05000346/LER-2019-003, Anticipatory Reactor Trip System Actuated During Turbine Stop Valve Testing Due to the Closure of a Main Turbine Stop Valve

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Anticipatory Reactor Trip System Actuated During Turbine Stop Valve Testing Due to the Closure of a Main Turbine Stop Valve
ML19312A071
Person / Time
Site: Davis Besse Cleveland Electric icon.png
Issue date: 11/06/2019
From: Bezilla M
FirstEnergy Nuclear Operating Co
To:
Document Control Desk, Office of Nuclear Reactor Regulation
References
L-19-228 LER 2019-003-00
Download: ML19312A071 (5)
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LER-2019-003, Anticipatory Reactor Trip System Actuated During Turbine Stop Valve Testing Due to the Closure of a Main Turbine Stop Valve
Event date:
Report date:
Reporting criterion: 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)(A)
10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition
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)(A), Completion of TS Shutdown
10 CFR 50.73(a)(2)(i)
3462019003R00 - NRC Website
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text

FENOC' RrstEnergy Nuclear Operating Company Mark B. Bezilla Vice President, Nuclear November 6, 2019 L-19-228 ATTN: Document Control Desk United States Nuclear Regulatory Commission Washington, D.C. 20555-0001

Subject:

Davis-Besse Nuclear Power Station, Unit 1 Docket Number 50-346, License Number NPF-3 Licensee Event Report 2019-003 5501 North State Route 2 Oak Harbor, Ohio 43449 419-321-7676 10 CFR 50.73 Enclosed is Licensee Event Report (LER) 2019-003, "Anticipatory Reactor Trip System Actuated Unexpectedly During Turbine Stop Valve Testing due to the Closure of a Main Turbine Stop Valve." This event is being reported pursuant to 10 CFR 50.73(a)(2)(iv)(A).

There are no regulatory commitments contained in this letter or its enclosure. The actions described represent intended or planned actions and are described for information only. If there are any questions or if additional information is required, please contact Mr. James M; Vetter, Manager - Site Regulatory Compliance (Acting), at (419) 321-7393.

JCS Enclosure: LER 2019-003 cc: NRC Region Ill Administrator NRC Resident Inspector NRR Project Manager Utility Radiological Safety Board

).JRCFQRM 366* _:_~:_*_-~- - :....._ * --.

  • U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY 0MB: NO. 3150-0104 EXPIRES: 3/31/2020 (04-2018)

, the NRC may not conduct or sponsor, and a person is not required to respond to, the informatlon collection.

3.Page Davis-Besse Nuclear Power Station, Unit 1 05000 346 1 OF 4

4. Title:

Anticipatory Reactor Trip System Actuated During Turbine Stop Valve Testing due to the Closure of a Main Turbine Stop Valve

5. Event Date
6. LER Number
7. Report Date
8. Other Facilities Involved Month Year Year I Sequential I Rev Facility Name Docket Number Day Number No.

Month Day Year 05000 Facility Name Docket Number 09 07 2019 2019 -

003 00 11 06 2019 05000

9. Operating Mode
11. This Report is Submitted Pursuant to the Requirements of 10 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) 1 D 20.2201(d)

D 20.2203(a)(3)(ii)

D 50.73(a)(2)(ii)(B)

D 50. 73(a)(2)(viii)(B)

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)

~ 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) 95 D 20.2203(a)(2)(v)

D 50.73(a)(2)(i)(A)

D 50. 73(a)(2)(v)(D)

D 73.77(a)(2)(i)

- ld-20.2203(a)(2)(vi)-- -
  • - -Q-50,73(a)(2)(i)(B)-- ~

--- -E]-50:73(a)(2)(vii)* -

- El-73:77(a)(2)(ii)-- -

D 50.73(a)(2)(i)(C)

D Other (Specify in Abstract below or in YEAR 2019

3. LER NUMBER SEQUENTIAL NUMBER 003 REV NO.

00 The EHC bulk fluid, contained in the 800 gallon fluid reservoir, is filtered and conditioned to minimize EHC fluid degradation. The EHC filter system maintains the fluid within acceptable vendor specifications and minimizes the corrosion potential in the system there in improving system reliability by extending the service life of the hydraulic components.

DESCRIPTION OF EVENT

On September 7, 2019, the DBNPS was operating at approximately 95 percent power to perform scheduled Main Turbine Stop Valve (MSV) testing. Following successful valve testing of MSV 4 and 3; MSV 2 was tested.

When MSV 2 was stroked closed, MSV 4 unexpectedly closed. Subsequently, the ARTS instrumentation associated with the EHC System sensed low Emergency Trip Supply (ETS) pressure and sent a trip signal to the reactor protection system tripping the reactor at 1309 hours0.0152 days <br />0.364 hours <br />0.00216 weeks <br />4.980745e-4 months <br />. Based on a low ETS pressure condition this was the expected response of ARTS.

