[en] Iron-impregnated and ash-rich graphites have been purified by leaching with gaseous I₂ at 900⁰C. With addition of H₂, the rate of removal of impurity iron can be markedly increased and becomes comparable to that obtained with Cl₂. I₂ has an advantage in that it can also volatilize Ca and perhaps Ba and Sr

[en] The effects of oxidizing atmosphere and temperature on the reactivities and strengths of PGX, H451, and IG-11 were examined. Preliminary measurements of the oxidation kinetics of these graphites in H₂O-, CO₂- and O₂-containing atmospheres indicated that the reactivities of H451 graphite toward O₂ and H₂O are quite similar to those of IG-11 graphite. The apparent activation energy for oxidation of these in O₂ were estimated to be approx. 175 kJ/mol while that in H₂O is probably approx. 200 kJ/mol. The apparent activation energy of IG-11 graphite oxidized in CO₂ is 255 +- 18 kJ/mol. PGX graphite was found to be quite variable in its reactivity toward H₂O. A linear dependence with [Fe] was determined, but other intrinsic properties were found to affect its absolute reactivity by as much as a factor of X50

[en] The nature of impurity iron in PGX graphite has been examined and its role during oxidation by steam has been clarified. The iron exists as mobile clusters which are accessible to H₂ and H₂O. It can be easily maintained in a reduced or oxidized state by variation of H₂/H₂ pressures. In the reduced state, iron is an active catalyst which can produce high localized rates of oxidation and form clearly defined etch pits

[en] The effect of gaseous environment on the compressive and tensile strengths of H451, PGX and IG-11 graphites is discussed. Oxidation was carried out in O²-, CO²- and H²O-containing environments. The strength losses incurred by H451 and IG-11 graphite did not appear to be affected by the nature of the oxidizing gas. However, the strength loss incurred by PGX graphite appeared to be greater in O² than in CO² or H²O. A mechanism consistent with the observed behavior of PGX graphite is proposed. No effect of reaction temperature on the strengths of the graphites was observed. Attempts to fit strength-burnoff data to a standard expression were only partially successful. Much improved fits were obtained when this expression was modified to account for the development of the micro/mesopore network during oxidation. (author)

[en] A thermochromatographic technique has been developed to investigate the chemical states of fission products from irradiated fuel as well as in fission product simulation studies. Some recent work on iodine transport and on release of fission products from irradiated fuel kernels will be discussed

No abstract available

[en] The nature of impurity iron in PGX graphite has been examined and its role during oxidation by steam has been clarified. The iron exists as mobile clusters which are accessible to H₂ and H₂O. It can be easily maintained in a reduced or oxidized state by variation of P sub(H₂)/P sub(H₂O). In the reduced state, iron is an active catalyst which can produce high localized rates of oxidation and form clearly defined etch pits. (author)

[en] On-going and recently completed studies of the effect of thermal oxidation on the structural integrity of HTGR candidate graphites are described, and some results are presented and discussed. This work includes the study of graphite properties which may play decisive roles in the graphites' resistance to oxidation and fracture: pore size distribution, specific surface area and impurity distribution. Studies of strength loss mechanisms in addition to normal oxidation are described. Emphasis is placed on investigations of the gas permeability of HTGR graphites and the surface burnoff phenomenon observed during recent density profile measurements. The recently completed studies of catalytic pitting and the effects of prestress and stress on reactivity and ultimate strength are also discussed

[en] A thermochromatographic technique has been developed to investigate the chemical states of fission products from irradiated fuel as well as in fission product simulation studies. Some recent work on iodine transport and on release of fission products from irradiated fuel kernels will be discussed. (author)