Immobilization of cesium and strontium radionuclides in zeolite-cement blends

A review of solidification/stabilization interferences

Numerous publications have examined the chemical and physical aspects of tributyl phosphate (TBP), TBP/nitric acid, and TBP/diluent/nitric acid systems, but there are some discrepancies within the available data. There is also a lack of data on the physical properties of TBP at temperatures above 60°C. A review of more than 100 references, covering the physical and chemical properties of TBP and related systems will be presented. Data on solvent degradation and kinetics of the interactions occurring in these systems will be provided and compared. Also the existing data on TBP vapor pressure, solubility, and density will be discussed.

Review of Physical and Chemical Properties of Tributyl Phosphate/Diluent/Nitric Acid Systems

The presented work represents a combined experimental and modeling approach to evaluate the role of carbon dioxide in the long-term performance of cementitious wasteforms. Small wasteforms were cast with Portland cement and synthetic wastewater containing known amounts of dissolved metals and nitrate as a tracer. A series of wasteforms was exposed to a control (C02-free) and an accelerated environment for carbon­ ation (50% CO2), The samples were subjected to dynamic leaching tests, and the results were fit to the two­ dimensional diffusional release equation. Comparison of results for carbonated and noncarbonated samples in­ dicated that both physical and chemical properties controlling release were altered by carbonation. Carbonation slowed the diffusional release of strontium and increased the release of nitrate, calcium, cadmium, lead, and cobalt. Comparison of the leaching rate of each metal relative to calcium was used to indicate solid solution in calcium hydroxide (cadmium) and calcium carbonate (cadmium and strontium). Leaching of cadmium and strontium appears to be heavily influenced by solid solution in calcium bearing phases.

Influence of carbonation on leaching of cementitious wasteforms

Non-ideal solid solution aqueous solution modeling of synthetic calcium silicate hydrate

A hydrazine oxalate [(N2H5)2C2O4] solution was used as an alternative wash method for cleaning 30% tributyl phosphate–70% normal paraffin hydrocarbon solvent. Experimental evidence shows the (N2H5)...

An Alternative Solvent Cleanup Method Using a Hydrazine Oxalate Wash Reagent

The leachabilities of technetium and nitrate wastes immobilized in cement-based materials (i.e., grouts) have been investigated using ANS 16.1 test procedures. Factors found to affect the leachabilities include (1) grout mix ratio, (2) grout fluid density, (3) dry solid blend composition (including ground blast furnace slag), and (4) waste concentration.

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Immobilization of technetium and nitrate in cement-based materials

The chemical degradation of normal paraffin hydrocarbon (NPH) diluents both in the pure state and mixed with 30% tributyl phosphate (TBP) was investigated in a series of experiments. The results show that degradation of NPH in the TBP-NPH-HNO/sub 3/ system is consistent with the active chemical agent being a radical-like nitrogen dioxide (NO/sub 2/) molecule, not HNO/sub 3/ as such. Spectrophotometric, gas chromatographic, mass spectrographic, and titrimetric methods were used to identify the degradation products, which included alkane nitro and nitrite compounds, alcohols, unsaturated alcohols, nitro alcohols, nitro alkenes, ketones, and carboxylic acids. The degradation rate was found to increase with increases in the HNO/sub 3/ concentration and the temperature. The rate was decreased by argon sparing to remove NO/sub 2/ and by the addition of butanol, which probably acts as a NO/sub 2/ scavenger.

Purex Diluent Chemical Degradation

The dissolution of refractory PuO2 in HNO3-HF-H2O dissolvents was studied. Results showed that increasing either the HNO3 or the HF concentration increases the dissolution rate, and that formation of a Pu(IV) fluoride complex decreases the rate. It was also found that oxidation of dissolved Pu(IV) helps maintain the presence of a fluoride ion as a catalyst and is thus highly beneficial to PuO2 dissolution.

Study of the Dissolution of Refractory PuO2 in Nitric-Hydrofluoric Acid Dissolvents at 100°C

Research at Oak Ridge National Laboratory (ORNL) has shown that cement-based waste forms can be tailored to tolerate wide fluctuations in waste-feed compositions and still maintain properties that are compatible with standard equipment and produce a product that meets regulatory requirements. The 20-year operational history of ORNL's grouting program has demonstrated this resilience and reliability on a spectrum of waste feeds encompassing the developmental history of the nuclear fuel cycle. Cement-based materials are the most frequently used waste forms for solidifying non-high-level waste. These materials are also perhaps the most misused for immobilizing wastes. This paper discusses the scientific basis for selecting a suitable cement-based waste form to solidify and immobilize radioactive waste. For instance, when a given amount of cement (the source of calcium) is replaced with class F fly ash, the strontium leachability is reduced proportionally. This paper discusses the use of gel clays such as bentonite and attapulgite to absorb excess fluids and thus increase waste loading. Also, cement-compatible natural materials such as nonswelling clays are used to ion exchange or absorb soluble ions such as cesium and thus reduce leachability. Recently, blast furnace slag has been the subject of much interest in cement-based immobilization technology. Data are presented to show that a waste form containing blast furnace slag and other cementing materials is very effective in reducing the release rates of 99 Tc.

O. K. Tallent

Papers

An Alternative Solvent Cleanup Method Using a Hydrazine Oxalate Wash Reagent

Immobilization of technetium and nitrate in cement-based materials

Purex Diluent Chemical Degradation

Study of the Dissolution of Refractory PuO2 in Nitric-Hydrofluoric Acid Dissolvents at 100°C

Basis for Selecting Cement-Based Waste Forms for Immobilizing Radioactive Waste