From kanterella
Jump to: navigation, search
Vc Summer.- Unit 1
Event date: 04-07-2017
Report date: 07-24-2017
Reporting criterion: 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications
3952017001R00 - NRC Website
LER 17-001-00 for V.C. Summer, Unit 1, Regarding C Main Feedwater Failure to Trip Results in Loss of Emergency Feedwater Auto Start Actuation Signal
Person / Time
Site: Vc Summer.- Unit 1, Summer South Carolina Electric & Gas Company icon.png
Issue date: 07/24/2017
From: Lippard G A
South Carolina Electric & Gas Co
Document Control Desk, Office of Nuclear Reactor Regulation
CR-17-01611, RC-17-0083
Download: ML17205A237 (5)

comments regarding burden estimate to the Informa':on Services Branch (T-2 F43), U.S. Nucicur Regulatory Commission, Washington. DC 70555 0001, or by e-mat to Infocollects.Resource©,nrc.gov, and to the Desk Officer, Office of Infornati

  • on and Regulatory Affa:rs, NEOB-10202, (3150-0104), Offior.: of Manage:nen'. airs Budget. Washington, BC 20503. Ifs means used to impose en information collection does not disp'ay a current!y vad OMB control number: the NRC may not conduct or sponsor, and a person is not required to respond to. the information colection.

05000- VC SUMMER - UNIT 1 395 I 1.0 EVENT DESCRIPTION On June 16, 2017, the station completed a past operability review and determined that an Emergency Feedwater Auto Start Actuation Signal was inoperable from November 12, 2016 until April 7, 2017. Technical Specification (TS) 3.3.2 Limiting Conditions for Operation (LCO) was entered due to there being less than the minimum number of channels operable for Motor Driven Emergency Feedwater Pump (MDEFWP) actuation per TS Table 3.3-3 Functional Unit 6.g.

'C' MFP (TPP0022C) failed to trip when given a trip signal from the Main Control Board (MCB), Digital Control System (DCS), and the local trip pull handle. Indications did not change when an attempt to trip was made from the MCB. The attempt to trip from DCS resulted in the DCS indicating "tripped" with no change in the 'C' MFP. Indications did not change when attempting to trip 'C' MFP locally. 'C' MFP was tripped by using an alternative method of starting the Emergency Lube Oil Pump and removing power from the Main and Auxiliary Lube Oil Pumps. There was no impact to the station as a result of this condition.

There were no issues with the feedwater isolation signal nor were there any issues with securing 'A' and 'B' MFPs during the RF23 downpower.

2.0 EVENT ANALYSIS As described in Virgil C. Summer Nuclear Station's Final Safety Analysis Report (FSAR) Section, the Feedwater System is designed to pump feedwater from the deaerator storage tank through two stages of high pressure heaters to the steam generators during normal operation, startup, and before shutdown. To perform this function, three 50% capacity, non-safety, variable speed, turbine driven feedwater pumps are included in the system. In the event of a loss of one feedwater pump, a power reduction may be necessary to prevent reactor trip, but the MFP turbines can be operated at runout capacity temporarily. There are no further specific criteria described for the MFP turbines in Section of the FSAR.

FSAR Section lists the automatic initiations of a MDEFWP. One of the five methods that provides an automatic MDEFWP initiation is a trip of all three MFPs.

TS 3/4.3.2 states that the Engineered Safety Feature Actuation System (ESFAS) instrumentation channels and interlocks shown in Table 3.3-3 shall be OPERABLE with their trip setpoints set consistent with the values shown in the Trip Setpoint column of Table 3.3-4 and with RESPONSE TIMES as shown in Table 3.3-5.

Action Statement 3.3.2.c states that with an ESFAS instrument channel or interlock inoperable take the ACTION shown in Table 3.3-3.

Table 3.3-3 Functional Unit 6.g states that Emergency Feedwater ESFAS instrumentation requires the Trip of MFPs to start Motor-Driven Pumps. In Modes 1 and 2 there must be three total channels (one per pump) of this trip present or Action 19 must be taken.

