05000324/LER-2017-002

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LER-2017-002, Plant Mode Change with Primary Containment Inoperable
Brunswick Steam Electric Plant (Bsep) Unit 2
Event date: 04-13-2017
Report date: 06-09-2017
Reporting criterion: 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications

10 CFR 50.73(a)(2)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident
Initial Reporting
ENS 52679 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident
3242017002R00 - NRC Website
LER 17-002-00 for Brunswick, Unit 1, Regarding Foreign Material in Switch Results in Unplanned Automatic Start of Emergency Diesel Generators
ML17163A366
Person / Time
Site: Brunswick Duke energy icon.png
Issue date: 06/12/2017
From: Gideon W R
Duke Energy Progress
To:
Document Control Desk, Office of Nuclear Reactor Regulation
References
BSEP 17-0054
Download: ML17163A366 (5)


This event is reportable per 10 CFR 50.73(a)(2)(v)(D) because the plant experienced a loss of the safety function of a system designed to mitigate the consequences of an accident. Since the containment was rendered inoperable by having the Drywell and Suppression Chamber airspaces in communication with each other, the safety function was lost.

On April 13, 2017, Unit 2 was in Mode 4 preparing to exit a refueling outage. At 20:48 EDT, Control Room personnel began ventilating the primary containment in preparation for a personnel entry into the Drywell to perform minor maintenance. The ventilation procedure requires valves be opened from the Suppression Chamber atmosphere and the Drywell atmosphere into a shared ventilation line. With both atmospheres communicating, the Primary Containment is not operable. However, Primary Containment is not required to be operable with the unit in Mode 4.

When the maintenance was completed in the Drywell, Control Room personnel resumed preparations for starting up the reactor. At 23:47 EDT, the reactor mode was changed from Mode 4 to Mode 2. In Mode 2, Energy Industry Identification System (EllS) codes are identified in the text as [XX].

Background

Initial Conditions This event is reportable per 10 CFR 50.73(a)(2)(i)(B) because the plant entered a condition which is prohibited by the plant's Technical Specifications (TS). Specifically, TS 3.6.1.1 requires the primary containment to be operable in Modes 1, 2, and 3. With the drywell and suppression chamber atmospheres communicating, the containment is inoperable. Additionally, TS Limiting Condition for Operation (LCO) 3.0.4 requires all LCOs to be met for the plant condition to be entered, prior to entry. Primary containment operability is required in Mode 2 (i.e., Startup). Therefore, at 23:47 EDT on April 13, 2017, when the plant changed modes from Mode 4 to Mode 2 without meeting the LCO for primary containment, this failed to meet TS LCO 3.0.4.

This event is also reportable per 10 CFR 50.72(b)(3)(v)(D) via an 8-hour telephone report. The telephone report was completed as Event Number 52679 at 07:37 EDT on April 14, 2017.

On April 13, 2017, at approximately 23:47 Eastern Daylight Time (EDT), Unit 2 was in Mode 4 (i.e. Cold Shutdown) in preparation for exiting a refueling outage. At that time, the ventilation valves for both the Drywell and Suppression Chamber were open to ensure the atmosphere in the containment was breathable for personnel performing maintenance in the Drywell.

Reportability Criteria

Event Description

(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/)

CONTINUATION SHEET

APPROVED BY OMB: NO. 3150-0104 EXPIRES: 03/31/2020 comments regarding burden estimate to the Information Services Branch (T-2 F43), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e-mail to used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

2017 - 002

3. LER NUMBER

- 000 the Primary Containment is required to be operable. Since it was still being ventilated as described above, it was not operable. Therefore, this mode change was not allowed per TS 3.0.4.

On April 14, 2017, at 00:15 EDT (i.e., 28 minutes later), a licensed operator was performing a routine survey of Control Room panels to verify expected plant condition and valve alignments during reactor startup. He observed the Drywell and Suppression Chamber atmospheres being simultaneously vented.

He immediately notified other shift personnel, and by 00:30 EDT on April 14, 2017, the ventilation paths were closed, terminating the event. The total time during which Primary Containment was inoperable while in Mode 2 was 43 minutes.

This event occurred because Control Room personnel did not issue an LCO for tracking (i.e., “tracking LCO”) primary containment inoperability in preparation for eventual plant mode change and startup.

Procedure 0OI-01.01, “BNP Conduct of Operations Supplement,” provides instructions for initiating a tracking LCO when a structure, system, or component (SSC) is removed from service while the plant is in a mode where that SSC is not required. In this instance, Unit 2 was in Mode 4 when the Drywell and Suppression Chamber were simultaneously vented, rendering the primary containment inoperable. Since the primary containment is not required in Mode 4, a tracking LCO should have been initiated to ensure it was restored to operable status before entering Mode 2. This step was not performed, so the condition was not identified during preparations for changing the plant mode.

The function of the primary containment is to isolate and contain fission products released from the Reactor Primary System following a design basis Loss of Coolant Accident (LOCA) and to confine the postulated release of radioactive material. The primary containment consists of two volumes, a Drywell and a Suppression Chamber. Steam and water piping for the nuclear process is located within the Drywell. A large volume of water is located in the Suppression Chamber for the rapid suppression of steam. The atmospheres of these two volumes are normally isolated from each other. In the event of a LOCA, steam released into the Drywell passes through downcomers into the Suppression Chamber below the water level where it is quenched. Should a LOCA occur while the Drywell and Suppression Chamber atmospheres are communicating, released steam could bypass the downcomers, potentially pressurizing both volumes of the containment. The containment would be susceptible to being pressurized beyond its capability, potentially causing containment to fail.

In this event, the two atmospheres of the primary containment were allowed to communicate via a shared ventilation line as described previously. During this time, the plant was emerging from a refueling outage, and the reactor coolant was still well below 212 degrees F as determined by the inlet temperature of the Residual Heat Removal [BO] heat exchanger and by the loop temperatures of the Reactor Recirculation [AD] system. If a LOCA had occurred during this time, the result would have been loss of cold water into the otherwise intact primary containment. No pressurization of the containment could have resulted. It Safety Assessment Event Cause (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/)

CONTINUATION SHEET

APPROVED BY OMB: NO. 3150-0104 EXPIRES: 03/31/2020 comments regarding burden estimate to the Information Services Branch (T-2 F43), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e-mail to used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

2017 - 002

3. LER NUMBER

- 000 should be noted that the ventilation valve alignment was identified promptly by a routine inspection of Control Room panels and was corrected within 15 minutes of discovery (i.e., 43 minutes from changing from Mode 2 to Mode 4).

Corrective Actions

The primary containment was restored to operable status at 00:30 on April 14, 2017.

A remediation plan was developed and implemented to assess the Shift Manager and Control Room Supervisor for watchstanding and being reinstated as appropriate. This action is complete.

Previous Similar Events

No events were identified in the past three years in which the primary containment was made inoperable when it was required to be operable.

Commitments This report contains no new regulatory commitments.

This event did not result in any adverse impact on the health and safety of the public. This analysis applies to the plant condition that existed at the time with reactor coolant below 212 degrees F.

(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/)

CONTINUATION SHEET

APPROVED BY OMB: NO. 3150-0104 EXPIRES: 03/31/2020 comments regarding burden estimate to the Information Services Branch (T-2 F43), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e-mail to used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

2017 - 002

3. LER NUMBER

- 000