How a nuclear power station makes electricity
Follow fission heat through a two-loop pressurised-water reactor, a separate steam cycle and a third cooling circuit. Inspect the cutaways, then balance thermal input against net electricity and rejected heat.
In 60 seconds: how it works
A nuclear power plant uses the heat from splitting atoms to boil water. The steam spins a turbine that drives a generator, just like in a coal or gas plant.
- Inside the reactor, splitting uranium atoms (fission) releases heat.
- Pressurised water in a sealed loop carries that heat away. In this design it never reaches the turbine.
- The hot water boils water in a separate loop to make steam.
- The steam spins a turbine connected to a generator, which makes electricity.
- The steam is cooled back into water by a third cooling circuit and sent back to be heated again.
- A transformer raises the voltage so the electricity can travel to the grid.
Want the engineering detail? Explore the 3D model, then read the engineering notes and the types and variations.
By Power Stations Worldwide · Related reading updated · Preparation and review scope. Educational illustrations; no independent engineering peer review is claimed.
Explore the equipment in 3D
Rotate equipment, follow energy flows and inspect each component. Read the steps below at any time.
Choose a step to read the process. Activate the 3D model or start a guided tour to use the animation controls.
Two-loop pressurised-water reactor (PWR), high-/low-pressure steam turbines, moisture separator/reheater (MSR) and four-pole synchronous generator. Separate primary, steam/feedwater and cooling circuits; opened pressure vessels and compressed distances are teaching cutaways. Fixed NIST steam states and illustrative losses form one steady-state case, not primary thermal-hydraulic, structural, operator-training or safety simulation. Motion is slowed for inspection. Coloured overlays reveal flow through enclosed equipment; gold pulses show net electrical energy transfer, not individual electrons. Outer containment is hidden in reactor, primary-loop, steam-generator and pressuriser inspection views only, to expose the teaching cutaways.
How it works
- Controlled nuclear fission
- Heat carried by coolant
- Steam production
- Turbine rotation
- Generator electricity
- Transformer and grid
A nuclear power station uses heat released when atomic nuclei split in a controlled chain reaction. Fuel transfers that heat to a coolant; the coolant’s route depends on the reactor design. In the pressurised water reactor shown here, normal primary bulk coolant remains liquid, while the connected pressuriser deliberately contains steam above liquid. Primary water passes through steam-generator tubes, heating separate secondary water into steam. That steam expands through a turbine connected to an electrical generator.
After the turbine, a condenser removes heat and turns the steam back into water for reuse. A separate cooling system carries the rejected heat to the environment. The reactor coolant, turbine steam and cooling water therefore have distinct jobs and normally remain separate in this arrangement. Control and protection systems manage the chain reaction, while barriers contain radioactive material. Cooling remains necessary after shutdown because radioactive decay in the fuel continues to release heat.
Follow the heat. Keep the fluids separate.
Two-loop pressurised-water reactor (PWR), separate steam/feedwater cycle and separate condenser cooling. The cutaways connect internal function to external equipment. The numbers describe one invented, fixed-state teaching case, not a named station or an operator-training simulator.
Selected: whole-system overview.
Simple explanation
The reactor makes heat, not electricity directly. Fission deposits energy in the fuel. Water carries heat from the core to U-tubes inside each steam generator. The surrounding secondary water boils, but the fluids stay separated by metal walls. Primary bulk coolant remains liquid in normal operation; the pressuriser deliberately contains steam above liquid. Small local subcooled bubbles are not a boiling bulk loop. [N1] [N3] [N6]
Steam does work; water comes back. Steam expands through the high-pressure (HP) turbine. A moisture separator/reheater (MSR) removes liquid, then uses a separate main-steam branch to heat the continuing steam through tube walls. Low-pressure (LP) turbines add shaft work. The condenser turns exhaust steam back into water; feed pumps return it to both steam generators. Heating-steam condensate and separated moisture also return through drains. [N1] [N6]
Heat and electricity have different exits. Third-circuit water flows inside condenser tubes, absorbing heat without mixing with turbine steam. The tower transfers heat to air; its visible plume contains condensed water droplets, not smoke. The shaft drives a synchronous generator; switchgear and a transformer connect three-phase alternating current (AC) to the grid. Pumps and other auxiliaries consume part of gross generation. [N1] [N2] [N6]
