Nuclear fuel pebble and method of manufacturing the same
Nuclear fuel elements may include: a fuel zone including fuel particles disposed in parallel layers in a matrix including graphite powder; and a shell comprising graphite and surrounding the fuel zone. The fuel particles may include fissile particles, burnable poison particles, breeder particles, or a combination thereof. The fuel zone may include a central region and a peripheral region surrounding the central region, and a fuel particle density of the peripheral region may be greater than a fuel particle density of the central region.
1. A nuclear fuel element, comprising:
a fuel zone comprising first and second layers of fuel particles, the fuel particles comprising fissile particles, burnable poison particles, breeder particles, or a combination thereof; and
a fuel-free shell surrounding the fuel zone,
wherein the nuclear fuel element is formed by a method comprising:
forming a graphite base portion;
forming a first graphite layer on the graphite base portion by depositing graphite powder on the base portion;
depositing the first layer of fuel particles in a predetermined pattern on the first graphite layer by controlling positioning of each particle within the first layer of particles;
forming a second graphite layer on the first layer of fuel particles by depositing graphite powder on the first layer of fuel particles;
depositing the second layer of fuel particles in a predetermined pattern on the second graphite layer by controlling positioning of each fuel particle within the second layer of particles; and
forming a graphite cap portion,
wherein:
the fuel zone comprises portions of the first and second graphite layers; and
the shell comprises the base portion, the cap portion, and portions of the first and second graphite layers.
2. The nuclear fuel element of claim 1 , wherein:
the first and second graphite layers comprise a mixture of graphite powder and graphite spheres; and
the graphite spheres and the fuel particles are approximately the same size.
3. The nuclear fuel element of claim 2 , wherein the fuel zone comprises:
a central region comprising the graphite spheres; and
a peripheral region surrounding the central region and comprising the graphite powder.
4. The nuclear fuel element of claim 2 , wherein:
the fuel zone comprises a central region and a peripheral region surrounding the central region;
the fuel particles comprise the fissile particles and the burnable poison particles; and
the central region has a higher burnable poison particle to fissile particle ratio than the peripheral region.
5. The nuclear fuel element of claim 1 , wherein the fuel particles comprise tri-structural-isotropic (TRISO) nuclear fuel particles that do not have an overcoat.
6. The nuclear fuel element of claim 1 , wherein:
the first layer of fuel particles is disposed in a first plane;
the second layer of fuel particles is disposed in a second plane that is substantially parallel to the first plane; and
the fuel particles of the first layer do not overlap the fuel particles of the second layer in a direction substantially perpendicular to the first and second planes.
7. The nuclear fuel element of claim 1 , wherein:
the first and second graphite layers have a thickness ranging from about 1 mm to about 3 mm; and
the base portion and the cap portion have a thickness ranging from 10 mm to 12 mm.
8. The nuclear fuel element of claim 1 , wherein:
the fuel element is a spherical fuel pebble suitable for use in a pebble bed high temperature gas cooled reactor;
the fuel element has a diameter ranging from about 5 cm to about 7 cm; and
the shell has a thickness ranging from about 0.5 cm to about 1.5 cm.