JPH1062593A - Method and equipment for removing radioactive iodine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To dispense with off-gas treatment equipment of a factory for manufacturing fuel for transmutation and to enable removal of radioactive iodine in a form suitable for a material of the fuel for transmutation by a method wherein the radioactive iodine is made to react with silver and removed from gas or a solution and then made into a compound with a metal element having a valence number of trivalence or above. SOLUTION: Radioactive I of a long half-life in spent atomic fuel is once dissolved in a nitric acid solution in a reprocessing dissolution process and then transfers into a vapor phase. The radioactive I existing in the fuel in the form of a solid cesium iodine CsI or the like transfers into a liquid phase in the form of a negative ion I-at the time of dissolution in a nitric acid and it is oxidized by the nitric acid or the like and transfers into the vapor phase in the form of I2. The I in the vapor phase is made to be absorbed by an alkali scrubber or adsorbed by a silver-series adsorbing material and removed. The I is removed by making it react with a metal element of at least trivalence being suitable for transmutation. By providing equipment for making it react with cerium Ce, for instance, the I in off-gas from the dissolution process reacts with the Ce and becomes CeI3 and can be separated from other components and removed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method and apparatus for removing radioactive iodine by reacting it with a metal element having a valence of three or more (preferably cerium) in a spent nuclear fuel reprocessing facility.

[0002]

2. Description of the Related Art Nuclear Chemical Engineering, Volume IV, Fuel Reprocessing and Radioactive Waste Chemical Engineering, M.A. As described in Benedict et al., Kiyose Ryohei, pp. 40-44, in a spent fuel reprocessing plant, conventional radioactive iodine is absorbed in an alkaline solution, converted to I ₂ O ₅ solid, mercury iodide. (Mercury is absorbed as a divalent metal element) or is reacted with silver (silver is a monovalent metal element).

[0003]

In the above prior art, no consideration has been given to removing the radioactive iodine and then extinguishing it.

It is said that it is desirable to convert radioactive iodine-129 having a very long half-life of 15.7 million years into a short half-life nuclide in a nuclear reactor or the like (annihilation treatment).
A proposal has been made to treat the annihilation in the form of CeI3. That is, the removal form of the radioactive iodine in the prior art is not a form suitable for the annihilation treatment, but it is expected that conversion to a suitable form is necessary.

[0005] The fuel and its raw material irradiated in the nuclear reactor are:
As it is currently prepared at a fuel plant, the radioactive iodine removed by the prior art should be converted to a form suitable for annihilation at the fuel plant. In this case, there is a problem that an off-gas treatment facility for preventing volatile iodine from scattering into the environment is required. Also, if alkali is absorbed,
There is also a problem that it is necessary to transport radioactive iodine in a relatively unstable form from a reprocessing facility or a storage facility for radioactive iodine after removal to a fuel manufacturing plant.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method and an apparatus for removing radioactive iodine in a form suitable as a raw material for a fuel for annihilation treatment by making an off-gas treatment facility in a fuel production plant for annihilation treatment unnecessary. .

[0007]

A feature of the first aspect of the present invention that achieves the above object is that a radioactive iodine is reacted with a metal element having a valence of three or more in a spent nuclear fuel reprocessing facility. Removal from gas or solution.

According to the first aspect of the present invention, the use of radioactive iodine and a metal element having a valence of three or more in the reprocessing facility obviates the need for a facility for removing iodine in off-gas in a fuel production process, and has a long half-life. Plays the role of immobilizing radioactive iodine at high density as metal iodide (solid).

A feature of the second aspect of the present invention that achieves the above object is that the compound of a metal element and iodine is a solid which is stable in the range of room temperature to 600 ° C.

According to the second aspect of the present invention, the metal element which forms an iodine compound which is stable even at a high temperature (several hundreds of degrees Celsius) is a fuel for annihilation treatment and iodine at the time of occurrence of a fire or the like at the time of storage of raw materials thereof and at the time of annihilation treatment. It acts to prevent volatilization and scattering.

A feature of the third aspect of the present invention that achieves the above object is that the composition ratio of iodine to a metal element (the number of atoms of iodine / the number of atoms of the metal element) is 3 or more.