Current operating balance
| Measurement / boundary | Power |
|---|---|
| Reactor heat supplied to secondary circuit | 1000.000 |
| Turbine shaft output (before generator) | 292.830 |
| Gross generator electricity | 286.973 |
| Feed-pump electrical input | 3.080 |
| Other plant auxiliary electricity | 8.609 |
| Transformer loss | 1.376 |
| Net electricity exported | 273.908 |
| Condenser heat rejection | 710.096 |
| Generator loss | 5.857 |
| Feed-pump motor loss | 0.154 |
| Total environmental heat (including other auxiliaries) | 726.092 |
1000.000 MWth = 273.908 MWe net export + 726.092 MW environmental heat. Unrounded residual: 0.00e+0 W.
Auxiliaries total 11.689 MWe. Actual feed-pump work transferred to water (including hydraulic dissipation), 2.926 MW, is already accounted for in the condenser/shaft balance; it is not counted again as lost heat. Other auxiliaries ultimately reject heat within the stated whole-plant boundary. All power readings use the same calculation.
Engineering details: one mass and energy model
Enthalpy h is energy per mass (kJ/kg); entropy s is in kJ/(kg·K); specific volume v is in m³/kg; pressure p is in pascals (Pa). Mass-flow rate ṁ is in kg/s; heat rate Q̇ and shaft/electrical power P are in watts (W). Quality x is the vapour mass fraction of a saturated mixture, not a volume fraction. Efficiency η is dimensionless. Subscripts identify equipment/state boundaries. K means kelvin; 1 MPa = 10⁶ Pa; 1 kJ = 1000 J.
x_HP,s = (s_SG − s_f,1MPa) / (s_g,1MPa − s_f,1MPa)
h_HP,s = h_f,1MPa + x_HP,s (h_g,1MPa − h_f,1MPa)
h_HP = h_SG − η_HP (h_SG − h_HP,s)
SG denotes steam generator; the subscript s denotes the ideal constant-entropy (isentropic) expansion; f/g denote saturated liquid/vapour. Actual HP quality follows from h_HP and the 1 MPa saturated enthalpies. An ideal separator sends only its vapour fraction onward. Saturated enthalpy/entropy differences use the rounded endpoint columns consistently, not independently rounded latent-heat columns. No kinetic/potential energy changes, piping heat losses or pressure drops are calculated. [N5] [N7]
β (h_SG − h_f,6MPa) = (1 − β) x_HP (h_RH − h_g,1MPa)
β is the main-steam mass fraction diverted to the reheater heating tubes; RH denotes reheated steam. The fixed 6 MPa heating steam condenses while the dry 1 MPa stream reaches 250 °C. Its 275.585 °C heating-side saturation temperature gives a positive terminal temperature difference. Both fluids are secondary-side water, but they occupy separate pressure passages. At this point β = 8.400%; the HP outlet quality is 86.773%.
ṁ_HP = (1 − β) ṁ; ṁ_LP = (1 − β) x_HP ṁ
ṁ_separator drain + ṁ_heater drain + ṁ_LP = ṁ
P_turbine = ṁ_HP (h_SG − h_HP) + ṁ_LP (h_RH − h_LP)
LP isentropic expansion uses the RH entropy and 0.010 MPa saturation data, followed by η_LP in the same enthalpy-drop definition. Both drains throttle at constant enthalpy into the condenser. Their flash vapour is condensed there and included in the heat ledger. No extraction is credited to the depicted feedwater heater: it is an unheated pass-through in this simplified case. The LP exit vapour mass fraction is 88.399%, a calculated teaching result, not a blade wetness limit or vendor guarantee.
w_pump = v_f Δp / η_pump; h_FW = h_f,condenser + w_pump
ṁ = Q̇_reactor / (h_SG − h_FW)
Q̇_reactor + P_pump,fluid = P_turbine + Q̇_condenser
Use joules/kg in power equations (multiply tabulated kJ/kg by 1000). FW means feedwater; Δp = 6.000 MPa − 0.010 MPa. The incompressible pump approximation uses the condenser-liquid specific volume and ideal/actual pump-work efficiency. Its derived enthalpy is not an independent temperature slider; compressed-water outlet temperature is not calculated. The two steam generators share total flow equally; the three parallel LP/condenser branches are grouped in the calculation. Primary flow, fuel temperature and pressuriser dynamics are not solved.
