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
  • G21F9/28—Treating solids
• • 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
  • G21F9/30—Processing

Definitions

• the present invention is in the field of the treatment of nuclear waste.
• It relates in particular to the treatment of a sheath containing sintered calcium hydride (Ca3 ⁇ 4).
• This material is generally in the form of slabs which are stacked in a cylindrical sealed steel sheath.
• the nuclear waste treatment sector must neutralize the chemical risk while reducing the volume of waste as much as possible and optimizing their subsequent conditioning. In order to meet this double constraint, it would therefore be desirable to have a treatment at the end of which, on the one hand, the waste resulting from the sheath, and on the other hand the waste resulting from the hydride wafers.
• calcium irradiated are evacuated by ways adapted to the nature of each waste.
• One of the aims of the invention is to provide a process for treating a sheath containing sintered calcium hydride and optionally a radioactive material, which exhibits all or some of the aforementioned advantages.
• the present invention thus relates to a process for treating a sheath, in which there is a sintered material which consists wholly or partly of sintered calcium hydride which may optionally contain at least one radioactive material.
• the method comprises a step in which the sintered material is contacted with a reaction mixture containing 0.5% to 5% by weight of water vapor, 5% to 25% carbon dioxide and 74.5% by molar percentage. % to 94.5% of a chemically inert gas, i.e. a gas preventing a reaction between oxygen (possibly present in the reaction atmosphere) and hydrogen (produced by the carbonation reaction described hereinafter).
• a chemically inert gas i.e. a gas preventing a reaction between oxygen (possibly present in the reaction atmosphere) and hydrogen (produced by the carbonation reaction described hereinafter).
• the contacting is carried out for a time to transform all the sintered calcium hydride into a calcium carbonate powder.
• This transformation can be interrupted and resumed at the moment chosen by the operator, or its kinetics modulated depending on the amount of reaction mixture injected.
• the particular treatment method of the invention is to convert the sintered calcium hydride into a calcium carbonate powder which is non-adherent to the sheath walls and chemically inert.
• the non-adherent powder obtained at the end of the treatment process of the invention comprising calcium carbonate, is therefore naturally extracted from the sheath by simple gravity, with the radioactive material and / or any other material that may be present. 'it contains.
• This property of non-adhesion avoids at best the dissemination of radioactive material possibly present in the calcium carbonate powder, as well as the contamination of the cladding by retention of material.
• the calcium carbonate powder can be discharged to a conventional die or adapted to radioactive waste.
• waste gas such as for example hydrogen (3 ⁇ 4), optionally tritiated (HT) and / or tritium ( 2 ).
• This gaseous effluent can be extracted during or after the treatment process.
• radioactive material possibly present is found at the end of the treatment in gaseous form (such as tritiated hydrogen or tritium), it is discharged as a radioactive gaseous effluent.
• gaseous form such as tritiated hydrogen or tritium
• radioactive material there is no longer any radioactive material in the calcium carbonate powder.
• the possible initial presence of radioactive material nevertheless requires the evacuation of this powder to a simplified pathway adapted to radioactive waste, which is however less restrictive than that which would be imposed by the actual presence of a radioactive material in the waste to be discharged.
• the sheath is not altered or destroyed during the treatment of the invention, because the calcium carbonate is a relatively chemically inert compound and its formation is accompanied by a limited expansion.
• the sheath is not or only slightly contaminated with traces of calcium carbonate or any other radioactive material it contains.
• the sheath can then be evacuated to a simplified stream adapted to radioactive waste to be scrapped or recycled in the nuclear industry.
• This separation of the dies reduces the volume of waste, since obtaining a powder makes it possible to obtain a compact package and the sheath can optionally be recycled.
• the method of the invention makes it possible to treat with a minimum of manipulation a sheath containing a sintered material, which is particularly advantageous when this material contains at least one radioactive material.
• the sintered material comprises sintered calcium hydride and optionally at least one radioactive material.
• the radioactive material is for example a material containing the tritium element (T).
• the treatment method of the invention comprises a step in which the sintered material is contacted with a reaction mixture containing 0.5 mol% of steam at 25% carbon dioxide and 74.5% at 25% carbon dioxide. 94.5% of an inert gas.
• any gas that is chemically inert to calcium hydride may be suitable.
• the inert gas is for example selected from nitrogen, argon, or mixtures thereof.
• the nature and the proportion of the components of the reaction mixture allow a controlled and complete treatment of the sintered calcium hydride according to the following overall carbonation reaction:
• the time of contacting the reaction mixture with the sintered calcium hydride depends on the amount of calcium hydride and the composition of the reaction mixture. Those skilled in the art can easily adapt this duration, in particular by prolonging it until the total treatment of the sheath is obtained, which results, for example, in the end of the evolution of a gas such as hydrogen.
• the duration of contacting is for example at least
• 1 day typically between 1 day and 15 days for amounts of sintered calcium hydride to be treated of the order of one hectogram.
• the contacting is preferably carried out at a temperature of between 40 ° C. and 55 ° C. in order in particular to adjust the molar percentage of water vapor to prevent the water from condensing and reacting violently with the hydride. of calcium.
