JP6020952B1 - Method for processing long-lived fission products - Google Patents

Abstract

Provided is a method for treating a long-lived fission product that optimizes the configuration of a target on which a charged particle beam is incident, thereby improving the efficiency of conversion to a stable nuclide. A long-lived fission product treatment method separates at least two elements (first element 11 and second element 12) of Cs, Zr, Se, Sn and Pd from radioactive waste 10 individually. Extract (S21), obtain range data when the charged particle beam 15 is incident (S22), and the first bulk body whose length size is in the range of 1.0 to 2.0 times the range data 21 is made of the first element 11 (S23 to S25), and a second bulk body arranged around the first bulk body is made of the second element 12 (S26, S27), and the energy value per nucleon is 0. Irradiation with a charged particle beam in the range of 0.5 to 1.5 GeV (S28 to S30).

Description

  The present invention relates to a technique for treating a long-lived fission product generated with combustion of nuclear fuel.

Electric power companies that own nuclear power plants store a large amount of spent nuclear fuel, and establishing these safe and effective treatment methods is an urgent issue.
Therefore, a nuclear fuel cycle has been promoted in which fissile U-235 and Pu are extracted from spent nuclear fuel and mixed with non-fissile U-238 by about 3-5% to regenerate new fuel.

A nuclear power plant with a capacity of 1 million kilowatts generates about 20 tons of spent nuclear fuel every year. Spent nuclear fuel of 3% enriched uranium fuel (U-235: 3%, U-238: 97%) contains 1% U-235, 95% U-238, 1% Pu, and other products. 3% is included.
The products are classified into minor actinoids (MA), platinum group, short-lived fission products (SLFP), and long-lived fission products (LLFP).

These products are highly neutron-absorbing and contain many nuclides that cause an increase in the fission chain reaction. Many of these nuclides are radionuclides.
For this reason, many of these products are contained in high-level liquid waste (HALW) that is inevitably generated as a result of reprocessing of spent nuclear fuel, and vitrified bodies in a form in which this high-level liquid waste can be disposed of. include.
The high-level waste liquid (HALW) vitrified material remains at a high level for a very long time (tens of thousands of years or more), so a disposal method that does not cause any problems even if human management is lost is required. ing. Actually, this vitrified body is already held, and is strictly managed before disposal.

Therefore, for the purpose of reducing the burden associated with disposal of high-level liquid waste (HALW) and management of vitrified solids already contained, the contained nuclides are separated into groups according to their half-life and chemical properties. The selection of disposal methods according to their properties is under consideration.
As a result, the period during which the high-level radioactive waste is highly radioactive can be shortened, and the storage space can be saved.

Among the groups separated from high-level liquid waste (HALW) and vitrified solids, the transmutation technology is applied to the group containing LLFP, and technology for transmutation to short-lived radionuclides or stable nuclides is studied. ing.
Specifically, the photonuclear reaction (γ, n) that emits neutrons by irradiating gamma rays and the neutron capture reaction (n, γ) that emits gamma rays by irradiating neutrons are applied to LLFP, and the half-life is further increased. Have been disclosed (for example, Patent Literatures 1 and 2).

JP-A-5-119178 JP-T-2002-519678

However, in the above-mentioned photonuclear reaction (γ, n) and neutron capture reaction (n, γ), the reaction cross section has a high dependence on the nuclide, so that LLFP capable of achieving efficient transmutation is limited.
In view of this, it is conceivable that the LLFP is directly irradiated with a high-energy charged particle beam for nuclear transformation.

By the way, in view of the amount of LLFP that already exists and the amount of LLFP that is newly generated in the future when a domestic nuclear power plant is in full operation, speeding up of the nuclear transmutation process is required.
The problem of speeding up the transmutation process can be solved by improving the performance of the accelerator so as to irradiate a charged particle beam of high energy and large current.
However, development of a high-energy accelerator that pursues such an upper limit of performance without limitation is not realistic in view of cost and facility scale.

  The present invention has been made in view of such circumstances, and a method for processing a long-lived fission product that optimizes the configuration of a target on which a charged particle beam is incident, thereby improving the efficiency of conversion to a stable nuclide. The purpose is to provide.

