05000331/LER-2019-001, Manual Reactor Scram Due to Lowering Reactor Water Level

Manual Reactor Scram Due to Lowering Reactor Water Level

ML19171A191
Person / Time
Site:	Duane Arnold
Issue date:	06/17/2019
From:	Dean Curtland NextEra Energy Duane Arnold
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
NG-19-0084 LER 2019-001-00
Download: ML19171A191 (5)

LER-2019-001, Manual Reactor Scram Due to Lowering Reactor Water Level

Event date:
Report date:
3312019001R00 - NRC Website

text

June 17, 2019 U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, D.C. 20555-0001 Duane Arnold Energy Center Docket 50-331 Renewed Op. License No. DPR-49 Licensee Event Report 2019-001 NEXTeraM ENERGX~

DUANE ARNOLD NG-19-0084 10 CFR 50.73 Please find attached the subject report submitted in accordance with 10 CFR 50.73. This letter makes no new commitments or changes to any existing

commitments

Dean Curtland Site Director, Duane Arnold Energy Center NextEra Energy Duane Arnold, LLC cc:

Administrator, Region Ill, USNRC Project Manager, DAEC, USNRC Resident Inspector, DAEC, USNRC NextEra Energy Duane Arnold, LLC, 3277 DAEC Road, Palo, IA 52324

NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY 0MB: NO. 3150-0104 EXPIRES: 0313112020 (04-2018)

, the NRC may not conduct or sponsor, and a oerson is not reouired to resoond to the information collection.

13. Page Duane Arnold Energy Center 05000-331 1 OF 4

4. Title Manual Reactor Scram Due to Lowering Reactor Water Level

5. Event Date

6. LER Number

7. Report Date

8. Other Facilities Involved Sequential Rev Facility Name Docket Number Month Day Year Year Month Day Year Number No.

N/A N/A 2019 0001 17 2019 Facility Name Docket Number 4

20 2019 00 6

N/A N/A

9. Operating Mode N/A N/A N/A

~bstract (Limit to 1400 spaces, i.e., approximately 14 single-spaced typewritten lines)

On April 20, 2019, while operating at 100% power, NextEra Energy Duane Arnold (DAEC) experienced a trip of both reactor feed pumps due to a loss of suction pressure. As a result, plant operators inserted a manual scram. All control rods inserted, as required. As a result of the feed pump trips and scram, the High Pressure Coolant Injection (HPCI) and Reactor Core Isolation Cooling (RCIC) automatically injected. In addition, containment isolations occurred, as expected for this event. This resulted in a 4-hour event report to the NRC under 10 CFR 5_0. 72 section 50. 72(b)(2)(iv)(A) - ECCS Injection, 50. 72(b)(2)(iv)(B) - RPS Actuation - Critical, 50.72(b)(3)(iv)(A) - Valid Specific System Actuation (reference EN#54012). The root cause of this event was brittle fracture of a condensate demineralizer in-line air filter bowl due to heat related age degradation. This event was of very low safety significance and had no impact on public health or safety. There were no systems, structures, or components inoperable at the time of the event and none that contributed to the event. This event is reportable pursuant to 10 CFR 50. 73(a)(2)(iv)(A). In addition to the event that occurred on April 20, 2019, this LER is reporting a related event that occurred on April 21, 2019 that resulted in an invalid Primary Containment Isolation System. There were no radiological releases associated with either of these event.

NRC FORM 366 (02-2018)

I.

Description of Event

YEAR 2019

3. LERNUMBER SEQUENTIAL NUMBER

- 001 REV NO.

- 00 On April 20, 2019, while operating at 100% power, DAEC experienced a trip of both reactor feed pumps. As a result, plant operators inserted a manual scram. All control rods inserted, as required. As a result of the feed pump trips and scram, HPCI and RCIC automatically injected. Also, containment isolations occurred, as expected for this event. This resulted in a 4-hour event report to the NRG under 10 CFR 50.72 section 50.72(b)(2)(iv)(A) - ECCS Injection, 50.72(b)(2)(iv)(B) - RPS Actuation - Critical, 50.72(b)(3)(iv)(A) - Valid Specific System Actuation (reference EN#54012).

The reactor feedwater pumps tripped on low suction pressure. The low suction pressure condition was caused by the condensate filter effluent valves from the condensate demineralizers going closed due to a loss of instrument air to condensate filter demineralizer control panel 1 C80.

The direct cause of the loss of instrument air pressure was the catastrophic failure of the in-line air filter bowl located upstream of PCV-80 (internal to 1 CSO).