Initial unit response to the reactor trip was as designed, and all control rods fully inserted. Following the event, the operators took manual control of the Turbine Bypass Valves to reseat the Steam Generator Safety Valves [SG-RV] per procedure.

CAUSE OF EVENT

The Direct Cause of the reactor trip was the loss of ETS header pressure within the MSV 4 control pac which caused inadvertent actuation of the MSV 4 internal Disk Dump Valve. This resulted in an unexpected fast closure of MSV 4, during the fast closure of MSV 2 as part of its normal testing sequence. This sequence of events caused the ETS fluid pressure as sensed by ARTS to drop below 275 psig, the ARTS pressure setpoint, initiating an ARTS trip on Loss of Turbine-Generator. With ARTS channel 2 in bypass for testing, the low ETS pres,sure at MSV 4 met the two out of four-coincidence logic, causing ARTS to open the four (4) CRD trip breakers.

The Apparent Cause of the inadvertent actuation of the internal Disk Dump Valve of MSV 4 was due to improper seating/positioning of MSV 4 Fast Acting Solenoid Valve (FASV) most likely caused by mechanical binding/ sticking or foreign material excursion due to recent degradation of EHC fluid quality.

The Contributing Cause of recent degradation of EHC fluid quality was due to the purification of EHC fluid being interrupted from June 21 to August 6, 2019 because the EHC purification skid was out of service. While not exceeding the OEM limit, the fluid quality could have possibly contributed to preexisting fluid/internal pipe surface contamination and produced or released accumulated foreign material throughout the system.

ANALYSIS OF EVENT

A Probabilistic Risk Assessment (PRA) evaluation was performed for the September 7, 2019 automatic scram.

A conservative analysis of this uncomplicated plant scram results in a delta Core Damage Frequency (CDF)

==ANALYSIS OF EVENT==2. DOCKET NUMBER 346 YEAR 2019

3. LER NUMBER SEQUENTIAL NUMBER 003 that is well below the acceptable threshold of 1x10-6/yr as discussed in Regulatory Guide 1.17 4. The risk of this event is therefore, considered very low safety significance in accordance with the Regulatory Guidance.

Reportability Discussion:

REV NO.

00 The automatic actuation of the Reactor Protection System (RPS) while the reactor is critical is reportable within four hours of occurrence per 10 CFR 50. 72(b)(2)(iv)(B). On September 7, 2019, at 1553 hours0.018 days <br />0.431 hours <br />0.00257 weeks <br />5.909165e-4 months <br /> this event was reported to the NRC Operations Center (Event Number 54263).

This issue is being reported in accordance with 10 CFR 50.73{a)(2)(iv)(A), which requires reporting of any event or condition that resulted in manual or automatic actuation of the RPS, including a reactor scram or reactor trip.

All safety systems performed as required in response to the event, and no loss of safety function occurred.

CORRECTIVE ACTIONS

Completed Actions:

The MSV 4 FASV was replaced during the September 2019 forced outage. Normal valve testing under DB-SS-04150 was completed successfully following replacement during power ascension. ARTS Channel 2 was tested and found to be functioning as required.

Scheduled Actions:

During the DBNPS refueling outage scheduled for Spring of 2020, the following actions are scheduled for completion: MSV 1 FASV, MSV 2 FASV, and MSV FASV 3 will be replaced; the EHC reservoir will be cleaned, inspected, and refilled with new fluid; the two (2) EHC pump suction strainers will be cleaned and inspected; the Jet-Tube strainers for the Main Turbine Control Valves will be replaced; and the Servo-Valves for MSV 2 and Combined Intermediate Valves 1 and 2 will be replaced.

PREVIOUS SIMILAR EVENTS

DBNPS Licensee Event Report {LER) 2016-009, dated 11/9/16, reported a reactor trip event due to rainwater intrusion into the Main Generator Automatic Voltage Regulator (AVR) cabinet due to an open roof vent caused a lockout of the Main Generator, resulting in a trip of the Main Turbine and Reactor. Following the Reactor trip, the Steam Feedwater Rupture Control System (SFRCS) actuated due to high Steam Generator 1 level and initiated the Auxiliary Feedwater System. The most likely cause of the SFRCS actuation was a failed operational amplifier in the Integrated Control System (ICS}, causing the ICS to not reduce Feedwater flow to Steam Generator 1 following the Reactor trip. The cause and action taken in response to the 2016 reactor trip event are.unrelated to the cause of the event being reported in this LER and there have been no LERs at the DBNPS involving a similar reactor trip in the past three (3) years. Page 4 of 4

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