05000414/LER-2018-001, Auxiliary Feedwater System Auto-Start Due to a Loss of Both Feedwater Pumps Signal
| ML18138A314 | |
| Person / Time | |
|---|---|
| Site: | Catawba  |
| Issue date: | 05/16/2018 |
| From: | Simril T Duke Energy Carolinas |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| CNS-18-024 LER 2018-001-00 | |
| Download: ML18138A314 (7) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(1), Submit an LER, Invalid Actuation 10 CFR 50.73(a)(2)(iv)(A), System Actuation 10 CFR 50.73(a)(2)(ii)(A), Seriously Degraded 10 CFR 50.73(a)(2)(viii)(B) 10 CFR 50.73(a)(2)(iii) 10 CFR 50.73(a)(2)(x) 10 CFR 50.73(a)(2)(v)(A), Loss of Safety Function - Shutdown the Reactor 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 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2)(i) |
| 4142018001R00 - NRC Website | |
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( ~ DUKE ENERGY CNS-18-024 May 16, 2018 U.S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, D.C. 20555
Subject:
Duke Energy Carolinas, LLC Catawba Nuclear Station, Unit 2 Docket No. 50-414 Licensee Event Report (LER) 414/2018-001-00 Tom Simril Vice President Catawba Nuclear Station Duke Energy CN01VP I 4800 Concord Road York, SC 29745 o: 803.701.3340 f: 803.701.3221 tom.simril@duke-energy.com 10 CFR 50.73 Pursuant to 10 CFR 50.73(a)(1) and (d), attached is LER 414/2018-001-00, entitled "Auxiliary Feedwater System Auto-Start Due to a Loss of Both Feedwater Pumps Signal."
This report is being submitted in accordance with 10 CFR 50.73(a)(2)(iv)(A).
There are no regulatory commitments contained in this letter or its attachment.
This event is considered to be of no significance with respect to the health and safety of the public.
Please direct any questions or concerns to Carrie Wilson, Sr. Engineer, at (803) 701-3014.
Sincerely, Tom Simril Vice President, Catawba Nuclear Station Attachment www.duke-energy.com
U.S. Nuclear Regulatory Commission CNS-18-024 May 16, 2018 Page 2 xc (with attachment):
C. Haney, Region II Administrator U.S. Nuclear Regulatory Commission Marquis One Tower 245 Peachtree Center Ave., NE Suite 1200 Atlanta, GA 30303 M. Mahoney U.S. Nuclear Regulatory Commission 11555 Rockville Pike Mailstop 0-881 A Rockville, MD 20852 J.D. Austin (without enclosure)
NRG Senior Resident Inspector INPO Records Center 700 Galleria Parkway, SE Suite 100 Atlanta, GA 30339-5943
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY 0MB: NO. 3150-0104 EXPIRES: 03/31/2020 (02-2018)
, the NRG may not conduct or sponsor, and a person is not required to respond to, the information collection.
- 3. Page Catawba Nuclear Station, Unit 2 05000 414 1
OF 5
- 4. Title Auxiliary Feedwater System Auto-Start Due to a Loss of Both Feedwater Pumps Signal.
- 5. Event Date
- 6. LER Number
- 7. Report Date
- 8. Other Facilities Involved I
Sequential I Rev Facility Name Docket Number Month Day Year Year Number No.
Month Day Year None 05000 Facility Name Docket Number 03 19 2018 2018 -
001 -
00 05 16 2018 None 05000
- 9. Operating Mode 11. This Report is Submitted Pursuant to the Requirements of 1 O CFR §: (Check all that apply)
D 20.2201 (b)
D 20.2203(a)(3)(i)
D 50.73(a)(2)(ii)(A)
D 50. 73(a)(2)(viii)(A)
D 20.2201 (d)
D 20.2203(a)(3)(ii)
D 50. 73(a)(2)(ii)(B)
D 50.73(a)(2)(viii)(B) 5 D 20.2203(a)(1)
D 20.2203(a)(4)
D 50.73(a)(2)(iii)
D 50. 73(a)(2)(ix)(A)
D 20.2203(a)(2)(i)
D 50.36(c)(1)(i)(A) 0 50. 73(a)(2)(iv)(A)
D 50.73(a)(2)(x)
- 10. Power Level D 20.2203(a)(2)(ii)
D 50.36(c)(1)(ii)(A)
D 50.73(a)(2)(v)(A)
D 73.71(a)(4)
D 20.2203(a)(2)(iii)
D 50.36(c)(2)
D 50.73(a)(2)(v)(B)
D 73.71(a)(5)
D 20.2203(a)(2)(iv)
D 50.46(a)(3)(ii)
D 50.73(a)(2)(v)(C)
D 73.77(a)(1) 000 D 20.2203(a)(2)(v)
D 50. 73(a)(2)(i)(A)
D 50.73(a)(2)(v)(C)
D 73.77(a)(2)(ii)
D 20.2203(a)(2)(vi)
D 50.73(a)(2)(i)(B)
D 50.73(a)(2)(vii)
D 73. 77(a)(2)(iii)
D 50.73(a)(2)(i)(C)
D Other* (Specify in Abstract below or in
EVENT DESCRIPTION
On March 19, 2018, Unit 2 experienced an Auxiliary Feedwater system (CA) auto-start due to Loss of both Feedwater (CF) Pumps signal while the unit was in Mode 5. Maintenance was supporting restoration of an Operations clearance which was closing the sliding links associated with the hydraulic oil pressure switches for the 28 Feedwater Pump Turbine (CFPT). At the time, 2A CFPT indicated TRIPPED on the main control board and Operator Aid Computer (OAC), and 28 CFPT indicated TRIPPED on the main control board, but indicated RESET on the OAC. Once 2 out of 3 hydraulic oil pressure switches were restored, 28 CFPT logic went to a TRIPPED condition. The 28 CA Pump then started due to a valid Loss of both CF Pumps signal. The Control Room then secured 28 CA Pump. The actuation occurred as designed and there was no adverse impact to plant operation.