P_gross = η_generator P_turbine
P_aux = P_pump,fluid / η_motor + 0.03 P_gross
P_net = η_transformer (P_gross − P_aux)
Q̇_environment = Q̇_condenser + P_generator loss + P_motor loss + P_other aux + P_transformer loss
η_net = P_net / Q̇_reactor
Illustrative constants: HP/LP isentropic efficiencies 0.85; ideal/actual pump-work efficiency 0.80; motor 0.95; generator 0.98; transformer 0.995. Other auxiliaries are 3% of gross output and exclude the separately counted feed pump. Their allowance covers unmodelled reactor-coolant/cooling pumps and station services without claiming individual pump ratings. Heater/separator efficiencies and extraction systems are idealised. No cooling-water flow, evaporative consumption, transient or equipment sizing is calculated.
n = 120 f / p_poles = 120 × 50 / 4 = 1500 rpm; ω = 2πn/60; T = P_turbine/ω
Here n is physical shaft speed in rpm; f is grid frequency in hertz (Hz), p_poles counts total poles (not pole pairs), angular speed ω is in radians/s, and torque T is in newton-metres (N·m). The current shaft torque is 1.864 MN·m. Display speed, selection and pause do not change these relationships. [N2]
Checked example: 1000 MWth, not a real station rating
With the assumptions above: total SG steam 386.813 kg/s; turbine shaft 292.830 MW; gross electricity 286.973 MWe; auxiliaries 11.689 MWe; net export 273.908 MWe. Environmental heat is 726.092 MW; the unrounded balance closes within floating-point precision. These values are derived from the table states below, not independently animated counters.
| State | Pressure MPa | Temperature °C | h kJ/kg | s kJ/(kg·K) |
|---|---|---|---|---|
| SG outlet, saturated vapour | 6.000 | 275.585 | 2784.6 | 5.8901 |
| Separator liquid / dry vapour | 1.000 | 179.878 | 762.52 / 2777.1 | 2.1381 / 6.5850 |
| Reheated LP inlet | 1.000 | 250.000 | 2943.1 | 6.9265 |
| Condenser saturated liquid / vapour | 0.010 | 45.806 | 191.81 / 2583.9 | 0.64920 / 8.1488 |
| Heating-steam drain before throttling | 6.000 | 275.585 | 1213.9 | — not used |
| Boundary | Pressure MPa | Temperature °C | h kJ/kg | Vapour mass fraction |
|---|---|---|---|---|
| 1 · Condenser liquid | 0.010 | 45.806 | 191.810 | 0.0000 |
| 2 · Feed-pump outlet | 6.000 | Not calculated | 199.374 | Not applicable |
| 3 · Main steam | 6.000 | 275.585 | 2784.600 | 1.0000 |
| 4 · HP turbine outlet | 1.000 | 179.878 | 2510.636 | 0.8677 |
| 5 · Reheated LP inlet | 1.000 | 250.000 | 2943.100 | Not applicable |
| 6 · LP turbine outlet | 0.010 | 45.806 | 2306.392 | 0.8840 |
Total secondary flow 386.813 kg/s splits into HP admission 354.320 kg/s and heating-steam bleed 32.493 kg/s. After separation, LP flow 307.455 kg/s, separator drains 46.865 kg/s and heating-steam drains all return to the condenser. Total feedwater return: 386.813 kg/s.
Pressure, movement and the cutaway
Tube sheets separate primary and secondary pressure spaces. The reactor vessel, pump casing and pressuriser wall contain pressure; a structural support carries loads to the foundation and is not a fluid passage. Pipe bends illustrate expansion accommodation; supports and saddle bearings remain fixed while shafts/couplings rotate. Removed wall sectors are for visibility, not an operating condition. Dimensions, tube/blade counts and access distances are compressed or enlarged; no stress, fatigue, thermal-growth, radiation-shielding, pressure-vessel or standards check is claimed. [N1]
Control rods and decay heat are not a safety simulator
Control rods absorb neutrons and influence the chain reaction; the displayed bank stays settled during this steady teaching case. Even after fission is suppressed, radioactive decay produces heat that must be removed. There is no rod-control, emergency, trip, accident or shutdown exercise here, no computed decay-heat curve and no claim to teach operating procedures. Actual safety systems and licensing are outside this visualization. [N6]
PWR and BWR are different circuits
PWR shown in 3D: bulk-liquid primary loops and a pressuriser; heat crosses steam-generator tube walls into a separate turbine steam/feedwater cycle. A third cooling circuit removes condenser heat.
