RC- Reactor Coolant System Flashcards
What are the six main purposes of the RCS?
1) transfer thermal energy to the S/G in form of steam to produce power
2) secondary barrier to prevent the release of fission products
3) provide core cooling during all normal plant conditions (except shutdown cooling
4) coolant circulation of boron and lithium concentration (increase pH prevent corrosion)
5) control pressurizer level & pressure
6) RC gas vent to remove gas from pressurizer and reactor head post-accident
How does the RCS interface with the CEDMCS system?
CEDMCS controls the position, direction, rate, and duration of CEA’s in reactor vessel
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)? (EXPLANATION Question)
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? (EXPLANATION Question)
nothing. it only collects data
How does the RCS interface with the CH system?
Letdown maintains pressurizer level & purification
Charging maintains pressurizer level & provides for RCS seal injection + aux spray header (when normal spray to pressurizer is unavailable)
Charging header is for chemistry control
CVCS maintains boron concentration (increases pH, and reduces reactivity) & collects drainage of RCS in RDT
RCS pump seal bleedoff goes to VCT or alt. RDT
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
NC provides cooling to the RCP Hx (priority load):
motor air cooler
Motor lube oil cooler
Pump thrust bearing cooler
HP + LP seal coolers
How does the RCS interface with the SI system?
SI: injects borated water into RC for emergency core cooling after ESFAS signal activation
SDC: reactor coolant is cooled by shutdown cooling to bring Hot Standby (350F) —> Cold Standby (<135F)
When does SDC provide cooling for the reactor?
When the S/G’s are unavailable
When does shutdown cooling provide long term injection of borated water cooling?
after a LOCA (loss of cooling accident)
How does the RCS interface with the 13.8 kV NA system?
Supply power for RCPs
How does the RCS interface with the IA system?
Pneumatic main spray valves of 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 by transferring it to secondary system via SG
How does the RCS interface with the SS (primary sampling) system? (EXPLANATION Question)
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? (EXPLANATION Question)
monitors neutron flux from detectors outside the vessel
How does the RCS interface with the reactor vessel level monitoring system (RVLMS)/QSPDS (SH)? (EXPLANATION Question)
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 (which support fuel, CEA, in-core)
Absorb static + dynamic loads & transmit to vessel
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
-lower support structure
-In-core instrumentation nozzle assembly
-upper guide structure assembly
-core shroud
-fuel + fuel rods
-fuel assembly
-CEA
-burnable poison rods
-reactor vessel head
In the reactor vessel, what allows for radial and axial expansion of the core? (EXPLANATION Question)
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 (sub-cooled)
removes gamma radiation heat from core support barrel
What do the surveillance capsule assemblies do? (EXPLANATION Question)
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? (EXPLANATION Question)
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?
neutron absorbing pellets (Boron Carbide)
There are 48 of which CEAs?
12 finger full strength poison rods
There are 28 of which CEA’s?
four finger full strength poison rods
There are 13 of which CEA’s?
four finger part strength poison rod
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? (EXPLANATION Question)
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/deformation
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 psia
what is the normal RCS pressure?
2250 psia
What do the four 6” spring loaded safety valves on the pressurizer do?
Over-pressure protection valves lift at 2475 psia to prevent the RCS from reaching safety limit pressure (limit of 110% design pressure 2250 psig) after a complete loss of Main Turbine Generator load without simultaneous reactor trip
Where do the four safety valves discharge to?
under the water line in the RDT (reactor drain tank) where steam is released under water to be condensed and cooled/quenched
What happens if the RDT (reactor drain tank) is over pressurized by up to 10 psi? Over 10 psi? (EXPLANATION Question)
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 of pressurizer
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 (4 non-class + 2 class)
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 (based on set point entered by RO
-manually remotely by Control Room operator
-manually locally by AO by directly opening breaker during loss of Control Power
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 loop 1 cold legs (1A, 1B) of the reactor
flow is controlled by diaphragm operated globe valves to control spray valves
Each spray control valves had 1” bypass valve that is opened during normal operations for small continuous spray
What pressures are associated with the main spray flow control valves? (EXPLANATION Question)
start to open at 2275
full open at 2300
describe auxiliary spray in the pressurizer
water supplied from charging pumps (CVCS) to provide sufficient differential pressure across vessel for pressurizer main spray flow
Mainly used during plant heat up, or to allow cooldown if RCP are shutdown
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?
1 shared 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?
12” pipe connecting flow path for coolant surging to or from pressurizer
transmits pressurizer pressure to entire RCS
How is main spray bypass flowrate controlled?
Bypass flow 475 gpm
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 (redundancy, 100% capacity)
-pressure sensors installed downstream to detect leakage past inner o-ring
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, inflating o-ring improves 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 inlet nozzles —>inner plenum where transfers heat to secondary water, then flows out of U-Tube into outer plenum —> RC flows out SG outlet nozzles into cold legs of each loop
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 13.8 kV (NA) system
What is the purpose of the RCP oil lift system?
During RCP startup/stop:
provides forced lubrication to the thrust bearing 5gpm of oil at 3000 psig to the upper bearings
During RCP trip:
Auto starts to maintain LO circulation for lubrication and cooling as RCP spins down
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
De-energizes 2 min time delay after RCP start
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?
20 gpm through the auxiliary impeller to the journal bearing and lower journal bearing cavity provides cooling and lubrication
2.6 gpm through seal cavity #1 and #1 seal cooler as seal bypass flow
In the RCP shaft seal system, what is the pressure drop across each of three seals?
1st drop: 2250 psia —> 1300 psia
2nd drop: 1300 psia —> 300 psia
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 fault
oil lift flow
NC water flow
RCP seal bleed off valve full open
What are the RCP trips?
under-voltage
over-current
coast-down trip signal after 20 sec due to LOOP
Speed <600 rpm after 14 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
When will backup heater automatically energize?
-pressurizer <2200 psia
-pressurize level is >set point level (to minimize effect when steam demand changes cause level to lower and CVCS restores it —> causing in-surge of cold water to pressurizer which decrease bulk water and lower pressure)
What is power supply of lift oil pump?
Non-class 480 VAC MCC (NH)
What cools the RCP?
Nuclear Cooling Water
1st nuclear cooling water line is routed to motor air coolers and motor lube oil coolers
2nd nuclear cooling water line cools pump high pressure seal cooler, pump #1 and #2 seal coolers and pump thrust bearing lube oil cooler
What is power supply for RCP solenoid valves?
Class 125 VDC (PK) system
