Reactor Coolant System & Rx Vessel Internals Flashcards
(40 cards)
What component(s) provide over pressure protection for the RCS and where do they relieve to?
Two Power operated relief valves and three spring-loaded safeties mounted on the pressurizer; each relieve to the pressurizer relief tank (PRT).
Describe the normal operating parameters of the U1 and U2 RCS (Unit two shown in parentheses in answer)
Volume - 95,000 (91,000)
Flow Rate - 403,700 (408,000)
Pressure - 2235 psig
Thot - 618 (620)
Told - 560 (559)
Tave - 557 - 585.4 (557 - 589.2)
Describe the design temperature and pressure of the RCS. How does it differ from the pressurizer?
Design temperature of the RCS is 650F and 2485 psig. The design temperature of the Pressurizer and surge line is 680F.
Of the RCS flow that enters the reactor vessel, a portion of the flow is utilized to cool the fuel assemblies while another portion ‘bypasses’ the fuel assemblies. Describe the percentage of flow that is utilized for cooling, and the percent-makeup of each bypass flow.
94% of the reactor coolant flow is available for heat removal, 6% of the flow bypasses the core.
1% - Nozzle bypass (from inlet nozzle to outlet nozzle)
0.5% - Baffle wall bypass
0.5% - Head cooling bypass flow
2% - Control Rod & Instrument thimble bypass.
2% - Baffle cooling flow
Where do the pressurizer spray lines pull off the RCS?
Cold legs 1 & 4
What are the normal and ‘alternate’ charging paths into the RCS from CVCS at power?
Normal - Loop 4 cold leg
Alternate - Loop 1 cold leg
Although they are described as ‘normal’ and ‘alternate’ the loops in which charging is aligned is alternated each cycle.
During cold leg injection, following a safety injection, the following pump(s) inject into each cold leg through a 10-inch pipe:
SI Accumulators
SI Pumps
RHR Pumps
During cold leg injection, following a safety injection, the following pump(s) inject into each cold leg through a 1.5-inch pipe:
CCPs
During hot leg recirculation, which two ECCS pumps can be aligned to the RCS hot legs, and to which hot legs can they be aligned?
RHR Pumps - Hot Legs 2 & 3
SI Pumps - All 4 Hot legs
Where does normal letdown pull off the RCS? What about Excess letdown?
Normal letdown - Intermediate leg 3
Excess letdown - Intermediate leg 1
Describe the design and parameters associated with RCP Seal Leakoff #1
RCP Seal #1 is a film-riding seal.
- Receives 3 gpm and travels up the shaft, lubricating the radial bearing and leaking through the #1 seal.
- Seal injection temperature should be limited to LESS than 130F
Describe the design and parameters associated with RCP Seal Leakoff #2
RCP Seal #2 is a face-rubbing seal
- VCT backpressure forces approx. 3 gph through RCP Seal #2 and is directed to the RCDT.
Describe the design and parameters associated with RCP Seal Leakoff #3
RCP Seal #3 is a face-rubbing seal
- Supplied via the RCP standpipe (maintained by RMUW)
- Approx. 800 cc/hr half of which is directed to the containment sumps, and the other half to the seal #2 leakoff (RCDT)
Describe the RCP Seal Package flows
8 gpm of seal flow is aligned to each of the reactor coolant pumps. 5 gpm of the seal flow flows down the shaft, through the thermal barrier, and into the RCS. 3 gpm of the seal flow is directed up the shaft to each of the three seal packages.
Describe the flow path of CCW to the RCP thermal barrier and any conditions or automatic actions that may affect it.
CCW enters containment through 1-HV-4700 and 1-HV4699 where it reaches a common header. This common header supplies CCW to each RCP thermal barrier and returns to the CCW system through containment isolations 1-HV-4696 and 1-HV-4709.
- Both CCW supply and return to the RCPs is isolated on a containment isolation phase B (6.2 psig CNTMT atmosphere)
- Each RCP thermal barrier outlet valve and the common return header isolation valve (ORC) 1-HV-4709 close on a high return temperature of 182.5F
- Common CCW return header isolation valve (IRC) 1-HV-4696 isolates on high return flow of 64 gpm from any RCP
What conditions must be met in order to open the RCP Seal water injection bypass valve u8142 and why would we want to?
u8142 may be opened to align more seal flow to the #1 seal or pump radial bearing on increasing temperature.
Required conditions:
1. RCS pressure is between 100 and 1000 psig
2. #1 seal leakoff valve is opened
3. #1 seal leakoff flow rate is <1 gpm
4. Seal injection water flow rate to each RCP is >/= 8 gpm
Why?:
Seal water injection temperature approaching 235F
What is the purpose of the RCP flywheel and ratchet plate?
Extend the coast-down of RCPs post-trip and prevent reverse rotation.
Describe the function of the RCP Cold Loop / Hot Loop switch
The RCP Cold Loop switch enables a higher over-current trip setpoint and the failure to accelerate / locked rotor automatic trips. These trips are disabled 30 seconds after pump start.
How many successive RCP starts are permitted?
Two successive RCP starts are permitted provided the motor is allowed to coast to a stop between starts (~5 mins).
A third start may be permitted when the winding and the core have cooled by running a period of 20 minutes, or by standing idle for 45 minutes. (Recall the motors are air cooled, air is only pulled in while the motor is running).
Describe the RCP Oil lift pump operation and associated interlocks
There are no automatic starts associated with the RCP Oil lift pump. Therefore, the lift pump must be manually run until the lift oil pressure has reached 600 psig (administrative minimum run time of two minutes).
After the RCP has been in operation for 1 minute, the oil lift pump may be turned off.
Describe the function and capacity of the pressurizer spray valves
Two pressurizer spray valves, PCV-0455B from cold leg 1 and PCV-0455C from cold leg 4, function to reduce pressure by cooling the pressurizer. Each valve is capable of 450 gpm of flow, 900 gpm together.
A manual bypass valve around the spray valves is throttled to maintain a constant flow into the pressurizer, which helps maintain chemical and thermal equilibrium with the rest of the RCS.
Describe the function and operation of the PORVs
PCV-0455A and PCV-0456 relieve steam from the top of the pressurizer at a nominal set point of 2335 psig. Each has a capacity of 210,000 lbm/hr.
Actuated by nitrogen pressure; fail closed on loss of nitrogen or power. Nitrogen accumulators (100 psig) allow for each PORV to be cycle 100 times over a 10 minute period.
Primarily function to prevent challenging the pressurizer safety valves and provide a means for LTOP.
Describe the function and operation of the pressurizer safety valves
Three 6-inch safety valves, each with a capacity of 420,000 lbm/hr ensure the RCS is protected from overpressure conditions by lifting at 2460 (less than 110% design pressure) psig with a 3% accumulation.
Each safety valves relieve to the PRT and each line has a strap-on temperature element to provide indication of an open or leaking safety valve
Magnetic Reed switches - Intermediate position results in both light indications dark.
Describe the function and operation of the pressurizer relief tank
The PRT functions to condense and cool the discharge from the pressurizer safety and relief valves. It is normally filled 64%-88% (RMUW) with a 1-7 psig nitrogen blanket at 113F.
The steam discharge line is submerged so that steam can be condensed by the water volume in the tank.
Two rupture disks prevent overpressure at 91 PSID (differential pressure between the inside of the tank and containment atmosphere).
