Information Notice No.80-23 – Loss of Suction to Emergency Feedwater Pumps
SSINS No.: 6835
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
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.
Page Last Reviewed/Updated Thursday, March 25, 2021