05000458/LER-2016-004, Regarding Actuation of the Division 1 Emergency Diesel Generator and Primary Containment Isolation Logic Due to Partial Loss of Offsite Power
| ML16097A416 | |
| Person / Time | |
|---|---|
| Site: | River Bend  |
| Issue date: | 03/29/2016 |
| From: | Maguire W Entergy Operations |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| RBG-47669 LER 16-004-00 | |
| Download: ML16097A416 (5) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 4582016004R00 - NRC Website | |
text
~Entergy RBG-47669 March 29, 2016 U. S. Nuclear Regulatory Commission A TIN: Document Control Desk Washington, DC 20555
Subject:
Licensee Event Report 50-458 I 2016-004-00 River Bend Station - Unit 1 Docket No. 50-458 License No. NPF-47 RBF1-16-0037
Dear Sir or Madam:
Entergy Operations, Inc.
River Bend Station 5485 U.S. Highway 61 N St. Francisville, LA 70775 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. JosephClarkat 225-381-4177.
Sincerely,
~-~9~~
Site Vice President Enclosure cc:
U.S. Nuclear Regulatory Commission Region IV 1600 East Lamar Blvd.
Arlington, TX 76011-4511
Licensee Event Report 50-458 I 2016-004-00 March 29, 2016 RBG-47669 Page 2 of 2 NRC Sr. Resident Inspector P. 0. Box 1050 St. Francisville, LA 70775 INPO (via ICES reporting)
Central Records Clerk Public Utility Commission of Texas 1701 N. Congress Ave.
Austin, TX 78711-3326 Department of Environmental Quality Office of Environmental Compliance Radiological Emergency Planning and Response Section Ji Young Wiley P.0. Box 4312 Baton Rouge, LA 70821-4312
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3160-0104 EXPIRES: 01/31/2017 (02-2014)
, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
YEAR
- 6. LER NUMBER I
SEQUENTIAL I REV NUMBER NO.
2016 004 00
- 3. PAGE 2
OF 3
On January 29, 2016, at 1518 CST, with the plant in cold shutdown, power was lost on reserve station service (RSS) line no. 1. This is one of two sources of offsite power required by Technical Specifications. The power loss de-energized the Division 1 onsite AC safety-related switchgear [EB], causing an automatic start of the Division 1 emergency diesel generator (EDG)(**DG**). The Division 1 reactor protection system (RPS)[JC] bus was also de-energized, causing a half-scram signal. Approximately 8 minutes later, a full actuation of the RPS occurred due to high water level in the control rod drive hydraulic system scram discharge volume header. All reactor control rods were already fully inserted. The loss of Division 1 RPS also caused the actuation of the Division 1 primary containment isolation logic. The Division 1 isolation valves in the balance-of-plant systems closed as designed. Both trains of the standby gas treatment system actuated. This event is being reported in accordance with 10 CFR 50.73(a)(2)(iv)(A)° as the automatic actuation of the Division 1 EDG, the Division 1 primary containment logic, and the reactor protection system (while subcritical).
INVESTIGATION AND IMMEDIATE CORRECTIVE ACTIONS At the time of the event, technicians from the company's transmission department were working in the local 230kV switchyard. A modification was being performed on relay setpoints to implement corrective actions stemming from a reactor scram that occurred on November 27, 2015, caused by a transient on a nearby 230kV transmission line. The investigation of that scram determined that one of two circuit breakers supplying RSS No. 1 tripped too soon during the transient. In developing the final corrective action, a change was made to the work package on the previous day regarding a specific relay setpoint. During the post-modification testing, a current signal was applied to the affected circuits without taking the necessary precautions to prevent an actuation of the protection logic, resulting in the unanticipated trip of the circuit breaker. This caused the loss of power to RSS No. 1.
This investigation determined that the late change in the as-left relay setpoint caused the work to proceed without the development of step-by-step instructions that conformed to nuclear industry standards for such documents.
As an interim measure, all work at the 230kV switchyard must be approved by the plant manager.
CORRECTIVE ACTIONS TO PREVENT RECURRENCE The following actions are planned in response to this event.
- 1. Revise the operating agreement between the station and the transmission department to identify and communicate respective responsibilities with regard to all switchyard work and work package detail during outage and online activities.
- 2. Based on the specific revisions to the nuclear operating agreement, revise transmission department procedure(s) to provide detailed step by step work instructions, evaluation ofrisk, and clarification ofownership.
