05000341/LER-2017-003

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LER-2017-003, Division 2 Residual Heat Removal Service Water System (RHRSW) Inoperable Due to an Inoperable RHRSW Flow Control Valve
Fermi 2
Event date: 05-22-2017
Report date: 07-21-2017
Reporting criterion: 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications

10 CFR 50.73(a)(2)(v)(B), Loss of Safety Function - Remove Residual Heat

10 CFR 50.73(a)(2)(v), Loss of Safety Function
3412017003R00 - NRC Website
LER 17-003-00 for Fermi 2 Regarding Division 2 Residual Heat Removal Service Water System (RHRSW) Inoperable Due to an Inoperable RHRSW Flow Control Valve
ML17202G758
Person / Time
Site: Fermi DTE Energy icon.png
Issue date: 07/21/2017
From: Polson K J
DTE Electric Company, DTE Energy
To:
Document Control Desk, Office of Nuclear Reactor Regulation
References
NRC-17-0048
Download: ML17202G758 (8)


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.

INITIAL PLANT CONDITIONS

Mode —1 Reactor Power — 100 Reactor Pressure Vessel Temperature — 518 degrees Fahrenheit There were no structures, systems, or components (SSCs) that were inoperable at the start of this event that contributed to this event.

DESCRIPTION OF THE EVENT

On May 22, 2017, at 5:10 am, while placing Division 2 Residual Heat Removal Service Water (RHRSW) [BI] in service to support biocide treatment of the Division 2 Residual Heat Removal (RHR) [BO] Reservoir, the Division 2 RHR Heat Exchanger Service Water Flow Control Valve [(FCV)] (E1150F068B) did not completely open as expected when the push button was pressed. The Division 2 RHRSW Flow Control Valve (FCV) (El 150F068B) failed to fully open. The RHRSW FCV indicated dual position after 5 seconds of operation in the open direction. When the RHRSW pump was started, indicated flow would not go above 2800 Gallons Per Minute (gpm). After the initial flow spike RHRSW flow settled out at 2,800 gpm and would not continue to rise as expected while holding the open pushbutton for El 1 50F068B valve. The Division 2 RHRSW Pump B was placed in off and valve position remained in dual indication. The Operator pushed the close pushbutton and no change in valve position was observed. The operator then depressed the Thermal Overload reset and verified continuity for all fuses in 72F-4A Position 3A, MCC for El 1 50F068B. The FCV was verified closed locally by stem position and manually checking close with hand-wheel. Troubleshooting discovered the direct cause was failure of the anti-rotation bushing stem key tack welds. The welds were repaired and the key was replaced. Post Maintenance Testing (PMT) was satisfactorily completed. The RHRSW FCV was returned to service at 4:04 pm on May 24, 2017.

Prior to the May 22, 2017, RHRSW FCV failure, troubleshooting did not identify cause of the failure.

On May 5, 2017, during shutdown of the Division 2 RHRSW, with flow lowered to 8500 gpm, the E1150F068B improperly indicated full closed. The RHRSW pumps were shutdown and E1150F068B was then stroked and timed with local position verification. When the open pushbutton was pressed, the open light did not come on until after approximately 55 seconds and the valve indicated full open after 125 seconds. On the close stroke, the open light went out after approximately 56 seconds (indicated full closed in the Main Control Room) and the valve was seen to be full closed locally at 124 seconds. The stroke times were longer than expected but still within acceptance criteria.

Troubleshooting activities were performed. The troubleshooting focused on the indication aspects of the Motor

3. LER NUMBER

APPROVED BY OMB: NO. 3150-0104 EXPIRES: 10/31/2018 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.

Operated Valve (MOV), which involved inspecting the Torque Switch, Limit Switch, and the associated wiring.

Hand wheel operation of the MOV was performed, and it was noted that the Limit Switches were not actuating when expected. The 4 train-limit switch assembly was replaced, and limits were reset.

On May 7, 2017 PMT was performed which included Equivalent Thrust diagnostic testing and Inservice Testing (IST) Stroke Time Testing Partial Surveillance 24.205.06. This PMT was performed at static conditions and in accordance with MMAll "Post Maintenance Testing Guidelines." Due to the static versus dynamic nature of the testing, the actual failure mechanism was missed and the results were accepted as satisfactory with the valve being returned to service.

The RHRSW FCV E1150F068B and Division 2 RHRSW Subsystem were considered inoperable from May 3, when the RHRSW FCV was last successfully stroked under dynamic conditions, to May 24, 2017. This is a condition prohibited by Technical Specification (TS) 3.7.1 and reportable under 10 CFR 50.73 (a)(2)(i)(B) "Operation or Condition Prohibited by Technical Specifications." Also, during this time, Division 1 RHRSW subsystem was inoperable on two occasions. This is additionally reportable under 10 CFR 50.73(a)(2)(v)(B) "Any event or condition that could have prevented the fulfillment of the safety function of structures or systems that are needed to: Remove Residual Heat.

SIGNIFICANT SAFETY CONSEQUENCES AND IMPLICATIONS

"[here were no safety consequences or radiological releases associated with this event. At no time during this event was there a potential for endangering the public health and safety.

UFSAR 3.8.4.1.2 The RHR complex is a reinforced-concrete structure designed to serve as the ultimate heat sink for the reactor during normal shutdowns and postulated accident conditions. The structure is approximately 280 by 127 ft in plan and is located west of the reactor/auxiliary building. The complex consists of two divisions: Division I and Division II. Each division is comprised of a water reservoir, a pump house, a two-cell mechanical draft cooling tower, and two emergency diesel generators. Division I is in the south side, and Division IT is in the north side of the complex. Each division has the capacity to safely and orderly shut down the reactor during normal and/or accident conditions completely independent of the other.