According to the third aspect of the present invention, the metal element that forms a high-density iodine compound reduces the volume of iodine during storage (can reduce the storage space) and annihilates iodine during annihilation treatment (nuclear transmutation). It works to keep efficiency high.

A feature of the invention according to claim 4 that achieves the above object is that the neutron absorption cross section of the metal element is 10 times or less the neutron absorption cross section of iodine-129.

According to the fourth aspect of the present invention, the metal element having a small neutron absorption cross section serves to prevent unnecessary consumption of neutrons during the annihilation treatment.

A feature of the invention of claim 5 that achieves the above object is that the metal element does not newly generate a radionuclide having a half life of 100 years or more by a neutron absorption reaction and a subsequent nuclear reaction. .

According to the fifth aspect of the present invention, the metal element that does not generate a nuclide having a long half-life by absorbing neutrons acts to prevent generation of new waste.

A feature of the invention of claim 6 that achieves the above object is that in a spent nuclear fuel reprocessing facility, radioactive iodine is once reacted with silver and removed from a gas or a solution and then trivalent or more. It is to convert to a compound with a valence metal element.

According to a seventh aspect of the present invention, there is provided a reprocessing plant for a spent nuclear fuel, wherein a radioactive iodine is once absorbed into an alkaline solution, and then a metal element having a valence of three or more is used. To react.

According to the sixth and seventh aspects of the present invention, the concentration of radioactive iodine can be increased by reacting radioactive iodine with silver or absorbing it in an alkaline solution, so that radioactive iodine and trivalent or higher valence can be efficiently obtained. Reaction with a metal element having

[0020] A feature of the invention of claim 8 that achieves the above object is that the metal element is a rare earth element, preferably a lanthanoid element, and more preferably cerium. According to the invention of claim 8, the rare earth element, especially the lanthanoid element, particularly cerium, forms a high-density, high-temperature stable compound with radioactive iodine, achieves high-efficiency extinction of radioactive iodine, and has a secondary long half-life. It serves to reduce the production of nuclides.

According to a ninth aspect of the present invention, there is provided a reprocessing facility for spent nuclear fuel, in which radioactive iodine is removed from a gas or a solution by reacting with radioactive metal nuclides in the spent fuel. Is to do.

In the ninth aspect of the present invention, the radioactive metal nuclide plays a role of immobilizing radioactive iodine without bringing in a metal element from outside the reprocessing plant.

According to a tenth aspect of the present invention which achieves the above object, in a spent nuclear fuel reprocessing facility, radioactive iodine removed by means such as adsorption and absorption is once separated from the adsorbed and absorbed substance. It is to react with radioactive nuclides in spent fuel.

In the tenth aspect of the present invention, once separating radioactive iodine by means such as adsorption and absorption contributes to efficient reaction between radioactive iodine and a radioactive metal element. The features of the invention of claim 11 that achieve the above object are as follows:
Radionuclide is rare earth element or actinoid element,
Preferably, it is a lanthanoid element, more preferably cerium.

According to the eleventh aspect of the present invention, the radioactive rare earth elements contained in the spent fuel, especially the lanthanoid elements,
In particular, cerium forms a high-density, high-temperature stable compound with radioactive iodine, achieves highly efficient extinction of radioactive iodine,
It acts to reduce the production of subsequent long-lived nuclides.

A feature of the twelfth aspect of the present invention to achieve the above object is to have a mechanism for introducing and reacting an off-gas containing radioactive iodine into a tank filled with a metal element having a valence of three or more.

In the twelfth aspect of the present invention, the introduction of radioactive iodine into a tank filled with a metal element serves to stabilize iodine in the gas phase as metal iodide by reacting the two.

A feature of the invention according to claim 13 that achieves the above object is that it has a mechanism for supplying a metal element having a valence of three or more to a solution containing radioactive iodine to cause a reaction. According to the thirteenth aspect, the supply of the metal element to the solution containing radioactive iodine serves to stabilize iodine in the solution as metal iodide by reacting the two.

According to a fourteenth aspect of the present invention, a mechanism for recovering a rare earth element, preferably Ce, a mechanism for recovering radioactive iodine from a reprocessing step of spent nuclear fuel, and a mechanism for reacting the same are provided. Is to have.

In the fourteenth aspect of the present invention, the mechanism for recovering a rare earth element, preferably Ce, the mechanism for recovering radioactive iodine, and the mechanism for reacting the same are such that radioactive iodine is removed in a form suitable for annihilation treatment. Works.

