05000458/LER-2018-007, Manual Reactor Scram Due to Reactor Recirculation Pump Trip Caused by Transformer Failure

Manual Reactor Scram Due to Reactor Recirculation Pump Trip Caused by Transformer Failure

ML18304A436
Person / Time
Site:	River Bend
Issue date:	10/31/2018
From:	Maguire W Entergy Operations
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
RBG-47907 LER 2018-007-00
Download: ML18304A436 (6)

LER-2018-007, Manual Reactor Scram Due to Reactor Recirculation Pump Trip Caused by Transformer Failure

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2) 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)(iv)(A), System Actuation
4582018007R00 - NRC Website

text

• =' Enter-gx RBG-47907 October 31, 2018 Attn: Document Control Desk U.S. Nuclear Regulatory Commission 11555 Rockville Pike Rockville, MD 20852-2738

Subject:

Dear Sir or Madam:

Licensee Event Report 50-458 I 2018-007-00 River Bend Station, Unit 1 Docket No. 50-458 License No. NPF-47 Entergy Operations, Inc.

River Bend Station 5485 U.S. Highway 61 N St. Francisville, LA 70775 Tel 225-381-4374 William F. Maguire Site Vice President In accordance with 10 CFR 50.73, enclosed is the subject Licensee Event Report. This document contains no commitments. If you have any questions, please contact Mr. Tim Sch en k at 225-381-4177.

Sincerely, WFM/twf Enclosure cc:

(with Enclosure)

U.S. Nuclear Regulatory Commission Attn: Ms. Lisa M. Regner, Project Manager 09-0-14 One White Flint North 11555 Rockville Pike Rockville, MD 20852 U.S. Nuclear Regulatory Commission Region IV 1600 East Lamar Blvd.

Arlington, TX 76011-4511

RBG-47907 Page 2 of 2 NRC Senior Resident Inspector Attn: Mr. Chris Speer 5485 U.S. Highway 61, Suite 1 St. Francisville, LA 70775 Public Utility Commission of Texas Attn: PUC Filing Clerk 1701 N. Congress Avenue P. O. Box 13326 Austin, TX 78711-3326 INPO (via ICES reporting)

RBF1-18-0186

NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO.3150'()104 EXPIRES: 03/31/2020 (04-2018)

Estimated burden per response to comply with th~ mandalofy collection request 80 hou...

~f.I...vAJtro,,<.,)o LICENSEE EVENT REPORT (LER)

RepOfte<j IeMOm Ie.rned are incorporated Into the lcenslng proaoss and fad back to IndUStry. Send comments regardng bu'den estimate to the Information ServIces Branch

+~o~

(T-2 F43), U.S. Nuclear Regulalofy Commission, Waslingtoo. DC 2055!HlOOt, or by ~I n

(See Page 2 for required number of digits/characters for each block) to Infacolects.ReSO\\ltO@nrc.gov, and to the Desk OftIcer, OftIce of Information and 0

Regutatory AffaI,., NEOB-l0202. (31~ 1 ().4 ), Office or Managemenl and 8udge~

~

(See NUREG-1022, R.3 for instruction and guidance for completing this form

'l:,

~

Washington, DC 20503. If a means used 10 Impose an Information colectlon does oot "i-.,

.0" blt~):lIwww nr!;; gov/reading-rm/doc-coliectiQns/nuregslstafflsr1 Q~,1[31 )

display a ClITentiy valid OM8 controt number. the NRC may not conduct or sponsor, and a p.""" Is not required to respond to, the Information coIection.

3. Page River Bend Station - Unit 1 458 4

05000 1

OF

4. Title Manual Reactor Scram due to Reactor Recirculation Pump Trip Caused by Transformer Failure

5. Event Date

6. LER Number

7. Report Date

8. Other Facilities Involved Month Day Vlar Year I SequentIal I Rev Month Day Year Facility Name Docket Number Number No.

