NANTeL Chemistry and Water Treatment 1 — Questions and Answers
Question 1: What is the primary purpose of maintaining proper pH levels in the Reactor Coolant System (RCS) of a PWR?
- To increase heat transfer efficiency
- To minimize corrosion of reactor components (Correct answer)
- To enhance neutron moderation
- To prevent steam formation
Correct answer: To minimize corrosion of reactor components
Maintaining proper pH (typically 6.9–7.4 for PWRs) minimizes corrosion of reactor coolant system materials including stainless steel and Inconel alloys.
Question 2: In a Pressurized Water Reactor (PWR), what chemical is dissolved in the reactor coolant to provide chemical shim reactivity control?
- Sodium hydroxide
- Lithium hydroxide
- Boric acid (Correct answer)
- Hydrazine
Correct answer: Boric acid
Boric acid is dissolved in PWR reactor coolant as a chemical shim for reactivity control because boron-10 is a strong neutron absorber.
Question 3: What is the purpose of adding lithium hydroxide (LiOH) to PWR reactor coolant chemistry?
- To absorb excess neutrons during power transients
- To maintain alkaline pH and minimize corrosion (Correct answer)
- To reduce dissolved oxygen concentration
- To prevent crud deposition on fuel pins
Correct answer: To maintain alkaline pH and minimize corrosion
LiOH is added to PWR coolant to maintain a slightly alkaline pH that minimizes corrosion while remaining compatible with the boric acid chemistry program.
Question 4: In nuclear plant chemistry, what is 'crud' and why is it operationally significant?
- Radioactive gases released through fuel cladding defects
- Corrosion products deposited on fuel assemblies that can become activated (Correct answer)
- Chemical byproducts formed when boric acid reacts with coolant
- Dissolved minerals introduced by makeup water
Correct answer: Corrosion products deposited on fuel assemblies that can become activated
Crud refers to corrosion products (primarily iron and nickel oxides) that deposit on fuel surfaces; these products can become activated in the neutron flux and increase plant radiation fields.
Question 5: In a Boiling Water Reactor (BWR), what is the primary chemistry strategy used to mitigate Intergranular Stress Corrosion Cracking (IGSCC) of stainless steel piping?
- Boric acid injection into the feedwater
- Hydrogen Water Chemistry (HWC) to suppress dissolved oxygen (Correct answer)
- Lithium hydroxide additions to raise coolant pH
- Periodic injection of zinc acetate only
Correct answer: Hydrogen Water Chemistry (HWC) to suppress dissolved oxygen
Hydrogen Water Chemistry (HWC) injects hydrogen into BWR feedwater to recombine with dissolved oxygen at the core, reducing electrochemical corrosion potential and mitigating IGSCC.
Question 6: What is the primary function of hydrazine (N₂H₄) when used in nuclear plant secondary water chemistry?
- To raise steam generator secondary-side pH above 9.5
- To serve as a supplemental neutron absorber in the feedwater
- To scavenge dissolved oxygen and prevent oxidative corrosion (Correct answer)
- To prevent mineral scaling on steam generator heat transfer surfaces
Correct answer: To scavenge dissolved oxygen and prevent oxidative corrosion
Hydrazine reacts with dissolved oxygen (N₂H₄ + O₂ → N₂ + 2H₂O) to scavenge oxygen from secondary feedwater, protecting steam generator tubes and feedwater piping from oxidative corrosion.
Question 7: What does the term 'Activity Transport' describe in nuclear plant chemistry operations?
- Movement of radioactive material in NRC-approved shipping casks
- Circulation of activated corrosion products through the reactor coolant system (Correct answer)
- Transfer of spent fuel assemblies from the reactor to the spent fuel pool
- Migration of fission gases through defective fuel cladding
Correct answer: Circulation of activated corrosion products through the reactor coolant system
Activity transport describes how activated corrosion products (activated crud) circulate through the RCS after passing through the neutron flux, elevating radiation fields on out-of-core piping and components.
NANTeL Chemistry and Water Treatment 1
What is the primary purpose of maintaining proper pH levels in the Reactor Coolant System (RCS) of a PWR?