In addition to the event that occurred on April 20, 2019, this LER is reporting a related event that occurred on April 21, 2019 that resulted in an invalid PCIS. Specifically, on April 21, 2019, at 1101, an invalid Primary Containment Isolation System (PCIS) Group 1 isolation initiated. This isolation occurred while taking the reactor Mode Switch from Shutdown to Startup & Hot Standby. The invalid actuation occurred due to the reactor Mode Switch traveling slightly beyond the Startup & Hot Standby position. A review of the RPS and PCIS logic schematics confirmed that any movement of the reactor Mode Switch past the Startup

& Hot Standby position will interrupt the Condenser High Backpressure logic and trip the Group 1 logic. Therefore, the system actuated as designed.

II.

Assessment of Safety Consequences

Due to the isolation of the condensate demineralizer effluent valves, the feed water suction pressure lowered to the trip set point of the feed water pumps. The plant response was as expected for a loss of feed water transient as described in Updated Final Safety Analysis Report (UFSAR) Chapter 15.1. The analyzed loss of feed water transient assumes HPCI is not able to operate. However, in this case, HPCI remained operable and injected in conjunction with RCIC after the initial loss of feed water and manual scram. Page 2 of 4 (04-2017)

U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY 0MB: NO. 3150-0104 EXPIRES: 3/31/2020 f

2.

\\

• .P LICENSEE EVENT REPORT {LER)

CONTINUATION SHEET (See NUREG-1022, R.3 for instruction and guidance for completing this form http://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1022/r3[J

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

Duane Arnold Energy Center 05000-331 YEAR 2019

3. LER NUMBER SEQUENTIAL NUMBER

- 001 As reactor water level recovery was in progress, HPCI was manually tripped to reduce cooldown rate. To further reduce the cooldown rate, the main steam lines were manually isolated. Reactor level continued to rise and RCIC eventually tripped on high level. A decision was made to continue controlling reactor level with RCIC, even though feed water was available through the condensate demineralizer bypass. RCIC was manually restarted initially to control reactor pressure and subsequently to control level and pressure by transferring RCIC pump discharge from condensate storage tanks to the reactor vessel. RCIC was primarily used to reduce reactor pressure and maintain level over the following 13 hours1.50463e-4 days <br />0.00361 hours <br />2.149471e-5 weeks <br />4.9465e-6 months <br />.

An immediate investigation of the event determined that the plant and operator response was as expected. Therefore, this event was of very low safety significance and had no impact on public health or safety. There were no systems, structures, or components inoperable at the time of the event that contributed to the event. There were no radiological releases associated with this event.

This event did not result in a Safety System Functional Failure.

Ill.

Cause of Event

A root cause evaluation was completed for the manual scram event and the following root and contributing causes were determined:

Root Cause: Brittle fracture of a condensate demineralizer in-line air filter bowl due to heat related degradation.

Contributing Cause

Organizational failure to recognize risk associated with using a non-standard alteration of filter bowl assembly.

For the invalid PCIS Group 1 isolation event, the cause was from the reactor Mode Switch traveling slightly beyond the Startup & Hot Standby position.

IV.

Immediate Corrective Action

Prior to plant restart, repairs to the air supply to the condensate demineralizer were completed under EC 293108 and work order 40660355. This modification removed the in-line air filter and replaced it with a piece of tubino per the applicable des ion specifications.

REV NO.

- 00 Page 3 of 4 (04-2017)

U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY 0MB: NO. 3150-0104 EXPIRES: 3/31/2020 LICENSEE EVENT REPORT (LER)

CONTINUATION SHEET (See NUREG-1022, R.3 for instruction and guidance for completing this form http://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1022/r3/l

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

Duane Arnold Energy Center 05000-331 Corrective Actions to Prevent Recurrence for Manual Scram Event YEAR 2019

3. LER NUMBER SEQUENTIAL NUMBER

- 001 Revise component criticality for in-line air filters that could cause a plant transient or unplanned Limiting Condition for Operability as Single Point Vulnerabilities.

Corrective Actions for Invalid Group 1 Isolation Train Licensed Operators on risk mitigating strategies when operating the reactor Mode Switch.

V.

Additional Information

Previous Similar Occurrences:

A review of NextEra Energy Duane Arnold LERs from the previous 5 years identified the following event:

LER 2018-004 - Automatic. Reactor Scram due to Feedwater Regulating Valve Failure EIIS System and Component Codes:

LO - Instrument Air Supply System

Reporting Requirements

This activity is being reported pursuant to the requirements of 10 CFR

50. 73(a)(2)(iv)(A).

REV NO.

• 00 Page 4 of 4