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How does a heat exchanger transfer energy from a reactor to a steam turbine?

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Labeled diagram showing the process of a nuclear power plant with a pressurized-water reactor. Water circulates through the reactor core, heats to produce steam in a steam generator, which drives a turbine connected to an electric generator. Steam is then cooled in a condenser using water from a cooling tower, which releases nonradioactive water vapor. Control rods, pumps, and transmission lines are also indicated. — nuclear power Schematic diagram of a nuclear power plant using a pressurized-water reactor.

In a nuclear power plant, a heat exchanger—often functioning as a steam generator—acts as the critical interface between the reactor's primary cooling loop and the power-generating secondary loop.12

The process works as follows:

Primary Loop: Water (or another coolant) circulates through the reactor core, where it absorbs the heat of reaction generated by nuclear fission. In systems like the pressurized-water reactor, this water is kept under high pressure to prevent it from boiling.12
Energy Transfer: This hot primary water flows through the heat exchanger, where it passes its thermal energy to a separate, secondary water circuit. Because the two loops are physically separated by a sealed barrier, the radioactive primary water does not contaminate the secondary loop.13
Steam Generation: Upon absorbing heat from the primary loop, the water in the secondary circuit reaches a temperature sufficient to boil, creating the steam required to drive the steam turbine.12