Abstract: A pressurized water reactor (PWR) includes: a pressure vessel divided into an upper plenum containing primary coolant, a lower plenum containing primary coolant, and a steam generator plenum interposed between the upper plenum and the lower plenum and containing secondary coolant; a nuclear reactor core comprising fissile material disposed in the lower plenum; one or more risers arranged to convey primary coolant upward from the nuclear reactor core to the upper plenum; and a plurality of tubes passing through the steam generator plenum and arranged to convey primary coolant downward from the upper plenum to the lower plenum. A steam separator is operatively connected with the steam generator plenum to separate secondary coolant in the steam phase from secondary coolant in the water phase.

Abstract: In a boiling water reactor, provision is made to sample the core bypass region immediate the top guide to determine the physical and chemical constituents of the moderating water. A conduit for a local power range monitor is fitted with a measurement assembly. The conduit and measurement assembly are inserted up to the vicinity of the top guide. A tube opening is provided to the bypass region immediate the top guide. During reactor operation, the saturated liquid in this region flashes to a steam water mixture (18% steam) at constant enthalpy and is rapidly removed from the reactor to measuring equipment in the reactor building. During removal, the radiolytic disassociated gases (namely hydrogen and oxygen) partition to the steam phase where their recombination is retarded and accurate measurement of their constituent content can be made. Also, temperature of the steam water mixture decreases thereby preserving unstable species like hydrogen peroxide that degrade much more rapidly a high temperatures.

Abstract: A pressurized water nuclear reactor has a reactor vessel arranged in a pool, which is filled with a neutron absorbing liquid, for example borated water. The reactor vessel is closed except for tubes connecting it with a tray above it. The coolant in the circuit rises from the vessel to the tray, gives up its heat by flashing, and flows back to the bottom of the vessel, driven by natural circulation. The tray is separated from the pool by a vapor-filled bell, which surrounds it. In the bell the vapor gives up its useful heat to a condenser. The relatively low boron content of the cooling circuit, compared to the pool, is achieved by continuous dilution of the condensate from vapor additionally generated out of the pool water. The dilution process is an equilibrium with continuous inflow of the pool water. The inflow is automatically controlled by the pool level, which rises when the pool water is pressed out from below the bell by overproduction of vapor.