PREVIOUS OCCURRENCE EVALUATION A similar event occurred at River Bend Station on March 7, 2015, when site electricians were working in the 230kV switchyard. The electricians were conducting post-modification testing inside a termination cabinet, when the RSS No. 2 was unexpectedly de-energized. The investigation determined that the likely cause of that event was the inadvertent contact with an adjacent terminal with ineter probes, which initiated a trip of the circuit breakers supplying RSS No. 2. Contributing factors were a cramped work environment and poor lighting.
That prior event, however, did not involve transmission department technicians implementing deficient work instructions. These factors differentiate the two events, such that the latter was not the result of inadequate corrective actions from the prior event.
SAFETY SIGNIFICANCE
Prior to the start of the work, the residual heat removal system had been aligned such that the operating shutdown cooling loop was in the division unaffected by the switch yard work. The Division 1 EDG responded as designed to the loss of power on its switchgear.
The reactor was already in cold shutdown, so the RPS safety function was already met. This event was, thus, of minimal significance to the health and safety of the public.
(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.)
REPORTED CONDITION
, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
YEAR
- 6. LER NUMBER I
SEQUENTIAL I REV NUMBER NO.
2016 004 00
- 3. PAGE 2
OF 3
On January 29, 2016, at 1518 CST, with the plant in cold shutdown, power was lost on reserve station service (RSS) line no. 1. This is one of two sources of offsite power required by Technical Specifications. The power loss de-energized the Division 1 onsite AC safety-related switchgear [EB], causing an automatic start of the Division 1 emergency diesel generator (EDG)(**DG**). The Division 1 reactor protection system (RPS)[JC] bus was also de-energized, causing a half-scram signal. Approximately 8 minutes later, a full actuation of the RPS occurred due to high water level in the control rod drive hydraulic system scram discharge volume header. All reactor control rods were already fully inserted. The loss of Division 1 RPS also caused the actuation of the Division 1 primary containment isolation logic. The Division 1 isolation valves in the balance-of-plant systems closed as designed. Both trains of the standby gas treatment system actuated. This event is being reported in accordance with 10 CFR 50.73(a)(2)(iv)(A)° as the automatic actuation of the Division 1 EDG, the Division 1 primary containment logic, and the reactor protection system (while subcritical).
INVESTIGATION AND IMMEDIATE CORRECTIVE ACTIONS At the time of the event, technicians from the company's transmission department were working in the local 230kV switchyard. A modification was being performed on relay setpoints to implement corrective actions stemming from a reactor scram that occurred on November 27, 2015, caused by a transient on a nearby 230kV transmission line. The investigation of that scram determined that one of two circuit breakers supplying RSS No. 1 tripped too soon during the transient. In developing the final corrective action, a change was made to the work package on the previous day regarding a specific relay setpoint. During the post-modification testing, a current signal was applied to the affected circuits without taking the necessary precautions to prevent an actuation of the protection logic, resulting in the unanticipated trip of the circuit breaker. This caused the loss of power to RSS No. 1.
This investigation determined that the late change in the as-left relay setpoint caused the work to proceed without the development of step-by-step instructions that conformed to nuclear industry standards for such documents.
As an interim measure, all work at the 230kV switchyard must be approved by the plant manager.
CORRECTIVE ACTIONS TO PREVENT RECURRENCE The following actions are planned in response to this event.
- 1. Revise the operating agreement between the station and the transmission department to identify and communicate respective responsibilities with regard to all switchyard work and work package detail during outage and online activities.
- 2. Based on the specific revisions to the nuclear operating agreement, revise transmission department procedure(s) to provide detailed step by step work instructions, evaluation ofrisk, and clarification ofownership.
PREVIOUS OCCURRENCE EVALUATION A similar event occurred at River Bend Station on March 7, 2015, when site electricians were working in the 230kV switchyard. The electricians were conducting post-modification testing inside a termination cabinet, when the RSS No. 2 was unexpectedly de-energized. The investigation determined that the likely cause of that event was the inadvertent contact with an adjacent terminal with ineter probes, which initiated a trip of the circuit breakers supplying RSS No. 2. Contributing factors were a cramped work environment and poor lighting.
That prior event, however, did not involve transmission department technicians implementing deficient work instructions. These factors differentiate the two events, such that the latter was not the result of inadequate corrective actions from the prior event.
SAFETY SIGNIFICANCE
Prior to the start of the work, the residual heat removal system had been aligned such that the operating shutdown cooling loop was in the division unaffected by the switch yard work. The Division 1 EDG responded as designed to the loss of power on its switchgear.
The reactor was already in cold shutdown, so the RPS safety function was already met. This event was, thus, of minimal significance to the health and safety of the public.
(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.)