05000397/LER-2017-004

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LER-2017-004, MANUAL REACTOR SCRAM DUE TO HIGH MAIN CONDENSER BACK PRESSURE
Columbia Generating Station
Event date: 08-20-2017
Report date: 10-17-2017
Reporting criterion: 10 CFR 50.73(a)(2)(iv)(A), System Actuation
3972017004R00 - NRC Website
LER 17-004-00 for Columbia Generating Station Regarding Manual Reactor Scram Due to High Main Condenser Back Pressure
ML17291A391
Person / Time
Site: Columbia Energy Northwest icon.png
Issue date: 10/18/2017
From: Schuetz R E
Energy Northwest
To: Schuetz R E
Document Control Desk, Office of Nuclear Reactor Regulation
References
GO2-17-178
Download: ML17291A391 (4)


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.

Columbia Generating Station 05000- 397 2017 - 004 - 00

PLANT CONDITIONS

At the time of the event, Columbia Generating Station (Columbia) was in Mode 1 operating at 100% reactor power. There were no safety related systems out of service prior to the event.

EVENT DESCRIPTION

On August 20, 2017 at 1605, in response to rising main condenser [SG] backpressure due to the Main Condenser Air Removal Suction Valve [SH] [V] (AR-V-1) failing closed, control room operators initiated a manual reactor scram after reducing reactor power to 80%. The main turbine [TA] and generator [TB] tripped due to the main condenser backpressure transient and both Reactor Recirculation (RRC) Pumps [AD] [P] tripped when an automatic signal was generated by the main turbine trip.

All rods fully inserted and the Main Steam Isolation Valves [SB][V](MSIVs) stayed open. Following the initial transient a subsequent Reactor Pressure Vessel [AB] [RPV] (RPV) low water level (Level 3) actuation occurred due to operator action per plant procedure to reduce RPV pressure, and level restored automatically with no operator action. Startup Flow Control Valve [SK] [V] (RFW-FCV-10B) then failed to automatically control RPV water level resulting in a RPV high water level (Level 8) trip and level was restored by throttling Reactor Feedwater Flow Control Valve [SK] [V] (RFW-V-118) per plant procedure. All other safety systems operated as designed.

All other plant systems responded as expected with the following exceptions: The Mode Switch [JC] [HS] was reportedly difficult to turn but did not impede the capability to scram. Reactor Feedwater Turbine Turning Gear [TA] [TGR] (RFT-DT- A) would not stay engaged; operator action was required to keep it engaged. These equipment issues did not impact the safety significance of the event.

IMMEDIATE CORRECTIVE ACTION

A temporary modification to gag open AR-V-1 for the remainder of the operating cycle has been implemented.

CAUSE

The direct cause of the shutdown was failure of Solenoid Pilot Valve [SK] [V] (AR-SPV-1/1) due to thermal aging which resulted in unexpected closure of AR-V-1. The apparent cause was a plant modification to address the known single point vulnerability (closure of AR-V-1) was not implemented in time to prevent a plant shutdown. The contributing cause was the management decision to not include the maintenance task to replace AR-SPV-1/1 in the most recent refueling outage.

EXTENT OF CONDITION

A review of all single point vulnerable components was conducted. The scope of the review included all normally energized components that could change state and cause a plant trip if electrical power were lost. The review revealed three relays that are in a normally energized state but were within their required replacement frequency.

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.

Columbia Generating Station 05000- 397 2017 - 004 - 00

PLANNED CORRECTIVE ACTIONS

Planned corrective actions include the following:

Eliminate the single point vulnerability of AR-V-1.

Develop and present a case study to station management placing emphasis on the timeliness and sensitivity of Single Point Vulnerability (SPV).

Revise the work and project management processes to align station priority for SPVs in Long Range Planning and Minor Modifications.

Review station SPVs to understand collateral effects from associated subcomponents and categorize appropriately.

For continuously energized components supporting function of SPVs, assess preventive maintenance tasks for adequacy to support a policy for zero failures.

ASSESSMENT OF SAFETY CONSEQUENCES

All control rods inserted in response to the manual scram and the MSIVs stayed open, thus the main condenser remained an available heat sink (via bypass valves) for decay heat control. RFW-FCV-10B failed to function automatically which necessitated throttling RFW-V-118 to control RPV level in accordance with plant procedures. All safety systems operated as designed and the plant safely entered Mode 4 without further challenges. The significance of this event was limited to loss of power operations.

PREVIOUS OCCURENCES

A review of Columbia LERs for the past three years was also performed and did not identify any previously reported similar events.

ENERGY INDUSTRY IDENTIFICATION

Energy Industry Identification System (EIIS) Information codes from IEEE Standards 805-1984 and 803-1983 are represented in brackets as [XX] and [XXX] throughout the body of the narrative.