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Hot isostatically pressed tailored hollandite waste forms were used to demonstrate the immobilization of Cs and Sr are separable from spent nuclear fuel, as well as Ba and Rb. Four hollandite formulations were investigated, two samples with ∼12 wt% waste loading (on an oxide basis) and two with ∼18 wt% waste loading. Two of the samples were Al‐substituted and the other two contained Mg. The hollandite in the Al‐substituted samples contained all the waste cations, as designed, but this was not the case in the Mg‐substituted samples. The hollandite in the Mg‐substituted samples did not contain all the waste cations, with ∼50% of the Sr forming SrTiO3 as a secondary phase. This resulted in waste forms that were not as durable, with respect to Cs, as their Al counterparts. The formation of SrTiO3 had little effect on the Sr release rates and was not detrimental to the Mg‐substituted hollandite waste form. For the Al‐substituted samples, the MCC‐1 normalized release rates were <0.06 g·(m2·day)−1 at 0–28 days for all elements, while the Cs release rates remained at 2.0 g·(m2·day)−1 at 0–28 days for the Mg‐substituted samples.

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Cementitious material is the most commonly used encapsulation medium for low and intermediate level radioactive waste. This paper focuses on the aqueous durability of a Materials Testing Reactor (MTR) cementitious wasteform -a possible candidate for the proposed intermediate level waste management facility in Australia. A series of medium term (up to 92 months) durability tests, without leachate replacement, were conducted on samples of this wasteform.The wasteform was made from cement, ground granulated blast furnace slag and a simulated waste liquor. The compressive strength (39 MPa) was typical of MTR cement wasteforms and well above that required for handling or storage. The wasteform was an inhomogeneous mixture containing calcite, a calcium silicate hydrate phase, hydrotalcite and unreacted slag particles. After leaching for 92 months the crystallinity of the calcium silicate hydrate phase increased.The majority of the releases of Ca, Si, Al, Sr, S, Na and K was reached within 4 days of leaching, with the maxima ie. the highest concentrations in the leachates, occurring at 3 months for Ca, Al, Sr, S, Na and K, and at 1 month for Si. For the longer leach periods (6 months and 3 months respectively) there was a slight reduction in concentration in the leachates, and these levels were similar to those for the longest period of 92 months, suggesting steady-state conditions prevailing after 3 to 6 months of leaching. The highest releases of matrix elements were for Na (37%), K (40%) and S (16%). Releases for elements such as Ca, Na, Al and Sr were similar in magnitude to those reported by the UKAEA in earlier MTR studies.After leaching for 92 months there was an alteration layer about 80 µm deep where calcium has been depleted. Na, K and Sr showed signs of diffusion towards the outer part of the cement samples.