[0031]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The basic concept of a radioactive iodine removal method according to an embodiment of the present invention is to reprocess spent nuclear fuel which is a source of radioactive iodine having a long half-life and which is equipped with an off-gas processing facility. In the facility, radioactive iodine in the spent fuel is reacted with a metal element having a valence of three or more,
To remove from gas or solution. At this time, even if the radioactive iodine once recovered by another method is converted into a compound with a metal element having a valence of three or more, the above object can be achieved. Also, if fission products such as cerium are recovered from the reprocessing step and used as the metal element, there is no need to carry in the metal element from the outside.

[0032] Iodine is a very volatile element,
When combined with a metal element, it can be stabilized as a solid. In the case of removing radioactive iodine by reacting it with a metal element in a reprocessing facility, taking into account that radioactive iodine after removal is molded into fuel pellets and annihilated, the following four conditions are required for the metal element. .

1) To produce a high-density iodine compound 2) To be stable even at high temperatures (several 100 ° C) 3) To have a small neutron absorption cross section 4) To absorb neutrons and not to produce nuclides having a long half-life First of all, the condition 1) is a constraint that comes from the fact that the annihilation efficiency is proportional to the atomic density of iodine in the fuel, and produces a compound in which two or three iodine atoms are bonded to one metal element. Is preferable. The condition 2) is a constraint that comes from the stability of the iodine compound during neutron irradiation. The coolant temperature during operation of a light water reactor or a fast reactor (300 ° C to 600 ° C)
Also, a metal element that generates a compound that does not decompose, melt, or volatilize is desirable. The condition 3) is a restriction from the viewpoint of neutron economy, and a metal element having a neutron absorption cross section smaller than that of iodine is desirable. The condition 4) is a constraint for avoiding the generation of a new long half-life nuclide, and a metal element that does not generate a nuclide having a half-life of 30 years or more by a nuclear reaction is desirable. In addition, 1) is also a constraint condition for storing fuel materials or fuels at high density, and 2) is a constraint condition for preventing scattering of radioactive iodine at the time of temperature rise such as a fire during storage. Become.

In view of the above, a rare earth element, particularly cerium, is desirable as the metal element. If MI ₃ (M is a rare earth element), particularly CeI _3, is formed by chemical bonding with radioactive iodine, an appropriate fuel for annihilation treatment can be obtained. And a fuel for annihilation treatment can be prepared. At this time, if a raw material is prepared directly from gaseous iodine in a reprocessing plant, a facility for removing iodine from off-gas in a fuel manufacturing plant becomes unnecessary.
In addition, scattering during transport of radioactive iodine can be prevented.

(Example 1) As a first example of the present invention, a method for reacting radioactive iodine in off-gas generated in a dissolving step of spent nuclear fuel reprocessing with a metal element and removing it will be described with reference to FIG. I do. FIG. 1 shows a basic configuration according to the present invention. (SF and FP in the figure
Denotes spent nuclear fuel and fission products, respectively.
(G), (s), (o) and (a) indicate that they are in the form of gas, solid, liquid organic phase and liquid aqueous phase, respectively. Most of the radioactive iodine with a long half-life in spent nuclear fuel is once dissolved in a nitric acid solution in a reprocessing dissolution step and then moves into the gas phase. That is, radioactive iodine existing in the form of solid cesium iodide (CsI) in the fuel transfers to the liquid phase in the form of a monovalent anion (I ~) when dissolved in nitric acid, and is oxidized by nitric acid or nitrous acid. Then, a gas phase is formed in the form of I ₂ . Iodine is a post-process of reprocessing (liquid medium extraction process)
Rather, it is actively driven out into the gas phase during the dissolution process for treatment. At this time, when iodine is strongly oxidized, it is non-volatile iodate ion (IO ₃ ~)
Since remaining solution in the form of, (a dissolved nitrite) NOx is mild oxidant iodine blown into the solution selectively expelled to only then gas phase forms I ₂ I have.

