05000353/LER-2002-001
| Docket Number | |
| Event date: | 7-23-2002 |
|---|---|
| Report date: | 9-18-2002 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 3532002001R00 - NRC Website | |
Unit Conditions Prior to the Event Unit 2 was in Operational Condition (OPCON) 1 (Power Operation) at approximately 100% power.
There were no structures, systems or components out of service that contributed to this event.
Description of the Event
On July 23, 2002, at 16:13 hours, the Unit 2 high-pressure main condenser (EIIS:COND) vacuum decreased to 23.4 inches Hg causing a main control room (MCR) alarm ; the procedure for loss of vacuum was entered. A power reduction was initiated as directed by the procedure. At 16:28 hours, the main turbine backpressure entered the limited operation region. Offgas system (EIIS:WF) flow decreased from a normal value of 13.4 scfm to 4 scfm during the period of decreasing vacuum indicating a malfunction of the air removal system (EIIS:SH).
At 16:32 hours, a manual scram was performed in accordance with the procedure for rapid plant shutdown; main condenser vacuum was at approximately 23 inches Hg and decreasing. All control rods inserted as designed.
Reactor pressure peaked at approximately 1042 psig and was controlled by the main turbine bypass valves (BPV). The lowest main steam relief valve (MSRV) setpoint of 1170 psig was not exceeded; therefore, no actuation of MSRVs occurred.
Reactor narrow range level dropped to approximately -12 inches as expected resulting in Group 2A and 2B residual heat removal (RHR) isolations that occurred as designed at +12.5 inches.
Reactor level subsequently increased to approximately +60 inches resulting in a high-level trip of the reactor feed pumps (RFP) and High Pressure Coolant Injection (HPCI) system at +54 inches.
The Main Turbine also received a high-level trip signal but had been previously manually tripped by the reactor operator. The 2A RFP was reset and used to control reactor level. The high level trip was due to RFP discharge pressure being greater than reactor pressure vessel (RPV) pressure when the RFPs were operating at minimum speed. Operating procedures have been revised to address this condition.
This event involved a valid manual actuation of the reactor protection system (RPS) system when the reactor was critical. The 4-hour ENS notification required by 10CFR50.72(b)(2)(iv)(B) and the 8-hour ENS notification required by 10CFR50.72(b)(3)(iv)(A) was completed on July 23, 2002 at 17:30 hours (Event# 39085).
This event involved a manual actuation of the reactor protection system. Therefore, this LER is being submitted pursuant to the requirements of 10CFR50.73(a)(2)(iv)(A).
Analysis of the Event
There were no actual safety consequences associated with this event. The potential safety consequences of this event were also minimal. The degrading main condenser vacuum resulted in a manual main turbine trip and manual reactor scram. Reactor critical parameters were monitored and controlled by Operations.
Main turbine retrofit projects were completed on Unit 1 in 1998 and on Unit 2 in 1999. The new turbines are able to function at higher backpressures, thus higher condensate temperatures would also be expected. Post event analysis indicated that the higher condensate temperatures were not properly evaluated for effects on the condenser air removal system at the time of the retrofit.
Because of this, plant operating limits allowed SJAE (EllS:EJR) system temperatures to exceed design limitations.
On the day of the transient outside air temperature increased to 95 deg F with very high humidity in the late afternoon. The high ambient temperature caused an increase in main condenser backpressure that resulted in higher than normal condensate temperature. The elevated condensate temperature caused insufficient cooling in the SJAE inter-condenser resulting in a "stalling" condition on the first stage SJAE. This stall condition caused a drop in condenser off- gas flow and further increased the main condenser backpressure. As non-condensables accumulated in the main condenser, the tube bundles became "air blanketed" reducing overall heat transfer, increasing backpressure, and rapidly increasing condensate temperature. The reactor power reduction performed was not effective in recovering condenser vacuum.
Cause of the Event
The cause of the event is that the impact of elevated condensate temperatures on the design limitations of the condenser air removal system was not addressed during the turbine retrofit project and was not adequately documented in plant design documents. Because the effect of condensate temperatures on SJAE performance was not fully realized, changes to plant-operating limits were implemented based solely on condensate demineralizer resin considerations. This allowed full power operation to continue at temperatures exceeding SJAE system design limits.
Corrective Action Completed Operating procedures and basis documents have been revised to reflect the proper operating conditions for SJAE condenser temperature and condenser backpressure.
Previous Similar Occurrences There were no previous occurrences of degraded condenser capacity that resulted in unit shutdown.
Component: � Cond (Steam Jet Air Ejector Condenser) Manufacturer: � F175 (Foster Wheeler Corp) Model: � 261-KA