Junk Plant Oconee: MULTIPLE MAIN STEAM RELIEF VALVES FAILED TO RESEAT

Update

Oconee is terrible accident or meltdown waiting to happen. It is too old and obsolete for them to keep up with maintenance...

***Hmm, This is PWR. It is pissing in your pants time if a steam generator feedwater side  is depressurized while the primary is still fully depressurized. As far as the steam generators tubes, if the secondary side of the system is depressurized at normal reactor pressure,  the d/p of the steam generator is additive across the tubes. In other words, with the secondary side depressurized, the tubes have to hold back the full brunt of the reactor pressure. With the secondary side pressurized, the d/p across the tubes is 1000 to 1500 psi less.

NRC: Main Steam Safety Valves 
 Main steam safety valves with sufficient rated capacity are provided to prevent the steam pressure from exceeding 110 percent of the main steam system design pressure:

• Following a turbine trip without a reactor trip and with main feedwater flow maintained, and • Following a turbine trip with a delayed reactor trip and with the loss of main feedwater flow. 

The total main steam safety valve rated capacity as indicated in Table 7.1-2 meets this requirement.  At the same time, each individual safety valve is limited to the maximum allowable steam relief valve capacity as indicated in Table 7.1-2 for a system pressure equal to main steam design pressure plus 10 percent overpressure.  This value sufficiently limits the potential uncontrolled blowdown flow and the ensuing reactor transient should a single safety valve inadvertently fail or stick in the open position. 

Six safety valves are provided per main steam line for the plant. Table 7.1-2 lists the set pressures for the main steam safety valves.  The main steam supply system safety valves are located in the safety-related portion of the main steam piping


USNRC HRTD 7.1-4 Rev 0209
upstream of the main steam isolation valves and outside the containment in the auxiliary building

Power Reactor	Event Number: 53329
Facility: OCONEE Region: 2 State: SC Unit: [1] [ ] [ ] RX Type: [1] B&W-L-LP,[2] B&W-L-LP,[3] B&W-L-LP NRC Notified By: JOE FRAVEL HQ OPS Officer: BETHANY CECERE	Notification Date: 04/13/2018 Notification Time: 06:07 [ET] Event Date: 04/13/2018 Event Time: 02:27 [EDT] Last Update Date: 04/13/2018
Emergency Class: NON EMERGENCY 10 CFR Section: 50.72(b)(2)(iv)(B) - RPS ACTUATION - CRITICAL	Person (Organization): MARVIN SYKES (R2DO)

Unit	SCRAM Code	RX CRIT	Initial PWR	Initial RX Mode	Current PWR	Current RX Mode
1	M/R	Y	24	Power Operation	0	Hot Standby

Event Text

MANUAL REACTOR TRIP FOLLOWING MAIN FEEDWATER CONTROL PROBLEM "On 4/13/2018 at 0227 [EDT], the Oconee Unit 1 Reactor was manually tripped from 24 percent power due to the inability to control main feedwater flow through the Main Feedwater Control Valves using the Integrated Control System. Due to the RPS actuation while critical, this event is being reported as a 4-hour Non-Emergency per 10 CFR 50.72(b)(2)(iv)(B). "Following the reactor trip, multiple Main Steam Relief Valves failed to reseat at the expected pressure. Using procedure guidance, Main Steam Pressure was lowered by 115 psig, resulting in the closing of all Main Steam Relief Valves. All other post-trip conditions are normal and all other systems performed as expected. Unit 1 is currently in Mode 3 and stable." Decay heat is being removed by the steam generators discharging steam to the main condenser using the turbine bypass valves. Units 2 and 3 are not affected by the Unit 1 reactor trip. The licensee notified the NRC Resident Inspector.