The idea of a nuclear power plant today evokes images of large cooling towers and expansive, warehouse-size buildings. Such facilities generate about a fifth of electricity in the United States without emitting greenhouse gases. A different picture of nuclear energy is emerging, however, in the form of micro-reactors that could fit on the back of a truck or inside a rocket to space. The promise of these micro-reactors is to provide the same reliable, zero-carbon power in remote settings or to support electrical power grid recovery. The idea of a nuclear power plant today evokes images of large cooling towers and expansive, warehouse-size buildings. Such facilities generate about a fifth of electricity in the United States without emitting greenhouse gases. A different picture of nuclear energy is emerging, however, in the form of micro-reactors that could fit on the back of a truck or inside a rocket to space. The promise of these micro-reactors is to provide the same reliable, zero-carbon power in remote settings or to support electrical power grid recovery.