Ceramicrete waste form

Wagh et al. [45] demonstrated stabilization of Cr, along with Cd, Pb, and Hg from contaminated soil and wastewater in the Ceramicrete waste form. Table 16.8 shows the contaminant levels in the waste and the wastewater, and the corresponding TCLP result for the stabilized waste. The wastewater in the Ceramicrete slurry was equal in amount to the stoichiometric water needed for the stabihzation process. Including this wastewater, the total waste loading was 77 wt%. The waste forms had open porosity of 2.7 vol% and a density of 2.17 g/cm. Compression strength was 34 MPa (4910 psi). 

The following three mechanisms play the major role in the immobilization of radioactive contaminants in a stabilized Ceramicrete waste form ... 

The acid-base reaction that forms the Ceramicrete waste forms also creates an oxidizing environment in which species of lower oxidation states are automatically converted to their fully oxidized states. Hence, pyrophoric components (such as PU2O3) should be converted to their most stable and fully oxidized forms (such as PUO2) that are no longer pyrophoric. Wagh et al. [10] have demonstrated such transformations in the Ceramicrete process by using surrogates of Pu (see the case study in Section 17.5.4). 

Acceptance Criteria and Examples of Ceramicrete Waste Forms that Meet the Criteria. 

In contrast to the two studies mentioned above, the work at ANL has been mainly in demonstrating treatment of a range of radioactive waste streams (both simulated and actual) from the US DOE complex in the Ceramicrete matrix. The reader is referred to Ref. [21] and additional references therein. In this section, we provide an overview in the form of case studies. Table 17.5 lists acceptance criteria and the corresponding case studies selected to demonstrate compliance by the Ceramicrete waste forms with those criteria. 

Results on the first four examples given in Table 17.10 are from the literature [10, 30-32]. The last two provide the results on Ceramicrete waste forms. The transuranic (TRU) combustion residue was obtained originally from Rocky Flats. It was fully calcined for safe transport to ANL. Therefore, all organics and combustibles were completely incinerated, and that step enhanced the Pu concentration. The U-Pu oxide mixture was a... 

As Table 17.10 indicates, the G values in Ceramicrete waste forms are lower than in most other grout systems and comparable to that in FUETAP (Formed Under Elevated Temperature and Pressure) concrete. These results indicate that the gas yield is minimal in the Ceramicrete waste forms. 

Ceramicrete cures to create final waste forms that are analogs of naturally occurring phosphate minerals. These minerals have been shown to be relatively insoluble over geologic time scales. The final waste form is stronger than typical room temperature, hydraulic cements and performs in the manner of high-temperature fused ceramics. The technology has been evaluated in bench-and operational-scale tests on contaminated wastewater, sedimenL ash, and mixed wastes. 

Disposal costs at various radioactive waste management facilities in the United States range from 20/ft to 1500/ft. ANL used an average disposal cost of 60/ft of treated waste form to estimate the total disposal costs for the hypothetical Ceramicrete prodnct. The estimated cost was 2836/m of waste. According to the ANL, this fignre is lower than the disposal costs for cement, which were estimated at 3700/m (D20934H, p. 15). 

The Ceramicrete process is based on the acid-base exothermic reaction. As a result, the exothermic heat evolution and its rate depend on the size of the waste forms produced. Larger forms generate more heat, which does not dissipate rapidly. Thus, the setting slurry heats up and accelerates the acid-base reaction, and the mixture is able to set even in cold surroundings. 

Five-gallon size waste forms were fabricated. Typical waste loading was 35-40 wt%. A small amount of potassium sulfide was added to the Ceramicrete binder mixture for stabilization of Hg, and dense and hard ceramic waste forms were produced. Just before solidification, TCLP results were obtained on small aliquots of the mixing slurry that was separated and allowed to set. Mercury levels in the leachate were found to be 0.05 /rg/1, well below the LfTS limit of 0.025 mg/1. The entire waste was treated, removed from the inventory, and sent to the Radioactive Waste Management Complex at the Idaho National Engineering and Environmental Laboratory for disposal. 

Na, and B from a glass waste form. If, on the other hand, this test is to be adopted for a CBPC waste form, such as Ceramicrete, one may look for Mg, K, and P as the matrix components. Thus, the PCX evaluates the durability of the matrix material, which is a result of the integrity of the individual elements within the matrix. 

As mentioned in Section 17.3.1, retention of quadrivalent actinide oxides within the phosphate matrix is not a major issue because these oxides are insoluble in water, and all that is needed is their microencapsulation by the phosphate components of the matrix. This was demonstrated in a number of studies on UO2 and PUO2 and their surrogate Ce02. If the actinides are found in a trace amount in the waste, their chemical form is not so important because the phosphate matrix immobilizes them very efiectively. For example, the wastewater in the case study given in Section 16.3.2.2 contained 32 pCi/ml of and 0.6 pCi/ml of The ANS 16.1 tests conducted on the waste forms with 18.6pCi/g loading of combined U in the waste form showed that the leaching index was 14.52. XCLP tests also showed that levels in the leachate were below the detection limit of 0.2 pCi/ml. This implies that microencapsulation of trace-level U is very efiective in the Ceramicrete matrix. 

As shown in Table 17.9, the alpha activity in the leachate was 25 2 pCi/ml, and the beta activity was 98 lOpCi/ml. These activities are small when compared with the activities of their counterparts in the waste, which were in p-Ci/g. The very low activity in the leachate was attributed to the efficient stabilization of Ra as insoluble radium phosphate in the waste form. In particular, because Ra is water soluble, the leachate would provide a pathway for it, but the levels in the leachate are only in pCi/ml and, hence, much lower than the levels in the waste. This finding implies that radium and most other isotopes are stabilized in the waste forms. Thus, the Ceramicrete process is a good method to arrest leaching of even the most soluble Ra. 

Ceramicrete is an ex situ stabilization technology that uses chemically bonded phosphate ceramics to stabilize low-level radioactive waste and hazardous waste containing radionuclides and heavy metals. The technology mixes phosphates with acidic solution, causing an exothermic reaction similar to that used in forming concrete. But while concrete is based on relatively weak hydrogen and van der Waals bonding, Ceramicrete uses a combination of ionic, covalenf and van der Waals bonds to stabilize contaminants. 

During Ceramicrete formation using H3PO4, the caustic soda reacts with the acid-phosphate and forms amorphous MgNaP04 H2O. The neutralized waste is micro-encapsulated in the Ceramicrete matrix, in which the MgNaP04 H20 also acts like a binding phase. 

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