Why nuclear powered space probe never needs refueling?

Nuclear-powered space probes use radioisotope thermoelectric generators (RTGs) that convert the heat released by the decay of radioactive isotopes, such as plutonium-238, into electricity. This process provides a continuous power source over long durations, often lasting decades, without the need for refueling. The decay of these isotopes occurs at a predictable rate, ensuring a steady supply of energy, which makes them ideal for missions that venture far from the Sun where solar power is insufficient. Consequently, once launched, these probes can operate autonomously for extended periods without any refueling requirements.