Usually, iodine in the gas phase is removed by absorbing it with an alkaline scrubber or by using a silver-based adsorbent (silver is a monovalent metal element). In this embodiment, iodine is removed by reacting with a metal element having a valence of three or more which is suitable for annihilation treatment. For example, if an apparatus for reacting with cerium (Ce) is installed, iodine in the off-gas from the dissolving process reacts with Ce to produce cerium iodide, which is separated and removed from other components in the off-gas such as air. it can. The reaction for combining iodine with cerium may be any of a gas phase reaction, a liquid phase reaction, a solid phase reaction, a gas-liquid reaction, a gas-solid reaction, and a liquid-solid reaction, but the reaction product is in the form of CeI _3. It is desirable. Offgas components other than iodine (air, etc.)
Is released into the environment after removing particulate impurities as necessary. Cerium iodide is used as a raw material for the fuel for annihilation treatment. In this case, it may be mixed with U and Pu recovered in a normal reprocessing process to be used as a raw material for the fuel for annihilation treatment. As described above, according to the present embodiment, there is an effect that radioactive iodine having a long half-life can be removed from off-gas for reprocessing in a form suitable for annihilation processing. Further, there is no need to provide an off-gas treatment facility for removing iodine in a plant for producing an annihilation fuel. Further, there is an effect that a relatively expensive silver-based iodine adsorbent used in conventional off-gas processing equipment can be omitted. In the above embodiment, cerium is used as the metal element, but the same effect can be obtained by using another lanthanoid element. In the case of a lanthanoid element, it takes the form of LnI ₃ (Ln is a lanthanoid element) similarly to cerium and the decomposition temperature of the compound is relatively high, so that it is suitable for storing and extinguishing radioactive iodine with high density and stability. Iodine can be removed from off-gas. In the case of a metal element other than the lanthanoid element, it is not as effective as the lanthanoid element, but can remove radioactive iodine in a form that can be stably stored and stably eliminated.

In this embodiment, since radioactive iodine can be transported to a fuel manufacturing plant or a temporary storage facility in a stable form, the scattering of radioactive iodine into the environment can be reduced and prevented.

In the above-mentioned embodiment, the same method can be applied not only to the dissolving step of reprocessing but also to the step of releasing other radioactive iodine. In addition, even when radioactive iodine is present in a solution, a metal element can be added to the solution to form an iodine compound and radioactive iodine can be removed.

(Embodiment 2) As a second embodiment of the present invention, in a reprocessing plant, radioactive iodine once adsorbed on a silver-based adsorbent is desorbed from the adsorbent and reacted with cerium.
The method of removing will be described with reference to FIG.

The iodine transferred into the gas phase in the reprocessing dissolution step is effectively removed by the silver-based adsorbent in the off-gas processing step. The removed iodine is very stably retained on the adsorbent, but when heated to 500 ° C. or more, the adsorbed silver iodide (AgI) is decomposed and the iodine is volatilized. Volatile iodine is introduced into a Ce removal device,
e and reacted with cerium iodide (preferably CeI ₃ )
From the off-gas. Since the form of the volatilized iodine is the same as the form (I ₂ ) of iodine released from the dissolution step, it can be removed from the off-gas in the form of cerium iodide in exactly the same manner as in Example 1. Cerium iodide can be used as it is or as a raw material of a fuel for annihilation treatment by mixing with U and Pu recovered in a normal reprocessing process. As described above, according to the present embodiment, there is an effect that radioactive iodine having a long half-life can be removed from off-gas for reprocessing into a form suitable for annihilation processing. In the above embodiment, cerium is used as the metal element, but the same effect can be obtained by using another lanthanoid element. In the case of a lanthanoid element, it takes the form of LnI ₃ (Ln is a lanthanoid element) in the same manner as cerium, and the decomposition temperature of the compound is relatively high, so that radioactive iodine can be stably stored at high density and can be removed in a form that can be eliminated. . In the case of a metal element other than the lanthanoid element, it is not as effective as the lanthanoid element, but can remove radioactive iodine in a form that allows stable storage and stable disappearance.

In this embodiment, as compared with the first embodiment, 3
It is necessary to remove iodine in a two-stage process, but once iodine is adsorbed with silver, which has a high reaction efficiency with iodine from lanthanoids such as cerium, and then desorbed, the iodine is concentrated to a higher concentration to make cerium etc. more efficient. By reacting with the lanthanoid element.

