Abstract: A power module assembly includes a reactor core immersed in a coolant and a reactor vessel housing the coolant and the reactor core. An internal dry containment vessel submerged in liquid substantially surrounds the reactor vessel in a gaseous environment. During an over-pressurization event the reactor vessel is configured to release the coolant into the containment vessel and remove a decay heat of the reactor core through condensation of the coolant on an inner surface of the containment vessel.

Abstract: A power module assembly includes a reactor vessel containing a reactor core surrounded by a primary coolant. A containment vessel is adapted to be submerged in a containment cooling pool and to prohibit a release of the primary coolant outside of the containment vessel. A secondary cooling system is configured to remove heat generated by the reactor core. The heat is removed by circulating liquid from the containment cooling pool through the primary coolant.

Abstract: A nuclear reactor module includes a reactor vessel containing coolant, a reactor core submerged in the coolant, and a heat exchanger configured to remove heat from the coolant. The nuclear reactor module further includes one or more heaters configured to add heat to the coolant during a startup operation and prior to the reactor core going critical.

Abstract: Thermal management devices and methods include branching networks comprising flow channels of varying cross-sectional area. The branching networks can be fractal-like in nature with an increase in the total flow area following a flow channel bifurcation. In representative embodiments, the branching networks are defined in a channel pattern that is laminated between cover plates to form a thermal management device. The channel pattern includes bridging portions so that the branching network is defined with a single pattern piece. The branching networks can exhibit radial symmetry or be aligned with respect to one or more axes. Heat exchangers and diffusive mixers that include such networks are also provided.