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