Boiling-water reactor (BWR), comparison only: water boils in the reactor vessel; separators/dryers prepare steam that goes directly to the turbine. Feedwater returns to the reactor, without a PWR-style steam generator separating those fluids. The same PWR model is not relabelled as a BWR. Read the separate BWR description. [N6]
Check your understanding
Does primary coolant pass through the turbine?
No. Heat crosses the steam-generator tube walls; secondary steam drives the turbine. A primary/secondary leak would be a fault, not the intended circuit.
Does a pressuriser contradict “primary bulk coolant stays liquid”?
No. Its deliberate steam space helps regulate pressure; the main loop is not described as entirely vapour-free.
Why doesn’t 2000 MWth mean 2000 MWe export?
Much of the input heat is rejected at the condenser. Generator, motor and transformer losses and plant auxiliaries further reduce net electricity. Doubling the illustrative heat load changes flow and torque, not the 50 Hz synchronous speed.
Sources, passage access and review
Selected book/property passages checked . Original lesson and software/geometric checks; not independently engineering peer reviewed. Only the listed passages were inspected. Required Lamarsh/Baratta technical passages were inaccessible; its catalogue is further reading, with the lawful Glasstone/Sesonske book preview supplying the checked nuclear foundation.
- [N1] Glasstone & Sesonske. Nuclear Reactor Engineering, Vol. 2: Reactor Systems Engineering, 4th ed., Chapman & Hall, 1994. DOI. Checked publisher previews: printed 501–502, §§9.1–9.5 and 759–760, §13.6. Heat conversion and vessel/support context, not a verified full plant design.
- [N2] Woodson & Melcher. Electromechanical Dynamics, Part I, Wiley, 1968. MIT-hosted Chapter 4, §4.1.8, equation (4.1.95), PDF page 48 (one-based). Pole pairs translated explicitly to total poles.
- [N3] J. Pongpuak. “Pressurized Water Reactors,” Nuclear Energy Materials and Reactors, Vol. I, EOLSS. Publisher sample, §2.1, PDF pages 4–5. Selected circuit passages checked; no publication year inferred from this sample.
- [N4] Lamarsh & Baratta. Introduction to Nuclear Engineering, 4th ed., Pearson, print ISBN 9780134570051, published 2017 / ©2018. Required starting bibliography; metadata/contents-only further reading. Relevant technical passages were not accessible or verified.
- [N5] Allan H. Harvey. Thermodynamic Properties of Water, NISTIR 5078, 1998, IAPWS-95 formulation. NIST record; Table 2, printed 11, 13, 14; Table 3, printed 38. Selected rows personally checked; fixed values, not an implemented water-property solver.
- [N6] Supplementary primary sources: US NRC PWR overview; Cook licence-renewal application, §2.3.1 pressuriser passage; AP1000 FSER §1.2.2.6, MSR arrangement; NRC glossary, decay heat; NRC PWR/BWR comparison; DOE EIS-0230 §4.3.5, cooling-plume droplets. Selected substantial indexed NRC passages were read; direct NRC document access returned HTTP 403, so full-manual review is not claimed. Plant-specific ratings are not transferred to this example.
- [N7] DOE. Fundamentals Handbook: Thermodynamics, Heat Transfer and Fluid Flow, Vol. 1, DOE-HDBK-1012/1-92, 1992. Official handbook. Checked printed 79–82, 84 and 90–91: steady-flow turbine/pump/heat-exchanger and steam-cycle relationships; supplementary to the checked textbook foundation.
Download the editable original Blender scene · Download the optimized browser model. Reproduction and calculation details accompany the source repository. Geometry is educational, not approved installation design.
Inside the engineering
Follow the machinery, the working fluids and the electrical connection.
Mechanical
Fixed vessel/pump/turbine pressure walls, tube sheets, saddles and bearing housings surround selected moving shafts. Two U-tube primary paths, a liquid/steam pressuriser, moisture-separation/reheat passages and condenser tube/hotwell cutaways explain flow boundaries. Rods stay settled. Coaxial shaft couplings carry torque; pipe supports and expansion bends are structural, not fluid passages.
Thermal & chemical
Fission heat reaches secondary steam across tube walls. Normal primary bulk coolant remains liquid while the pressuriser deliberately has a steam space. Main-steam bleed reheats separated secondary steam; both MSR drains and LP exhaust return to the condenser. Separate cooling water removes heat without entering feedwater. The depicted heater receives no numerical extraction credit; cooling-tower fog is water droplets.