Further, in a fuel production plant for annihilation treatment without iodine removal equipment, conversion of an iodine compound into a form suitable for annihilation treatment can be avoided, and the probability of radioactive iodine scattering into the environment can be reduced.

In the above embodiment, iodine was continuously removed as cerium iodide from the dissolving step in the reprocessing process. However, radioactive iodine was recovered together with the adsorbent, and desorption and C
The same effect can be expected even if the e-adsorption operation is carried out to remove. In this case, there is no need to change (remodel) the current reprocessing step, and there is an effect that it can be applied to the used iodine adsorbent generated in the reprocessing step. Further, the same method can be applied not only to the dissolution step of reprocessing but also to a step of releasing other radioactive iodine.

(Example 3) As a third example of the present invention, cerium as a fission product is recovered from a reprocessed high-level waste liquid and reacted with radioactive iodine released into a gas phase in a dissolution step. A method for removing iodine from off gas will be described with reference to FIG.

Cerium is also present as a fission product in the spent fuel, and the amount of cerium is greater than the amount of iodine. Therefore, if cerium as a fission product is recovered and reacted with iodine, it is not necessary to bring a cerium reagent from the outside. Since cerium is not extracted into the organic solvent in the co-decontamination step in the reprocessing step, it finally migrates into the high-level waste liquid. When a strong oxidizing agent such as ozone, divalent silver, potassium permanganate or the like is added to the high-level waste liquid, cerium is oxidized from trivalent to tetravalent. 3
Unlike tetravalent cerium, tetravalent cerium can be easily separated (group separation) from other fission products because it is extracted with an organic solvent. Since cerium has a higher fission yield,
The recovery rate of cerium does not have to be high, and a sufficient amount to react with iodine can be recovered. The cerium thus recovered from the high-level waste liquid and the iodine which has been transferred to the gas phase in the dissolving step are introduced into a reaction device and reacted to remove iodine in the form of cerium iodide (preferably CeI ₃ ) from the off-gas. I do. The form of cerium recovered from high level effluent is nitrate, which can react with iodine (I ₂ ) released from the dissolution process. Cerium iodide can be used as it is or as a raw material of the fuel for annihilation treatment by mixing with U and Pu recovered in a normal reprocessing process.

As described above, according to the present embodiment, there is an effect that radioactive iodine having a long half-life can be removed from off-gas for reprocessing in a form suitable for annihilation processing. Since CeI ₃ is high-density and stable at high temperatures, space saving and safety can be secured when storing raw materials (fuel), and efficiency can be eliminated and iodine can be prevented during iodine combustion (neutron irradiation). Also, cerium has a small neutron absorption cross section and does not produce long-lived nuclides.
Neutron economic efficiency (extinction efficiency) can be improved, and generation of new long-half-life waste can be prevented. In the above embodiment, cerium was used as the metal element. However, depending on the conditions, the actinoid element can be recovered. Therefore, the same effect can be obtained by reacting iodine with the actinoid element to remove it. In this case, since the actinoid element also has a long half-life, there is an effect that radioactive iodine (and the actinoid element) can be removed in a form suitable for storing or eliminating long-life nuclides collectively.

In the above-described embodiment, iodine was continuously removed in the form of cerium iodide from the dissolving step and the group separation step in the reprocessing process, but the radioactive iodine and the recovered cerium (actinoid element) were temporarily separated. The same effect can be expected even if iodine is removed as iodide by reacting them with each other. In this case, there is no need to connect the current reprocessing step and a reaction (iodine removal) device for iodide generation with a pipe or the like, and the reprocessing step and the iodine removal step can be kept independent. Further, the same method can be applied not only to the reprocessing process but also to a process in which other radioactive iodine is released.

Example 4 As a fourth example of the present invention, cerium as a fission product is recovered in the reprocessing co-decontamination step and reacted with radioactive iodine released into the gas phase in the dissolution step. A method for removing iodine will be described with reference to FIG.

