Information Notice No.80-23 – Loss of Suction to Emergency Feedwater Pumps

                                                            SSINS No.:  6835
                                                            Accession No.:  
                                                            8005050061      

                               UNITED STATES 
                        NUCLEAR REGULATORY COMMISSION
                    OFFICE OF INSPECTION AND ENFORCEMENT
                           WASHINGTON, D. C. 20555

                                May 29, 1980 

                                            Information Notice No. 80-23 

LOSS OF SUCTION TO EMERGENCY FEEDWATER PUMPS 

Description of Circumstances: 

On April 7, 1980, Arkansas Nuclear One, Unit 2, suffered a loss of offsite 
power due to tornado damage to 500 kv transmission towers. The unit tripped 
from 98% power; the diesel generators started and supplied vital loads; 
natural circulation in the reactor coolant system was established; and the 
emergency feedwater (EFW) pumps supplied feedwater to the steam generators. 

The suction of the EFW pumps was aligned to the Condensate Storage Tanks 
(CST) and to the Startup and Blowdown Demineralizer effluent in parallel. 
Approximately 15 minutes after the unit tripped, both EFW pumps lost 
suction. Prompt operator action was taken to isolate the EFW pump suction 
from the Startup and Blowdown Demineralizer and to vent the EFW pumps. EFW 
flow was re-established within one minute. 

Investigation revealed that the EFW pump suction loss was caused by flashing
in the main feedwater train forcing hot water through the Startup and 
Blowdown Demineralizers to the EFW pump suction where it flashed to steam. 
The steam caused cavitation of the EFW pumps, and the pressure in the EFW 
suction header prevented flow from the CST. 

The licensee has submitted Licensee Event Report No. 50-368/80-18/03L-0, 
dated May 5, 1980, describing this event. Action to prevent recurrence 
included revising the EFW system operating procedure and the Plant Startup 
Procedure to require shutting the EFW suction valve from the Startup and 
Blowdown Demineralizers during plant startup at about 5% full power after 
the steam generator feedwater source has been shifted to a main feedwater 
pump. In addition, the EFW suction valve from the Startup and Blowdown 
Demineralizers will be verified closed once per shift during Mode 1 
operation. 

This Information Notice No. is provided as an early notification of a 
possibly significant matter that is still under review by the NRC staff. It 
is expected that recipients will review the information for possible 
applicability to their facilities. No specific action or response is 
requested at this time. If NRC evaluations so indicate, further licensee 
actions may be requested or required. 

No written response to this Information Notice No. is required. If you have 
any questions regarding this matter, please contact the Director of the 
appropriate NRC Regional Office.