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152. The slug injection process for fabricating HTGR fuel rods
691
ABSTRACTS VII.
NUCLEAR
FUELS
AND NUCLEAR
GRAPHITE
149. Graphite in nuclear reactors-an historic perspective (Plenary Lecture) H. G. MacPherson (The University of Tennessee, Knoxville?, Tennessee). 150. Relationships betxeen three-dimensional structural models and properties in carbon fibers E. W. Tokarsky and R. J. Diefendorf (~~~u~ D&&on, Rme&r Polytechnic Z~~itu~, Troy, New York). In carbon fibers two kinds of preferred o~entation of the basal plane have first-order effects on mechanical properties. The axial elastic modulus is determined primarily by the axial preferred orientation, while strength is determined not only by axial, but aiso radial preferred orientations. Fibers studied were of PAN and rayon base, and represented a modulus range of 6-116 Msi. With increasing modulus, the average axial preferred orientation and crystallite perfection increased; in several of the higher modulus PAN fibers, modulation of the (1010) into six spots in electron diffraction was commonly obseyved. The arrangement of these spots with respect to the (0002) arcs suggests a tendency of one of the [lOlO] to lie parallel to the fiber axis within the rippled ribbon structural units. As the modulus increases the amplitude to wavelength ratio of the rippled ribbons decreases along with fibril-fibril bonding; as a consequence, the fracture mode of the fiber becomes analogous to a macro-composite. Optically determined radial and axial preferred orientations indicate that radial preferred orientations develop along with axial. Measurements also indicate that the outer surfaces of most fibers have a higher axial preferred orientation than the core-as a result, when fibers are loaded in tension, the surface sustains most of the load. On the other hand, the poorer axial preferred orientation of the core will place the surfaces of fibers in longitudinal compression on cool down from final heat-treatment temperatures, thus lowering flaw sensitivity. The tendency toward the development of centrosymmetric radial textures will cause circumferential cracks to form on cool down from final heat-treatment temperatures exceeding about 1300X- this will have a deleterious effect on fiber strength. A model of a 60 Msi fiber illustrating basic preferred textures is presented. 151. Development and irradiation testing of graphite and matrix materials for high temperature reactors in tbe Federal Republic of Germany W. Delle, D. F. Leushacke (Kermfwschungsanluge Jiilich GmbH, W. Germany), W. Rind (HochtemperatweBrennelewnt GmbH, GroBauheim, W. Germany), H. Rosswurm (Sigri-Elektrographit GmbH, FrankfurtGriesheim, W. Germany), and W. Theymann (Hochtemperature-Reaktorbau GmbH, Man&km, W. Germany). The report summarizes the present status and programme in the development and accompanying basic studies of graphite and matrix materials for power scale HTGR in Germany. The main points of the work are development, production and testing under irradiation of graphites and matrix materials for fuel elements and reflectors. The chemical and physical properties of these materials are discussed in terms of reactorphysical and design specifications. Results of irradiation up to the core requirements are presented and the ability of these materials in HTGR is proved. 152. The slug injection process for fabricating HTGR fuel rods* R. A. Bradley and J. D. Sease (Metals and Ceramics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee). The slug injection process has been developed for fabricating High-Temperature Gas-Cooled Reactor (HTGR) fuel rods remotely. The process has been shown in the laboratory to be completely suitable for this application. This paper describes the slug injection process and automatic equipment for fabricating HTGR fuel rods. *Research sponsored by the U.S. Atomic Energy Commission under contract with Union Carbide Corporation. 153. Behavior of restrained pyrolytic carbons during irradiation J. L. Kaae (Gulf General Atomic Company, San Diego, California). Data are presented that show that fracture of restrained isotropic carbons during irradiation cannot be predicted from the dimensional changes and mechanical properties of unrestrained specimens. Several possible explanations of the inconsistency are discussed, and data are presented to show that one, increased preferred orientation and subsequent increased dimensional changes due to restraint, occurs and can explain the observed differences.
