Patent Number: 043274439
Section: description

More particularly, FIG. 1 illustrates a typical cross section normal to the longitudinal axes of the capillary fuel elements comprising the fuel components which are constructed as integral units from moderator material and are arranged to form channels for coolant circulation. 1 is the fuel component which contains horizontal capillary troughs, slightly inclined to vertical, which are nonadhesive to the fuel and which have longitudinal openings that approximately equal twice the capillary constant of the fuel at the environment of the core. 2 is the liquid fuel which flows under gravity through the capillary troughs and which forms a meniscus that has an approximately circular cross section and projects above the trough edge. The combination of moderator construction material and fuel forms a critical mass which generates heat through a nuclear chain reaction. Heat is removed from the core by a coolant which circulates through the channel 3. FIG. 2 shows, in exaggeration, the helical flow direction of fuel through a fuel element of a cylindrical fuel component. Fuel is fed to the trough from an upper fuel reservoir and flows at a rate predetermined by the pitch of the fuel element helix down to the lower fuel reservoir. FIG. 3 is a longitudinal cross section through a cylindrical reactor. Cylindrical fuel components 1, constructed as integral units from moderator material are arranged concentrically to form a core with coolant channels 3. The core is surrounded by a neutron reflector 4. Fuel 2 from the upper fuel reservoir 5 is distributed through the distribution means 6 to the fuel components 1 through which it flows into the lower fuel reservoir 7 from where a pump 8 returns it through conduit 9, which is the inner surface of the center fuel component, to the upper fuel reservoir. Coolant is admitted through inlet 10, circulates through the core channels 3 and exists through outlet 11. The core is surrounded by a neutron reflector 4 and is enclosed in containment vessel 12. Because the reactor has a negative temperature coefficient, it will tend to operate at the same average moderator temperature at all power levels. This temperature is maintained by controlling the uranium fuel concentration. A more particular example is a cylindrical reactor, illustrated by FIG. 3, which employs 4.6 percent enriched uranium dissolved in molten bismuth to form a 8.5 percent solution as fuel at an average 850.degree. C. (1560.degree. F.) temperature. The fuel capillary constant at 850.degree. C. is 0.28 cm (0.11 in). The fuel component 1, a magnified cross section of which is illustrated by FIG. 1, are 25 concentric, 2.8 cm (1.1 in) thick, 180 cm (70.9 in) high, graphite cylinders constructed as an integral unit of capillary troughs and moderator material. The distance between the cylinders, i.e., the coolant channel 3 width, is 0.75 cm (0.30 in); and the width of the cylinder lips which contain the fuel 2, is 0.90 cm (0.35 in). There are 183 equally spaced lips per vertical surface of a cylinder. The outside radius of the outermost cylinder is 90 cm (35.4 in), and the inside radius of the innermost cylinder is 5.0 cm (2.0 in). The neutron reflector 4, constructed of graphite, is 30 cm (11.8 in) thick. The coolant is methane at 134 atmospheres (2000 psi) pressure. The physical parameters of the bare example reactor have been determined to be as follows: Regeneration factor (.eta.) 1.89 PA0 Thermal utilization factor (f): 0.980 PA0 Infinite multiplication factor (k.infin.): 1.85 PA0 Diffusion area (corrected for coolant channel voids) (L.sup.2): 156.9 cm.sup.2 PA0 Neutron age (.tau.): 486 cm.sup.2 PA0 Geometric buckling factor (B.sup.2): 0.00098/cm.sup.2 PA0 Critical mass: 28.6 kg (62.9 lb) uranium-253 dissolved in 5883 kg (12,943 lb) of molten bismuth. PA0 Core thermal power: 50 Mw PA0 Neutron energy: thermal PA0 Fuel (clean): 3900 ppm uranium-235 in molten bismuth; 8.5 at. % of 4.6% enriched uranium in molten bismuth. PA0 Fuel capillary constant: 0.28 cm (0.11 in) at 850.degree. C. (1560.degree. F.) PA0 Moderator: graphite (1.9 gm/cm.sup.3) as an integral part of fuel component. PA0 Coolant: Methane at 134 atm (2000 psi) PA0 Core height: 180 cm (70.9 in) PA0 Core radius: 90 cm (35.4 in) PA0 Total number of fuel components: 25 concentric cylinders PA0 Total number of capillary troughs per cylinder vertical surface: 183 equally spaced. PA0 Coolant channel width (distance between cylinder surfaces): 0.75 cm (1.90 in) PA0 Fuel volume: 0.65 m.sup.3 (22.9 ft.sup.3) PA0 Moderator volume: 2.15 m.sup.3 (75.7 ft.sup.3) PA0 Coolant (void) volume: 1.78 m.sup.3 (62.7 ft.sup.3) PA0 Fuel volume fraction: 14.7% PA0 Moderator volume fraction: 46.8% PA0 Coolant volume fraction: 38.9% PA0 Maximum fuel temperature: 1100.degree. C. (2012.degree. F.) PA0 Maximum moderator temperature: 1000.degree. C. (1832.degree. F.) PA0 Coolant inlet temperature: 600.degree. C. (1112.degree. F.) PA0 Coolant outlet temperature: 900.degree. C. (1652.degree. F.) PA0 Coolant flow rate: 129,102 kg/hr (284,024 lb/hr) PA0 Coolant core channel velocity: 2.7 m/sec (9.0 ft/sec) PA0 Coolant flow frontal area: 0.52 m.sup.2 (5.8 ft.sup.2) PA0 Total heat transfer surface: 821 m.sup.2 (8834 ft.sup.2) The operating characteristics of the example reactor are as follows: Although the invention had been described with a certain degree of particularity, especially in the use of a nuclear reactor that utilizes fuel components which are constructed as integral units from moderator materials, it is to be understood that the present disclosure is made by way of example and illustration only and that numerous changes in application, in construction details, and in the arrangement and combination of parts may be made without departing from the spirit and scope of the invention hereinafter claimed.