SC-Secondary Chemical Addition Flashcards
Why is hydrazine added to the CD system?
To scavenge oxygen, reducing the potential for steam generator and feed system piping corrosion
promotes a protective oxide layer on metal surfaces, etc.
reduces oxygen concentration to .01 PPM from the 5 PPM the main condenser accomplished via AR system
Why is Ammonia, ETA (ethanolamine) and hydrazine added to the CD system during power operation?
ammonia and ETA:
- To elevate secondary pH, minimizing corrosion
- they reduce general corrosion at elevated temperatures
- promote a protective oxide layer
hydrazine:
oxygen scavenging
Where is Hydrazine and Ammonia added into the CD system? Where else can chemicals be added?
Into the condensate line downstream from the condensate polishing demineralizer resin traps
Into the suction lines of the non-class auxiliary feedwater pump, the blowdown system, and the steam generator downcomer feed lines
Which Unit has been modified to inject hydrazine down stream of #5 and #7 HPFW heaters? Why?
Unit 3
To help reduce the iron transport (carry over) in the secondary
What is the general flowpath of the Secondary Chemistry Control system?
Hydrazine and Ammonia are manually injected as needed with associated pumps taking suction on their respective storage tanks
There are three different addition pumps inn both systems. The steam generator pumps can add chemicals to the downcomer feed lines only. The condensate and wet layup addition pumps can add chemicals into the condensate line downstream from the condensate polishing demineralizers and resin traps, the suction of ‘N’ AFP, shell side of the #5 and 7 HPFW heaters and the steam generator blowdown lines
Other Amines may be added with this system
What system provides the normal supply of dilution water for ammonia and hydrazine tanks? Where else can this water be provided from?
DW
Condensate Service Header
What is the purpose of the Bulk ammonia storage tank? What is used as the driving force to move ammonia from the delivery truck to the bulk storage tank?
provides ammonia to the ammonia addition tanks via transfer pumps
Service Air
The SC hydrazine and Ammonia addition pumps can discharge to the S/Gs at what two different points?
First point is in the downcomer feed line between the FW regulating valves and the FW isolation valves through the wet layup recirc line
Second point is the downcomer feed line downstream of the FWIVs and upstream of the double check valves
What does QM do for the SC system?
Heat tracing
What is the purpose of the two SC Ammonia Addition Tanks?
Filled with ammonia from the bulk storage tanks and supply the ammonia added to condensate to maintain pH at 9.3 to 9.6
also filled with ETA from a liquibin
What is the purpose of the SC Ammonia Transfer pumps and what would stop them automatically? Where are they located?
Two redundant pumps are furnished for transferring ammonia from the bulk storage tank to the ammonia addition tanks
Pumps automatically stopped upon a low-low level condition in the bulk ammonia storage tank or an electrical protection trip
north yard by bulk storage tank
Each of the Chemical Addition/Metering Pumps has a relief valve. What are they set to and where does the water get directed to?
650 psig
Routes the fluid to the pump suction
What dictates the concentration of chemicals of the day tanks?
Chemistry Control Instruction (CCI)
What would a loss of Ammonia Addition system have on the plant?
Loss of pH control on secondary systems. pH will decrease which will increase the corrosion rates in the secondary.
Chemistry department will make recommendations that may include shutting down the plant
How is the plant affect by a loss of Hydrazine Addition System?
A loss of oxygen control in the secondary, increasing corrosion rates
Extended operation at high oxygen concentration will require a plant shutdown
What is an adverse effect on the secondary chemistry control system of full flow through the CD demin vessels?
Very rapid decreases in chemical concentration
Loss is more gradual when on full bypass
What are the two subsystems of the secondary chemical addition system? What is the purpose of these systems?
chemical monitoring and chemical addition
continuously monitor and inject chemicals to establish and maintain the proper
chemistry within the Condensate, Feedwater, and Steam Generator secondary side water to minimize corrosion during all modes of operation.
What is powered by NH in the secondary chemistry control system?
ammonia and hydrazine pumps
Where in the ED system is ammonia and hydrazine injected?
shell side of the #5 and #7 feedwater heaters
it then drains with the ED fow to the heater drain tank and pumped to the suction of the main feed pumps
What does the turbine building HVAC system do for the SC system?
ammonia and hydrazine addition tanks are vented to the turbine building roof, through the chemical addition tanks exhaust fan
What are some chemical handling precautions for ammonia hydroxide?
