Charging and Let Down Subsystem Flashcards
What are the basic functions of the CVCS system?
a) maintain boron concentration, purity, chemistry and inventory in the RCS
b) means of removing gases from solution
c) means of processing and recycling liquid radwaste
d) provide RCP seal injection, controlled bleed off, and aux spray
e) provide borated water source for boration, ESF, and SFP
f) provides leak detection, limited make-up capability, and sampling
The CVCS system is designed to accept let down and provide required makeup for what heatup and cool down rate?
75F/hr heat up or cool down
How does the CVCS system provide for boron concentration adjustments?
feed and bleed
How long will the RWT last as a source of borated water after a LOCA and safety injection initiates?
20 minutes plus 10% margin
Where is let down initiated at from the RCS?
just upstream of RCP 2B
What is the delay coil and what does it do?
it is a larger section of piping (16”) designed to slow flow enough for N-16 to decay. They give a 95 second delay
What are the two fluids exchanging heat in the regenerative heat exchanger?
Letdown is giving its heat to charging
Where do the letdown flow control valves get a signal from to control their positions?
pressurizer level controller
Where does shutdown purification tap into let down?
upstream of the letdown HX so that purification can occur during shutdown
What cools the letdown Hx?
nuclear cooling water on the shell side of the hx.
What is the purpose of the two backpressure regulating valves downstream of the let down hx?
maintain upstream pressure so that flashing does not occur in the letdown line
What is the purpose of the 3 ion exchangers that let down flows through?
two are purification IX and the third is a deborating IX.
What do the IX’s remove from the system?
one is always dissolved ionic materials and particulate. A second is used periodically to remove lithium from rx coolant for pH control. The third is used near the end of core life to remove boron in order to minimize liquid waste accumulation.
What will cause letdown to bypass the IX?
High temperature
How does let down enter the VCT?
through a spray nozzle at the top of the tank gas space. The space is filled with hydrogen during normal ops to scavenge O2.
What does the VCT do?
a) acts as a surge tank for RCS to accommodate small mismatches between actual and program Pzr level
b) collect RCP bleed off
c) provide NPSH for charging pumps
How many charging pumps are normally in service?
2 (1 always, 1 normally, and 1 in standby)
Where does charging tap into RCS?
between 2A rcp discharge and the rx vessel
What will automatically close CHB-UV-515?
413F on the outlet of the Regen HX or SIAS
What will close CHA-UV-516?
SIAS or CIAS (containment isolation actuation signal)
What will close CHB-UV-523?
CIAS or let down HX outlet temp of 135F
Why don’t valves 515, 516, and 523 (unit 1 only) have handwheels?
because the handwheels could no longer operate against the increased spring pressure. spring pressure was increased to ensure that the valves will isolate on a LOCA (letdown line)
What is the biggest safety concern with the RHX?
it is a large crud trap with high rad levels during outages
Why would we want to preheat the charging water with the RHX?
minimize thermal shock on the RCS inlet nozzle
How do the letdown control valves fail on a loss of air or power?
closed
What flow values do the let down control valves limit flow to and why?
lower limit 30 GPM because the valve can’t really control at any lower flow rate.
upper limit of 135 GPM to prevent channeling in the IX.
When are both let down control valves placed in service?
when RCS pressure is less than 1050 psia to allow adequate let down flow (flow is limited by RCS pressure and D/P)
What is the purpose of the letdown control valve bypass valve?
it allows 1/2 GPM of flow around the letdown control valves through an orifice to warm the Let down HX and downstream components if let down has been secured while at power.
How long must the bypass be opened for if let down has been secure for >22 minutes?
at lease four minutes prior to initiating let down to minimize thermal stresses
What pressure do the let down backpressure control valves maintain upstream and downstream of the valves?
350-375psig upstream
40-95psig down stream
At what temperature do the back pressure control valves isolate the let down HX?
148F
When are the purification filters replaced?
D/P >25 psid at 72GPM flow or rad levels > 5R/hr
What is the set point of RU-155 and where is it located?
85 mR/hr
it is in the middle of a loop in the let down piping in the aux building on the 120Ft level
What type of resin is in the purification IX?
mixed bed H-OH
What type of ion exchanger is used for de-borating?
Anion
What are the flow and temperature limits for the purification IXs?
