Steam Generator Blowdown Flashcards
What is the purpose of the SC system?
To compensate for the impurity concentration effect on the steam generators by continuous blowdown
Also maintains the SG in wet lay-up by providing the capability to mix, sample and add chemicals to the SGs
What are the 3 types of blowdown used?
Normal, abnormal and high rate
Where are the 3 blowdown connections on the SG and what does each line have?
Hot leg blowdown, cold leg blow down and down comer blow down
Each line has 2 auto containment isolation valves that will isolate blowdown system on AFAS, MSIS & SIAS
Which blowdown line is the primary connection used?
Down comer blowdown
When a blowdown is aligned to the BFT, where does the resultant vapor discharge to?
To the heater drain tank equalizing line or the condenser
What happens to the liquid in the flash tank?
processed for reuse by cooling in the blowdown heat exchanger, filtering, demineralizing and discharging to the condenser hotwell
What allows the plant to divert secondary water with unsatisfactory chemistry and where does it go?
Steam generator overboard piping
To the retention basin
What happens if radioactive concentration gets above a predetermined setpoint?
Isolation valve SCN-HV1283 will auto close
What provides cooling to the blowdown heat exchanger?
CD system
What is used to backflush the blowdown basket strainer?
DS
Which LPFW heater can the BFT liquid be directed to?
3
Where is the condensate cooling water for the BDHX returned to?
Discharge of the ED pump just prior to the suction of the main feedwater pumps
What is used to cool the blowdown demin sample coolers?
Normal chill water WC
If there is any activity present in the low TDS sump, where can I send it to?
LR TDS system
The SGBD demin High TDS sump is normally pumped to where?
CWNT
How are the blowdown flow control valves operated?
What position do they fail in?
air operated
Fail closed on loss of air or power
Where is the blowdown normally controlled from?
control room
How is the BFT sized?
For processing continuous abnormal rate blowdown from 1 SG and normal rate for the other
How is operation affected when Demin/reten LV (HG-3B/3C) is selected?
Demin outlet valve (HV-3B) is modulating to maintain BFT level and the blowdown flow to the condenser or HV-3C is lined up and the blowdown flow is going to the retention pond.
The demin bypass HV-3A is closed
How is operation affected when “BYP DEMIN MODE” is selected?
HV-3A is modulating to maintain BFT level with the flowdown flow going to feedwater heaters 3A, B, and C. Vlave HV-3B is closed
What is SCN-PV-4A and what does it do?
A pressure regulating valve in the vapor line from the BFT
Maintains flash tank pressure at nominal setting of 200psig but is adjustable by the operator
When would SCN-PV-4B be opened?
When both heater drain tanks are out of service of it is desirable to discharge the vapor directly to the condenser, the isolation valves downstream of PV-4A are closed and 4B is opened
Also opens when valve 4A cannot maintain the flash tank pressure at its proper setting
How are the 2 valves operated and what is their fail fail position? (SCN-PV-4A & -4B)
Air operated
Fail open on a loss of air or loss of power
After the plant power is changed by greater than 5% why does the operating procedure direct an operator to close the BFT to the heater drain tank equalizing valves?
To reduce secondary chem hideout by having all blowdown that ends up in the BFT to go to the condenser
What makes up the blowdown demin package?
2 mixed bed regen type units in series
a filter that removes suspended solids from the blowdown liquid before demineralization
What could cause the demin outlet valve (SCN-HV-3B) to auto shut?
In this case how would we reestablish blowdown flow?
If that outlet valve is controlling BFT level and a high demin inlet temp is sensed
Take switch to “BYP DEMIN MODE”
What happens if high sodium greater than 1 ppb is detected in one of the vessels?
The affected vessel is removed from service
What happens if just one vessel is in service and a high sodium is received?
Vessel goes into 30 min rinse to see if the concentration will be reduced
What would be considered high D/P for a vessel?
25 psi
What flows thru the tube side of the BDHX?
Condensate
What is the outlet temp of the BDHX controlled at?
less than 135F
When is a situation where the abnormal rate of blowdown would be used?
To correct abnormal steam generator chemistry
What is the SG blowdown systems role in SG wetlay up operations?
2) What would be different during wet layup cleanup operations?
Water from the SG is recirculated using the SG wet layup pumps.
This water is pumped from the SGs thru the blowdown lines and recirculated back to the SGs via the downcomer lines
The blowdown system provides a means of chemistry to add chemicals to the SGs during wet lay up operations
2) same as above except the water is processed thru the blowdown demins prior to returning to the SG downcomer lines
What else can we use the wet layup pumps for?
To pump down SGs during drain and refill operations as required for maintenance
What is the rated shutoff head for wet lay up pumps?
220 psi
What is the optimal flow and maximum flow for these pumps?
Optimal flow @ 160gpm @ 180psi
Maximum flow @ 220gpm @ 100psi
Where are the switches for the recirc pumps located and where do they get power from?
located in containment next to the pumps on the 80’
NH
How is the system affected by the loss of IA?
Blowdown to flash tank control valves fail closed and blowdown to condenser control valves fail closed stopping blowdown.
Also, the flash tank condensate level control valve to FW heater fails closed, the BFT pressure control valve to heater drain tank fails open and the BFT control valve to condenser fails open
How is the system affected by a loss of condensate flow to the blowdown heat exchanger?
Inlet water temp to the blowdown demins will rise to the point that the demin outlet valve will auto close
Blowdown is secured to prevent overfilling and over pressurizing the BFT
How is the plant affected by loss of blowdown system?
While at power conductivity increases in the SGs leading to significant corrosion rates in the SGs
This requires chemistry to initiate CCIs or direct control room to shut down the system
Demand for SG feed will drop during loss of blowdown
How much of the wet layup recirc water enters the tube bundle area of the SG thru the recirc line?
40%