400 gallon or more spill may impact control room habitability of all units and upon any large spill the control room must be contacted
must wear skin and eye protective equipment
don’t breath it in or get it on your skin
flush contacted areas with water
ventilate area of spill
Concening the SC ammonia addition tanks, what mixes its contents and what is the maximum concentration and why?
motor driven mixer
12%
to ensure the control room has 2 minutes to don the breathing apparatuses
What is the normal line up for the SC ammonia addition tanks? Where are these tanks located?
both feeding the in-service addition pump
southwest corner of the 100’ turbine building, in the secondary chemistry addition basin
How often are the SC ammonia addition pumps running? where are they located?
one is running continuously because the volatile ammonia will be scrubbed from the condensing steam in the Air Removal section of the Main Condenser or be removed by the condensate demineralizers (if in-service)
(two running pumps should be minimized)
Turbine Building 100’ southwest, in the
Secondary Chemical Addition basin
Why is ETA more effective than ammonia in the SCCS (secondary chemistry control system)?
lower distribution coefficient at all
temperatures
(ETA will stay in solution longer and condense more readily than Ammonia will).
Therefore, ETA will significantly reduce the corrosion of the piping in the Extraction Steam and
Drains (ED) system.
What is the downside of using ETA in the secondary chemistry control system?
more expensive and fouls the CD demin resin
What are some of the handling precautions for the chemicals added to the secondary system?
wear chemical resistant PPE, safety goggles and face shield
don’t get it on/in you
What is the purpose of the ETA transfer pump? Location?
transfers the ETA from the liquibin to either of the ammonia addition tanks
Turbine Building 100’ southwest, in the Secondary Chemical Addition basin.
When do area operators know that its time to refill the ETA liquibins? Who fills them? Who verifies they are the correct bin prior to refilling? Location of liquibin?
when the level gets below the lowest metal frame bar of the bin
Utilities and chemistry
operations and chemistry
Turbine Building 100’ southwest, in the Secondary Chemical Addition basin.
What chemicals are added to the secondary system while in outage and why?
Dimethylamine (DMA) is added for scale control and pH control
Carbohydrazide is added for oxygen scavenging during outages when personnel will be entering secondary side for maintenance
What is special about the hydrazine liquibin outlet valve? How is bin level obvserved? Where is the liquibin located?
reverse acting, to prevent inadvertent operation
no local level on bin, subtract number of inches in the addition tank from recorded liquibin level
Turbine Building 100’ southwest, in the Secondary Chemical Addition basin.
What is the purpose of the hydrazine transfer pump? location?
to transfer hydrazine from the liquibin to one of the hydrazine addition tanks
Turbine Building 100’ southwest, in the Secondary Chemical Addition basin.
Purpose of the hydrazine addition tanks? Location?
- store diluted hydrazine for injection into the secondary system
- accepts dilution water from DW or condensate service header
- one tank in-service at a time
- vents to the HT HVAC system
Turbine Building 100’ southwest, in the
Secondary Chemical Addition basin.
What is the purpose of the hydrazine liquid control panel? Electric control panel? Locations of both?
(liquid) used to monitor, control and establish flow between:
- the liquibin and the addition tanks
- hydrazine addition pump discharge to secondary components
(electric) used to monitor and control the Hydrazine Transfer and Addition Pumps.
Turbine Building 100’ southwest, in the
Secondary Chemical Addition basin.
What is the flowpath of the PAA (polyacrylic acid) injection system?
PAA pumps take suction on PAA tote, discharge to vertical section of feedwater lines directly downstream of #7 FW heaters
What is the purpose of adding PAA (polyacrylic acid) to the secondary system?
it reduces the accumulation of iron oxide in the steam generators by promoting suspension of particulates in the water
removed by S/G blowdown system
Purpose of the hydrazine addition pumps? Location?
- inject hydrazine from the addition tanks into the secondary systems
- parallel use of these pumps is limited
- VFDs
- feedrate is controlled by stroke length
- PRV at 650
Turbine Building 100’ southwest, in the
Secondary Chemical Addition basin.
What are the major components in the PAA (polyacrylic acid) injection system?
180 gallon tote
control panel- power supply switch, pump switches, suction and discharge valves
carboys- supply suction to the PAA pumps when the chemical tote is unavailable
PAA pumps- posi. disp., flow rate in mL/min, DC powered, must be flushed when shutdown
What is he purpose of the hydrazine vacuum drag modification?
to reduce the risk of shutdown due to problematic hydrazine pumps
injects from a new hydrazine addition tank and the motive force is the suction of the condensate pumps and main condenser vacuum
only usable when at power and CD demins are bypassed
Where will the hydrazine vacuum drag tank be located? How will it be filled? What is provided as a secondary containment for this tank? Where is this tank vented to?
100’ turbine building, north east corner, next to condensate pump suction lines
by the existing hydrazine transfer pump
double walled tank
system must be open to atmosphere, but a tank vent will exhaust outside the turbine building
Flow path of the hydrazine vacuum drag system?
two injection lines controlled by two metering valves each, gross flow control and fine flow control
full flow isolation valves in each line
thermowell in the CD pump suction lines for good mixing
