What are PWRs?

Pressurised Water Reactors (PWRs) have been developed into small modular reactors that could be used onboard. They use uranium as fuel to generate heat through a controlled nuclear fission chain reaction. The heat is transferred to the coolant, which in a PWR is typically ordinary water. The heated coolant remains in a liquid state at the high temperatures due to the high pressure maintained within the reactor vessel. This heat can then be used for conversion to electrical power or direct thermal energy for heating purposes.