In the method for treating a long-lived fission product, at least two elements (first element) of radioactive waste from cesium (Cs), zirconium (Zr), selenium (Se), tin (Sn), and palladium (Pd) are used. And the second element) separately as a group of isotope elements having the same atomic number and different mass numbers, and charged particles having a predetermined performance value in a virtual target composed of the first element. A step of acquiring range data when the beam is incident, and a length size of the charged particle beam in a direction along the incident axis is in a range of 1.0 to 2.0 times the range data. Creating a first bulk body from the first element, and creating a second bulk body arranged around the first bulk body so that the incident axis is a rotationally symmetric axis, from the second element. Tep and a charged particle beam having an energy value per nucleon within the range of 0.5 to 1.5 GeV among the performance values, to a target obtained by combining the first bulk body and the second bulk body, Irradiating along the incident axis.

  According to the present invention, there is provided a method for treating a long-lived fission product that optimizes the configuration of a target on which a charged particle beam is incident, thereby improving the efficiency of the conversion process to a stable nuclide.

The flowchart explaining embodiment of the processing method of the radioactive waste which concerns on this invention. The block diagram of the target irradiated with a charged particle beam in this embodiment. The table which shows the isotopic composition of what this embodiment makes object among long-lived fission products (LLFP) contained in a spent nuclear fuel. FIG. 4 is a table showing the annual generation amounts of LLFP nuclides and their isotopes in FIG. 3 and their densities when the annual processing target amount of spent nuclear fuel is 800 tons. Graph showing the neutron flux distribution LLFP nuclides ^{(135 Cs, 107 Pd, 93} Zr, 79 Se, 126 Sn) in the interior of the target. LLFP nuclides ^{(135 Cs, 107 Pd, 93} Zr, 79 Se, 126 Sn) of (n, γ) reaction and (n, 2n) graph illustrating the reaction cross-sectional area of the reaction. The graph showing the number of particles of LLFP in which charged particles per one shot are extinguished in a Cs + Pd composite target having a size of R2 = 15 cm fixed and R1 = 0 to 15 cm variable. The graph showing the number of particles of LLFP in which charged particles per one shot are extinguished in a Zr + Pd composite target having a size of R2 = 15 cm fixed and R1 = 0 to 15 cm. The graph showing the number of particles of LLFP in which charged particles per one shot are extinguished in a Se + Pd composite target having a size that is fixed at R2 = 15 cm and variable within a range of R1 = 0-15 cm. The graph showing the number of particles of LLFP in which charged particles per one shot are extinguished in a Cs + Zr composite target of a size that is fixed at R2 = 15 cm and variable within a range of R1 = 0-15 cm. Necessary to convert one LLFP nuclide for a virtual target composed of LLFP nuclides ( ¹³⁵ Cs, ¹⁰⁷ Pd, ⁹³ Zr, ⁷⁹ Se) with proton beam energy E (MeV) as the horizontal axis The graph which represented conversion energy E / h (MeV) on the vertical axis | shaft. ^The graph which expressed the energy per nucleon of the charged particle beam by a proton (proton), a deuteron (deuteron), and carbon about a virtual target comprised by ¹³⁵ Cs nuclide, and expressed conversion energy on the vertical axis. ^The graph which represented the energy per nucleon of the charged particle beam by a proton (proton), a deuteron (deuteron), and carbon about the virtual target comprised by a ¹⁰⁷ Pd nuclide, and expressed conversion energy on the vertical axis. ⁹³ A graph in which the energy per nucleon of a charged particle beam of proton (proton), deuteron (deuteron), and carbon is plotted on the horizontal axis and the conversion energy is plotted on the vertical axis for a virtual target composed of ⁹³ Zr nuclides. ⁷⁹ A graph in which the energy per nucleon of a charged particle beam of proton (proton), deuteron (deuteron), and carbon is plotted on the horizontal axis and the conversion energy is plotted on the vertical axis for a virtual target composed of ⁷⁹ Se nuclides. ^The graph which shows quantity distribution of the nuclide converted and produced | generated by the charged particle per shot at the time of producing a target by isolating the group of isotope elements containing ¹³⁵ Cs, and irradiating the proton beam of 1.0 GeV. ^The graph which shows the quantity distribution of the nuclide converted and produced | generated by the charged particle per shot at the time of producing the target by even-odd concentration of the group of isotope elements containing ¹³⁵ Cs, and irradiating the proton beam of 1.0 GeV. ^The graph which shows quantity distribution of the nuclide converted and produced | generated by the charged particle per shot at the time of producing a target by isotope extraction of ¹³⁵ Cs and irradiating a proton beam of 1.0 GeV. ^The graph which shows the quantity distribution of the nuclide converted and produced | generated by the charged particle per shot at the time of producing a target by separating the group of isotope elements containing ¹⁰⁷ Pd, and irradiating the proton beam of 1.0 GeV. ^The graph which shows the quantity distribution of the nuclide converted and produced | generated by the charged particle per shot at the time of producing the target by even-odd concentration of the group of isotope elements containing ¹⁰⁷ Pd, and irradiating the proton beam of 1.0 GeV. ^The graph which shows the quantity distribution of the nuclide converted and produced | generated by the charged particle per shot at the time of producing a target by ¹⁰⁷ Pd isotope extraction and irradiating the proton beam of 1.0 GeV. ⁹³ is a graph showing the quantity distribution of nuclides converted and generated by charged particles per shot when a target is produced by separating a group of isotope elements including ⁹³ Zr and irradiated with a proton beam of 1.0 GeV. ^The graph which shows the quantity distribution of the nuclide converted and produced | generated by the charged particle per shot when a target is produced by even-odd concentration of the group of isotope elements containing ⁹³ Zr, and the proton beam of 1.0 GeV is irradiated. ^The graph which shows the quantity distribution of the nuclide converted and produced | generated by the charged particle per shot at the time of producing a target by isotope extraction of ⁹³ Zr and irradiating the proton beam of 1.0 GeV. ⁷⁹ A graph showing the quantity distribution of nuclides converted and generated by charged particles per shot when a target is produced by separating a group of isotope elements including Se and irradiated with a proton beam of 1.0 GeV. ⁷⁹ A graph showing the quantity distribution of nuclides converted and generated by charged particles per shot when a target is produced by even-odd enrichment of an isotope element group containing ⁷⁹ Se and irradiated with a proton beam of 1.0 GeV. ⁷⁹ A graph showing the number distribution of nuclides converted and generated by charged particles per shot when a target is produced by isotopic extraction of Se and irradiated with a proton beam of 1.0 GeV. A table in which a composite target and a single target were prepared by elemental separation, even-odd concentration, and isotope extraction, respectively, and the number of LLFP nuclides annihilated when a 1.0 GeV proton was incident on one shot.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
As shown in the flowchart of FIG. 1 (refer to FIG. 2 as appropriate), the method for treating a long-lived fission product (hereinafter referred to as LLFP) according to the embodiment starts with radioactive waste 10 from cesium (Cs), zirconium (Zr ), Selenium (Se), tin (Sn), and palladium (Pd), at least two elements (first element 11 and second element 12) are separately separated and extracted (S21), and the first element A step (S22) of acquiring range data when a charged particle beam 15 (FIG. 2) having a predetermined performance value 13 is incident on the virtual target constituted by 11, and an incident axis 16 of the charged particle beam 15; A first bulk body 21 having a length L in the direction along the range of 1.0 to 2.0 times the range data by the first element 11 (S23 to S25); A step (S26, S27) of creating a second bulk body 22 arranged around the first bulk body 21 so that 16 is a rotationally symmetric axis with the second element 12; A step of irradiating the target 23 combined with the first bulk body 21 and the second bulk body 22 along the incident axis 16 with the charged particle beam 15 having an energy value in the range of 0.5 to 1.5 GeV ( S28 to S30).

