Patent ID: 8437446

Claim:
A power module assembly comprising: a reactor vessel that comprises a substantially sealed enclosure; a primary fluid coolant enclosed in the sealed enclosure of the reactor vessel; a reactor core located in a lower portion of the reactor vessel, the reactor core comprising a primary fluid coolant outlet near an upper end of the reactor core and a primary fluid coolant inlet near a lower end of the reactor core; a riser conduit that extends from near the top of the reactor core to an upper portion of the reactor vessel; a heat exchanger located about a portion of the riser conduit in the upper portion of the reactor vessel; a fluid bypass path defined between a lower end portion of the riser conduit and the upper end of the reactor core and substantially enclosed within the sealed enclosure of the reactor vessel between the primary fluid coolant outlet of the reactor core and the heat exchanger, the fluid bypass path hydraulically coupling a fluid coolant path that extends between the primary fluid coolant inlet of the reactor core and the primary fluid coolant outlet of the reactor core with an annulus between the riser conduit and the reactor vessel; and a flow restriction positioned within the fluid bypass path and between the lower end portion of the rise conduit and the upper end portion of the reactor core.