FR2479541A1 - METHOD FOR BLOCKING ALKALI AND ALKALINE-EARTH RADIO-ACTIVE ELEMENTS - Google Patents

Abstract

THE INVENTION RELATES TO THE FIELD OF PROTECTION AGAINST RADIO-ACTIVITY OF CONTAMINATED MATERIALS AND WASTE INCLUDING IN PARTICULAR ALKALINE AND ALKALINO-EARTH ELEMENTS OF STRONTIUM 90 AND CESIUM 137 TYPES. ACCORDING TO THE INVENTION, WASTE, GENERALLY INTRODUCED INTO WASTE. CONTAINERS IN CONCRETE OR OTHER MATERIAL ARE BLOCKED BY A METALLURGIC SLAG EITHER IN THE FORM OF A GROUT WITH SETTING ACTIVATOR OR IN THE FORM OF FINE SILICO-ALUMINOUS SAND ADDED WITH ANHYDROUS TAKE CATALYST. THE CONTAINERS THEY ARE ADVANTAGEOUSLY MADE FROM ALL DAIRY CONCRETE.

Description

The present invention relates to the field of protection against

  radioactivity of materials, materials, contaminated objects or

  waste of any kind in general.

  It is known that during the manufacture of nuclear fuels, their use in a reactor, the reprocessing of

  used, there are residues and wastes with

  towards degrees of radioactivity. Irradiated materials, gear or

  tools, clothing or other contaminated objects must be

  considered radioactive waste. Sludge and radioactive solutions are also residues that need to be treated

before any final storage.

  Usually, all types of residues and wastes are drummed on the premises of their production and then shipped to the final storage sites. Most often, we use to

  the moderately or weakly radioactive residues of the bere-

  with appropriate mechanical properties, such as compressive, tensile or cracking resistance, impact resistance, etc. However, it has been found that concrete

  always have sufficient mechanical characteristics, do not

  do not feel absolute durability with regard to the aggressive action of the

  environments where the concrete containers must be stored.

  Thus, it is well known that concrete can not resist

  not perfectly suited to the action of sea water, certain mineral waters

  such as selenous waters) or too pure waters. There is then a gradual destruction of the concrete casing by the action of dissolved salts which penetrate the network of hydrated silicates by causing the swelling and then the disintegration of the concrete. Similarly,

  concretes made from Artificial Portland Cement still contain

  days a little lime free. It is strongly dissolved by water

  pure and we observe the phenomenon called leaching.

  This explains why CPA-based concrete containers do not have all the guarantees of durability and do not ensure perfect containment of the waste containing radioactive elements of the alkaline and alkaline-earth groups. These elements have more or less long periods; when they do not exceed several days or even a few months, the problem does not arise. However, when the period is longer, concrete containers based on

CPA is no longer sufficient.

  Among the radioactive elements with

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  significant migration from solubilization by concrete water and

  placement of the ions in this concrete, as well as a period long enough to

  being able to migrate from the inside of the concrete shell, it is necessary to

  ter: Strontium 90 28.8 years (beta radiation), cesium 137 30 years (beta radiation)

  The latter being part of the alkaline group, its compounds are

  particularly soluble and the mass corresponding to an activity of I cu-

  is 11.5 mg; for Strontium 90, the equivalent mass is 7.05 mg. Rubidium 86, which is in the alkaline group of moderate radioactivity, can also be added to these two elements. Plutonium 239 poses a problem as a result of its long period (24,300 years), which requires containers of longevity virtually without

  measures with those of containers intended to preserve

  containing Cesium 137 and Strontium 90.

  The invention provides a solution to the problem of

  waste containing cesium 137, Strontium 90 and other long-lived elements by providing a means of conditioning for solid residues or solutions previously

  appropriate method described in the patent application no.

dant.

  The method of the invention consists essentially of blocking

  waste, introduced into concrete containers or other

  riau, using metallurgical slag of vitreous and crushed structure

finely.

  This slag can be used in two forms - either in the form of a slurry of great fluidity that fills all the gaps left between the waste. In order for the slurry to set, it is necessary for it to contain a setting activator (clinker

  crushed, lime, or alkali salts). After setting and hardening, the

  chets are held in place and the container is sealed; either in the form of dry fine sand supplemented with an anhydrous setting activator. The filled container is vibrated so that the mixture can fill all the voids so that the waste is perfectly

  wrapped; the container is then closed.

