The present invention relates to a detritiation device and process. The present invention relates particularly to a detritiation device and process by bubbling fusible metallic radioactive wastes.
Detritiation is a heat and/or chemical treatment with the objective of extracting tritium trapped in the radioactive waste matrix, particularly fusible metallic radioactive wastes. The radioactive wastes that may need to be detritiated are those originating from nuclear facilities making use of tritium.
Detritiation of fusible metallic radioactive wastes strongly reduces their radioactivity, so as to simplify their subsequent storage, particularly due to the significant reduced requirements for protection of the environment and persons.
However, detritiation processes according to prior art produce large quantities of strongly tritiated water (HTO), for which management is complex.
One purpose of the present invention is therefore to disclose an advanced detritiation process and device capable of strongly reducing or even completely preventing the production of tritiated water at the end of this process.
This purpose is achieved particularly by a detritiation device comprising:
This purpose is also achieved by a detritiation process comprising the steps of:
Hydrogen isotopes are obtained at the end of this isotopic exchange, thus strongly reducing or completely preventing the production of tritiated water at the end of the detritiation process of the invention.
The combination of the crucible furnace and the membrane reactor results in an efficient detritiation process that produces almost no tritiated water at the end the process. Indeed, the melting and bubbling of the wastes in the crucible enables efficient and almost complete evacuation of tritium in gas form, and the gases such loaded are immediately treated in a membrane reactor that enables the tritium to be recovered also in the form of a gas mix, that is then easier to treat and/or store than tritiated water.
The present invention will be better understood after reading the following description illustrated by the figures where:
With reference to
One non-limitative embodiment of the crucible 10 is shown in
For example, according to this embodiment, the crucible 10 is a segmented cylindrical copper crucible. The segments 100 are at a slight spacing from each other over the majority of their periphery, and are connected together for example only around the center of the bottom of the crucible 10. The division of the crucible 10 into different segments 100 at a spacing from each other can minimize, or even completely prevent, formation of induced currents in the crucible material when the induction furnace is activated, thus preventing undesirable heating of the crucible 10.
However other materials and/or forms can be envisaged in the framework of the invention for the crucible of the induction furnace. For example, according to one alternative embodiment, the crucible is formed in a single non segmented piece of a non-magnetic material.
The crucible 10 preferably comprises a nozzle 102, for example in its bottom, for introducing a hydrogenated bubbling gas into the crucible 10 and consequently in the mass of the molten wastes during its treatment. The nozzle 102 is connected through a conduit not shown to a source not shown of hydrogenated bubbling gas, for example to a gas reservoir preferably located outside the furnace.
The hydrogenated bubbling gas is composed of a chemically inert gas (for example, argon, helium . . . ) to which hydrogen (H2) is added. For example, the composition by volume is Ar+1 to 10% of H2, preferably Ar+2 to 4% of H2.
According to one alternative embodiment, the crucible comprises several hydrogenated bubbling gas inlet nozzles to achieve a uniform distribution of the hydrogenated bubbling gas in the mass of the wastes in fusion. According to one variant of the invention, the hydrogenated bubbling gas is introduced into the mass of the wastes in fusion through one or several tubes introduced into the crucible 10 through its upper opening and immersed in the mass of the wastes in fusion.
For example, the crucible 10 is a cold crucible, that is the detritiation device further comprises a cooling device to cool the crucible 10. Consequently, the crucible 10 is actively kept by means of a cooling device, at a temperature significantly lower than the temperature of the wastes in fusion that it contains. This in particular enables the structural integrity of the cold crucible to be best protected at the time the furnace is heated during which a temperature that can reach between 1000° C. and 1600° C. can be reached.
The cold crucible also enables a reduction in the contamination of the crucible by the tritiated wastes, an easier removal from the mold after melting of the treated wastes, and a better control over tritium flows by reducing any losses other than through the planned outlets.
For example, the cooling device to cool the crucible 10 comprises channels 101 formed in the walls of the crucible 10 and through which a heat transfer fluid, for example a gas or a cooling liquid, can circulate inside the walls of the crucible 10. As shown in
With reference to
The crucible 10 is preferably capped by a thermally insulating device not shown, and for example confined in a quartz glove finger 105 through which a vector gas can be introduced.