150 GPM to prevent channeling and 140F to prevent resin bed damage
What happens in the IX when let down/NCW temperature increases?
boron will come out of the ions and drop RCS temperature
What is the capacity of the VCT?
4900 gallons
What is the normal level in the VCT?
33-44%
When will CHV-501 close?
when level in the VCT is at 5% (prevents air binding of the CH pumps)
What will cause CHV-536 to open automatically?
if CHV-514 loses power and VCT is <5%
What pressure is the VCT normally maintained at?
between 20 & 25psig
What do the charging pumps provide?
a) RCS makeup
b) aux spray
c) RCS boration
d) RCP seal injection
Where do the charging pumps get power from?
PGA or PGB
What are the 3 modes of operation for the charging pumps?
a) always running (no automatic signals or controls will stop the pump)
b) normal running mode (high pzr level will stop the pump, but when the alarm clears, the pump will re-start)
c) standby mode (low level in pzr will start the pump and the pump will stop when the condition clears)
When does the charging pump seal water pump start?
when its associated CH pump starts if the seal water pump is in auto.
How long can you run a charging pump without seal water in an emergency?
50 hrs
What are the bladders on the suction stabilizer and pulsation dampeners filled with?
N2
What is the purpose of the charging line backpressure control valve (CHN-PDV-240)?
a) maintain back pressure for Aux spray
b) back pressure for RCP seal injection
c) back pressure to minimize charging pump pulsations
d) fails closed on loss of power or instrument air
What is the purpose of CH-V239?
if CH-V240 fails open, it would close to ensure Aux spray is available
Why is there a spring loaded check valve installed to bypass CH-V239 & CH-v240?
maintain 200 psid back pressure and allow for isolation of the two valves for maintenance or failure
What are the power supplies to the Aux spray valves?
PKA & PKB
What is used to heat the seal injection heat exchanger?
Nothing, the aux steam is currently blanked off.
How many filters are normally in service in the seal injection line?
One
What will cause the RCP seal injection bleed off valves to auto close?
CSAS, but flow will still be available via a relief valve to the RDT.
What components make up the chemical addition unit?
Chem add tank, outlet strainer, and chem add pump
Where does the chem add pump discharge to and why?
Charging header just upstream of the RHX.
Allows addition of chemicals to RCS when charging header containment isolation valve is closed and prevents the addition of a high pH fluid directly into CH pump suction
What is the capacity of the chem add tank?
8 gallons
What supplies water to the chem add tank?
RMW
What is the capacity and power supply to the chem add pump?
Max of 25 GPH and it’s powered from NH.
What chemicals are added to the RCS while the plant is shut down?
Hydrazine and hydrogen peroxide
What does hydrazine do?
Scavenges O2 at <250F
What is Lithium added to the primary for?
Increase pH near end of life.
Lithium 7 is also used to reduce tritium production.
Where can the RMWPs discharge to?
RX makeup supply header, RWT, batch tank eductor, or directly to CH pump suction.
What type of water is stored in the RWT?
Borated water
Where do the BAMPs take a suction from?
Refueling water tank
What is the capacity of the RMWT?
480,000 gallons.
What tank is an alternate source of water for the A & B AFPs?
RMWT
Where is the RMWT vented to and where does it overflow to?
Vented to atmosphere
Over flows to hold up tank sump
What type of valve is CH- 210X?
CCI drag disk stack valve
What does ch-210x do?
Controls flow of RX m/u water flow to the VCT through make up stop valve 512.
Where does the operate signal come from for 210X?
From the makeup controller and is controlled from B03. With the VCT makeup controller in dilute mode, the flow control valve closes when the flow reaches the desired total.
What is the capacity of the RWT?
750,000 gallons
What is the required boron concentration for the RWT?
4000-4400 ppm
Where can the RWT send water to?
BAMPs, CH pump suctions, spent fuel pool, spent fuel pool clean up pumps, ESF pumps
Where is the RWT vented to?
Fuel building normal exhaust
Where can the BAMPs take a suction from?
RWT or spent fuel pool
What limits the output capacity of the BAMPs?
BAMPs can put out 165 gpm, but CH-V210Y can only pass 150 gpm, so the BAMPs may not be able to exceed the capacity of 3 charging pumps running like they should.
What valve is the boric acid flow control valve and what type of valve is it?
CH-210Y. And it is a drag disk stop valve
