05000387/LER-2012-002
| Susquehanna Steam Electric Station Unit 1 | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v), Loss of Safety Function |
| Initial Reporting | |
| ENS 47807 | 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident |
| 3872012002R00 - NRC Website | |
EVENT DESCRIPTION
On April 4, 2012 at 1517, the "A" Emergency Diesel Generator (EDG) [EllS Code: EK] was declared inoperable for performance of a surveillance. At 1835 on April 4, 2012, the "B" Control Structure (CS) chiller [EllS Code: KM] was declared inoperable due to an unrelated problem (degradation of refrigerant piping associated with the chiller). With the "B" CS chiller inoperable coincident with the "A" EDG inoperable, the "A" CS chiller would not be available to perform its design function on a loss of offsite power. This is a condition that, at the time of discovery, could have prevented fulfillment of a safety function and was reported in EN 47807 in accordance with 10 CFR 50.72(b)(3)(v) as an 8 hour9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> notification. This event is also reportable as an LER in accordance with 10 CFR 50.73(a)(2)(v).
The Susquehanna Technical Specifications allow four hours to correct the condition before the features ('A' Control Structure Chiller) supported by the inoperable EDG inoperable are required to be declared inoperable. The "A" EDG was restored to operable status on April 4, 2012 at 2200 which restored safety function capability for the "A" Control Structure Chiller and the "A" CS chiller was not required to be declared inoperable.
Background Information Degradation of refrigerant piping on chillers has been an ongoing issue at Susquehanna. The most significant problem is external corrosion of the piping. During operation, the temperature of the evaporator on plant chillers is frequently below the due point of the ambient air and condensation occurs on the steel surfaces of the evaporator. Insulation is applied to the chillers to minimize condensation; however, corrosion has been found on joints in the insulation and under the insulation.
Susquehanna has experienced leaking on control structure chillers since 2006. Although the trend in chiller leaks was identified and evaluated in the corrective action program (CAP), leaks continued to occur.
CAUSE OF THE EVENT
The direct cause of the component failure was:
- The refrigerant line degradation was the result of external corrosion.
The causes of the event were determined to be as follows since the external corrosion is a known problem:
- The station lacks an agreed upon documented system recovery plan fix for chiller leaks because the station failed to identify the complexity and need for a plan.
- The corrective action program (CAP), System Health, aid Work Management processes are not linked so that they work together to produce reliable, failure free operation of statioi chillers.
ANALYSIS/SAFETY SIGNIFICANCE
Actual Consequences:
There were no actual consequences. The "A" CS chiller remained in service for normal operation cooled by Service Water duriQg the event. All cooling loads were maintained by the "A" CS chiller and the associated CS ventilation fans remained in-service. Temperatures within the Control Structure remained within normal limits.
The "B" CS chiller was declared inoperable due to an identified wall thickness issue with a Freon piping connection at the evaporator. No actual Freon leak was identified.
Potential Consequences:
During LOCA/LOOP conditions, the "A" CS chiller is cooled via the Emergency Service Water (ESW) system. During the period the "A" EDG was inoperable, EDG power to the ESW return valve was not available. With the ESW return valve inoperable for emergency conditions, an ESW flow path through the chiller condenser could not be established thereby preventing chiller operation.
CORRECTIVE ACTIONS
Key corrective actions:
1. The degraded piping on the "B" CS chiller that resulted in the chiller inoperability was replaced.
2. A chiller project plan will be developed and approved by Senior Station Leadership and the Station Health Committee.
3. The refrigerant lines on the CS chillers and other applicable chillers will be replaced.
4. The Equipment Reliability and Station Health Process procedure will be revised to include a template that directs that a project plan be developed that includes a systematic and thorough analysis for a system or component recovery.
5. The station work management process procedure will be revised to align with the CAP program.
6. The corrective action program procedure will be changed to provide direction for linking work orders that are corrective actions such that they are given sufficient priority.
PREVIOUS SIMILAR EVENTS
The following LER was also the result of chiller reliability issues:
- LER 387/2012-01-00, "Both Control Structure Chillers Inoperable" identified a condition that could have prevented the fulfillment of a safety function associated with the CS chillers.