Two options were developed for the inner core of the multibarrier concept: supercalcine pellets and glass marbles. The multibarrier concept aims to separate the radionuclide-containing inner core material and the environment by the use of coatings and matrices. Glass and P圜/Al/sub 2/O/sub 3/ coatings provide effective inert leaching barriers.
Supercalcine may offer no advantage over waste glasses in leach resistance. Hot-pressed supercalcine ceramics may offer no increase in impact resistance or leach resistance over that of a glass monolith. CVD-coated supercalcine in a sintered 410 SS matrix offers up to two orders of magnitude decrease. mu.m released after impact as compared to a glass monolith.
more » Glass marbles in a cast lead alloy offer approximately an order of magnitude decease in the wt % fines < 37. The weight loss of supercalcine-ceramics after 4 h in dry air ranges between 0.01 and 1.6 wt % from 1000 to 1200/sup 0/C and is dependent upon composition. This report discusses the characterization of the multibarrier waste forms and compares them to reference calcine and glass waste forms. The four multibarrier waste forms were evaluated for thermal stability (volatility), mechanical strength (impact resistance), and leach resistance. The multibarrier concept for the storage of radioactive waste is to use up to three barriers to isolate radionuclides from the environment: a solidified waste inner core, an impervious coating, and a metal matrix. Four multibarrier products were demonstrated: (1) Glass marbles encapsulated in vacuum-cast Pb-10Sn (2) uncoated, sintered supercalcine pellets encapsulated in vacuum-cast Al-12Si (3) glass-coated, sintered supercalcine pellets encapsulated in vacuum-cast Al-12Si and (4) P圜/Al/sub 2/O/sub 3/-coated supercalcine encapsulated in gravity-sintered Cu. The development of gravity sintering and vacuum casting techniques for matrix encapsulation are discussed. The purpose of the metal matrix is to improve impact resistance, protect the inner core rom any adverse environments, provide radiation shielding, and increase thermal conductivity, yielding lower internal temperatures. Py/Al/sub 2/O/sub 3/ coatings deposited by chemical vapor deposition (CVD) and glass coatings have been applied to supercalcine cores to improve inertness. The coating barrier provides enhanced leach, impact, and oxidation resistance as well more » as thermal protection during encapsulation in the metal matrix. Two inner core materials, sintered supercalcine and glass marbles, have been demonstrated. The multibarrier concept is to utilize up to three barriers to isolate radionuclides from the environment: a solid waste inner core, an impervious coating, and a metal matrix. This report describes research and development activities resulting in the demonstration of the multibarrier concept for nonradioactive simulated waste compositions. The multibarrier concept produces a composite waste form with enhanced inertness through improvements in thermal stability, mechanical strength, and leachability by the use of coatings and metal matrices.
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