--- title: "Thermal, geothermal and nuclear plants compared" subject: "Power Plant Design" chapter: 1 key: "semester_8/power_plant_design:thermal-geothermal-nuclear" source: https://www.bctengineer.com/q/semester_8/power_plant_design/thermal-geothermal-nuclear site: BCT Engineering --- # Thermal, geothermal and nuclear plants compared Power Plant Design · Chapter 1: Energy Sources and Electric Power Generation - Asked in: 2073 Magh, 8 marks - 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-geothermal-nuclear - Whole chapter: https://www.bctengineer.com/md/semester_8/power_plant_design/chapter-1 ## Question Compare the operational characteristics of thermal, geothermal and nuclear plant on the basis of reliability, grid-connection, efficiency, operating range and maintainability. ## Short answer Thermal plants are firm and dispatchable with 30–40% efficiency, minimum load about 40–50%, and complex maintenance. Geothermal and nuclear are steady base-load plants with high capacity factors, but geothermal efficiency is only 10–20% and nuclear 30–35%; nuclear has very high capital cost and strict radiation safety. ## Answer All three plants use steam turbines, but the heat source differs: **thermal** plants burn fossil fuel, **geothermal** plants use heat from the earth, and **nuclear** plants use fission of uranium. #### Comparison | Basis | Thermal (coal/oil/gas) | Geothermal | Nuclear | |---|---|---|---| | Heat source | Fuel combustion in boiler | Steam/hot water from wells | Fission in reactor | | Reliability | Firm if fuel supply is assured; availability about 70–85% | Very steady; capacity factor about 90%; reservoir may decline | Very steady; capacity factor about 85–90%; long refuelling outages | | Grid connection | 100–800 MW units; near load or mines | Small to medium units (5–100 MW); only at geothermal fields, often remote | Large units (600–1600 MW); remote sites; needs strong grid | | Efficiency | About 30–40% (steam), 50–60% combined cycle | Low, about 10–20% (low steam temperature) | About 30–35% | | Operating range | Moderate; minimum stable load about 40–50%; start in hours | Base load only; little flexibility | Base load; load following difficult; start takes long | | Maintainability | Complex: boiler, coal and ash handling, many auxiliaries | Corrosion and scaling from minerals; well maintenance | Highly specialised; radiation safety; strict regulation | | Fuel cost | High | Nil | Low | | Capital cost | Moderate | High (drilling) | Very high | | Emissions | CO₂, SO₂, NOx, ash | Low; some H₂S | No CO₂; radioactive waste | #### Remarks - Thermal plants are the most flexible in location and output but polluting and fuel-dependent. - Geothermal and nuclear are base-load plants with high availability and low fuel cost; geothermal is site-limited, nuclear needs very large investment and strict safety. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Which ranking of efficiency is correct? A. Geothermal > nuclear > thermal B. Nuclear > geothermal > thermal C. Thermal (steam) and nuclear are about 30-40%, geothermal is low at about 10-20% D. All three are about 30-40% Answer: C. Geothermal steam has low temperature, so its efficiency is only about 10-20%. (Key point: Efficiency comparison) 2. Which plant types are essentially base-load with little flexibility? A. Geothermal and nuclear B. Thermal only C. Thermal and geothermal D. None; all three follow load easily Answer: A. Geothermal and nuclear are base-load plants; thermal has a moderate range with minimum stable load about 40-50%. (Key point: Operating range) 3. What is the main maintenance problem of a geothermal plant? A. Radiation safety B. Ash handling C. Corrosion and scaling from dissolved minerals, and well maintenance D. Sediment erosion of turbines Answer: C. Geothermal fluids carry minerals that corrode and scale equipment, and wells need maintenance. (Key point: Maintainability of geothermal) 4. Which is correct about grid connection? A. Nuclear units are small (5-100 MW) and near load B. Geothermal units are 600-1600 MW C. Thermal units are only at remote fields D. Nuclear units are large (600-1600 MW) at remote sites and need a strong grid Answer: D. Nuclear plants are large, remote and need a strong grid; geothermal units are small to medium at geothermal fields. 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