Patent Number: 
Section: claims

1. A liquid fluoride salt cooled, high temperature reactor, comprising:a pebble-bed reactor core configured for containment within a reactor vessel;wherein the reactor core comprises a pebble injection inlet located at a bottom end of the reactor core and a pebble defueling outlet located at a top end of the reactor core;said reactor core cooled by a liquid fluoride salt coolant;said reactor core comprising an inner reflector, outer reflector, and an annular pebble-bed region comprising an annular channel disposed in between the inner reflector and outer reflector;said annular channel configured for receiving pebble fuel comprising a combination of seed and blanket pebbles having a density lower than the coolant such that the pebbles have positive buoyancy and migrate upward in said annular pebble-bed region toward the defueling outlet;said annular pebble-bed region comprising a pebble injection annulus extending from the pebble injection inlet, the pebble injection annulus leading into a diverging annular conical region at the bottom end of the reactor core, and converging annular conical region leading into a pebble defueling slot at the top end of the reactor core; andwherein the annular pebble-bed region comprises alternating radial layers of seed pebbles and blanket pebbleswherein inner reflector comprises an inlet plenum leading to a plurality of inner injection ports in the bottom end of the pebble bed region;wherein the inlet plenum is configured to inject coolant into the annular pebble bed region via the plurality of inner injection ports;wherein the outer reflector comprises a plurality of outlet ports in the top end of the pebble bed region, the outlet ports leading to an outlet plenum;wherein the pebble bed region is configured such that the coolant exits the pebble bed region primarily into the outlet ports in the outer reflector;wherein the location of the coolant injection and outlet ports is selected to generate a radially outward and upward flow of coolant through the pebble bed region. 2. A reactor as recited in claim 1, wherein the annular pebble bed region comprises a driver fuel layer disposed between an inner radial blanket pebble layer and outer radial pebble blanket layer;the inner radial blanket pebble layer being adjacent the inner reflector, and outer radial pebble blanket layer being adjacent the outer reflector. 3. A reactor as recited in claim 2, wherein the driver fuel layer comprises a plurality of axial layers comprising alternating seed and blanket pebble zones;the alternating seed and blanket pebble zones configured to allow reduced power peaking. 4. A reactor as recited in claim 3, wherein the blanket pebbles comprise graphite blanket pebbles or thorium-bearing blanket pebbles containing coated particles of thorium. 5. A reactor as recited in claim 4, wherein the blanket pebbles comprise a mixture of thorium and uranium. 6. A reactor as recited in claim 4, wherein the seed pebbles comprise coated particles containing fissile uranium or plutonium fuel. 7. A reactor as recited in claim 6, wherein the seed pebbles comprise recycled U-233, plutonium, or a mixture of plutonium and other transuranics. 8. A reactor as recited in claim 2, further comprising:a plurality of partition rings disposed at the pebble injection inlet;wherein the partition rings control the radial location for pebbles injected into the annular pebble-bed region to generate the alternating radial layers of seed pebbles and blanket pebbles. 9. A reactor as recited in claim 2, further comprising:a plurality of dividers disposed at the pebble injection inlet;wherein the dividers control the azimuthal location for pebbles injected into the annular pebble-bed region to generate alternating azimuthal layers of seed pebbles and blanket pebbles. 10. A reactor as recited in claim 8, wherein the partition rings comprise an outer partition ring that delineates the outer radial blanket pebble layer from the driver fuel layer provide shielding of the outer reflector from neutrons generated by fission in seed pebbles, and an inner partition ring that delineates the inner radial blanket-pebble zone from the driver fuel layer to provide shielding of the inner reflector from neutrons generated by fission in seed pebbles. 11. A reactor as recited in claim 1, wherein the pebble injection annulus and the pebble defueling slot are configured to be substantially subcritical. 12. A reactor as recited in claim 1, wherein the angle of the coolant flow reaching the outer reflector is configured such that a transverse hydrodynamic force on the pebbles is capable of overcoming friction between the pebbles and outer reflector. 13. A reactor as recited in claim 1:wherein the outer reflector further comprises a plurality of outer injection ports leading into the bottom end of the pebble bed region;wherein the reactor is configured such that coolant may be injected into the lower portion of the annular pebble bed core from the outer injection ports of the outer reflector and oscillated periodically between the outer injection ports and inner injection ports to agitate the pebble bed. 14. A reactor as recited in claim 1:wherein the inner reflector has a control channel at its center;wherein the control channel is configured such that pebbles may be injected at a bottom inlet of the control channel, and defueled from a top outlet of the control channel; andwherein reactivity of the reactor may be controlled by varying the rate of injection and defueling of pebbles into the control channel to vary the inventory of pebbles in the channel. 15. A reactor as recited in claim 1, further comprising:a pebble injector at the pebble bed inlet;the pebble injector comprising a plurality of entrance vanes;wherein a coolant flow entering the bottom of the pebble injection annulus is swirled by the entrance vanes; andwherein the swirling flow in the annulus alters a deposition pattern of injected pebbles at a bottom of the pebble bed. 16. A reactor as recited in claim 1:wherein the defueling slot is configured to permit sufficient residence time for decay of short-lived fission products prior to removal from the core. 17. A reactor as recited in claim 3:wherein the outer radial pebble blanket layer is configured to provide neutron shielding.