According to one preferred embodiment of the invention shown diagrammatically in
A first chamber 21 of the membrane reactor is integrated into a circuit A, B, C, D, E shown diagrammatically in
The detritiation process according to the invention is for example a batch type process comprising a series of sequences that is repeated for each batch of treated tritiated wastes.
During a start up sequence, the tritiated wastes are loaded into the furnace 1 of the detritiation device that is shown by arrow 6 in
A vector gas is introduced into the circuit A, B, C, D, E, as shown by arrows 7 and 8. It may be hydrogenated and comprises a chemically inert gas (for example argon, helium . . . ) and preferably less than 4% (typically between 0.1% and 4%) by volume of hydrogen H2. The vector gas for example is brought in from cylinders not shown fitted with pressure reducers and valves. The flow of the vector gas can vary as a function of quantities and activity of the tritiated wastes and capabilities of the system for trapping tritiated gases downstream.
The startup sequence is followed by a melting and detritiation sequence during which the furnace 1 is heated so as to melt the batch of tritiated wastes. According to one embodiment, the furnace 1 is an induction furnace and the wastes are metallic tritiated wastes that heat and melt under the effect of the magnetic field generated in the furnace 1.
The crucible in which the mass of molten or melting wastes are located is then for example kept at a temperature substantially lower than the temperature of the melting material by means of the cooling device. The use of a cold crucible facilitates removal of the ingot obtained after melting.
Once the wastes have been melted, a hydrogenated bubbling gas is introduced into the melting material, for example through the nozzle 102 located at the bottom of the crucible 10. The hydrogenated bubbling gas then passes through the melting material and an isotopic exchange takes place between the gas and the molten wastes, such that the gas phase is enriched in tritium.
Bubbling in the lower part has several advantages, for example the design is optimized for better gas distribution and therefore the detritiation factor is improved, and the gas produced by detritiation can be confined as much as possible.
The vector gas in circuit A, B, C, D, E is made to circulate in the detritiation device between the furnace 1 and the catalytic membrane reactor 2, for example using the pump 3 thus entraining tritiated gases from the furnace 1 to the membrane reactor 2.
The flow of tritiated gases from furnace 1 enters into the first chamber 21 through the inlet 23a of the membrane reactor 2, whereas a hydrogen flow H2 is introduced in the opposite direction through the inlet 23b of the second chamber 22.
The tritiated gases are usually composed of a mix of gases with general formula Q2 or Q2O comprising tritium and at least one of the hydrogen isotopes denoted “Q” (where Q is either H=Hydrogen, D=Deuterium or T=Tritium), for example a gas chosen from among T2, HT, DT, T2O, HTO or DTO.
The tritiated gases are mixed with the vector gas when they reach the membrane 2.
Since the membrane that separates the flows is permeable to Q2 but not Q2O, the following isotopic exchange between the two flows takes place for example according to the following general formula:
H2+Q2OH2O+Q2;
namely for example: H2+T2OH2O+T2,
or H2+HTOH2O+HT
Thus, the gas output from the first chamber 21 through the outlet 24a and returning to the furnace 1 via the pump 3 is essentially detritiated and comprises mainly the vector gas and water vapor. Hydrogen isotopes are recovered at the outlet 24b from the second chamber 22 of the membrane reactor 2, in the form of a gas mix (reduced species such as for example H2, HT and/or T2) which for example is stored directly in the form of hydrides or sent to a purification system.
During the melting and detritiation sequence, the pressure inside the detritiation device of the invention is preferably tested continuously or at regular intervals using a manometer not shown. The pressure is preferably kept at a constant value and is corrected if necessary by the addition of hydrogenated vector gas. The concentration of hydrogen in the hydrogenated bubbling gas is also measured and is regulated by the addition of hydrogen to optimize the isotopic exchange with the melting material and thus guarantee efficient detritiation of the wastes.
Once the batch of wastes has been treated, the power input to the detritiation device and particularly the furnace 1 is gradually reduced during a shutdown sequence. The circuit A, B, C, D, E is drained through an outlet 9 diagrammatically shown in
Example application of the detritiation process according to one embodiment of the invention:
The following operations are identified during the start up phase:
The following operations are identified during the detritiation operation:
The following operations are identified during the shutdown phase:
The above description shows that the detritiation device and process according to the invention have in particular at least one of the following advantages:
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/FR2012/050882 | 4/23/2012 | WO | 00 | 10/21/2013 |