Coated fuel

The Tj-carbides are not specifically synthesized, but are of technical importance, occurring in alloy steels, stelUtes, or as embrittling phases in cemented carbides. Other complex carbides in the form of precipitates may form in multicomponent alloys or in high temperature reactor fuels by reaction between the fission products and the moderator graphite, ie, pyrographite-coated fuel kernels. 

Ogawa, T., and Ikawa, K., High Temperature Heating Experiments on Unirradiated ZrC-Coated Fuel Particles, J. Nucl. Mater., 99(l) 85-93 (July 1981)... 

Fuel Coated fuel particles in prismatic block... 

Sawa, K. et al., Investigation of irradiation behavior of SiC-coated fuel particle at extended burnup, /. Nucl. Tech., 142, 250, 2002. 

Gulden, T.D. and Nickel, H., Preface, Coated Fuel Particles, Nuclear Technology, 1977,35,206 213. 

Hannon, D.P. and Scott, C.B., Properties influencing high-temperature gas-cooled reactor coated fuel particle performance, Nuclear Technology, 1977, 35, 343 352. 

Figure 1. Photomicrographs of typical BISO coated fuel particles before and after irradiation (60X)...

Numerous studies by other workers (I, 10) have shown that the releases of iodine and the noble-gas fission products from pyrolytic carbon-coated fuel particles are controlled by diffusion of these nuclides through grain boundaries, cracks, and defects in the isotropic pyrolytic carbon coating. When coatings are intact, however, the release of these fission product nuclides is low. However, the pyrolytic carbon coating constitutes only a delaying barrier to the metallic nuclides barium and strontium through which they diffuse with diffusion coefficients of the order of 10 9 cm.2/sec. (at — 1400°C.). The steady-state release of these metallic nuclides is controlled instead by diffusion out of the fuel kernel,... 

Postactivation annealing fission product release measurements have shown that the excellent retention of iodine and noble fission gases by pyrolytic carbon-coated fuel particles is unaffected by irradiation up to 24% FIMA. These data are interpreted as indicating that the pyrolytic carbon coatings remain undamaged by these high levels of irradiation. 

Figure 3 briefly shows the structure, major specification and the history of the HTTR R D by JAEA. The reactor core is composed of graphite prismatic blocks. Fuels are inserted in the blocks as a shape of cylindrical graphite compacts in which tri-isotropic (TRISO)-coated fuel particles with U02 kernel are dispersed. The coolant helium gas of the HTTR is circulated at 4 MPa to an intermediate heat exchanger where high temperature heat is transferred to hydrogen production process. 

Fuel Coated fuel particle / Prismatic block type... 

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