RESUMEN
Reprocessed high-level nuclear waste (HLW) contains range of radioactive components. Crystalline oxyphosphate apatite ceramic of the formula LaSr4(PO4)3O [LSS] was investigated as a host for HLW immobilisation. The systematic study of solid solubility limit of individual rare earth ion substitution leads to the formulation of simulated wasteform of the formula La0.6Pr0.1Nd0.1Sm0.1Gd0.1Sr4(PO4)3O (WF1) with the waste loading of 17.95 wt% of rare-earth ions. Both parent and WF1 were synthesized by precipitation method. The thermal stress and groundwater inventory at the repository site can severely affect the wasteform performance, in addition to radiation and mechanical effects. Hence, the fabricated composition with high-level nuclear waste loading must be screened basically for chemical, thermal and radiation resistance. The present study investigated the thermal stability (by TGA), thermal expansion behaviour (by HT-XRD) and chemical durability (MCC-5) of the composition (WF1). The weight loss of WF1 being 2.2% and the average thermal expansion co-efficient (αavg) of 10.7 ± 1.2 × 10-6 K-1 in the temperature range (298-973 K) were comparatively lower than the parent phase, LaSr4(PO4)3O. The WF1 showed resistance to leaching of RE3+ and P5+ with only the leaching of Sr2+ ion whose leach rate was of the order 10-3-10-4 gm-2d-1.
RESUMEN
Leaching behaviors and mechanisms of commercialized glass wasteforms to sequester low-level solid-wastes were investigated: SG glass for resin waste and DG-2 glass for dry active waste. After ANS 16.1 leaching test, leachabilities of the nuclides, Co, Cs, and Sr, were all lager than 14, which met the requirement of the US-Nuclear Regulatory Commission. Holes of diameters 5-10⯵m remained on the surface of the SG and crevices of lengths 10-50⯵m were observed on the surface of the DG-2. We analyzed elemental compositions of the SG and the DG-2 with depths. For the SG, Si, Al, Ca, and Mg were accumulated and Na was depleted up to nearly 1.5⯵m compared to an internal glass. For the DG-2, concentrations of B, Na, Al, Ca and Sr started to decrease from 2.5⯵m even though other minor elements are still remained their concentrations. We suggested leaching mechanisms: alkali elements including H would diffuse through the holes on the SG, while most of the elements including Si and Al would diffuse through the crevices on the DG-2.
RESUMEN
Cement-based stabilization/solidification (S/S) is used to decrease environmental leaching of contaminants from industrial wastes. In this study, two industrial metal treatment filtercakes were characterized by X-ray diffractometry (XRD), thermogravimetric and differential thermogravimetric analysis (TG/DTG) and Fourier transform infrared (FTIR); speciation of nickel was examined by X-ray absorption (XAS) spectroscopy. Although the degree of carbonation and crystallinity of the two untreated filtercakes differed, α-nickel hydroxide was identified as the primary nickel-containing phase by XRD and nickel K edge XAS. XAS showed that the speciation of nickel in the filtercake was unaltered by treatment with any of five different S/S binder systems. Nickel leaching from the untreated filtercakes and all their stabilized/solidified products, as a function of pH in the acid neutralization capacity test, was essentially complete below pH â¼5, but was 3-4 orders of magnitude lower at pH 8-12. S/S does not respeciate nickel from metal treatment filtercakes and any reduction of nickel leaching by S/S is attributable to pH control and physical mechanisms only. pH-dependent leaching of Cr, Cu and Ni is similar for the wastes and s/s products, except that availability of Cr, Cu and Zn at decreased pH is reduced in matrices containing ground granulated blast furnace slag.