NANTeL Chemistry and Water Treatment 2 — Questions and Answers
Question 1: What is the primary function of a demineralizer (ion exchange unit) in nuclear plant water treatment?
- To filter suspended particulate matter from process water
- To remove dissolved minerals and ionic impurities from water (Correct answer)
- To add pH-control chemicals to reactor makeup water
- To reduce gross radioactivity in liquid radwaste streams
Correct answer: To remove dissolved minerals and ionic impurities from water
Demineralizers use cation and anion exchange resins to remove dissolved ionic impurities, producing the high-purity water required for reactor coolant makeup and other critical systems.
Question 2: Which water quality parameter is most commonly used to assess the ionic purity of nuclear plant makeup water?
- Total hardness (mg/L as CaCO₃)
- Specific conductivity (µS/cm) (Correct answer)
- Turbidity (NTU)
- Total organic carbon (ppb)
Correct answer: Specific conductivity (µS/cm)
Specific conductivity directly measures dissolved ionic content; nuclear makeup water targets are typically a fraction of a microsiemen per centimeter, making it the primary purity indicator.
Question 3: What are the primary functions of the Chemical and Volume Control System (CVCS) in a pressurized water reactor?
- To provide high-pressure emergency core cooling during a LOCA
- To maintain RCS inventory, control boron concentration, and purify reactor coolant (Correct answer)
- To regulate steam generator secondary-side chemistry and level
- To process and store liquid radioactive waste streams
Correct answer: To maintain RCS inventory, control boron concentration, and purify reactor coolant
The CVCS maintains RCS water inventory, adjusts boric acid concentration for reactivity management, and continuously purifies coolant via letdown filters and mixed-bed demineralizers.
Question 4: Why are resin traps or fine-mesh strainers installed downstream of ion exchange vessels in nuclear plant systems?
- To monitor resin exhaustion by measuring differential pressure
- To capture resin beads that break free and prevent downstream contamination (Correct answer)
- To allow periodic regeneration of exhausted resin in place
- To measure specific conductivity of the demineralizer effluent
Correct answer: To capture resin beads that break free and prevent downstream contamination
Resin traps prevent loose or broken resin beads from traveling downstream into pumps, valves, and the reactor coolant system, where they could cause mechanical damage or chemistry upsets.
Question 5: In nuclear plant secondary chemistry, what is the operational purpose of steam generator 'blowdown'?
- Emergency venting of radioactive steam from the secondary loop
- Removal of concentrated water to control dissolved-solid buildup in steam generators (Correct answer)
- Rapid depressurization of the steam generator during a tube leak event
- Discharge of treated secondary water to the environment under an NPDES permit
Correct answer: Removal of concentrated water to control dissolved-solid buildup in steam generators
Blowdown removes a continuous or intermittent stream of concentrated secondary water from the steam generator to prevent scaling, corrosion, and tube fouling caused by accumulation of dissolved solids.
Question 6: Which water purification process uses pressure to force water through a semi-permeable membrane, rejecting dissolved salts and minerals?
- Activated carbon adsorption
- Reverse osmosis (Correct answer)
- Coagulation and flocculation
- Electrodeionization
Correct answer: Reverse osmosis
Reverse osmosis applies pressure greater than osmotic pressure across a semi-permeable membrane, allowing water molecules to pass while rejecting dissolved salts, minerals, and other contaminants.
Question 7: What is the primary reason for controlling chemistry in the Spent Fuel Pool (SFP)?
- To maintain spent fuel in a subcritical configuration
- To prevent corrosion of fuel assemblies, maintain water clarity, and control radioactivity (Correct answer)
- To recover recyclable uranium from dissolved fuel material
- To actively reduce the decay heat of recently discharged fuel
Correct answer: To prevent corrosion of fuel assemblies, maintain water clarity, and control radioactivity
SFP chemistry programs control pH, conductivity, and radionuclide concentrations to prevent corrosion of aluminum and zirconium fuel components, maintain pool water clarity for visibility, and minimize worker dose from contaminated water.
NANTeL Chemistry and Water Treatment 2
What is the primary function of a demineralizer (ion exchange unit) in nuclear plant water treatment?