Method of decontaminating a cementitious or a metallic surface

Details Method of decontaminating a cementitious or a metallic surface Method of decontaminating a cementitious or a metallic surface

1997-01-17

1998-11-17

Mai, Ngoclan

Hazardous or toxic waste destruction or containment

Destruction or containment of radioactive waste

Chemical conversion to a stable solid for disposal

4352625, 976DIG376, G21F 900

Patent

active

058390790

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to a method for the decontamination of a cementitious or a metallic surface, particularly, though not exclusively, to the in-situ decontamination of such surfaces.
The decommissioning of chemical plants and reactors in the nuclear industry is an often lengthy and costly process, which desirably takes the site from closure to a state where it is free for other unrestricted use. Due to the very high costs involved with decommissioning, it is essential that decommissioning strategies are as cost effective as possible.
The decommissioning of, for example, a nuclear reactor or contaminated nuclear facilities is carried out in a number of stages. Firstly, fuel and accessible loose radioactive materials are removed from reactors and plant, then these and associated pieces of equipment are decontaminated as appropriate and dismantled; contaminated waste materials are disposed of and finally, the remaining buildings are demolished and the debris disposed of.
Contamination, as opposed to activation products, is located at the surface or accessible areas such as cracks and pores for example.
Decontaminating techniques are used within the decommissioning procedure to remove contaminants prior to demolition or re-use of buildings and other facilities for example. Decontamination is an important procedure because it not only reduces radiation dose rates within the working area, but also has the potential for reducing the impact of the waste and reclassification to a lower and less expensive category so as to achieve lower disposal costs. Reclassification of waste is achievable in the case of concrete and metal surfaces, for example, because the contaminants are concentrated at the exposed surfaces, near the surface or at accessible cracks. Therefore if those surfaces can be removed, the bulk of the remaining material can be disposed of as lower level waste.
Conventional methods for the decontamination of concrete surfaces have mainly employed physical methods such as shot blasting, scabbling, high pressure water jets, high energy processes such as lasers and plasmas, milling, sawing and explosives for example. Depending on the circumstances, each technique has its own advantages. However, common and inherent disadvantages are that these techniques generate comparatively large and difficult to manage volumes of waste; they are labour intensive and also involve high capital expenditure. Chemical methods employ aggressive materials and/or large volumes of liquid waste.
GB 2 261 316, of common ownership herewith, describes the decontamination of cementitious surfaces by the use of microorganisms to degrade the surface. The residue produced by such degradation being subsequently removed. This document is concerned with the use of sulphur oxidising bacteria to produce sulphuric acid to attack the surface.
However, the toxic materials which are being removed from the contaminated surface and the residue generated from the micro organisms or biomass are chemically separate and need to be dealt with separately.
Decontamination of metal surfaces has, in the past, been largely confined to washing down of surfaces with suitable chemicals, electrochemical, shot blasting, strippable coatings, ultrasonics and detergents for example.
We have now found that biosystems may be used which have particular and unforseen advantages.
According to the present invention there is provided a method for the decontamination of a cementitious or metallic surface having contaminants, the method comprising the steps of supplying to said surface at least one microorganism under conditions conducive to growth of said at least one microorganism; maintaining said conditions conducive to growth of said microorganism and the generation of an acid or other metabolites to degrade said surface to a desired depth; terminating said conditions conducive to growth upon achieving at least said desired depth of degradation, removing the products of said degradation; treating said degradation products; and, disposing of said treated degra

REFERENCES:
patent: 3558434 (1971-01-01), Herschler
patent: 3660278 (1972-05-01), Mimura et al.
patent: 5292456 (1994-03-01), Francis et al.
patent: 5414196 (1995-05-01), Jennings

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