EsIlmated burden per response to comply vt,11h this mandatory collection request 00 boors. Reported lessons learned are incorporated into tbe licensing process and led back to industry. Send comments regarding burden estimate to tile Information Services Branch (T-2 F43), U.S. Nuclee Regu'atory COMMiSS.01, Washington. DC 20555-0001. or by e-mail to Infocollects.Resource(CMT.gov. and to the Desk Ofrcer. Office of Information and Regulatory Affairs, NEOB-10202, (3150-0104). Office of Management and Budget. Washington, DC 20503. If a means used In impose an information collection does no: disp:ay a curren:.y valid OMB control number, the NRC way rot concoct or sponsor, and a person is not required to respond to, the information coloction.

05000- VC SUMMER - UNIT 1 395 Action 19 states that with the number of OPERABLE channels one less than the Total Number of Channels. STARTUP and/or POWER OPERATION may proceed provided the following conditions are satisfied:

a. The inoperable channel is placed in the tripped condition within one hour.

b. The Minimum Channels OPERABLE requirement is met; however, the inoperable channel may be bypassed for up to two hours for surveillance testing of other channels per Specification

When the electronic and manual trips were attempted on April 7, 2017, no indication was received that the MFP turbine had tripped (i.e. stop valve closure, speed reduction, local indicator lights). Because the trip system would not actuate, one of three channels for MFP trip under TS 3/4.3.2 was inoperable.

LCO for TS 3.3.2 was entered at 21:15 on April 7, 2017, requiring the operable channel be placed in the trip condition within an hour. At 22:09, 'C' MFP was secured and LCO for TS 3.3.2 was exited. Therefore, Action 19 under TS 3.3.2 was satisfied as 'C' MFP was able to be placed in the tripped condition by securing the Lube Oil Pumps that supplied high pressure oil to the stop valves ultimately satisfying Emergency Feedwater ESFAS instrumentation requirements.

An evaluation found that water intrusion into the 'C' MFP oil system resulted in the corrosion of its carbon steel components such that the Secondary Operating Cylinder and Pilot Valve were bound. This bound condition would not allow the steam inlet valves to close resulting in the inoperable ESFAS.

The past adverse condition leading to the Emergency Feedwater ESFAS instrumentation channel being inoperable was the inability of the 'C' MFP to trip as a result of the Secondary Operating Cylinder and associated Pilot Valve being corroded. Review of MFP oil samples, which are taken on a monthly basis, indicated that possible water contamination began November 12, 2016. Since there is no evidence suggesting that the trip signals would have changed state from November 12, 2016 to April 7, 2017, 'C' MFP input to the Emergency Feedwater Auto Start Signal was determined to be inoperable for that period of time.

3.0 SAFETY SIGNIFICANCE This event has no impact on the Probabilistic Risk Analysis (PRA) model. The PRA model includes start signals for Emergency Feedwater from: Low Steam Generator Level, Manual, Load Sequencer, and Anticipated Transient Without SCRAM Mitigation System Actuation Circuitry (AMSAC). Loss of Feedwater is not modeled as a separate actuation.

4.0 PREVIOUS OCCURRENCE No previous occurrence within the last three years.

commrmts regarding burden estimate to the Information Services B'anch (T-2 F43). U.S. Nuclear Regulatory Commission, Washing-on, DC 20555-00Y.. or by e-mail to In'.3colle:As.ResourcegnT.gov, and to the Desk Officer, Office o' Inkymation and Reg:Ilalnry Affairs, NE013.10202, (3150 0104): OTce of Management and Butget, Wash'Von, DC 20503. If a means used to impose an information collection does rot display a currently yard OMB control mumbo-. the NRC May rot conduct or sponsor, and a person is rot required to respond to, the information collection.

05000- VC SUMMER - UNIT 1 395 5.0 CORRECTIVE ACTIONS 'C' MFP was tripped by starting the Emergency Lube Oil Pump and removing power from the Main and Auxiliary Lube Oil Pumps.

'C' MFP was repaired under Work Orders (WOs) 1704018, 1616104, and 1603349.

The WOs inspected the SV-12 Stern and Cylinder for damage and replaced parts as appropriate. It also inspected and cleaned the front standard trip assembly and other components as required. Leak detection for tube and tubesheet joint leaks on 'C' Main Feed Pump Lube Oil Cooler was also performed. Tube to tubesheet joints that were found to have leaks were rolled and the seals were tested to confirm that no further leakage was present.