--- title: "Thermal versus nuclear power plant" subject: "Power Plant Design" chapter: 1 key: "semester_8/power_plant_design:thermal-vs-nuclear" source: https://www.bctengineer.com/q/semester_8/power_plant_design/thermal-vs-nuclear site: BCT Engineering --- # Thermal versus nuclear power plant Power Plant Design · Chapter 1: Energy Sources and Electric Power Generation - Asked in: 2081 Shrawan, 6 marks; 2078 Kartik, 6 marks (asked 2 times) - Video: [Comparison between Coal-fired Thermal and Nuclear Power Plants](https://www.youtube.com/watch?v=8S-LpEi7DBw) — The Learning Curve - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_8/power_plant_design/thermal-vs-nuclear - Whole chapter: https://www.bctengineer.com/md/semester_8/power_plant_design/chapter-1 ## Question Compare thermal power plant with nuclear power plant on the basis of availability, grid connectivity, easiness to control, environmental effect, cost factors and so on. ## Short answer Thermal plants burn coal/oil/gas, have moderate availability (70–85%), can follow load, emit CO₂ and pollutants, and have high fuel cost. Nuclear plants use uranium, have high availability (85–90%), run best at constant base load, emit almost no CO₂ but produce radioactive waste, and have very high capital cost but low fuel cost. ## Answer Both thermal (coal/oil/gas fired) and nuclear plants produce steam to run a steam turbine–generator. They differ in the heat source: combustion of fossil fuel in a boiler versus nuclear fission in a reactor. #### Comparison | Basis | Thermal power plant | Nuclear power plant | |---|---|---| | Fuel | Coal, oil, gas; large quantity | Uranium-235, plutonium; very small quantity | | Fuel availability | Widely available; transport of bulk coal needed | Limited suppliers; strict international control | | Availability (plant) | About 70–85%; boiler outages | About 85–90%; long refuelling outages every 12–24 months | | Grid connectivity | Units 100–800 MW; can be near load centres | Large units 600–1600 MW; away from populated areas; needs a strong grid | | Easiness to control | Moderate load following; slow start (hours) | Best run at constant base load; control by control rods is complex | | Starting time | Few hours | Long (many hours to days) | | Efficiency | About 30–40% | About 30–35% (lower steam temperature) | | Environmental effect | CO₂, SO₂, NOx, fly ash, thermal pollution | Almost no CO₂; radioactive waste, risk of radiation accident | | Capital cost | Moderate | Very high (reactor, shielding, safety systems) | | Running (fuel) cost | High | Low | | Cost factors | Fuel price dominates | Capital, decommissioning and waste disposal dominate | | Space | Large (coal yard, ash pond) | Smaller for same output, but large exclusion zone | | Maintenance | Boiler, ash handling, coal mills | Highly skilled, radiation-safe procedures | | Life | About 25–30 years | About 40–60 years | #### Remarks - Thermal plants are flexible and cheaper to build but costly to run and polluting. - Nuclear plants are clean in CO₂ terms and cheap to run, suited only for steady **base load** in large grids. - Nuclear power is not practical for Nepal due to small grid size, cost, lack of fuel and expertise, and seismic risk. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. What is the basic difference between thermal and nuclear plants? A. Nuclear uses water turbines B. Thermal burns fuel in a boiler; nuclear uses fission in a reactor C. Thermal makes no steam D. Nuclear has no generator Answer: B. Both use a steam turbine-generator; they differ in the heat source. (Key point: Heat source) 2. What dominates cost in each type? A. Thermal: capital; nuclear: fuel B. Both: fuel price C. Thermal: fuel price; nuclear: capital, decommissioning and waste disposal D. Both: land Answer: C. Nuclear has very high capital but low fuel cost; thermal cost is mainly fuel. (Key point: Cost structure) 3. How is a nuclear plant best operated? A. Frequent load following B. Constant base load C. Only as peaking plant D. Started daily Answer: B. Control by rods is complex, so nuclear suits steady base load. (Key point: Control) 4. Which environmental effect is specific to nuclear? A. CO2 emission B. SO2 and NOx C. Fly ash D. Radioactive waste and radiation accident risk Answer: D. Nuclear emits almost no CO2 but has radioactive waste and accident risk. 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