05000400/LER-2016-004

From kanterella
Jump to: navigation, search
LER-2016-004, Reactor Trip and Safety Injection During Turbine Control Testing at Low Power
Shearon Harris Nuclear Power Plant - Unit 1
Event date: 10-08-2016
Report date: 12-07-2016
Reporting criterion: 10 CFR 50.73(a)(2)(iv)(A), System Actuation
4002016004R00 - NRC Website
LER 16-004-00 for Shearon Harris, Unit 1, Regarding Reactor Trip and Safety Injection During Turbine Control Testing at Low Power
ML16342B682
Person / Time
Site: Harris Duke energy icon.png
Issue date: 12/07/2016
From: Hamilton T M
Duke Energy Progress
To:
Document Control Desk, Office of Nuclear Reactor Regulation
References
HNP-16-108
Download: ML16342B682 (4)


comments regarding burden estimate to the FOIA, Privacy and Information Collections Branch (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e-mail to Inf000llects.Resource@nrc.gov, and to the Desk Officer, Office of Information and Regulatory Affairs, 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.

05000- Shearon Harris Nuclear Power Plant - Unit 1 400 Note: Energy Industry Identification System (EllS) codes are identified in the text within brackets [ ].

A. Background

Event Date: October 8, 2016 Initial Mode: 1 Initial Reactor Power: -8 percent Event Time: 0150 EDT Final Mode: 3 Final Reactor Power: 0 percent This event is reportable per 10 CFR 50.73(a)(2)(iv)(A) as "an event or condition that results in valid actuation of any of the systems listed in paragraph (a)(2)(iv)(B) of [10 CFR 50.73]..." due to actuation of the reactor protection system [JC], general containment isolation signal [JE], emergency core cooling systems [BQ], auxiliary feedwater systems [BA], and emergency diesel generators [EK]. All actuated safety systems functioned as designed.

B. Event Description

On October 8, 2016, at 0150, the Shearon Harris Nuclear Power Plant (Harris) was reducing power to enter a planned refueling outage (RFO-20). The plant was at approximately 8 percent power in MODE 1 when the unit experienced an unplanned reactor trip with a safety injection (SI) and main steam line isolation (MSLI). The SI was terminated in 6 minutes with pressurizer level at 80 percent. Pressurizer safety valves did not actuate.

The licensee was performing testing on the turbine mechanical overspeed trip system. The digital-electrohydraulic (DEH) control system [TG] was in throttle valve (TV) [FCV] control. Operators initiated the swap from TV control to governor valve (GV) [FCV] control per the test procedure. The GVs unexpectedly opened to about 15 percent with the TVs still at full open. This valve alignment caused excessive steam flow through the main turbine [TRB], drawing down the steam generator (SG) [SG] pressure. This resulted in the actuation of SI and MSLI signals on Low Steam Line Pressure (rate compensated), as steam line pressure rapidly dropped from 1050 psig to 1000 psig. The SI and MSLI signal initiated a reactor trip, turbine trip, feedwater isolation signal, and closed the main steam isolation valves.

This event was caused by a combination of degraded equipment within the DEH control system, which failed to align the TVs and GVs to properly control turbine speed. Two of the five high-pressure hydraulic accumulators [ACC] were out-of- service at the time of the event. In addition, an oil pressure switch [PS] was found to be improperly functioning. The combination of high hydraulic fluid demand due to the TV to GV control swap and the degraded equipment caused the GVs to not properly position to control turbine speed.

The high-pressure DEH accumulators are Parker Hydraulics series A7L hydraulic accumulators. One accumulator had been found with low pressure in August 2015 and was scheduled for repair. A second accumulator was found to have low pressure during troubleshooting following the event. The pressure switch is a United Electric Controls series 400 switch, and was identified deficient after the event.

comments regarding burden estimate to the FOIA, Privacy and Information Collections Branch (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e-mail to Inf000llects.Resource@nrc.gov, and to the Desk Officer, Office of Information and Regulatory Affairs, 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.

05000- Shearon Harris Nuclear Power Plant — Unit 1 400 C. Causal Factors

  • The test procedure did not contain a validation that at least four out of five of the high-pressure DEH accumulators be in service prior to performing turbine testing.
  • The hydraulic oil pressure switch was not functioning properly, causing the turbine to improperly position the control valves.

D. Corrective Actions

Completed Actions:

  • All five accumulators have been restored to service and the hydraulic oil pressure switch was replaced with a switch verified to be functioning properly.
  • The Turbine Mechanical Overspeed Trip testing procedure has been revised to add verifications for ensuring at least four accumulators are in service prior to testing.
  • The Power Operation (Mode 2 to Mode 1) procedure was revised to include additional verifications for ensuring at least four accumulators are in service prior to turbine start-up. (Accumulators are required for turbine start-up, but are not necessary during normal operation. The turbine will still be able to trip in the event of a loss of all accumulators. No actions required for ensuring normal turbine operation.)

Planned Actions:

  • A new calibration procedure will be implemented for the deficient oil pressure switch to ensure better quality control over verifying switch function.

E. Safety Analysis

At the time of the event, Harris was at approximately 8 percent power and descending. The safety injection was terminated six minutes after initiation, with pressurizer level at 80 percent. All Engineered Safety Features [B] and Reactor Protection Systems [J] functioned as designed. No loss of reactor coolant system (RCS) inventory or excessive RCS cooldown occurred. Pressurizer safety valves did not actuate. Thus, this event is low risk significant per Probabilistic Risk Assessment analysis. This event represents a minimal challenge to the health and safety of the public, with no actual dose consequence.

F. Additional Information

No similar events have occurred over the past three years.