Then, the irradiation of the charged particle beam 15 on the target 23 is continued (S31 No), and the irradiation is stopped when the set time has elapsed (S31 Yes).
Then, the irradiated target 23 is carried out of the irradiation system of the charged particle beam 15 (S32) and replaced with a new target 23 and arranged in the irradiation system (S33, S29).
Thereafter, the above flow is repeated.

It is assumed that the radioactive waste 10 to be applied in the present embodiment includes a fission product (FP). This fission product (FP) refers to a nuclide separated by fission of a fissionable nuclide such as uranium U-235 or plutonium Pu-239 into two or more.
There are about 40 kinds of elements of the fission product (FP) of uranium U-235, from nickel (atomic number 28) to dysprosium (atomic number 66).
And the yield distribution with respect to the mass number of the fission product (FP) of uranium U-235 ranges from 72 to 160, and has a double peak shape having maximum values in the vicinity of the mass numbers 90 and 140.

In this way, fission products (FP) are classified into hundreds of types when the isotopes are distinguished, and these are further classified into stable nuclides and radionuclides, of which radionuclides change to more stable nuclides due to nuclear decay. .
A radionuclide (SLFP) with a short half-life of nuclear decay emits a large amount of radiation in a short time, but its radioactivity rapidly decays with time, so it can be rendered harmless by storage for a predetermined period.

