Kairos’ design differs from existing nuclear reactors in two key ways: The fuel is made of uranium coated in carbon and ceramic shells, which are intended to be durable enough to contain fissile material in the case of an accident. And the reactor isn’t cooled by water but by molten salt.
The small modular reactor (SMR) startup, which has received a $303 million award from the U.S. Department of Energy, has been working for years to refine its molten salt-cooling system. Fluoride salts’ extremely high boiling points allow the coolant to flow under low pressure. That means in the case of an accident, there won’t be any high-pressure, radioactive material waiting to burst forth should pumping systems fail. Plus, Oak Ridge National Laboratory says that, should power to the pumps fail, molten-salt reactors can rely on passive convection to move salt through the reactor to cool it.