RC- Reactor Coolant System Flashcards
What are the three main purposes of the RCS?
transfer thermal energy to the S/G
secondary barrier to the release of fission products
provide core cooling during all normal plant conditions
How does the RCS interface with the CEDMCS system?
CEDMCS controls the direction, rate, and duration of CEA’s
also controls the magnetic jack coils to CEDM’s
Can CEA motion be controlled automatically or manually?
both
How does the RCS interface with the RI (Fixed in-core instrumentation system, or FICS)?
measures neutron flux,
coolant temp. in 61 locations
monitors core characteristics to assure we do not exceed allowable limits
In the RCS, what does the RI system control?
nothing. it only collects data
How does the RCS interface with the CH system?
maintains pressurizer level,
chemistry control,
boron concentration
provides RCP seal injection
collects RCS discharges
supplies aux spray to pressurizer when normal spray path unavailable
purifies RCS
What discharges from the RCS does the CH system collect?
drainage for maintenance
RCP seal bleed off
Primary safety valve discharge
identified leakage
How does the RCS interface with the NC system?
intermediate barrier between RCS and the PW system
provides cooling to the RCP motor air cooler, lube oil cooler, thrust bearing lube oil cooler, and seal coolers
How does the RCS interface with the SI system?
emergency core cooling and boron injection for reactor shutdown
long and short term cooling
When does SDC provide cooling for the reactor?
When the S/G’s are unavailable
When does shutdown cooling provide long term cooling?
after a LOCA
How does the RCS interface with the NA system?
powers reactor coolant pumps
How does the RCS interface with the IA system?
supplies control air to the pressurizer spray valves, controlled bleed-off containment isolation valves, and RDT bleed-off isolation valves
How does the RCS interface with the SG (main steam) and FW (feed water) systems?
remove heat from RCS
How does the RCS interface with the SS (primary sampling) system?
samples PCS loop 1 hot leg, surge line, and pressurizer steam space
used for chemistry and boron control
How does the RCS interface with the SE (Ex-core neutron monitoring)system?
monitors neutron flux from detectors outside the vessel
How does the RCS interface with the reactor vessel level monitoring system (RVLMS)/QSPDS (SH)?
provides reliable (class) indication of the vessel level online and during accidents
What is the purpose of the reactor vessel?
contains the core and vessel internals
directs flow of coolant through the core
part of RCS pressure boundary to prevent fission product release
What are the internals of the reactor vessel?
core support barrel assembly and the upper guide structure assembly
In the reactor vessel, what allows for radial and axial expansion of the core?
the core support barrel assembly
What components make up the core support barrel assembly?
Core support barrel
lower support structure and instrument nozzle assembly
core shroud assembly
In the reactor vessel, what supports the upper ends of the fuel assemblies and protects the CEAs from coolant cross flow?
the upper guide structure assembly
What components make up the upper guide structure assembly?
CEA shroud assembly
upper guide structure support barrel
What is the main flow path of the coolant within the reactor vessel?
through inlet nozzles, down between vessel wall and core barrel, through flow skirt section and into lower plenum, up through core to outlet region, through CEA shroud tubes and through outlet nozzles
In the reactor vessel, what purpose does the core bypass flow serve?
prevents stagnation of water in low flow areas
keeps primary coolant below saturation temp
removes gamma radiation heat from core support barrel
What do the surveillance capsule assemblies do?
monitor radiation induced changes in vessel materials
How many CEA’s are in the core?
89 total
What are the three types of CEAs and how many are there of each?
5 regulating groups (1, 2, 3, 4, 5)
2 shut down groups (A and B)
2 part strength groups (P1 and P2)
What are CEA pellets made of?
Boron Carbide
There are 48 of which CEAs?
12 finger full strength
There are 28 of which CEA’s?
four finger full strength
There are 13 of which CEA’s?
four finger part strength
How many Fuel assemblies do the 12 finger CEAs interact with?
5
How many fuel assemblies do the four finger CEAs interact with?