NA 05000 NA 02 01 2018 2018 007 00 Facility Name Docket Number 10 31 2018 NA 05000 NA

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)(vlil)(A)

D 20.2201 (d)

D 20.2203(a)(3)(II)

D 50.73(a)(2)(II)(B)

D 50.73(a)(2)(vlll)(B) 1 D 20.2203(a)(1 )

D 20.2203(a)(4)

D 50.73(a)(2)(ill)

D 50.73(a)(2)(lx)(A)

D 20.2203(a)(2)(1)

D 50.36(c)(1 )(I)(A) 0 50.73(a)(2)(lv)(A)

D 50.73(a)(2)(x)

10. Power Level D 20.2203(a)(2)(1I)

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)(lv)

D 50.46(a)(3)(II)

D 50.73(a)(2)(v)(C)

D 73.77(a)(1 )

27 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)(1)

D 20.2203(a)(2)(vl)

D 50.73(a)(2)(I)(B)

D 50.73(a)(2)(vll)

D 73.77(a)(2)(II)

D 50.73(a)(2)(I)(C)

D Other (Specify in Abstract below or in quality. Although the value for the point closely matched core monitor predicted flow for this plant condition and was consistent with what flow should be, the color and quality of the computer point led to confusion, The control room team engaged Nuclear Information Technology to help resolve the anomaly. The control room team attempted to use several alternate indications of core flow, but ultimately was unable to reconcile the anomaly with the quality and color of WTX. The decision was made to conservatively shutdown the reactor. A manual reactor scram was initiated at 10:57. Nuclear IT contacted the operating crew several minutes after the shutdown to inform them that the data provided by WTX was indeed valid.

All plant systems responded as expected following the scram. The cause of the Reactor Recirculation Pump 'B' trip was determined to be a fault in the pump motor transformer. The transformer was replaced and the plant was returned to normal

full power operation.

D.CAUSE Reactor Recirculation Pump 'B' Trip IThe Reactor Recirculation Pump motor transformer was sent to a third party vender for an as found inspection. An internal ransformer fault was found on the high voltage 'A' phase winding connection from the winding exit leads to the transformer bushing. This connector was crimped together with some amount of fill (solid copper bar) added to provide uniform pressure across the crimp. The fill used was inappropriately sized resulting in an inadequate crimp. This flaw in addition to thermal cycling of the connection/crimp over the service period of the transformer (through pump starts/shifts to fast speed),

developed a hotspot due to higher resistance and, ultimately, resulted in connection failure.

Uncertainty of Computer Data Point Validity IThe quality of WTX in this case is determined by the input used in the calculation that produces the data. If the default input is used in the calculation WTX quality is flagged as "Good". If an alternate input value is used WTX quality is flagged as "Suspect".

Because RBS was in Single Loop Operation (SLO), WTX was automatically calculated using the core plate delta-pressure based value which is an alternate method. This alternate method is accurate regardless of pump speed and loop flows.

However, because the input used in the calculation was an alternate method, WTX quality was tagged as "Suspect". All data points tagged as "Suspect" are automatically turned to magenta in ERIS.

To conclude, for this event the Validated Core Flow ERIS point, WTX, which was referenced by the Operators per AOP-0024 and GOP-0004, was accurate regardless of pump speed and loop flows. The point was magenta on ERIS because it was correctly using an alternate method to calculate core flow using core plate delta-pressure. The alternate method was in use due to SLO.

E. REPORTABILITY

This event is being reported under 10CFR50.73(a)(2)(iv)(A) as an event or condition that resulted in manual or automatic actuation of the Reactor Protection System including a reactor scram or a reactor trip.

F. CORRECTIVE ACTIONS

iAOP-0024 and GOP-0004 were revised to include diverse computer points and a means to determine core flow that is not dependent on plant computer systems.

Irhe color for a "Suspect" data point has been changed to orange.

IAn extent of condition review was performed to determine if other transformers with the same vulnerability encountered with

~he failed transformer exist.

G. SAFElY SIGNIFICANCE Irhe condition of the station after the trip of Reactor Recirculation Pump 'B' during the upshift from slow to fast speed was stable and permissible in accordance with Technical Specifications and station normal operating procedures. The inability to reconcile the ERIS computer point was aggressively pursued by the station, but did not reach a conclusion until after the plant had been shut down. At no time was River Bend Station required to shut down by any station procedures or Technical Specification. The decision to shutdown was conservative, deliberate and controlled. This event had minimal significance to he health and safety of the public.

H. PREVIOUS SIMILAR OCCURRENCES The WTX data point was noted as "Suspect" and magenta in color in 2012 during SLO operation. However, this information was not adequately distributed to Operations Department Training nor was it added to AOP-0024 or GOP-0004.

There have been several instances of the Reactor Recirculation Pumps tripping during transfers to fast speed. However, his was the first time a Reactor Recirculation Pump tripped due to a failure of the pump motor transformer.

(NOTE: Energy Industry Identification System component function identifier and system name of each component or system referred to in the LER are annotated as (""XX**) and [XX], respectively.) Page 4

of 4