Electrical
Steam-turbine shafts drive a synchronous generator at the selected 50 Hz / four-pole / 1500 rpm state independently of thermal load; greater power changes torque. Three-phase switchgear and step-up transformation export power. Gross output, feed-pump and other auxiliary loads, transformer losses, net export and environmental heat share a checked balance; reactive power, excitation and protection are not solved.
Main types and variations
The 3D cutaway represents a pressurised water reactor (PWR), not every nuclear station. Reactor families differ in coolant, neutron behaviour and heat-transfer equipment. “Small modular reactor” describes size and construction approach and can overlap with several of those families.
Pressurised water reactor (PWR)
Pumps circulate pressurised water through the core and steam generators. Heat crosses the steam-generator tube walls to a separate steam circuit. A pressuriser maintains primary-system pressure, while the secondary steam drives the turbine and returns through the condenser and feedwater system.
What changes in practice
Keeping reactor coolant separate from turbine steam defines the main layout. Steam-generator tubes are both heat-transfer surfaces and an important separation barrier.
Boiling water reactor (BWR)
Water boils inside the reactor vessel. Separators and dryers remove entrained droplets before steam travels directly to the turbine. The condenser turns the exhaust steam back into water, and feedwater pumps return it to the vessel. A separate PWR-style steam generator is unnecessary.
What changes in practice
The reactor and turbine share the steam-water circuit, so this design cannot be understood by simply copying the PWR’s separate primary and secondary loops.
Pressurised heavy-water reactor (PHWR)
In a CANDU-type PHWR, fuel sits in individual pressure-tube channels. Heavy water serves as coolant and as the moderator that slows neutrons, in separate systems. The hot coolant carries heat to steam generators. Special fuelling machines can replace fuel bundles while the reactor operates.
What changes in practice
Fuel channels and online refuelling distinguish this layout from a single-vessel light-water reactor. Pressure-tube condition is a major inspection and maintenance consideration.
Gas-cooled reactors: AGR and HTGR
A circulating gas transports heat out of the core instead of liquid water. Advanced gas-cooled reactors use carbon dioxide; high-temperature gas-cooled reactor designs use helium. The recovered heat can supply electricity generation and, in suitable high-temperature designs, industrial processes that also need heat.
What changes in practice
Gas cooling changes the heat-transfer equipment and temperature requirements. These are nuclear reactors; the coolant gas is a heat carrier, not a combustion fuel.
Fast-neutron reactors
Fast reactors sustain fission using high-energy neutrons rather than first slowing them with a moderator. Different concepts use sodium, lead or gas to transport heat. The reactor’s heat still needs a power-conversion system; the word “fast” describes neutron energies, not turbine speed or start-up time.
What changes in practice
Fuel composition, coolant choice and the intended fuel cycle must be considered together. A fast reactor is not automatically a breeder in every configuration.
Small modular reactors (SMRs)
SMRs package a smaller reactor in a design intended to use modular manufacturing or construction. Some are compact water-cooled reactors; others use different coolants and reactor physics. Each still needs fuel, heat removal, power conversion, protection systems and a suitable connection to its users.
What changes in practice
“SMR” alone does not identify the coolant or steam cycle. Compare the actual design and licensing status rather than assuming all small reactors operate alike.
Worth knowing
- Nuclear stations produce very little carbon dioxide while operating.
- They usually run near full output for long periods between refuelling outages.
- Spent fuel is highly radioactive and must be stored and managed for a long time.
See real examples
The atlas includes 196 nuclear records worldwide.
Show on the mapRelated answers
Textbook references
Suggested technical background for this topic. These books are further reading, not proof that every explanation was checked against every edition. See the full bibliography and review scope.
- Introduction to Nuclear EngineeringFission, neutron physics, reactor types, heat removal and radiation protection.
- Thermodynamics: An Engineering ApproachRankine steam cycles used on the secondary side of the plant.
Sources
- EIA: Nuclear power plants ↗
- US NRC: Primary and secondary steam-generator circuits ↗
- Glasstone/Sesonske: checked nuclear engineering textbook preview ↗
- NIST: checked water/steam property tables ↗
- EIA: How electricity is generated ↗
Cutaways reveal enclosed equipment. Layouts, dimensions, materials and animation speeds are illustrative; this is an educational model, not a plant design. The fixed-state calculation is not a transient thermal-hydraulic or safety simulation.