1
Which type of CEA do the shutdown banks A and B use?
12 finger only
Which type of CEA do the regulating groups use?
12 and 4 finger
What are the major components of the fuel assemblies?
fuel spacer grids
upper end fitting
hold down plate
lower end fitting
guide tubes
fuel rods
describe the construction of a fuel rod
filled with uranium pellets with a compression spring and spacer disks at each end of a zirconium alloy tube seal welded with end caps and pressurized with helium
Why are fuel rods pressurized with helium?
improve thermal conductivity of pellet to clad gap
prevent clad collapse
Why are the fuel pellets “dished” at the ends?
account for thermal expansion and fuel swelling
What maintains the RCS in a sub-cooled condition?
the pressurizer
What acts as a surge volume to minimize pressure changes during load transients?
pressurizer
What prevents the RCS from over pressurizing?
the pressurizer
What is the RCS safety limit pressure?
2750
what is the normal RCS pressure?
2250
What do the four spring loaded safety valves on the pressurizer do?
prevent the RCS from reaching safety limit pressure
Where do the four safety valves discharge to?
under the water line in the RDT (reactor drain tank)
What happens if the RDT (reactor drain tank) is over pressurized by up to 10 psi? Over 10 psi?
tank reliefs to gaseous radwaste
tank relieves to containment through a rupture disk
What is the purpose of the pressurizer heaters?
to boil the water to increase the mass of steam in the vapor space
How many pressurizer heaters are there? How many banks are they divided into?
36
8
How many of the pressurizer heater banks are back ups? How many proportional banks are there?
6
2
How many heaters are in the proportional pressurizer heater banks?
3 each
How many heaters are in the back up pressurizer heater banks?
banks B1 and B2 each have 3
banks B3, 4, 5, and 6 all have 6 heaters each
How many kW are each of the pressurizer heaters rated at?
50
How can the pressurizer heaters be controlled?
automatically by the pressurizer pressure control system
manually by operator
Where are the pressurizer heaters powered from?
two back up banks are class powered from PGA/PGB
all other heaters are powered from NG
What is the purpose of the pressurizer spray system?
to reduce pressure by condensing steam in the vapor space of the pressurizer using subcooled water
Describe Main spray in the pressurizer
subcooled water is supplied from the cold leg of the reactor
flow is controlled by diaphragm valves
What pressures are associated with the main spray flow control valves?
start to open at 2275
full open at 2300
describe auxiliary spray in the pressurizer
water supplied from charging pumps
two solenoid valves to control flow
Why is Aux spray more effective than main spray?
charging water is 110* less than cold leg temp (555*).
How many spray heads are there for main spray and aux spray?
they share one spray head
Where does the pressurizer surge line connect the pressurizer to?
loop 1 hot leg
What is the purpose of the pressurizer surge line?
flow path for coolant surging to or from pressurizer
transmits pressurizer pressure to entire RCS
How is main spray bypass flowrate controlled?
manually adjusted to establish a temp differential of less than 70* between cold leg and spray nozzle piping
Why won’t the main spray flow function without the RCPs in service?
reactor vessel differential pressure isn’t sufficient to maintain spray flow without the RCPs
why is maintaining constant main spray valve bypass flow important?
minimizes thermal shock on pipes, valves and spray nozzle
minimizes thermal stratification in piping
keeps chemistry uniform throughout RCS and pressurizer
If the pressurizer spray valve bypass valves are NOT isolation valves, what are they?
metering valves
Describe the sealing mechanism between the reactor vessel and the closure head.
two silver plated inconel, self- energizing, metal O-rings sit in machined grooves on the closure head flange.
the outer o-ring is passive until the inner o-ring fails
In reference to the reactor vessel head, what is a self-energizing o-ring?
the O-rings are drilled around the inside allowing RCS pressure to pressurize the o-ring and form the seal
What is the reactor vessel head seal drain valve? Where does it drain to?