On the other hand, LLFP with a long half-life has a low radiation dose but a slow decay rate. Therefore, when possessing a large amount, LLFP requires a disposal method that does not cause any problems even if human management is lost. .
For this reason, if LLFP can be transmuted to short-lived radionuclides (SLFP) or stable nuclides, the management burden of radioactive waste can be reduced.

FIG. 3 shows the isotope composition of the target LLFP included in the spent nuclear fuel.
Major LLFPs contained in the fission product (FP) (half-life in parentheses) include selenium Se-79 (2.95 × 10 ⁵ years), palladium Pd-107 (6.5 × 10 ⁶ years), Zirconium Zr-93 (1.5 × 10 ⁶ years), Cesium Cs-135 (2.3 × 10 ⁶ years), Iodine I-129 (1.57 × 10 ⁷ years), Technetium Tc-99 (2.1 X 10 ⁵ years) and tin Sn-126 (2.3 x 10 ⁵ years).

Among these, iodine I-129 and technetium Tc-99 are excluded from the examination in the present embodiment because there is a report example of effectively shortening the life by other methods, but are the subject of the present invention. You can also.
Radionuclides with a half-life of 10 ¹⁰ years or more are considered metastable nuclides and are not included in long-lived fission products.

  FIG. 4 shows the annual generation amounts of LLFP nuclides and their isotopes in FIG. 3 and their densities when the annual processing target amount of spent nuclear fuel is 800 tons.

The process of FIG. 1 (S21) is a process of separating and extracting a group of isotope elements including the focused LLFP nuclide from the radioactive waste 10 in which many nuclides are mixed.
That is, a group of elements having the same atomic number (proton number) Z as the LLFP nuclide of interest ( ¹³⁵ Cs, ¹⁰⁷ Pd, ⁹³ Zr, ⁷⁹ Se, ¹²⁶ Sn) and having a mass number (proton number + neutron number) A (Cs, Pd, Zr, Se, Sn) are extracted separately.

  A general element separation method can be applied to the method for separating and extracting the first element 11 and the second element 12 which are such isotope element groups. Examples of such element separation methods include an electrolytic method, a solvent extraction method, an ion exchange method, a precipitation method, and a dry method, or a combination thereof. In addition, when a vitrified body is a target for radioactive waste, it is necessary to dissolve or decompose the vitrified body in the previous step of separation and extraction, but a general dissolution / decomposition method can be applied, for example, an alkali melting method, Examples include molten salt methods (electrolytic reduction, chemical reduction), high temperature melting methods, halogenation methods, acid dissolution methods, and alkali dissolution methods. After the vitrified body is dissolved or decomposed, the above-described general element separation method can be applied.

Further, in the step (S21), even-odd concentration of nuclides based on the number of neutrons is further performed on at least one of the first element 11 and the second element 12 after being extracted from the radioactive waste 10, and the LLFP nuclide The concentration may be increased.
Even-odd enrichment means a process of concentrating to either an isotope group with an odd number of neutrons or an isotope group with an even number of neutrons based on the even-oddity of the enrichment effect in the isotope element group.

An isotope shift phenomenon is known in which the frequency of atomic spectral lines slightly shifts depending on the isotope, and the selection rule of the optical transition with respect to the polarization of light is different between the odd and even nuclei. This isotope shift phenomenon is based on the property that the transition selection rule in the electronic excitation process by the left and right circularly polarized lasers is different between an even-numbered nucleus and an even-numbered nucleus when the number of protons is an even number.
The even-odd concentration treatment step specifically includes irradiating a laser with controlled polarization to ionize only odd-numbered nuclides, but is not particularly limited.
Through this even-odd concentration treatment step, the concentration of LLFP nuclides can be increased, and the number of LLFP nuclides to be extinguished by charged particles per shot can be increased.

In the step of FIG. 1 (S22), range data is calculated when a charged particle beam 15 (FIG. 2) having a predetermined performance value 13 is incident on a virtual target composed of the first element 11.
Assume that a high-energy charged particle beam 15 is incident on a target composed of the first element 11. The charged particle beam 15 passing through the inside of this isotope group interacts with electrons and loses energy. If the target is sufficiently large, the charged particle beam 15 stops halfway.

  The distance from when the charged particle beam 15 enters until it stops is called the range. This range is determined by the beam performance value 13 such as the charge amount, mass and energy of the incident charged particles, and the electron density of the target. Therefore, when the common charged particle beam 15 is used, the range has a relationship of decreasing according to the charge density of the nuclide constituting the target.

