Classifications

• • G—PHYSICS
  • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
  • G21F—PROTECTION AGAINST X-RADIATION, GAMMA RADIATION, CORPUSCULAR RADIATION OR PARTICLE BOMBARDMENT; TREATING RADIOACTIVELY CONTAMINATED MATERIAL; DECONTAMINATION ARRANGEMENTS THEREFOR
  • G21F9/00—Treating radioactively contaminated material; Decontamination arrangements therefor
  • G21F9/02—Treating gases
• • G—PHYSICS
  • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
  • G21F—PROTECTION AGAINST X-RADIATION, GAMMA RADIATION, CORPUSCULAR RADIATION OR PARTICLE BOMBARDMENT; TREATING RADIOACTIVELY CONTAMINATED MATERIAL; DECONTAMINATION ARRANGEMENTS THEREFOR
  • G21F9/00—Treating radioactively contaminated material; Decontamination arrangements therefor
  • G21F9/28—Treating solids
  • G21F9/34—Disposal of solid waste

Definitions

• This invention relates to a method for treatment of concrete wastes, especially, but not exclusively, radioactive concrete wastes.
• Nuclear reactors employed in the production of electricity generally comprise, surrounding the nuclear reactor, a steel reactor vessel for containing the nuclear reactor and then, outside this, a thick concrete structure to serve as a biological shield.
• a steel reactor vessel for containing the nuclear reactor and then, outside this, a thick concrete structure to serve as a biological shield.
• an integrated circuit has been used and the reactor has been housed in a prestressed concrete structure in which the various cavities are lined with steel.
• the steel vessels and considerable quantities of the concrete used for shielding or other purposes become significantly radioactive. This poses problems during the dismantling of nuclear installations, not only because of the mass of active material to be disposed of, but also because of its form.
• a method for the fixing of concrete dust produced on demolition of a concrete installation which comprises collecting such dust which is airborne and taking it up in a liquid medium which has the ability to wet and bind the dust particles together and set to a cohesive mass under ambient temperature conditions and conditions such that the setting is solely the result of reaction involving the chemical contents of the dust particles and said solution.
• a variety of materials may in principle, be used to carry out the method of this invention. However, many have inherent characteristics which detract from their ease and convenience of use. Among these drawbacks are the presence of inflammable or noxious components, the necessity of including in them additives in order to bring about a reaction by which the mixture of dust and liquid will set to a firm and readily handleable solid, high cost or limited availability, or lack of resistance to atomic radiation.
• the materials which have been found most suitable for use in carrying out this invention are aqueous solutions of the alkali metal silicates and more particularly those aqueous solutions which are based on sodium silicate.
• Sodium silicate is manufactured in a range of silica/alkali ratios and the properties of the solution are largely defined by this ratio. It might be thought that a solution of high silica/alkali ratio will be more effective in carrying out the method of the invention than a solution of lower silica/alkali ratio and will enable the volume of material used to be kept down. In fact this is not the case. It is preferable to use relatively low silica/alkali ratios whereby a stronger product is obtained. Thus there is no advantage to be obtained in using silica/alkali ratios in the range of 3.4-4:1 and higher and in fact better results are usually obtained at much lower ratios e.g. 2-2.5:1.
• the solids content of the silicate solution employed is concerned it is preferred to use a solution strength of from 5-50% by weight solids.
• a solution strength of from 5-50% by weight solids.
• silica/alkali ratio and solids content are interrelated, and for silica/alkali ratios in the range 2-2.5:1 it is preferred to use a sodium silicate solution having a solids content of 25-40% by weight, the higher solids contents being more suitable for the coarser concrete dusts.
• the setting of sodium silicate solution to form substantially solid material is a well known phenomenon in itself.
• a variety of processes are known for achieving this setting, for example loss of relatively small quantities of water and reaction with acid in solution or absorption of carbon dioxide from the atmosphere.
• This phenomenon has been employed for many years in the binding of sand in the production of foundry moulds, where the use of carbon dioxide and heat is required.
• the speed of reaction and strength of the gel formed depends inter alia upon the silica/alkali ratio and upon the solids content of the sodium silicate solution. It is a general characteristic of these known procedures that either heat or a chemical treatment is required to promote the setting reaction.
• the method of the present invention can be carried out under ambient conditions without the need for either application of heat or addition of any outside chemical agents. It is thought that the presence of calcium ions from lime in the concrete is sufficient to bring about the setting reaction. In fact the age of the concrete may affect the speed of the setting reaction. Thus old concrete in which the lime has largely been converted to carbonate may react with the silicate solution more slowly.
• the containment vessel in which the concrete rubble and dust are present after demolition can be held at below atmospheric pressure to prevent escape of the dust into the atmosphere and the finer dust can be extracted by suction, separated from the air stream by one of a variety of available methods using cyclones, filters or electrostatic precipitators and thereafter mixed with the silicate solution to form a slurry which is allowed to set, or otherwise mixed with the silicate solution to form pellets or lumps of a convenient size.
• the dust which is left adhering to the lumps of rubble may be fixed thereto by spraying with the same silicate solution after dilution thereof.
• silicate solution it is possible in carrying out this invention to employ the silicate in powdered form, to mix it with the concrete dust, and then to add water to enable the setting reaction to take place.

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• Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• General Engineering & Computer Science (AREA)
• High Energy & Nuclear Physics (AREA)
• Environmental & Geological Engineering (AREA)
• Processing Of Solid Wastes (AREA)

Applications Claiming Priority (2)

Publications (2)

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ID=10529862

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Country Status (3)

Cited By (4)

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Family Cites Families (5)

• 1983
  • 1983-04-14 EP EP83302113A patent/EP0092941A3/fr not_active Withdrawn
  • 1983-04-21 AU AU13849/83A patent/AU1384983A/en not_active Abandoned
  • 1983-04-22 JP JP58070163A patent/JPS58192000A/ja active Pending

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