TIMELINE:
3/17/2018 0810 28 CA removed from standby readiness 3/17/2018 2130 28 Solid State Protection System (SSPS) placed in Test 3/18/2018 0056 Tags were hung and verified for the clearances that support work on the hydraulic oil pressure switches for 28 CFPT On 3/18/18, CA/CF turbine interlock testing was performed. Prior to the testing, both feed pumps indicated tripped on the main control board and both U2 CA pump breakers were racked out. However, the 28 CFPT tripped annunciator was not lit and the OAC showed "reset." When the Senior Reactor Operator (SRO) leading the CA/CF turbine interlock testing questioned this, he found that these indications were due to a the clearance in place supporting work on the 28 CFPT hydraulic oil pressure switches. During the interlock testing, both Unit 2 CA pumps were racked to TEST. The test was completed with no issues.
3/18/2018 1645 28 CA Pump racked in (part of CA/CF interlock testing)
Following the testing, 2A CA Pump breaker was returned to racked out (its initial position) and the 28 CA Pump breaker was racked in to support upcoming 28 Engineered Safety Features (ESF) testing. At the time 28 CA Pump breaker was racked in, 28 SSPS was in test. As a result, the 28 CA PUMP AUTO-START DEFEAT pushbutton was not pressed.
(This is aligned with the direction provided in the procedure) Upon completion of racking in the 28 CA Pump breaker, the DEFEAT light was not lit, as expected.
3/18/2018 2050 28 SSPS placed in Normal (preparation for 28 ESF testing)
The completed procedure for placing 28 SSPS in Normal was reviewed. The procedure includes steps to defeat CA Pump Auto Start prior to returning 28 SSPS to Normal. This was in accordance with the 28 ESF procedure alignment.
ESF testing preparations were ongoing. A procedure step resets the 28 CA Pump Auto Start Defeat. This step was performed during preparations and prior to removing tags supporting 28 CFPT hydraulic oil pressure switch replacement.
3/19/2018 0306 Tags were approved for removal by the clearance. The work was completed on the hydraulic oil pressure switches for 28 CFPT and calibration was to be performed after clearance was lifted.
28 CA pump auto start occurred when the sliding links were restored to the closed position in accordance with the clearance removal. When the sliding links were closed, this change in logic completed the 2/3 logic for low pressure which caused the 28 CA auto start.
3/19/2018 0423 Outage Log Entry: Initial investigation of 28 CFPT trip and 28 CA auto start indicates that the isolation for the pressure switch replacement caused the circuitry to indicate reset for the 28 CFPT TECHNICAL INFORMATION ABOUT LOGIC FUNCTION:
The 28 CFPT trip signal is fed from 2/3 logic from three pressure switches. When these pressure switches sense pressure <75psig, their output contacts go closed. Each one of these pressure switches pick up control relays which are configured to check for the 2/3 logic. If the 2/3 logic is met, there are more control relays that enable the logic for the Annunciator, 28 CFPT Tripped OAC point, and 28 CA Auto-Start.
When the sliding links were opened, it looked the same to the circuit as if the three pressure switches were seeing normal system pressure (>75psig). This is why the indications were showing 28 CFPT as RESET on the OAC.
When the sliding links were closed, the three pressure switches were reading <75psig. The 2/3 logic was met, and the CF and CA system responded as designed.
CAUSAL FACTORS:
The cause of this event was determined to be that the system impacts associated with the clearance and restoration were not sufficiently evaluated to prevent an undesired system response with the CF and CA Systems, which resulted in an auto-start of the 28 CA Pump.
CORRECTIVE ACTIONS
Completed:
- 1. Issue a crew learning via a stand down with all qualified clearance preparers, clearance reviewers, clearance approvers, and subject matter experts that reinforces the responsibilities associated with assessing and understanding of plant impacts, and the standards associated with logic circuits, leads, and instrumentation. Establish the expectation that Clearance SME Sheets "Identify Plant Impacts" section effectively document results of SME review.
- 2. Complete a Performance Analysis to determine if clearance preparers, reviewers, and approvers are able to consistently and effectively apply the standards associated with understanding the impact of clearances on logic circuits.
Planned:
- 1. Ensure work on CA auto-start circuitry is not scheduled during Aux Shutdown Panel Transfer Testing, ESF Testing, or CA/CF Interlock testing.
SAFETY ANALYSIS
At the time of the CA system actuation, Unit 2 was in Mode 5 with the Residual Heat Removal system in service to remove decay heat. No actual loss of feedwater occurred. Both the CF system and CA system had previously been removed from service. Per Tech Spec 3.3.2, the signal that caused the actuation, Trip of all Main Feedwater Pumps, is required in Modes 1 and 2. Per Tech Spec 3-7.5, the CA system is required to be operable in Modes 1, 2, 3 and Mode 4 when the steam generators are relied upon for heat removal.
In conclusion, this event is considered to be of low safety significance as decay heat removal was not challenged. The CA system responded as designed. There was no impact to the health and safety of the public.
ADDITIONAL INFORMATION
A three year search of the Catawba corrective action database revealed no other CA actuation events resulting from insufficient evaluation of the impact of clearances on logic circuits.
This event is not considered a Safety System Functional Failure as defined in NEI 99-02, Regulatory Assessment Performance Indicator Guidelines. Page 5
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