In the step of FIG. 1 (S23), a value obtained by expanding the range data acquired by calculation in the range of 1.0 to 2.0 times is set as the length size L of the target 23 (FIG. 3).
The primary particles with the charged particle beam 15 incident on the target 23 transmutate the first element 11 constituting the target 23 by nuclear reaction in this range.
For this reason, when the length size L of the target 23 is smaller than 1.0 times, the primary particles penetrate the target 23, and the number of LLFP nuclides in which the charged particles per one shot disappear is reduced.
And if the length size L of the target 23 is larger than 2.0 times, the area | region where the primary particle has not reached increases, and the conversion rate of the nuclide averaged by the target 23 will fall.

By the nuclear conversion by the primary particles, LLFP contained in the target 23 is extinguished and at the same time, many new nuclides are generated.
Furthermore, secondary particles such as protons, neutrons, and light particles are generated along with the nuclear reaction by the primary particles. Among these secondary particles, high-energy protons and neutrons pass through the target again to induce a new nuclear reaction.

The graph of FIG. 5 shows the neutron flux distribution of LLFP nuclides ( ¹³⁵ Cs, ¹⁰⁷ Pd, ⁹³ Zr, ⁷⁹ Se, ¹²⁶ Sn) inside the target. The graph of FIG. 6 shows reaction cross sections of the (n, γ) reaction and the (n, 2n) reaction in the LLFP nuclide ( ¹³⁵ Cs, ¹⁰⁷ Pd, ⁹³ Zr, ⁷⁹ Se, ¹²⁶ Sn).
In view of the fact that the peak of the neutron flux distribution of each nuclide in FIG. 5 is in the range of 0.2 to 2.0 MeV, the reaction channel of nuclear conversion of these nuclides is (n, γ) reaction from FIG. (Capture). Furthermore, the value of the reaction section (Cross Section) in this (n, γ) reaction is greatly different among nuclides.
Among the secondary particles generated when the charged particle beam 15 is incident on the target 23, the nuclear reaction newly induced by neutrons is frequently performed in the order of Pd>Se>Cs>Zr> Sn.

Thus, it is known that when the charged particle beam 15 is incident on the target, a complicated nuclear reaction is induced inside the target.
As such a numerical simulation code 14 for analyzing a complicated nuclear reaction, PHITS (Particle and Heavy Ion Transport code System) is used.

PHITS is a code that simulates transport of particles and nuclei developed mainly by the Advanced Information Science and Technology Research Organization (RIST), Japan Atomic Energy Agency (JAEA), and High Energy Accelerator Research Organization (KEK).
This PHITS can handle the transport of almost all particles such as nucleons, mesons, photons, electrons, nuclei, etc. in the material, the sequential nuclear reactions that these particles cause in the macroscopic system, The ionization process of particles can be analyzed.
The numerical simulation code 14 used for analyzing the nuclear reaction of the present invention is not particularly limited to PHITS.

Here, in the step of FIG. 1 (S <b> 26), the second radius R <b> 2 that is the outer diameter of the target 23 or the outer diameter of the second bulk body 22 is the size of the facility (not shown) irradiated with the charged particle beam 15. It is determined.
In the step of FIG. 1 (S24), the first radius R1 that is the outer diameter of the first bulk body 21 or the inner diameter of the second bulk body 22 is that the LLFP contained in the target 23 is caused by charged particles per one shot. It is set from the viewpoint of disappearing as much as possible.

From the same viewpoint, a combination of the first element 11 constituting the first bulk body 21 and the second element 12 constituting the second bulk body 22 is also set.
Specifically, this combination is determined in consideration of the range of the incident charged particle range, the size of the reaction cross section in the (n, γ) reaction, and the like.

FIG. 7 to FIG. 10 show the number of LLFP particles in which charged particles (one GeV proton) per one shot are extinguished in the target 23 having a size of R2 = 15 cm fixed and R1 = 0 to 15 cm variable. Represents.
The length size L of the target 23 in FIGS. 7 to 10 is set to L = 300 cm, 80 cm, 110 cm, and 330 cm, respectively, corresponding to the nuclide range adopted for the first bulk body 21. . Moreover, the result by the target 23 produced by performing the process of even-odd concentration is shown.

