05000461/LER-2013-004
| Clinton Power Station, Unit 1 | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident |
| Initial Reporting | |
| ENS 49286 | 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident |
| 4612013004R00 - NRC Website | |
PLANT AND SYSTEM IDENTIFICATION
General Electric -- Boiling Water Reactor, 3473 Megawatts Thermal Rated Core Power Energy Industry Identification System (EDS) codes are identified in test as [XX].
EVENT IDENTIFICATION
Loss of Emergency Diesel Room Ventilation Due to Damper Hydramotor Failure
A. Plant Operating Conditions Before the Event
Unit: 1 Event Date: 8/15/13 Event Time: 0915 hours0.0106 days <br />0.254 hours <br />0.00151 weeks <br />3.481575e-4 months <br /> CDT Mode: 1 Mode Name: Power Operation Reactor Power: 92 percent
B. DESCRIPTION OF EVENT
On 8/15/13, component maintenance personnel were performing planned performance testing of the Division 3 Emergency Diesel Generator (EDG) [EK] Room Ventilation System [VJ]. At 0850 hours0.00984 days <br />0.236 hours <br />0.00141 weeks <br />3.23425e-4 months <br /> Operations placed the Division 3 EDG ventilation fan into service. At about 0915 hours0.0106 days <br />0.254 hours <br />0.00151 weeks <br />3.481575e-4 months <br />, the component maintenance personnel noticed the supply air damper [DMP] did not demonstrate the expected behavior of opening when the Division 3 EDG room ventilation fan [FAN] started, and noticed the flow data results were not consistent with previous testing data.
Operators suspected that the cause of the damper not opening was that outside air temperature was below the damper setpoint of 70 degrees Fahrenheit (F), determined that the test should be run again later in the day when intake air temperature would be higher, and initiated Issue Report 1546973 to document their conclusion. At about 1400 hours0.0162 days <br />0.389 hours <br />0.00231 weeks <br />5.327e-4 months <br />, operators restarted the fan with the temperature controller set at 70 degrees F and actual air temperature reading 84 degrees F, but the damper again failed to open. At about 1420 hours0.0164 days <br />0.394 hours <br />0.00235 weeks <br />5.4031e-4 months <br />, operators secured the fan and declared the Division 3 EDG and the supported High Pressure Core Spray System [BG] inoperable based on low confidence that the VJ system was capable of controlling EDG room temperature to support the EDG mission time, and entered the required Technical Specification actions.
The Clinton Power Station Updated Safety Analysis Report sections 9.4.5.1.1.2.b and d state that the EDG ventilation system is designed to limit the maximum EDG room temperature to 130 degrees F. During extreme weather conditions EDG room temperatures may rise to 140 degrees F maximum for 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />.
The supply air damper/hydramotor [NOVA] assembly is designed to fail closed. The damper control is designed to fully open and then modulate the damper to maintain supply air temperature at a setpoint of 70 degrees F on fan start if supply air temperature is greater than 70 degrees F. During troubleshooting the damper did not open when temperature reached the 70 degrees F setpoint and failed to stroke open on demand.
This event was determined to be reportable under the provisions of 10 CFR 50.73(a)(2)(v)(D), as an event or condition that could have prevented fulfillment of a safety function needed to mitigate the consequences of an accident. The station notified the NRC of this event via Emergency Notification 49286 at 1653 hours0.0191 days <br />0.459 hours <br />0.00273 weeks <br />6.289665e-4 months <br /> on 8/15/13. Issue Report 1547294 was initiated to investigate this event.
C. CAUSE OF EVENT
Based on review of the hydramotor maintenance history and failure analysis from the vendor, the apparent cause of the supply air damper failure to open was that the damper hydramotor experienced an end-of-life failure due to being installed beyond its recommended service life. The hydramotor failed as result of normal age-related degradation of the internal hydraulic pump [P]. The hydramotor had been installed for about 26 years and the recommended service life is 10 years.
The hydramotor was never replaced due to a significant change in hydramotor preventive maintenance (PM) scope in 2005 which should have treated the change as a first-time PM and revised the due date accordingly.
However, the change to the PM retained the original scheduling date and allowed the hydramotor to remain in the system beyond the recommended service life.
D. SAFETY CONSEQUENCES
This event had no actual consequences. The Division 3 EDG was in its normal standby lineup at the time of this event. A failure of the supply air damper to open limits the amount of outside air that can be introduced into the EDG engine and fuel storage rooms to maintain room temperature and remove heat loading from the EDG operation. If an event occurred requiring the Division 3 EDG to run at full load, the EDG could have exceeded the analyzed heat load for the Division 3 EDG room prior to completion of the system's mission time. During this event, the recirculation damper was open and allowing recirculation air flow; therefore, some cooling and heat removal was occurring. Additionally, there is some inlet airflow due to seal leakage around the damper blades and door seals in the fan room, but the amount of cooling this may provide is unknown.
Prior to the event, on 8/14/13, the Division 3 EDG was satisfactorily started for Technical Specification surveillance testing at 0924 hours0.0107 days <br />0.257 hours <br />0.00153 weeks <br />3.51582e-4 months <br /> and run for approximately two hours without any evidence of damper failures and no unexpected room temperature or pressure conditions noted.
At the time of this event the Reactor Core Isolation Cooling System [BN] was operable and all Emergency Core Cooling Systems (with the exception of HPCS) were operable as well as AC power, including Divisions 1 and 2 EDGs. Although HPCS was declared inoperable, HPCS was available with offsite power.
E. CORRECTIVE ACTIONS
The failed hydramotor was replaced, post maintenance testing was completed and functionality/operability was restored on 8/17/13.
An evaluation determined that critical, non-EQ hydramotors have the correct 10-year frequency PM established. (EQ hydramotors have established PM strategies based on their EQ analyses and are not affected by the cause of this event.) Ten additional hydramotors have been identified as being installed beyond the 10-year recommended life and will be replaced.
Applicable Engineering and Work Management staff will receive a tailgate on the failure to treat the significant change in PM scope as a new PM task.
F. PREVIOUS OCCURRENCES
A review for previous occurrences did not identify similar events at Clinton Power Station.
G. COMPONENT FAILURE DATA
Component Description: Modulating Air Damper Hydramotor/Actuator Manufacturer: ITT General Controls Model: NH91