ABSTRACTS VII.
NUCLEAR
FUELS
AND NUCLEAR
GRAPHITE
149. Graphite in nuclear reactors-an historic perspective (Plenary Lecture) H. G. MacPherson (The University of Tennessee, Knoxville?, Tennessee). 150. Relationships betxeen three-dimensional structural models and properties in carbon fibers E. W. Tokarsky and R. J. Diefendorf (~~~u~ D&&on, Rme&r Polytechnic Z~~itu~, Troy, New York). In carbon fibers two kinds of preferred o~entation of the basal plane have first-order effects on mechanical properties. The axial elastic modulus is determined primarily by the axial preferred orientation, while strength is determined not only by axial, but aiso radial preferred orientations. Fibers studied were of PAN and rayon base, and represented a modulus range of 6-116 Msi. With increasing modulus, the average axial preferred orientation and crystallite perfection increased; in several of the higher modulus PAN fibers, modulation of the (1010) into six spots in electron diffraction was commonly obseyved. The arrangement of these spots with respect to the (0002) arcs suggests a tendency of one of the [lOlO] to lie parallel to the fiber axis within the rippled ribbon structural units. As the modulus increases the amplitude to wavelength ratio of the rippled ribbons decreases along with fibril-fibril bonding; as a consequence, the fracture mode of the fiber becomes analogous to a macro-composite. Optically determined radial and axial preferred orientations indicate that radial preferred orientations develop along with axial. Measurements also indicate that the outer surfaces of most fibers have a higher axial preferred orientation than the core-as a result, when fibers are loaded in tension, the surface sustains most of the load. On the other hand, the poorer axial preferred orientation of the core will place the surfaces of fibers in longitudinal compression on cool down from final heat-treatment temperatures, thus lowering flaw sensitivity. The tendency toward the development of centrosymmetric radial textures will cause circumferential cracks to form on cool down from final heat-treatment temperatures exceeding about 1300X- this will have a deleterious effect on fiber strength. A model of a 60 Msi fiber illustrating basic preferred textures is presented. 151. Development and irradiation testing of graphite and matrix materials for high temperature reactors in tbe Federal Republic of Germany W. Delle, D. F. Leushacke (Kermfwschungsanluge Jiilich GmbH, W. Germany), W. Rind (HochtemperatweBrennelewnt GmbH, GroBauheim, W. Germany), H. Rosswurm (Sigri-Elektrographit GmbH, FrankfurtGriesheim, W. Germany), and W. Theymann (Hochtemperature-Reaktorbau GmbH, Man&km, W. Germany). The report summarizes the present status and programme in the development and accompanying basic studies of graphite and matrix materials for power scale HTGR in Germany. The main points of the work are development, production and testing under irradiation of graphites and matrix materials for fuel elements and reflectors. The chemical and physical properties of these materials are discussed in terms of reactorphysical and design specifications. Results of irradiation up to the core requirements are presented and the ability of these materials in HTGR is proved. 152. The slug injection process for fabricating HTGR fuel rods* R. A. Bradley and J. D. Sease (Metals and Ceramics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee). The slug injection process has been developed for fabricating High-Temperature Gas-Cooled Reactor (HTGR) fuel rods remotely. The process has been shown in the laboratory to be completely suitable for this application. This paper describes the slug injection process and automatic equipment for fabricating HTGR fuel rods. *Research sponsored by the U.S. Atomic Energy Commission under contract with Union Carbide Corporation. 153. Behavior of restrained pyrolytic carbons during irradiation J. L. Kaae (Gulf General Atomic Company, San Diego, California). Data are presented that show that fracture of restrained isotropic carbons during irradiation cannot be predicted from the dimensional changes and mechanical properties of unrestrained specimens. Several possible explanations of the inconsistency are discussed, and data are presented to show that one, increased preferred orientation and subsequent increased dimensional changes due to restraint, occurs and can explain the observed differences.