7 to 9 show results of the target 23 in which Pd having the largest (n, γ) reaction cross-sectional area value is used as the second bulk body 22 and Cs, Zr, and Se are used as the first bulk body 21, respectively. It is.
7 and 10, Cs having the longest range (the smallest density) of the incident charged particles is used as the first bulk body 21, and Pd and Zr are used as the second bulk body 22, respectively. This is a result of the target 23.
For Sn, the reaction cross section shown in FIG. 6 which is the basis of this study is close to Zr, and the results of replacing Zr with Sn show the same tendency, so the results of study including Sn individually Will be omitted hereinafter.

Here, the number of annihilation of LLFP nuclides when R1 = 15 cm corresponds to the result of the target 23 composed solely of the first element 11.
In addition, the number of LLFP nuclides annihilated when R1 = 0 cm corresponds to the result of the target 23 composed solely of the second element 12.

In the graphs of FIG. 7 to FIG. 9, the range of R1 where the number of annihilation is larger than when R1 = 0 cm is formed by combining a plurality of nuclides rather than the target 23 being constituted by one kind of nuclides. It can be said that this is a range in which the effect of this is noticeable.
Further, in the graphs of FIGS. 7 to 10, a line is drawn on the addition average value of the number of disappearances of the LLFP when R1 = 0 cm and the number of disappearances when R1 = 15 cm.
The range of R1 in which the number of annihilation is larger than the average value can also be said to be a range in which the effect of being composed of a plurality of nuclides is shown rather than the target 23 being composed of one kind of nuclides.

That is, when the charged particle beam 15 is incident on the target 23, secondary particles are emitted in all directions in a process in which the primary particles internally pass along the incident direction.
In the LLFP nuclide in which the contribution of the secondary particles to the transmutation is lower than that of the primary particles, the generated secondary particles are discharged outside the target without being effectively used.
Therefore, the second bulk body 22 including the LLFP nuclide having a high degree of contribution of secondary particles to the nuclear transformation is disposed around the first bulk body 21 including the LLFP nuclide. By combining the target 23 in this way, it is possible to effectively use secondary particles and increase the number of LLFP nuclides in which charged particles per one shot disappear.

1 (S25), (S27), and (S28) are steps for manufacturing the target 23.
The combination of the first bulk body 21 and the second bulk body 22 and the first radius R1 in the target 23 are the inventory ratio of Cs, Pd, Zr, Se, and Sn shown in FIG. It is determined in consideration of the number of annihilation of the exemplified LLFP nuclides.
In the present embodiment, the second bulk body 22 disposed around the first bulk body 21 is illustrated as having a hollow cylindrical shape. However, the form of the second bulk body 22 is not particularly limited, and includes a case where a plurality of separated parts are arranged around the first bulk body.
The steps (S21) to (S28) are continued until the radioactive waste 10 is out of stock.

The steps of FIG. 1 (S29) to (S31) are steps of irradiating the manufactured target 23 with the charged particle beam 15. Hereinafter, the specification of the charged particle beam 15 to be applied will be considered.
When irradiating the charged particle beam 15 and transmutating the LLFP nuclides contained in the virtual target, the following relationships (1) to (4) are derived.
ΔN (t) / Δt = −Φ · σ · N (t) (1)
N (t) = N ₀ exp (−Φ · σ · t) (2)
T _1/2 = ln (2) / (Φ · σ) (3)
h = φ ・ σ ・ ρ ・ V (4)
ρ: virtual target particle density V: virtual target volume σ: effective cross-sectional area of transmutation N ₀ (= ρ · V): number of LLFP nuclides included in virtual target at time t = 0 N (t): time Number of LLFP nuclides contained in the virtual target at t T _1/2 : Time taken to decrease from N ₀ to 1 / 2N ₀ (half-life)
h: Number of LLFP nuclides converted by charged particles per shot φ: Amount of primary particles and secondary particles (neutrons) generated from charged particles per shot and contributing to nuclear reactions Φ (= φ x beam current value ): Flux of primary particles and secondary particles (neutrons) generated by beam incidence and contributing to the nuclear reaction (flow rate per unit time)

In the graph of FIG. 11, the charged particle beam 15 is a proton beam, the energy E (MeV) of this proton beam is taken on the horizontal axis, and the conversion energy E / h required to convert one LLFP nuclide on the vertical axis. (MeV) is taken to represent the case where a virtual target is constituted by each of the LLFP nuclides of ¹³⁵ Cs, ¹⁰⁷ Pd, ⁹³ Zr, and ⁷⁹ Se extracted with isotopes.
The graph of FIG. 11 shows that LLFP nuclides are efficiently converted with less energy by applying a charged particle beam in the energy range of the horizontal axis where the vertical axis shows a small value.

