H.M. Saleh

Assessment study for multi-barrier system used in radioactive borate waste isolation based on Monte Carlo simulations

Radioactive waste generated from the nuclear applications should be properly isolated by a suitable containment system such as, multi-barrier container. The present study aims to evaluate the isolation capacity of a new multi-barrier container made from cement and clay and including borate waste materials. These wastes were spiked by (137)Cs and (60)Co radionuclides to simulate that waste generated from the primary cooling circuit of pressurized water reactors. Leaching of both radionuclides in ground water was followed and calculated during ten years. Monte Carlo (MCNP5) simulations computed the photon flux distribution of the multi-barrier container, including radioactive borate waste of specific activity 11.22KBq/g and 4.18KBq/g for (137)Cs and (60)Co, respectively, at different periods of 0, 15.1, 30.2 and 302 years. The average total flux for 100cm radius of spherical cell was 0.192photon/cm(2) at initial time and 2.73×10(-4)photon/cm(2) after 302 years. Maximum waste activity keeping the surface radiation dose within the permissible level was calculated and found to be 56KBq/g with attenuation factors of 0.73cm(-1) and 0.6cm(-1) for cement and clay, respectively. The average total flux was 1.37×10(-3)photon/cm(2) after 302 years. Monte Carlo simulations revealed that the proposed multi-barrier container is safe enough during transportation, evacuation or rearrangement in the disposal site for more than 300 years.

Mortar composite based on wet oxidative degraded cellulosic spinney waste fibers

Textile industry has become an essential part of modern society, and waste production is an inevitable outcome of the developmental activities. Present paper outlines a direct approach toward a real problem of managing spinney waste fibers generated during textile industry. Simultaneously, shortage in landfill disposal space is another trouble associated with dumping of these hazardous wastes. Direct incorporation of these wastes into cementitious materials faces some disadvantages, so a partial oxidative degradation treatment was performed for those wastes in laboratory-scale experiments. Slurry resulted from the degradation process was incorporated into a mixture of cement/sand as hydrating agent to produce a mortar composite. Mechanical integrity and weight stability of the mortar composite produced were evaluated at the end of setting and hardening period under different variables. Based on the experimental results, the nominated mortar composite could be considered as an added-value product suitable for various applications, for example inert matrix for immobilization of some low and intermediate levels radioactive wastes, decorative tiles, building bricks, light concrete.

Bitumen Coating as a Tool for Improving the Porosity and Chemical Stability of Simulated Cement-Waste Forms

Coating of simulated cement-based waste form was investigated by performing physical and chemical experimental tests. Moreover, X-ray diffraction, Fourier transform infrared spectroscopy, and electron microscope examination were applied on coated and noncoated simulated waste forms. Experimental results indicated that coating process improved the characterizations of cement-based waste form such as porosity and leachability. Diffusion coefficients and leach indecies of coated specimens were calculated and showed acceptable values. It could be stated that by coating cemented-waste form by bitumen emulsion, the radioactive contaminants were isolated, thus reducing the back release to surrounding environment during flooding by groundwater and consequently, saving the environment.

On the Role of Iodine in the Oxidation of Zr in KI Medium

Summary. The influence of I2 on the kinetics of spontaneous as well as galvanostatically induced growth of insulating oxide films on Zr metal was studied in KI solutions as a function of concentration. The stability of the anodic oxide films on Zr surfaces was investigated by measuring the potential and the two impedance components of the electrode-solution interface under currentless conditions. In all cases, the passivating oxide films were found to grow with time. The anodic polarization carried out at different current densities produced charging curves whose potentials increases with current density. The presence of increasing amounts of I2 in the KI medium always shifts the potential of ZrO2 films towards more positive values, most probably because the formed triiodide ion (I3− in the electrolyte enhances the formation of zirconium-iodine species at the electrode surface. A dissolution-precipitation mechanism was proposed which is consistent with the above results as well as with the results of the effect of temperature on the currentless film growth process.Zusammenfassung. Der Einfluß von I2 auf die Kinetik von sowohl spontanem als auch von galvanostatisch induziertem Oxidfilmwachstum auf metallischem Zr wurde in kaliumjodidhaltigen Lösungsmitteln als Funktion der Konzentration untersucht. Die Stabilität der anodischen Oxidfilme auf der Zirkonoberfläche wurde durch Messung des Potentials und der beiden Impedanzkomponenten der Elektroden-Lösungs-Grenzflächen bestimmt. In allen Fällen nahm die Dicke der passivierenden Oxidfilme als Funktion der Zeit zu. Die anodische Polarisation wurde bei verschiedenen Stromdichten ausgeführt; man erhielt Ladungskurven, deren Potentiale mit der Stromdichte ansteigen. Die Gegenwart von I2 im kaliumjodidhaltigen Medium verschiebt das Potential des ZrO2-Films zu positiven Werten, wahrscheinlich durch vermehrte Bildung von Zirkon-Iod-Species an der Elektrodenoberfläche, die durch I3− begünstig wird. Es wird ein Lösungs-Kristallisations-Mechanismus vorgeschlagen, der sowohl mit den obigen Resultaten als auch mit Ergebnissen bezüglich der Temperaturabhängigkeit des stromlosen Filmwachstumsvorgangs in Einklang steht.