• the treatment according to the invention is most often carried out in a confinement enclosure such as a glove box or a shielded cell.
• the reaction mixture is then generally introduced into the confinement chamber at a rate allowing its continuous renewal at least once an hour.
• the propagation mode of the reaction by successive transformations in powder form of the sintered material, makes it possible to treat a sheath in which this material is relatively inaccessible, for example a sheath of complex geometry or large size.
• the sintered calcium hydride is converted into a calcium carbonate powder, but obtaining this powder does not limit the kinetics of the reaction, which makes it possible to treat the entire sintered calcium hydride present in the sheath.
• the sintered material can be in contact with the reaction mixture. Moreover, this contacting allows the calcium hydride powder to be removed from the sheath. When the sheath is sealed, it is then necessary to make at least one opening, for example by drilling or cutting the sheath.
• the sheath can be in an inclined or vertical position, in order to promote the extraction by gravity of the calcium carbonate powder (and if necessary of any material that it contains).
• the sintered calcium hydride is converted into a calcium carbonate powder containing the radioactive material (s), if appropriate, and / or any other material present initially in the sintered material or resulting from its treatment.
• This powder has no chemical reactivity with respect to water and air. In the absence of radioactive material, it can be evacuated as such to a conventional die.
• radioactive material In the presence of radioactive material, it can be incorporated in glass or cement, or dissolved in the form of Ca (HC03) 2 in most of the acids used in the nuclear waste treatment sector.
• the gases produced during the treatment process of the invention may be extracted as gaseous effluents and discharged into a specific stream in order to to be treated,
• the sheath is most often intact or has not undergone any major alteration.
• it may consist of metal (preferably a steel), plastic or ceramic.
• FIGS. 1, 2, 3 and 4 show photographic photographs taken during treatment of a sheath according to the process of the invention, the sheath containing fried pellets of calcium hydride.
• the following example deals with the treatment of a steel sheath. It is representative of a section of a sheath from a nuclear reactor type RNR that would be cut in the upper and lower part.
• the treated sheath consists of an inner tube positioned along the axis of an outer tube. It contains four pancakes obtained after the sintering of calcium hydride.
• the purity of the calcium hydride is 99% by mass. Trace impurities consist essentially of aluminum and magnesium.
• the dimensions of the sheath and a slab are as follows:
• the assembly is maintained by placing the lower part of the sheath on a removable grid disposed above a recovery tank.
• calcium hydride slabs do not contain radioactive material.
• the sheath is placed in a glove box with a volume of 550 liters serving as a reaction chamber.
• the temperature is regulated at 43 ° C.
• a reaction mixture is continuously introduced at a rate of 12 liters per minute.
• This mixture consists, in percentage by volume, of 2.5% of water vapor, 10% of carbon dioxide, the remainder being nitrogen as an inert gas.
• composition is analyzed upstream and downstream of the glove box by gas chromatography to determine the content of the following gases: N 2 , CO 2 , O 2 , H 2 .
• the amount of water vapor introduced is measured with a Peltier-type mirror hygrometer.
• the hydrogen content produced is also constantly monitored by an explosimeter.
• the carbonation reaction can be stopped by stopping the introduction of the reaction mixture. and replacing it entirely with inert gas.
• the carbonation reaction can be resumed according to its initial regime by reintroduction of steam and carbon dioxide in the glove box without this affecting the overall efficiency of the treatment process.
• the method of the invention thus allows a controlled and secure treatment.
• the reaction mixture is brought into contact with the sintered calcium hydride mainly at the outer face of the first and the last slab, but also, to a lesser extent, on the inner and outer perimeter of the slabs, which is spaced 0.5 mm from the facing surfaces of the sheath.
• Figures 1, 2, 3 and 4 reproduce the photographs taken respectively at the following times: introduction in the glove box of the reaction mixture (time to), to + 2 days, to + 4 days, to + 14 days.
• the vertical position of the sheath allows the spontaneous fall of the calcium carbonate powder and any other material it contains, such as the impurities initially present in the patties.
• the monitoring of the hydrogen content evolved during the carbonation reaction makes it possible, from the stoichiometric coefficients of the carbonation reaction, to calculate the mass of sintered calcium hydride which is converted.
• the residual mass of calcium hydride is in the recovery tank. It can be transformed in turn by extending the duration of treatment.
• the metal sheath emptied of its contents, the calcium carbonate powder and the hydrogen are evacuated according to separate channels.
• the treatment method of the invention makes it possible to completely treat a sheath, in which there is a sintered material which consists wholly or partly of sintered calcium hydride and which optionally contains at least one radioactive material, while limiting the volume of waste obtained, and by authorizing the evacuation see the valorization of this waste by adapted channels.

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• Physics & Mathematics (AREA)
• Engineering & Computer Science (AREA)
• General Engineering & Computer Science (AREA)
• High Energy & Nuclear Physics (AREA)
• Processing Of Solid Wastes (AREA)
• Silver Salt Photography Or Processing Solution Therefor (AREA)
• Solid-Sorbent Or Filter-Aiding Compositions (AREA)
• Separation, Recovery Or Treatment Of Waste Materials Containing Plastics (AREA)

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