The shape of the virtual target is set as follows. The length size is set to 1.1 times the range of the constituent nuclides. The radius size of the circular section is set so that the charged particle beam 15 of 200 mA is irradiated and the half-life of the formula (3) is 3 years.
In the virtual target set in this way, those whose mass exceeds 300 kg and are not realistic are indicated by white marks in the graph.

The graphs of FIGS. 12 to 15 show that the LLFP nuclides constituting the virtual target are ¹³⁵ Cs, ¹⁰⁷ Pd, ⁹³ Zr, ⁷⁹ Se, the charged particle beam 15 is proton (proton), deuteron (deuteron), and carbon. The conversion energy with respect to the energy per nucleon of the particle beam 15 is expressed for each LLFP nuclide.
In addition, regarding the length size of the virtual target, when the charged particle beam 15 is proton and deuteron, it is the same as FIG. 11 (1.1 times the range), but in the case of carbon, the effect of secondary neutrons is obtained. In consideration, Pd is set to 2.0 times the range, and other Cs, Zr, and Se are set to 1.5 times the range.

From the graphs of FIGS. 11 to 15, the energy value 13 per nucleon of the charged particle beam 15 is in the range of 0.5 to 1.5 GeV, preferably 0.5 to 1.0 GeV in any of protons, deuterons, and carbon. In the range, the conversion energy is small and the conversion of LLFP nuclides is highly efficient.
Further, it has been obtained that the use of a proton beam as the charged particle beam 15 can reduce the size of the target.

In the steps of FIGS. 1 (S29) to (S31), the charged particle beam 15 is irradiated for a set time, whereby the LLFP nuclides contained in the target 23 disappear at a predetermined rate.
Then, the target 23 that has been subjected to the beam irradiation is transported to the next step (S32), and the beam irradiation is resumed for the new target 23 that has been replaced (S33).
Note that the steps (S29) to (S33) are continued until the manufactured target 23 is out of stock.

In the above, the series of flow of the processing method of the long-lived fission product which concerns on embodiment was demonstrated.
Next, in FIG. 1 (S21), when only element separation including LLFP nuclides is performed, even odd-even enrichment is performed, and isotope extraction is performed to extract only LLFP nuclides. The annihilation effect of LLFP nuclides is analyzed.

The graphs from FIG. 16 to FIG. 27 show the case where ¹³⁵ Cs, ¹⁰⁷ Pd, ⁹³ Zr, and ⁷⁹ Se are respectively prepared by element separation, even-odd concentration, and isotope extraction, and irradiated with a proton beam of 1.0 GeV. It shows the quantity distribution of nuclides converted and generated by charged particles per shot.
In addition, the data of the isotope composition in element separation and even-odd enrichment uses the data of the isotope composition in the general spent nuclear fuel.

In the graphs of FIG. 16 to FIG. 27, the quantity distribution is classified into four reaction channels: proton incident reaction (proton), (n, γ) reaction, (n, 2n) reaction, and other neutron reactions. ing.
Further, with the vertical axis of 0 as the base point, the nuclide quantity distribution converted by charged particles per shot is shown on the upper side, and the generated nuclide quantity distribution is shown on the lower side.
Therefore, a value obtained by subtracting the lower generation number from the upper conversion number corresponds to the corresponding nuclide disappearance number.

  From the graphs of FIGS. 16 to 18, Cs-135 has a low annihilation number of 0.226 when elemental separation is performed with the spent fuel composition, and even if it is even-odd enrichment, it hardly changes to 0.229. This is due to the fact that almost even isotopes are not contained in the spent fuel composition. Cs-135 has a annihilation rate of only 2.36 even after isotope extraction, which is the lowest among other LLFP nuclides. The reason is considered to be that the density is the lowest and the cross-sectional area of (n, γ) is small.

  From the graphs of FIG. 19 to FIG. 21, Pd-107 has an extinction number of 0.916 when elemental separation is performed with the spent fuel composition. large. Furthermore, Pd-107 has an extinction rate of 8.52 when isotope extraction is performed, which is the highest among other LLFP nuclides. The reason is considered to be that the density is the highest and the cross-sectional area of (n, γ) is large.

