Patent Number: 
Section: claims

1. A nuclear reactor comprising a cylindrical pressure vessel, an elongated annular core centrally disposed within and spaced from the pressure vessel, and a plurality of ducts disposed longitudinally of the pressure vessel about the periphery thereof, said core comprising an annular active portion, an annular reflector just inside the active portion and an annular reflector just outside the active portion, said annular active portion comprising rectangular slab, porous fuel elements radially disposed around the inner reflector and extending the length of the active portion, wedge-shaped, porous moderator elements disposed adjacent one face of each fuel element and extending the length of the fuel element, the fuel and moderator elements being oriented so that the fuel elements face each other and the moderator elements do likewise, adjacent moderator elements being spaced to provide air inlet channels, and adjacent fuel elements being spaced to provide air outlet channels which communicate with the interior of the peripheral ducts, and means for introducing air into the air inlet channels which passes through the porous moderator elements and porous fuel elements to the outlet channel. 2. A nuclear reactor according to  claim 1  wherein said fuel elements comprise interlaced wires of an alloy consisting of 15-16% chromium, 59-62% nickel, about 24% iron, and 0.1% carbon containing uranium dioxide at the center thereof extending between side plates, and said moderator elements comprise a row of spaced wedge-shaped, radially-disposed bars of zirconium hydride. claim 1 3. A nuclear reactor comprising a cylindrical pressure vessel, an elongated annular core disposed in said pressure vessel, and a plurality of ducts disposed longitudinally of the pressure vessel in an annular channel about the periphery thereof, said core comprising an annular active portion, an annular inner reflector, an annular outer reflector, and a pair of porous end reflectors, said outer reflector, active portion and end reflectors being formed of the radial assembly of a plurality of identical segments, each of said segments comprising a pair of side plates covering the outer reflector and inner reflector but not the active portion, side plates of adjacent segments being spaced to provide air outlet channels, said air outlet channels communicating with the peripheral ducts, said active portion being divided into sections, each section containing two radial porous fuel elements, and two porous moderator elements disposed adjacent the inner faces of the fuel elements, said active portion depending from the above-mentioned side plates, dividers separating the outer reflector from the end reflectors, bulkheads extending between the side plates between the dividers, all of said bulkheads except the two at the ends of the outer reflector containing an elongated radial slot, control blades mounted for radial movement in the said slots within the outer reflector, and means for introducing air to the above-mentioned annular channel. 4. A nuclear reactor according to  claim 3  wherein the two sections at the ends of the segment are shorter than the remaining segments, and including air scoops designed to direct a portion of the air traversing the annular channel to the end reflectors, and means establishing channels directing the air after its passage through the end reflectors to the short end sections. claim 3