Waste Volume Reduction Using Surface Characterization and Decontamination By Laser Ablation
The U.S. Department of Energy's nuclear complex, a nation-wide system of facilities for research and production of nuclear materials and weapons, contains large amounts of radioactively contaminated concrete[1]. This material must be disposed of prior to the decommissioning of the various sites. Often the radioactive contaminants in concrete occupy only the surface and near-surface ({approx}3-6 mm deep) regions of the material. Since many of the structures such as walls and floors are 30 cm or more thick, it makes environmental and economic sense to try to remove and store only the thin contaminated layer rather than to treat the entire structure as waste. Current mechanical removal methods, known as scabbling, are slow and labor intensive, suffer from dust control problems, and expose workers to radiation fields. Improved removal methods are thus in demand[2-5]. Prior to decontamination, the surface must be characterized to determine the types and amounts of contaminants present i n order to decide on an appropriate cleaning strategy. Contamination occurs via exposure to air and water-borne radionuclides and by neutron activation. The radionuclides of greatest concern are (in order of abundance) [1]: 137Cs & 134Cs, 238U, 60Co, and 90Sr, followed by 3H, radioactive iodine, and a variety of Eu isotopes and transuranics. A system capable of on- line analysis is valuable since operators can determine the type of contaminants in real time and make more efficient use of costly sampling and characterization techniques. Likewise, the removed waste itself must be analyzed to insure that proper storage and monitoring techniques are used. The chemical speciation of radionuclides in concrete is largely unknown. Concrete is a complex material comprising many distinct chemical and physical phases on a variety of size scales[6-8]. Most studies of radionuclides in cements and concrete are for the most part restricted to phenomenological treatments of diffusion of ion s, particularly Cs, in and out of model waste forms and engineered barriers[9-21]. Few studies exist on the chemical speciation of the contaminants themselves in concrete [22-25]. For example, the extent to which various contaminants react with the cement and various aggregate particles is currently unknown, as is the role of the high pH of the cement pore water on ion partitioning and chemical speciation. DOE has designated understanding the chemical nature of the contaminants as important in the rational design of characterization, decontamination, and waste handling strategies[26, 27]. We have investigated laser ablation as a means of concrete surface removal[28-31]. Lasers are attractive since the power can be delivered remotely via articulated mirrors or fiber optic cables and the ablation head can be manipulated by robots, thus avoiding exposing workers and the laser system to the radiation field. In addition, lasers can be instrumented with spectrometers or effluent sampling devices to provide for on-line analysis. In contrast to mechanical scabbling systems, laser beams can penetrate cracks or follow very rough or irregularly shaped surfaces. Finally, a laser ablation system produces the smallest possible waste stream since no cleaning agents such as detergents or grit (from grit blasting systems) are mixed with the effluent.
- Research Organization:
- Argonne National Lab., Argonne, IL (US)
- Sponsoring Organization:
- USDOE Office of Environmental Management (EM) (US)
- OSTI ID:
- 829914
- Report Number(s):
- EMSP-60283; R&D Project: EMSP 60283; TRN: US0405126
- Resource Relation:
- Other Information: PBD: 1 Oct 2000
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
54 ENVIRONMENTAL SCIENCES
ABLATION
CLEANING
CONCRETES
CONTAMINATION
DECOMMISSIONING
DECONTAMINATION
DETERGENTS
DUSTS
ECONOMICS
EXPLOSIVE FRACTURING
FIBER OPTICS
IODINE
LASERS
NEUTRONS
RADIATIONS
RADIOISOTOPES
SPECTROMETERS
STORAGE
WASTE FORMS