⚛️ NPCIL Interview Experience – Mechanical Engineering (GATE 2025)

• Type: Technical + Conceptual
• Mode: Offline Interview
• Duration: ~35–40 minutes
• Panel: Friendly yet probing with both basic and application-based questions

🔍 Key Interview Questions & My Responses

✅ General Motivation & Nuclear Concepts

1. Why do you want to join NPCIL?
   • I explained my strong interest in working on national infrastructure, clean energy, and contributing to India’s nuclear technology advancements. I emphasized NPCIL’s role in sustainable power generation and public service.
2. Difference between Nuclear and Thermal Power Generation
   • I elaborated on:
     • Energy Source: Nuclear uses fission; thermal uses fossil fuels.
     • Forms of Energy: Nuclear uses nuclear binding energy; thermal uses chemical energy.
     • Fuel Efficiency & Emissions: Nuclear is more efficient and cleaner.
3. Is Fission a Chemical Reaction?
   • I clarified that fission is a nuclear reaction, not chemical.
   • It involves changes in the nucleus, unlike chemical reactions that involve electrons and bonds.

🔄 Reaction Kinetics & Thermodynamics

4. Reversible and Irreversible Reactions – Explain with Graph
   • I was asked to draw a concentration vs. time curve for a sequential reaction:
     A → B → C
   • I explained:
     • A decreases sharply.
     • B increases and then decreases.
     • C increases gradually.
   • I also discussed characteristics of reversible vs. irreversible reactions.

🧲 Adsorption & Surface Chemistry

5. What Are the Favorable Conditions for Adsorption?
   • High surface area
   • Low temperature
   • High pressure (for gas adsorption)
   • Nature of adsorbent and adsorbate

🧴 Materials & Fabrication

6. Various Types of Plastics:
   • I explained:
     • Thermoplastics (e.g., PVC, polyethylene)
     • Thermosetting plastics (e.g., Bakelite, epoxy)
7. Difference Between Pipes and Tubes:
   • Pipes: Focus on internal diameter (for flow)
   • Tubes: Focus on external diameter (for structure)
8. Schedule Number in Pipes:
   • Indicates wall thickness of pipe
   • Higher schedule = thicker pipe
9. How Are Tubes Joined?
   • Welding, brazing, threading, and flange connections
10. How to Store Tubes Properly?

• In horizontal racks, grouped by size and material
• Avoiding corrosion with caps and dry storage
• Stacked with spacers to prevent deformation

♨️ Power Cycles & Heat Transfer

11. Draw the Rankine Cycle – Explain Each Process

• I drew and explained:
  • 1–2: Isentropic compression (Pump)
  • 2–3: Constant pressure heat addition (Boiler)
  • 3–4: Isentropic expansion (Turbine)
  • 4–1: Constant pressure heat rejection (Condenser)

12. How to Increase Efficiency of Rankine Cycle?

• Use regenerative feedwater heating
• Apply reheat cycle
• Increase boiler pressure
• Lower condenser pressure (to a practical minimum, limited by cooling water and ambient conditions)

13. To What Extent Can We Reduce Condenser Temperature?

• Only up to the ambient wet bulb temperature
• Further cooling is limited due to thermodynamic constraints and condenser material design

💧 Boiling & Heat Transfer

14. Draw the Boiling Curve – Explain Stages Clearly

• I drew and discussed:
  • Natural convection
  • Nucleate boiling
  • Critical heat flux (CHF)
  • Transition boiling
  • Film boiling
• Explained heat flux vs. surface temperature relationship

🌟 Overall Experience

• The panel was technically sound, friendly, and encouraging.
• They allowed diagram drawing and gave conceptual hints where necessary.
• Questions spanned nuclear principles, thermal systems, material knowledge, and practical fabrication—testing both core engineering concepts and application sense.