When the inner reactor head o-ring starts leaking, causing an increase in pressure between the O-rings, this valve drains the coolant between the O-rings
RDT
What two sections of the steam generator interfaces with the RCS?
primary chamber
tube sheet and U-tubes
Where is the primary chamber located in the steam generator and what is its purpose?
its in the bottom of the steam generator
part of the RCS boundary and directs flow through the steam generator
What is the design pressure and temperature of the steam generator primary chamber?
650*F
2500 PSI
What is the purpose of the steam generator tube sheet and U-tubes? How thick is the tube sheet?
separate primary from secondary sides of the steam generator
permit heat removal from the primary side without radioactive material transfer
23.5”
What is the difference between a steam generator tube rupture and a primary leakage?
S/G tube rupture is when the tube penetration is bad enough that the CVCS can’t maintain pressurizer level
primary leakage is when the CVCS can maintain pressurizer level
Why is a steam generator tube rupture bad?
reactor coolant would be leaking into the main steam system allowing passage of radioactive material
What are the primary functions of the reactor coolant pumps?
RCS boundary
provide flow in RCS
add heat to primary loop during plant heat ups
provide motive force for main spray valves
Are the reactor coolant pumps powered from class or non-class ?
non-class
What is the purpose of the RCP oil lift system?
provides forced lubrication to the thrust bearing
How long before an RCP start is its respective oil lift pump started and why? how long after start up will the oil lift pump run?
7 minutes before so the oil can push the thrust bearing pads away from the thrust runner
2 after
What components make up the RCP oil lift system?
oil reservoir, filter, accumulator and oil lift pump
What is the RCP oil lift pump auto feature?
prior to stopping RCP, oil lift pump handswitch must be put to auto–
RCP will stop, oil pump will turn on until operator secures handswitch
What minimizes leakage along the RCP shaft, also being an RCP boundary?
shaft seal assembly
What components make up the RCP shaft seal assembly?
casing, three tandem mechanical pressure reduction seals, auxiliary impeller
What system injects water at 6.6 gpm to the RCP shaft seal assembly?
charging
What is the total flow through the RCP shaft seal assembly?
22.6 gpm
In the RCP shaft seal assembly, where does majority of the seal water flow get routed to?
through the auxiliary impeller to the journal bearing and lower journal bearing cavity
In the RCP shaft seal system, what is the pressure drop across each of three seals?
42% of system pressure for first two seals, 16% across third seal
In the RCP shaft seal system, where is leakage past the vapor seal directed to?
Reactor Drain Tank
Will the seal bleedoff isolation valves close while the RCP is running?
no
What is the purpose of the RCP motor flywheel?
increases rotating inertia of the RCP which increases coast down time during LOP to pump motors
What is the purpose of the anti-reverse rotation device?
stops a pump when it reaches zero speed so it can withstand reverse torques
Name the start permissives of the RCPs.
no motor fauls
oil lift flow
NC water flow
RCP seal bleed off valve full open
What are the RCP trips?
under-voltage
over-current
coast-down
less than 600 for a few seconds during start up
What is the tech spec limit for RCS pressure?
2750 psia
What is the tech spec range for pressurizer pressure?
2130-2295 psia
What is the tech spec Tcold RCS loop temperature limit?
545*F
Per tech spec, in mode 1 and 2, how many RCS loops have to be OPERABLE and in operation?
two
Per tech spec, in mode 3, how many RCS loops must be OPERABLE and in operation?
1
Per tech specs, in mode 4, how many SDC loops must be OPERABLE? How many in operation?
2
1
Per tech spec, How many pressurizer safety valves must be OPERABLE with lift settings between 2450-2549 psia
4
What is the heat sink to the RCS under normal operations?
Main steam and main feedwater systems
Where can I get samples of the RCS?
Loop 1 hot leg
Surge line
Pressurizer steam space
What affect does the data collected from the surveillance capsule assemblies have on the plant?
Can have an effect on allowable heat up and cool down rates and the minimum temperature for reactor vessel pressurization
