Work out reactor thermal power instantly with clear inputs, formula shown and shareable results.
Core thermal power is a simple energy balance on the coolant: mass flow times specific heat times temperature rise. Pressurised water reactors run a 30-40 degree rise across the core at around 155 bar, where water's specific heat is about 5.5 kJ/kg.K rather than the 4.18 of ambient water.
Core heat balance
Thermal power (kW) = mass flow (kg/s) x cp (kJ/kg.K) x (T_out - T_in)
Reactor power measurement and limits are safety-critical and governed by the plant licence. This calculation is illustrative only.
At 300 C and high pressure, water approaches its critical region and its specific heat rises substantially. Using the ambient value would understate power by 25% or more.
By a secondary-side heat balance using feedwater flow, temperature and steam conditions, calibrated against a primary-side calculation. Thermal power measurement uncertainty directly limits licensed output.