Journal of Nuclear Energy Science & Power Generation TechnologyISSN: 2325-9809

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Editorial, J Nucl Ene Sci Power Generat Technol Vol: 2 Issue: 1

Which Is More Essential for Immobilized Radioactive Waste Form: Durability or Impermeability?

Hosam El-Din M. Saleh*
Radioisotope Department, Nuclear Research Center, Atomic Energy Authority, Dokki 12311, Giza, Egypt
Corresponding author : Hosam El-Din M. Saleh
Radioisotope Department, Nuclear Research Center, Atomic Energy Authority, Dokki 12311, Giza, Egypt
Tel: +201-005191018; Fax: +202-37493042
E-mail: [email protected]
Received: December 03, 2012 Accepted: December 05, 2012 Published: December 07, 2012
Citation: Saleh HM (2013) Which Is More Essential for Immobilized Radioactive Waste Form: Durability or Impermeability? J Nucl Ene Sci Power Generat Technol 2:1. doi:10.4172/2325-9809.1000e105

Abstract

Which Is More Essential for Immobilized Radioactive Waste Form: Durability or Impermeability?

Before the answer of this question, which of them is more essential for immobilized radioactive waste form durability or impermeability, it could be favorable to give a brief background about radioactive wastes and its immobilization. A rapid industrial growth and high technological progress are the main sources of the accumulation of these hazardous materials. Nuclear applications have been rapidly developed recently, and several nuclear power plants have been started to work throughout the world.

Keywords:

Before the answer of this question, which of them is more essential for immobilized radioactive waste form durability or impermeability, it could be favorable to give a brief background about radioactive wastes and its immobilization. A rapid industrial growth and high technological progress are the main sources of the accumulation of these hazardous materials. Nuclear applications have been rapidly developed recently, and several nuclear power plants have been started to work throughout the world. The potential impact of released radioactive contaminants into the environment has received growing attention due to nuclear accidents, which poses serious problems to biological systems [1].
Radioactive waste is defined as the material that contains or is contaminated with radionuclides at concentrations or activities greater than clearance levels as established by regulatory authorities. The higher the concentration of radionuclides is above the established levels, the greater the hazard the waste possesses. The hazard of radioactive waste also depends on the nature of the radionuclides and, at the same concentration; different radionuclides have different levels of hazard. Radioactive waste that be accompanied by significant levels of radiation requires not only immobilization to prevent radionuclides spreading around the biosphere, but also shielding and, in some cases, remote handling [2].
The radioactive waste present in various states; liquid, solid or gas is the ethic issue facing the modern world. Contamination of soil and water by radionuclides due to natural processes, global fall-out from nuclear weapon testing, discharges from nuclear installations, disposal of nuclear waste and occasional nuclear accidents poses serious problems immediately or at long-term to biological systems including humans, animals, plants, or the environment.
The long-term performance and surface radiation dose of waste packages are crucial components of the safety strategy for the transportation, storage and disposal processes. Safety strategy for radioactive waste containment and isolation of the proposed storage and transportation focuses on two objectives: (i) to provide stabilization of the radioactive waste within the including package; (ii) to limit the radiation exposure dose of the public during the transportation or other handling processes [3].
Processes of treatment and solidification/stabilization of radioactive waste are important steps in a radioactive management scheme, (Figure 1). Immobilization of radioactive waste is an attractive technology to reduce their risks and facilitate their handling prior to disposal. The long-term safe landing of the solidified hazardous waste is an important request for keeping the surrounding environment more secure for the coming generations [4].
Figure 1: Main processes of radioactive waste management scheme.
For environmental safety, the release of hazardous radioactive materials from the disposal site into the surrounding should be prevented or delayed. Cement and bitumen have been used individually as immobilization matrices for the radioactive waste from the beginning of the nuclear industry in the 1960’s [5].
Cement materials are currently the preferred one for embedding most of low and intermediate level radioactive wastes due to the acceptable strength characterizing a cemented waste form and hence could be handled, transported and disposed safely. In addition, bitumen has good coating properties resistant to attack by microorganisms; consequently, more optimal characterization of the immobilized waste form was achieved. Cemented waste form could be immersed in bitumen emulsion for coating, (Figure 2). Bitumen is chemically inert matrix, insoluble in water, and it shows a remarkable lower leach rate of the final waste form when compared to the uncoated cemented waste forms [6]. Mechanical integrity and porosity characterizations of the obtained solidified waste form were evaluated under chemical and physical investigations. The chemical stability of the coated waste forms was more valuable compared to the uncoated ones due to leachability of radionuclides in different leachants [6].
Figure 2: Photo image of cemented blocks before and after coating by bitumen.
Long-term resistivity of solidified radioactive waste forms is a major area of research in the radioactive waste management intending to minimize the back release of hazardous materials which could be occurring at environmental impacts during the disposal period [7].
Immobilization of radioactive waste have to reduce the potential migration and dispersion of radionuclides from waste forms to the environment, the primary objectives were to provide possible options helping in choosing the proper immobilization media, to improve the quality of the final waste forms and process technology. Various composite materials were developed to attain the durability as well as the resistivity of the immobilized radioactive waste form to leaching effect. Polymers such as polyethylene terephthalate are very durable, resistant to most chemicals, stretching and shrinking, wrinkle resistant, mildew and abrasion resistant [8].
The leaching mechanisms of simulated low and intermediate level radioactive waste forms immobilized in cement–polymer composite are being determined as support for the development of their chemical stability under different leaching parameters such as static and dynamic conditions, various dipping media, environment temperatures, etc.
The leach test characterizations, of solidified cement–polymer composite waste form exposed to flooding in various media, were taken to evaluate the resistance of the final waste form towards leaching of the studied radionuclides to the surrounding environment, (Figure 3). Based on the experimental results, it was found that combination of cement with water extended polyester based on recycled poly(ethylene terephthalate) (PET), is acceptable for immobilization of borate waste as one of low and intermediate levels radioactive wastes, performs adequately in the final disposal site and permits some secure against the radionuclides back release through the leaching process [4].
Figure 3: Mechanical integrity and permeability represented as compressive strength and porosity of cement-polymer composite waste form during extended leaching period.
Waste disposal is the final step of waste management and ideally comprises placing radioactive waste in a dedicated disposal facility. Discharging of effluents into the environment within permitted limits is also a disposal option. All types of radioactive waste need to be carefully managed to keep the public safe, protect the environment and ensure security from accidental or deliberate intrusion. Disposal of radioactive wastes in a disposal facility is intended to isolate the waste both from human activity and from natural dynamic processes. It is important to distinguish between disposal (permanent and irretrievable removal of waste) and storage (temporary residence with waste irretrievability).
It could be concluded from the previous illustration that immobilized waste form have to be more durable and more impermeable to attain the safety requirements for radioactive waste long-term disposal. By using bitumen emulsion for coating solidified waste form as well as, premixing polymer with cement-waste paste to form cement-waste-polymer composite, the produced waste form could be characterized by proper mechanical integrity acquired from cement and the impermeability from bitumen coating or polymer premixing.

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