By design, the
Steam Generator (
SG) Dry-out Protection Circuit actuates whenever two level indications (two of two actuation logic) in either
SG are lower than the setpoint for more than 30 seconds. This start circuit is not credited in any
ONS safety analysis, therefore this signal is considered an INVALID signal with respect to 50.73 (a)(2)(iv)(A). Upon actuation, the circuit starts both Motor Driven Emergency
Feedwater Pumps (MDEFWPs) on the affected unit. It does not send a start signal to the Turbine Driven Emergency
Feedwater Pump.
Shortly after entering Mode 4, a control operator stopped one of two operating Reactor Coolant Pumps per the Unit shutdown procedure. A second control operator was manually controlling Feedwater and reduced flow to control the system cooldown rate, without recognizing that the 2B SG had reached the low level setpoint for SG Dry-out Protection Circuit actuation.
In this event, the 2B SG level trains A and B indicated lower than the setpoint value (-21 inches) for more than 30 seconds, so the SG Dry-out Protection Circuit started the 2A and 2B MDEFWPs. The actuation was considered complete and the system started and functioned successfully. Both MDEFWPs started. The 2B SG control valve, 2FDW-316, opened and fed the 2B SG from the 2B MDEFWP for approximately one minute until the SG level reached the EFDW control setpoint (30 inches). The 2A pump did not feed the 2A SG because 2A SG level remained well above the EFDW control setpoint so there was no demand for the 2A SG control valve, 2FDW-315, to open.
The licensee notified the NRC Resident Inspector.
- * * UPDATE ON 4/26/04 AT 16:23 FROM R. TODD TO A. COSTA * * *
This update is to clarify a typographic misspelling on the first sentence of the last paragraph of this event notification which should read (~[approximately] 21 inches) instead of (-21 inches). Notified R2DO(Julian).