As described in Example 3, in the reprocessing step, cerium is not extracted into the organic solvent in the co-decontamination step, so that it finally shifts to high level disposal. However, when a strong oxidizing agent such as ozone, divalent silver or potassium permanganate is added to the solution, cerium can be converted from trivalent to
And is extracted together with U and Pu. Neptunium (Np) is also oxidized to hexavalent and extracted. Since cerium is the most easily reduced among the elements extracted into the organic solvent, only cerium is reduced after extraction and back-extracted into the aqueous phase. The cerium thus recovered and the iodine which has been transferred to the gas phase in the dissolving step are introduced into a reactor to cause a reaction, and cerium iodide (preferably Ce)
Iodine is removed in the form of I ₃ ). The final form of cerium recovered is nitrate, which can be reacted with iodine (I ₂ ) released from the dissolution step. Cerium iodide can be used as it is or as a raw material of a fuel for annihilation treatment by recovering U, Pu and Np remaining in the organic phase in the back extraction step to form an oxide and then mixing.

As described above, according to this embodiment, there is an effect that radioactive iodine having a long half-life can be removed in an improved reprocessing process in a form suitable for annihilation. Particularly, the difference from the third embodiment is that cerium can be recovered in the process of recovering U and Pu, so that there is no need to provide an extra step such as group separation. Since CeI ₃ is high-density and stable at high temperatures, space saving and safety can be secured when storing raw materials (fuel), and efficiency can be eliminated and iodine can be prevented during iodine combustion (neutron irradiation). In addition, cerium has a small neutron absorption cross section and does not generate long-lived nuclides, so that neutron economy (extinction efficiency) can be improved, and generation of new long-half-life waste can be prevented.

In the above embodiment, cerium was used as the metal element.
m) and other trivalent actinoid elements or Np (a kind of actinoid element) can be recovered, and the same effect can be obtained even if iodine is removed by reacting the actinoid element with iodine. The same effect can be obtained as a fuel for annihilation treatment or its raw material. In this case, since the actinoid element also has a long half-life, there is an effect that radioactive iodine can be removed in a form suitable for storing or eliminating long-life nuclides collectively.

In the above embodiment, cerium iodide was continuously produced from the dissolving step and the co-decontamination step in the reprocessing process to remove iodine, but the radioactive iodine and the recovered cerium (actinoid element) were once removed. Move it to another location,
Therefore, the same effect can be expected even if iodine is removed by reacting the two. In this case, there is no need to connect the current reprocessing step and the iodine removing device for generating iodide with piping or the like, and the reprocessing step and the iodine removing step can maintain their independence. Further, the same method can be applied not only to the reprocessing process but also to a process in which other radioactive iodine is released.

[0053]

According to the present invention, radioactive iodine can be removed in a reprocessing process in a form suitable for the production of iodine fuel for annihilation treatment. It is possible to avoid transporting the iodine to a temporary storage facility or converting the recovered iodine form in a reprocessing plant to a form suitable for disappearance, and installing an iodine removal off-gas treatment facility in a fuel manufacturing plant. In addition, since long-lived nuclides do not migrate into the waste liquid, the burden on waste management can be reduced.

If a fission product is used as the metal to be combined with iodine, it is not necessary to prepare a metal element.

According to the first aspect of the present invention, the equipment for removing iodine in off-gas in the process of producing a fuel for annihilation treatment of radioactive iodine becomes unnecessary, and radioactive iodine having a long half-life is converted from off-gas into metal iodide (solid). It can be removed and fixed at high density.

According to the second aspect of the present invention, the effects obtained by the first aspect of the invention are obtained, and at the same time, the occurrence of a fire or the like at the time of storage of the fuel for extinguishing treatment and its raw material, and the volatilization of iodine during the extinguishing treatment, Scattering can be prevented.

According to the third aspect of the present invention, the effect obtained by the first aspect of the present invention is obtained, the volume of iodine during storage is reduced (storage space can be reduced), and the iodine disappears during the annihilation process ( Transmutation) efficiency can be improved.

According to the fourth aspect of the present invention, the effect obtained by the first aspect of the present invention can be obtained, and unnecessary consumption of neutrons during the annihilation process can be avoided.

According to the fifth aspect of the invention, the effects obtained by the first aspect of the invention can be obtained, and the generation of new waste can be prevented and reduced.

According to the sixth and seventh aspects of the present invention, the concentration of radioactive iodine can be increased, the reaction between radioactive iodine and a metal element having a valence of three or more is efficiently promoted, and the radioactive iodine is removed. be able to.

According to the invention of claim 8, claims 1 to 7 are provided.
In addition to the effects obtained by the above inventions, it is possible to achieve more effective densification of radioactive iodine, high temperature stabilization, and high efficiency extinction, and to reduce the generation of secondary long half-life nuclides during extinction treatment .

