (AFW) [BA] actuated as expected on low level in SG C and was secured at approximately

1933 hours
0.0224 days
0.537 hours
0.0032 weeks
7.355065e-4 months

. At the time of the event, the Turkey Point site was experiencing high winds with rain associated with Hurricane Irma.

The Reactor Protection System (RPS) [JC], and AFW actuations were reported in accordance with 10 CFR 50.72 in Event Notification 52960 and are also reportable in accordance with 10 CFR 50.73(a)(2)(iv)(A).

The direct cause of the event was a degraded signal due to water intrusion into the 4C Main Feedwater Regulating Valve (MFRV) [SJ, FCV] positioner hand selector switch enclosure. The root cause was a latent weakness in the installation of the enclosure. A contributing cause was a less than adequate design change that installed the enclosures.

1. Modifications were completed on the Unit 3 and 4 MFRV hand selector switch enclosures and enclosure penetrations. The broken wire associated with the 4C MFRV was repaired. Other enclosures in safety significant systems were also included in the scope of work.

2. The terminal/pull box specifications will be revised to improve direction for installation of enclosures needing protection from water intrusion.