Decontamination of radioactive concrete

Abstract

A substantial quantity of solid radwastes consists of contaminated building materials, primarily, different grades of concrete. The largest amount of concrete arises during decommissioning of objects of nuclear power and radiochemical enterprises which have outlived their service life, are unprofitable, or do not meet modern safety requirements [1]. To make these objects radiation-safe, building structures must be completely or partially disassembled, primarily by mechanical methods (explosions, breaking or sawing into pieces, and so forth) [2]. This debris ranges in size from dust particles to pieces with mass up to hundreds of kilograms and is placed in special long-term storage (burial) sites. Since it is expensive to build and service such sites, it is economically desirable to develop technologies that decrease the volume of the wastes which are to be stored for a long time (buried). According to OSPORB-99 [1], building materials from which radionuclides have been removed are largely low-level wastes and accordingly need not be classified as radioactive wastes.Radioactive building materials which are contaminated with long-lived α emitters present the greatest danger. The most stringent norms have been established for them -these materials are considered to be radioactive when their content of uranium or transuranium elements ranges from 1 kBq/kg and higher for 226 Ra (in equilibrium with the decay products) to 10 kBq/kg and higher [1]. For materials contaminated with radionuclides with a long half-life, the method of delayed disassembly or cool-down to allow the activity to drop to acceptable levels is unacceptable, which makes the problem of handling such materials of great current interest.Our objectives in the present work were to study the particularities of the contamination of real concrete wastes by uranium isotopes and to develop a method for decontaminating such wastes.Real radioactive concrete wastes from the research center and an industrial enterprise of the nuclear fuel cycle were the object of the present investigations (Fig. 1). The wastes were represented by debris containing residues of the binder (Fig. 1a) and fragments of a thin-wall (35 mm thick) reinforced concrete structure with two plane-parallel boundaries (Fig. 1b). For radiometry and radiochemical analyses, the waste fragments were ground and medium samples were taken. The analysis was performed in the central laboratory of the MosNPO Radon, which is accredited in the system of radiation-monitoring laboratories. x-Ray phase analysis of the waste samples was performed with a DRON-4 diffractometer which automatically recorded the diffraction pattern in steps using filtered FeK α radiation. A binder fraction with particle size less than 2.5 mm was sieved to investigate the concrete sample (see Fig. 1a). The x-ray phase analysis data show that CaCO 3 (calcite), SiO 2 (α quartz), 3CaO·Al 2 O 3 ·CaCO 3 ·12H 2 O, 4CaO·Al 2 O 3 ·13H 2 O are present in the binder fraction. The radionuclide composition of the binder is represented by 234,235...

Deciphering past and present atmospheric metal pollution of urban environments: The role of black crusts formed on historical constructions

“…Even if there are many protocols to conduct decontamination of metals from construction materials [7,8], there is not a standardized analytical methodology to detect this contamination in the material itself or in the formed crusts. Considering the ability of this patina to accumulate organic and metallic contaminants, its contribution can be considered harmful not only for the users of the construction, but also for the workers that can repair, renovate, restore or conduct demolition works of the building.…”

Decontamination of radioactive concrete using electrokinetic technology

“…Radioactive concrete contaminated with long-lived nuclides, especially, uranium isotopes, can be cleaned by means of a liquid decontamination of fragmented wastes by solutions of sodium carbonate and hydrocarbonate. Increasing the temperature of the decontamination solution and imposing an electric field greatly accelerate the decontamination of wastes [6].…”