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Conference Article: Fracture Mechanics Based Coated Particle Fuel Failure Models

Abstract

The most modern gas reactor coated particle fuel design consists of a kernel of fuel, either UO2, UCO, or PuO2, surrounded by a low density pyrocarbon “buffer” layer, and a three-layer structure consisting of an inner dense pyrocarbon (IPyC), a SiC, and an outer dense pyrocarbon (OPyC) layer. The integrity of this layer is the key to the overall reliability of the fuel. During operation the effect of fuel fission and irradiation damage is to cause internal pressurization of the fuel as well as and increase in tensile stresses in the pyrocarbon layers. Eventual cracking of the pyrocarbon layers can cause stress concentration at the interface between the pyrocarbon and SiC layers. A fracture mechanics based model has been developed to allow analysis of fuel failure due to SiC cracking induced by pyrocarbon layer cracking. The physics of the model includes: (1) an accounting for the relaxation of stress in the pyrocarbon layers after cracking, (2) following the evolution of the stress in the pyrocarbon layer and the induced stress intensity factor in the SiC after initial PyC cracking but no SiC failure, and (2) an accurate crack tip stress intensity calculation.

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Reference:

Proceedings of the Conference on High Temperature Reactors, Beijing, China, September, 22-24, 2004

International Atomic Energy Agency, Vienna (Austria)

HTR-2004, pp:1-12