  According to an alternative embodiment, it is possible to use the slurry-based grout firstly until the waste is collected and then to add the dry slag mixture added with the activator.

  take and then close the container.

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  To carry out these operations, it is recommended to use slag of particle size less than 2 mm, preferably ground to less than 0.1 mm and having a specific surface area greater than 1500.

  cm2 / g (measured according to Blaine's method).

  This way of operating prevents the dissemination of

  dioactives out of the container because the metallurgical slags

  zeolitic properties that allow them to capture and retain the radioactive elements (Cesium 137 and Strontium 90) whose compounds have a power of dissolution allowing them to migrate

  through barriers that do not have these zeolite properties.

  When coating the waste in a slurry of slag, this

  last prevents the diffusion of radioactive elements. According to the hypo-

  theses on the zeolite effect of silico-aluminum slags

  natures, there exist in the network of free sites in which come to lodge preferably the alkaline and alkaline-earth ions, but also

  other ions (chromate, zincate manganate, etc.) which are also insoluble

  and the release of the adsorbed adsorbed ions, precipitated and

adsorbed is extremely weak.

  It has been found experimentally that some fine milled slags can fix at least 15 mg of cesium per 100 g of slag, which is considerable since 11.5 mg of cesium 137 corresponds to

a radioactivity of I curie.

  In the case of a dry coating of the waste by a mixture of fine slag supplemented with anhydrous activator, the fixing of the elements

  harmful is done more slowly. In the case of a deterioration of the envelope

  outside, the water that could be introduced into the container

  would hydrate the activated slag and there would be formation of a

  mortar which, as a result of its setting, would consolidate the container while

  serving its adsorption properties of radioactive elements.

  JO It is possible to use either silico-aluminous slag alone, -

  either in mixture with fly ash from thermal power plants, or

  with natural or artificial pozzolans.

  Finally, since concretes made from CPA cement do not provide sufficient guarantees of durability due to the phenomena of water aggression, it is of great interest to manufacture concrete slag granulate containers using cements as binders. high slag content (CLK or CHF). It has indeed been demonstrated in the context of the work of the invention, that all-slab concrete has a high resistance to aggressive water (seawater, sulphated water, acidic water) and form a barrier which has

  zeolite properties thus preventing the migration of radio-

  assets. It is therefore recommended that all-slag concrete containers be used to contain waste containing cesium 137, Strontium 90 or other long-lived radioactive elements. Most slags and slags are suitable for

  implementation of the method of the invention. Among the best, it is necessary to classify

  those containing a significant proportion of alumina, as these are

  essentially silico-aluminates which have zeo-

  lithic. It is advisable to use mainly blast-furnace slag, foundry slags, slags from the manufacture of ferro-alloys mainly silico-chromium, silico-manganese,

  lead-zinc furnaces, refining of copper and the manufacture of phos-

phorus. di

Claims (7)

R E V E N D I C A T IO N S   1. Method of blocking alkaline and alkaline earth elements   radioactive waste contained in industrial waste and residues   nuclear trie; the process being characterized in that   as a means of blocking metallurgical slag products. 2. Method according to claim 1, characterized in that the   blocking material consists of silico-aluminous slag of   vitreous or viteocrisalline, with particle size less than 2 mm   and preferably ground to less than 0.1 mm and having a special surface   at least 1500 cm2lg measured by the Blaine method.   3. Method according to claim 2, characterized in that the fine silico-aluminous slag is supplemented with a setting catalyst and   is used as a grout that perfectly encapsulates   dioactives in containers, hermetically closed, intended to be stored on the final site.   4. Method according to claim 2, characterized in that the   silico-aluminous slag, supplemented with an anhy-   dre is used in the form of sand put in place by vibrating envelop-   the radioactive waste placed in the   intended to be stored on the final site.   5. Process according to any one of claims 2 to 4,   in that the operation is carried out in two stages. -   sludge-based slurry then overlaying with a fine slag mixture supplemented with an anhydrous setting catalyst and closure hermetic container.   6; Process according to any one of claims 2 to 5,   % actérisé in that the fine silico-aluminous slag is used in mixture   ge with fly ash, pozzolana natural or artificial.   7. A process according to any one of claims 3 to 6,   characterized in that the containers for storing waste containing radioactive alkaline and alkaline earth elements are made of concrete whose components, aggregates and cement, are based on metallurgical slags, including: blast furnace, foundry slag, slags from the manufacture of ferroalloys, metallurgy of non-ferrous metals and metalloids such as phosphorus produced by thermal path.