The cooling tower system is designed such that it can function even if one tower division is damaged and rendered out of operation (UFSAR 3.5.1.3.2.2).

The RHRSW system transfers heat from the RHR system to the Ultimate Heat Sink (UHS). The UHS includes two 3,465,000-gal reservoirs. Mechanical Draft Cooling Tower (MDCT) fans cool the UHS. The ultimate heat sink design conforms to the requirements of USNRC Regulatory Guide 1.27.

Fermi 2

3. LER NUMBER

APPROVED BY OMB: NO. 3150-0104 EXPIRES: 10/31/2018 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 Past Operability determination for El 150F068B found that the MOV was unable to perform its design basis functions from May 3, 2017 at 5:48 am, when the RHRSW FCV was last successfully stroked under dynamic conditions, through May 24, 2017 at 4:04 pm, when the RHRSW FCV was returned to service.

The Division 1 RHRSW was available throughout the event except on two occasions. Division 1 of RHRSW was declared inoperable for MDCT Nozzle Cleaning activities on May 9, 2017 from 8:41 am to May 9, 2017 at 11:18 pm. Division 1 of RHRSW was again declared inoperable for MDCT Nozzle Cleaning activities on May 11, 2017 at 8:35 am through May 11, 2017 at 10:01 pm.

The UHS and RHRSW capabilities were analyzed and available equipment would have prevented exceeding design basis limits in the event of a design basis accident.

Each UHS/RHRSW division has the capacity to safely and orderly shut down the reactor during normal and accident conditions completely independent of the other division. The degraded Division 2 RHRSW flow, required an analysis when UHS/RHRSW Division 1 was out of service. Division 1 RHRSW was out of service on May 9, 2017 and May 11, 2017 for maintenance on MDCT Cell sparger nozzles. During maintenance, only a single Division 1 MDCT cell was made unavailable with the other Division 1 MDCT cell left intact and available. The analysis showed that sufficient cooling capability was available for the suppression pool with degraded Division 2 RHRSW flow. The availability of remaining Division 1 equipment coupled with the flow from the Division 2 RHRSW FCV (E1150F068B) would have been sufficient to remove the heat from the Division 2 RHR system.

CAUSE OF THE EVENT

The Direct Cause was Abnormal Stress- Failure of the Anti-Rotation Key (Dropped out of keyway).

The Apparent Cause is System/Equipment Operation — High Vibration. E1150F068B experiences high vibrations during throttling activities to support RHRSW initiation and shutdown. The anti-rotation key tack welds failed and the key dropped out of the keyway allowing the stem to rotate under dynamic conditions.

The first Contributing Cause is inadequate performance monitoring. The MOV Preventive Maintenance procedures do not inspect all anti-rotation devices.

The second Contributing Cause is troubleshooting. The MMA26 "Troubleshooting" pursued Routine Troubleshooting on May 5 through May 7, 2017. The Routine Troubleshooting did not identify a true fault failure mechanism. The limit switches were replaced. The FCV PMT produced satisfactory results which were accepted as completion of troubleshooting and repair activities. The valve was stroked in a static, no RHRSW flow environment without the anti-rotation key. The anti-rotation key failure was not considered as a failure mechanism on May 5, 2017. The troubleshooting performed was inadequate. The potential failure mechanisms were not all considered.

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.

3. LER NUMBER 1. FACILITY NAME Fermi 2 05000-341 2017 -003 -00

CORRECTIVE ACTIONS

The anti-rotation key was replaced and the RHRSW FCV passed PMT. Division 2 RHRSW was returned to service.

The anti-rotation key design is used on 17 other Generic Letter (GL96-05 "Periodic Verification of Design-Basis Capability of Safety-Related Motor-Operated Valves") program MOVs at Fermi 2. Walkdowns including keyway weld inspections have been completed. The inspections verified the integrity of the anti-rotation device.

There are no MOVs exhibiting the symptoms observed on the RHRSW FCV (El 150F068B) prior to the failure of the anti-rotation key.

Internal and external Operating Experience (OE) was searched. There was no other similar internal or external OE identified that identified anti rotation key welds as a failure mechanism.

The RHRSW FCVs, Division 2 E1150F068B and Division 1 E1150F068A, experience high vibrations during throttling activities to support RHRSW system startup and shutdown. Using System Operating Procedure (SOP) 23.208, "RHR Complex Service Water Systems," which directs the operation of RHRSW FCV E1150F068B during startup of Division 2 RHRSW (Procedure Section 5.4), the E1150F068B is throttled open for 5 seconds for one of the Division 2 RHRSW Pumps. One pump was then started. The RHRSW FCV is then throttled open to obtain 5400 gpm to 6300 gpm as indicated on El 1-R602B, "Division 2 RHR HX SW Flow Indicator." After flow is verified, the second pump is started, if available, before throttling E1150F068A (B) fully open.

Procedure SOP 23.208 is being evaluated for revision to prevent vibration damage on RHRSW FCV valves E115017068A and E1150F068B.

Procedures 35.306.003 "Motor Operator Periodic Inspection" and 35.306.020 "Motor Operated Valve Mini Periodic Inspection," will be revised to include inspection steps for anti-rotation devices on Globe Valves.

The functional testing and PMT were ineffective in discovering the failure and its associated pre-cursors on May 7, 2017. The troubleshooting performed was inadequate. The potential failure mechanisms were not all considered. An evaluation will be performed to assess additional training on the expectations for troubleshooting performance.

PREVIOUS OCCURENCES

None.

APPROVED BY OMB: NO. 3150-0104 EXPIRES: 10/31/2018 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.

Failed Component: Powell, William Company Globe Valve due to high system vibration transferred to the RHRSW FCV.