According to the ninth aspect, radioactive iodine can be removed and fixed without carrying in a metal element for removing iodine from outside the reprocessing plant.

According to the tenth aspect of the present invention, the reaction between iodine and a radioactive metal element can proceed efficiently, and radioactive iodine can be efficiently removed.

According to the eleventh aspect of the present invention, the effects obtained by the tenth and the eleventh aspects of the present invention can be obtained, and the radioactive iodine can be more effectively densified, stabilized at a high temperature, and efficiently annihilated. The generation of secondary long-lived nuclides during processing can be reduced.

According to the twelfth aspect, iodine in the gas phase can be removed and stabilized as metal iodide.

According to the thirteenth aspect, iodine in a solution can be removed and stabilized as metal iodide.

According to the fourteenth aspect, radioactive iodine can be removed in a form suitable for annihilation treatment.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a nuclear fuel reprocessing apparatus including a radioactive iodine removing apparatus according to one embodiment of the present invention.

FIG. 2 is a configuration diagram of a nuclear fuel reprocessing apparatus including a radioactive iodine removing apparatus according to one embodiment of the present invention.

FIG. 3 is a configuration diagram of a nuclear fuel reprocessing device including a radioactive iodine removing device according to one embodiment of the present invention.

FIG. 4 is a configuration diagram of a nuclear fuel reprocessing device including a radioactive iodine removing device according to an embodiment of the present invention.

Claims (14)

[Claims] 1. A method for removing radioactive iodine, comprising removing radioactive iodine from a gas or a solution by reacting radioactive iodine with a metal element having a valence of three or more in a spent nuclear fuel reprocessing facility. Method. 2. A compound of a metal element and iodine, wherein the compound is
2. The method for removing radioactive iodine according to claim 1, wherein the solid is stable in the range of 00 ° C. 3. The method for removing radioactive iodine according to claim 1, wherein the composition ratio of iodine to the metal element (the number of atoms of iodine / the number of atoms of the metal element) is 3 or more. 4. The neutron absorption cross section of a metal element is iodine-
129. The method for removing radioactive iodine according to claim 1, wherein the diameter is not more than 10 times the neutron absorption cross-sectional view. 5. The method for removing radioactive iodine according to claim 1, wherein the metal element is an element that does not newly generate a radionuclide having a half life of 100 years or more by a neutron absorption reaction and a subsequent nuclear reaction. . 6. In a spent nuclear fuel reprocessing facility, radioactive iodine is once reacted with silver and removed from a gas or a solution and then converted into a compound with a metal element having a valence of three or more. A method for removing radioactive iodine, comprising: 7. A method for removing radioactive iodine, characterized in that a radioactive iodine is once absorbed in an alkaline solution and then reacted with a metal element having a valence of three or more in a spent nuclear fuel reprocessing facility. . 8. The method for removing radioactive iodine according to claim 1, wherein the metal element is a rare earth element, preferably a lanthanoid element, more preferably cerium. 9. A method for removing radioactive iodine, comprising removing radioactive iodine from a gas or a solution by reacting radioactive iodine with a radioactive metal nuclide in a spent fuel in a spent nuclear fuel reprocessing facility. 10. A reprocessing facility for a spent nuclear fuel,
A method for removing radioactive iodine, comprising separating radioactive iodine removed by means of adsorption, absorption or the like from a substance absorbed and absorbed once and reacting with radioactive metal nuclides in spent fuel. 11. The method for removing radioactive iodine according to claim 9, wherein the radionuclide is a rare earth element or an actinoid element, preferably a lanthanoid element, more preferably cerium. 12. An apparatus for removing radioactive iodine, comprising a mechanism for introducing and reacting an off-gas containing radioactive iodine into a tank filled with a metal element having a valence of three or more. 13. An apparatus for removing radioactive iodine, comprising a mechanism for supplying a metal element having a valence of three or more to a solution containing radioactive iodine to cause a reaction. 14. An apparatus for removing radioactive iodine, comprising: a mechanism for recovering a rare earth element, preferably Ce from a reprocessing step of spent nuclear fuel, a mechanism for recovering radioactive iodine, and a mechanism for reacting them. .