Abstract Nuclear fuel particles having fissile or fertile central cores surrounded by a buffer layer of low density pyrolytic carbon. A shell of dense silicon carbide, zirconium carbide or niobium carbide surrounds the buffer layer, and a layer of isotropic pyrolytic carbon may be disposed therebetween. To maintain the dense carbide shell in compression during the fuel particle lifetime, an outer isotropic carbon shell is provided which shrinks down onto the carbide shell as a result of high temperature, fast neutron irradiation. To prevent stresses of too great a magnitude from being created early in the fuel particle lifetimes, an intermediate layer of compressible pyrolytic carbon is disposed immediately exterior of the carbide shell. Nuclear reactors utilizing such particles can be operated at temperatures about 800* C. to a fast neutron dosage over 4 X 1021 neutrons/cm.2 while maintaining good fission product retentivity within the coated fuel particles.
A nuclear fuel particle in accordance with claim 1 wherein said intermediate layer is between about 10 and about 30 microns thick.
Claim 2
Dependent Claim
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A nuclear fuel particle in accordance with claim 2 wherein said carbide shell is made of silicon carbide having a density between about 3.17 and about 3.20 g./cm.3.
Claim 3
Dependent Claim
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A nuclear fuel particle in accordance with claim 1 wherein said carbide shell is at least about 20 microns thick.
Claim 4
Dependent Claim
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A nuclear fuel particle in accordance with claim 1 wherein said isotropic carbon shell is at least about 20 microns thick.
Claim 5
Dependent Claim
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A nuclear fuel particle in accordance with claim 5 wherein said isotropic carbon has a Bacon Anisotropy Factor between 1.0 and about 1.2.
Claim 6
Dependent Claim
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A nuclear fuel particle in accordance with claim 1 wherein an isotropic carbon layer is disposed interiorly of said carbide shell.
Claim 7
Dependent Claim
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A nuclear fuel particle in accordance with claim 7 wherein said interior isotropic carbon layer is at least about 15 microns thick and has a density between about 1.7 g./cm.3 and about 1.95 g./cm.3.