From the graphs of FIGS. 22 to 24, Zr-93 has an extinction number of 0.501 when elemental separation is performed with the spent fuel composition. large. Furthermore, Zr-93 has an extinction rate of 3.5 when isotope extraction is performed.
From the graphs of FIG. 25 to FIG. 27, Se-79 has an extinction number of 0.072 when the elements are separated by the spent fuel composition, which indicates that the number of generations and the number of conversions are almost the same. And even-even concentration becomes 2.74, and it turns out that even-odd concentration is essential. Further, Se-79 has an extinction rate of 3.2 when isotope extraction is performed.

FIG. 28 is a table in which the composite target 23 and the single target are prepared by elemental separation, even-odd concentration, and isotope extraction, respectively, and the number of LLFP nuclides annihilated when a 1.0 GeV proton is incident on one shot is obtained. is there.
Here, the composite target 23 is set to R1 = 5 cm and R2 = 15 cm in the combination shown in FIG. The single target has an outer diameter that is the same volume as the first bulk body 21 and the second bulk body 22 constituting the composite target 23.
The total column of the composite target in FIG. 28 shows the number of annihilation of LLFP nuclides for one shot by protons. On the other hand, the total column of single targets shows the addition average of the number of annihilation numbers of LLFP nuclides for two shots by protons incident on each of the two types of single targets.

According to FIG. 28, the number of LLFP nuclides annihilated by changing from a single target to a composite target is 2.8 times for the combination of Cs-Pd, 1.6 times for the combination of Zr-Pd, Se- As a result, it was possible to increase the efficiency by 1.6 times with the combination of Pd and 1.3 times with the combination of Cs-Zr.
Similarly, in even-odd enrichment, Cs-Pd combination is 1.9 times, Zr-Pd combination is 1.6 times, Se-Pd combination is 1.7 times, and Cs-Zr combination is 1.3 times. As a result, the efficiency was improved.
Similarly, in the isotope extraction, the Cs-Pd combination is 1.8 times, the Zr-Pd combination is 1.5 times, the Se-Pd combination is 1.5 times, and the Cs-Zr combination is 1.4 times. The result was that the efficiency was doubled.

  According to the radioactive waste processing method of at least one embodiment described above, at least two types of elements including LLFP nuclides are extracted, and a target on which a charged particle beam is incident is configured in a double cylindrical shape. The conversion process to the nuclide can be made efficient.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, replacements, changes, and combinations can be made without departing from the scope of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and the equivalents thereof.

  DESCRIPTION OF SYMBOLS 10 ... Radioactive waste, 11 ... 1st element, 12 ... 2nd element, 13 ... Beam performance value, 14 ... Numerical simulation code, 15 ... Charged particle beam, 16 ... Incident axis, 21 ... 1st bulk body, 22 ... 2nd bulk body, 23 ... target, R1 ... 1st radius R, R2 ... 2nd radius R, L ... length size.

Claims (7)

At least two kinds of elements (first element and second element) among cesium (Cs), zirconium (Zr), selenium (Se), tin (Sn) and palladium (Pd) from the radioactive waste, the same atomic number And separately separating and extracting as a group of isotope elements having different mass numbers ,
Obtaining range data when a charged particle beam having a predetermined performance value is incident on a virtual target composed of the first element;
Creating a first bulk body with the first element having a length size in a direction along the incident axis of the charged particle beam in a range of 1.0 to 2.0 times the range data;
Creating a second bulk body with the second element disposed around the first bulk body so that the incident axis is a rotationally symmetric axis;
A charged particle beam having an energy value per nucleon within a range of 0.5 to 1.5 GeV among the performance values is applied to the target obtained by combining the first bulk body and the second bulk body with the incident axis. And a step of irradiating along a long-lived fission product. The method for treating a long-lived fission product according to claim 1,
At least one of the first element and the second element is subjected to the even-odd enrichment of nuclides based on the number of neutrons after the separation and extraction, and the concentration of the long-lived fission product is increased. A method for treating long-lived fission products. In the method of processing a long-lived fission product according to claim 1 or claim 2,
The method of treating a long-lived fission product, wherein the first element is cesium (Cs). In the processing method of the long-lived fission product according to any one of claims 1 to 3,
The method for treating a long-lived fission product, wherein the second element is palladium (Pd). In the processing method of the long-lived fission product according to any one of claims 1 to 4,
The method for treating a long-lived fission product, wherein the charged particle beam is a proton beam.   In the processing method of the long-lived fission product according to any one of claims 1 to 4,
  The method for treating a long-lived fission product, wherein the charged particle beam is a deuteron beam.   In the processing method of the long-lived fission product according to any one of claims 1 to 4,
  The method for treating a long-lived fission product, wherein the charged particle beam is a carbon beam.

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