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An analysis of strains and stresses in four-point bending creep tests in the limit of small beam deflections resulted in a general equation which relates the load-point deflection, the applied load, the creep exponent (N), and the geometrical parameters of the loading system. Measurements of load-point deflection rates, which are experimentally easy to accomplish in ceramic systems, vs the applied load lead to the direct determination of the creep exponent and the creep compliance in a steadystate creep test. The creep compliance is a function of the temperature, grain size, and all other factors except stress. The elastic equation relating the load-point deflection and the outer fiber strain is strictly valid for viscous creep and a p proximately valid for nonviscous creep (i.e. N>1) if the ratio of the distance between the support points to the distance between the load points is not very large.

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Executive SummaryThe U.S. Department of Energy is constructing a waste treatment plant at the Hanford Site in southeastern Washington State to vitrify the large amount of radioactive waste stored in underground tanks. Supplemental treatment technologies were studied to accelerate the cleanup of low-activity waste, and a decision was made to proceed with a pilot-scale test and demonstration facility to further evaluate bulk vitrification (BV).Experimental research, engineering-scale (ES) tests, and the science of glass melting provide ample evidence that a small fraction of Tc and Re were transferred out of the low-activity waste (LAW) glass feed and molten LAW glass and deposited on the surface and within the internal pore surfaces of the castable refractory block (CRB), both by low-temperature molten salt penetration and by hightemperature evaporation-condensation. In this task, laboratory experiments were undertaken to evaluate the capability of these two mechanisms to transport Tc/Re into the CRB during vitrification and to evaluate various means of CRB protection against the deposition of leachable radioactive Tc (and Re, its nonradioactive surrogate). All tests conducted in this task and described in this report used Re as a chemical surrogate for Tc.Both standard and newly designed experimental methods were applied to assess the extent of Tc/Re transport to the CRB, both unprotected (the baseline) and protected with a glaze or a tile. These methods include:• the measurement of Re concentration distribution in an unprotected CRB sample taken from an ES test • suspended refractory rod test for vapor deposition• simulant condensate penetration tests to determine the penetration of vapor condensates• gas permeability test and porosity measurement for vapor penetration• partially immersed rod test for molten salt penetration• manufacturing demonstration testing to determine the compatibility of tiles and CRB and the adherence of tile to CRB • refractory corrosion test for tiles.In many cases, experimental conditions were selected to enhance the transport mechanism so as to make the very small levels of Tc/Re normally transported easier to detect.The tests with unprotected (baseline) CRB showed that the molten LAW penetrates into CRB pores before it converts to glass, leaving deposits of sulfates and chlorides when the nitrate components decompose. Na 2 O from the LAW reacts with the CRB to create a durable glass phase that may contain limited quantities of insoluble Tc/Re. Limited data from a single CRB sample taken from an ES experiment indicates that, while a fraction of Tc/Re is present in the CRB in a readily leachable form, most of the Tc/Re deposited in the refractory is retained in the form of a durable glass phase.In addition to the direct penetration into the porous CRB, the molten salts from the LAW, mainly sulfates, chlorides, and nitrates, begin to evaporate from BV feeds at temperatures below 800°C and condense on iv solid surfaces at temperatures below 530°C. The condensed salt readily wets and pe...

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Steady-state creep was studied in hot-forged polycrystalline Al,O, (3 to 42 pm) of nearly theoretical density doped with51 cation % of Fe, Ti, or Cr. Tests were conducted at stresses beheen 10 and 550 kg/cmz at 1375O to 1525OC under 0, partial pressures of 0.86 to lo-" atm. Except in the 10-pm Fe-doped material tested at very small stresses, slightly nonviscous creep behavior was generally observed. The effects of Po, on the creep rate indicated that increased concentration of a divalent (Fez+) or quadrivalent (Ti4+) impurity in solid solution enhances the creep rate of polycrystalline Also3. The activation energies for the creep of Fe-and Ti-doped AhO, samples (148 and 145 kcal/mol, respectively) were significantly higher than that for Cr-doped material (114 kcal/mol). Taking into account the effects of Po,, temperature, and grain size, it was concluded that the steady-state creep of transition-metaldoped AI,O, is controlled by cation lattice diffusion.