05000416/LER-2016-008

LER-2016-008, Entry into Mode of Applicability with the Alternate Decay Heat Removal System Inoperable

Grand Gulf Nuclear Station Unit 1
Event date:	09-09-2016
Report date:	10-27-2016
4162016008R00 - NRC Website

LER 16-008-001 for Grand Gulf, Unit 1, Regarding Entry into Mode of Applicability with the Alternate Decay Heat Removal System Inoperable

ML17228A233
Person / Time
Site:	Grand Gulf
Issue date:	08/16/2017
From:	Neve D A Entergy Operations
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
GNRO-2017/00001 LER 16-008-001
Download: ML17228A233 (7)

Reported lessons learned are incorporated into the licensing process and fed back to industry.

Send 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 Infocollects.Resource@nrc.gov, and to the Desk Officer, Office of Information and Regulatory Affairs, NEOB-10202, (3150-0104), Office of Management and Budget, Washington, DC 20503. If a means 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.

PLANT CONDITIONS PRIOR TO THE EVENT

MODE 4 'A' RHR Pump inoperable 'B' RHR Pump in service providing shutdown cooling Alternate Decay Heat Removal System inoperable

DESCRIPTION

Entergy manually shutdown the Grand Gulf Nuclear Station (GGNS) reactor on September 8, 2016, at approximately 1104 hours0.0128 days <br />0.307 hours <br />0.00183 weeks <br />4.20072e-4 months <br />, to replace Residual Heat Removal (RHR) [BO] Pump 'A' after it failed its technical specification surveillance. The reactor entered MODE 4, Cold Shutdown, at approximately 0509 hours0.00589 days <br />0.141 hours <br />8.416005e-4 weeks <br />1.936745e-4 months <br /> on September 9, 2016. Residual Heat Removal Train 'B' was placed in shutdown cooling mode (SDC) to maintain Reactor coolant temperature 110 degrees Fahrenheit (F) to 120 F. At approximately 1742 hours0.0202 days <br />0.484 hours <br />0.00288 weeks <br />6.62831e-4 months <br /> on September 9, 2016, The Alternate Decay Heat Removal (ADHR) [BO] System was placed into standby.

Grand Gulf Nuclear Station Technical Specification (TS) 3.4.10, Residual heat Removal (RHR) Shutdown Cooling System — Cold Shutdown, requires two trains of RHR to be OPERABLE. Condition A, One or two RHR shutdown cooling subsystems inoperable requires the verification of an alternate method of decay heat removal is available for each inoperable RHR shutdown cooling subsystem. This action is required to be completed within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> and once per 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> thereafter during the mode of applicability.

At the time of entry into MODE 4, and throughout the time period the 'A' RHR pump was inoperable, the ADHR System was not available because the ADHR heat exchangers tube-side cooling water system had been clearance-tagged closed to support cleaning of the heat exchanger tubes since August 10, 2016.

This condition was not identified until September 23, 2016, after the 'A' RHR train was returned to OPERABLE status.

Alternate Decay Heat Removal Background Information:

The ADHR System provides an alternate method of reactor decay heat removal during cold shutdown and refueling conditions. It is designed for use during MODEs 4 and 5 to provide decay heat removal when maintenance is being performed on RHR shutdown cooling loops or associated support systems. An alternative method of decay heat removal must be demonstrated for each required RHR SDC loop that is inoperable. The cause of the event is under investigation and this licensee event report will be supplemented upon completion of the causal evaluation. The direct cause of this event appears to be the lack The ADHR System is an auxiliary cooling loop included as part of the RHR System with separate pumps, heat exchangers, and controls. The ADHR System is completely isolated mechanically and electrically from connected plant systems during MODEs 1, 2, and 3. The functional design basis for the ADHR System is to maintain Reactor coolant temperatures below TS limits during cold shutdown and refueling operations, accomplishing this task by operating in either a Reactor to Reactor cooling mode or Spent Fuel Pool to Reactor cooling mode.

The ADHR pumps and heat exchangers are located in RHR 'C' Pump Room. Cooling water for the ADHR he'at exchangers is supplied by the Plant Service Water (PSW) System.

Grand Gulf Nuclear Station Unit 1 05000-416 Reported lessons learned are incorporated into the licensing process and fed back to industry.

Send 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 Infocollects.Resource@nrc.gov, and to the Desk Officer, Office of Information and Regulatory Affairs, NEOB-10202, (3150-0104), Office of Management and Budget, Washington, DC 20503. If a means 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.

Two identical ADHR pumps provide the needed head to pump water at a maximum combined flow of 3600 gpm when operated in parallel.

Two ADHR heat exchangers, also located in the RHR "C" Pump Room are operated in a parallel arrangement to provide the required decay heat removal. Each heat exchanger is a horizontally mounted, 50% capacity, two-pass, U-tube type heat exchanger with a single-pass shell. Plant Service Water passes through the tubes, while the water being cooled passes through the shell.

Plant Service Water provides the cooling source to the ADHR System heat exchangers and the ADHR System Air Conditioning Unit. A loss of PSW would prevent the ADHR System from performing its intended function.

CAUSE

The cause of the event is under investigation and this licensee event report (LER) will be supplemented upon completion of the causal evaluation. The direct cause of this event appears to be the lack of adequate information validation and verification by station personnel.

CORRECTIVE ACTIONS

Entergy personnel verified both RHR trains were operable and available on September 23, 2016, when the ADHR Heat Exchangers were identified as clearance-tagged CLOSED.

Entergy established a causal evaluation to determine the cause and to establish corrective actions as appropriate. This LER will be supplemented upon completion of this causal evaluation.

SAFETY SIGNIFICANCE

There were no actual nuclear safety consequences or radiological consequences during the event. The `B' RHR train remained OPERABLE and in service, maintaining shutdown cooling throughout the duration of the event.

PREVIOUS SIMILAR EVENTS

Reactor Steam Dome High Pressure Interlock For Residual Heat Removal System Isolation Resulting In A Technical Specification 3.4.11 RCS Pressure And Temperature (PFF) Limits Violation Resulting In A Technical Specification 3.4.11 RCS Pressure And Temperature (PFF) Limits Violation Entergy has reviewed the above identified licensee event reports and has concluded that the causes and corrective actions associated with these licensee event reports could not have prevented the occurrence of the event documented in this licensee event report.

Grand Gulf Nuclear Station Unit 1 05000-416