JPH07239397A - Method for quenching and treating radioactive waste by using nuclear fusion - Google Patents

Abstract

PURPOSE:To make it possible to efficiently quench and treat the radioactive waste containing fissionable products and transuranic elements (TRU) by irradiating it with muons generated through the natural decay of minus pions. CONSTITUTION:Minus pions pi<-> are generated by irradiating a beryllium (Be) target with high-energy deuteron beams generated by a deuteron accelerator. These pions pi<-> naturally decay into muons mu<->, which are used for the muon- catalystic nuclear fusion reaction. Muon beams focused by a beam condenser are radiated on a gas target located in the center of a quenching reactor. The gas target contains compressed deuterium (D), tritium (T) and D-T molecules, and muons mu<-> induce the muon-catalystic nuclear fusion reactuib to generate 14MeV neutrons. The use of these neutrons makes the efficient quenching treatment of both fissionable products and TRUs possible.

Description

Detailed Description of the Invention

[0001]

This invention relates to fission products (F
P) and transuranic element (TRU) radioactive waste containing long-lived radionuclides, which are short-lived or stable nuclides by transmutation, to rapidly eliminate radioactivity of radioactive waste More specifically, the present invention relates to a new and improved method for extinguishing radioactive waste by using neutrons produced by nuclear fusion.

[0002]

2. Description of the Related Art As an annihilation treatment method utilizing transmutation, a neutron capture reaction is carried out by irradiating neutrons to radionuclides having a long annihilation half-life such as fission products and transuranium elements (hereinafter abbreviated as "TRU") Conventionally, a method of inducing (n, γ) or fission reaction (n, f) to convert to a nuclide having a short annihilation half-life or a stable nuclide has been attracting attention.

In addition, the fission product ⁹⁰ Sr and
^A method using a (n, 2n) reaction with neutrons having an energy of 14 MeV has also been proposed to extinguish ¹³⁷ Cs [eg, H. Takahashi, "The Role.
of Accelerators in the Nuclear Fuel Cycle ", Proc.
2nd Int. Symp. Advanced Nuclear Energy Research, Mi
to, Japan, January 24-26, 1990, p.77 (1990)].

14 MeV neutrons are efficiently produced by muon catalyzed fusion. The principle of this muon-catalyzed nuclear fusion is briefly described. When an unstable elementary particle called muon (μ ⁻ ) is introduced into deuterium (D) and tritium (T) molecules, this muon attracts two atomic nuclei and becomes small. A molecule is produced and nuclear fusion proceeds rapidly in the molecule. In addition, it has a cyclic reactivity that muons become free after the fusion reaction and are used for the reaction many times.

There is also a report of calculating the electric energy required for converting ¹³⁷ Cs nuclide using 14 MeV neutrons generated by muon-catalyzed fusion [T. Kase, K. Konashi, N. Sasao, H . Takahasi and Y.
Hirao, "Transmutation of ¹³⁷ Cs Using Muon-Catalyze
d Fusion Reaction ", Muon Cat. Fusion, 5/6, 521, (1
990/1991)]. The transmutation method adopted here is to irradiate a beryllium (Be) target with a high-energy deuteron beam generated by a deuteron accelerator to produce negative pion (π
^- ) Is generated and muons generated by the spontaneous decay of the negative pions are irradiated to a gas target containing a high-pressure mixed gas of deuterium and tritium to cause a muon-catalyzed nuclear fusion reaction in the gas target to generate 14 MeV. Generates neutrons. Then this 14
¹³⁷ Cs arranged around the gas target is transmuted by (n, 2n) reaction by MeV neutrons.

[0006]

However, according to the above-mentioned conventional method of converting ¹³⁷ Cs nuclide using 14 MeV neutrons generated by muon-catalyzed fusion, in order to convert one ¹³⁷ Cs nuclide, 195
It has been reported that a huge amount of electric energy called MeV is required, and in order to put this method into practical use for annihilation processing, it is an important issue to reduce such enormous energy load. . In addition, since tritium is consumed as a fuel in the muon-catalyzed fusion reaction, the supply of tritium is also important.

Therefore, an object of the present invention is to efficiently dissipate radioactive waste containing fission products and transuranium elements (TRU) by using 14 MeV neutrons produced by muon catalyzed fusion, and further, it is necessary. It is to provide an extinction processing method capable of reducing the enormous energy burden.

Another object of the present invention is to use 14MeV neutrons produced by muon catalyzed fusion to efficiently dissipate fission products and radioactive wastes containing transuranium elements (TRUs). Moreover, it is an object of the present invention to provide an extinction treatment method that can reduce the enormous burden of energy required and can supply the tritium fuel required for muon catalytic fusion by itself.

[0009]

According to the method for annihilation of radioactive waste utilizing nuclear fusion according to the present invention, 14M is obtained by muon-catalyzed nuclear fusion by a conventional method.
Generate eV neutrons. That is, a high-energy deuteron beam generated by a deuteron accelerator is applied to a beryllium target to generate negative pions, and muons generated by spontaneous decay of the negative pions are generated in a gas target containing a high-pressure mixed gas of deuterium and tritium. By irradiating Mn to cause a muon catalyzed fusion reaction in the gas target to generate 14 MeV neutrons.

In the present invention, a first fission product cell containing a radioactive first fission product selected from ⁹⁰ Sr or ^{1 37} Cs is arranged around a cylindrical gas target, and the first fission product is produced. It disposed the TRU cell containing TRU around the object cell, and disposed ⁶ Li inner cells containing ⁶ LiAl around the TRU ^cell, around the 6 Li inner cells
^A second fission product cell containing a radioactive second fission product selected from ⁹³ Zr, ⁹⁹ Tc, ¹²⁹ I or ¹³⁵ Cs is provided, and a moderator filling section is provided around the second fission product cell to provide D the _{2 O} was charged as a moderator, using the extinction furnace comprising surrounding the periphery of the moderator filling part in ⁶ Li outer cell containing ⁶ LiAl.

By irradiating the gas target arranged at the center of the annihilation furnace with muons, a muon-catalyzed nuclear fusion reaction is caused in the gas target to generate 14 MeV neutrons. With this 14 MeV neutron, first the first fission product in the first fission product cell (n, 2
n) Extinguish by the reaction. Next, the neutrons leaking from the first fission product cell cause the TR in the TRU cell to
U is extinguished by fission reaction (n, f). Further, the second fission product in the second fission product cell is extinguished by the neutron capture reaction (n, γ) by the neutrons that have leaked from the TRU cell and are heated by the D ₂ O moderator.

Further, in the present invention, the thermal energy generated by the fission reaction of TRU is converted into electric energy and used as the electric energy supply source of the deuteron accelerator.

Further in a preferred embodiment of the present invention, the neutrons heat-treated by the D ₂ O moderator
The ⁶ Li ⁶ Li of the inner cell and the ⁶ Li outer cell ⁶ L
It is converted into tritium by i (n, α) T reaction, and the obtained tritium is used as a supplementary source of tritium consumed in the muon-catalyzed nuclear fusion reaction in the gas target.

[0014]

[Operation] Radiofission product nuclides can be generally classified into two groups in the study of extinction treatment. The first group, the first fission product, is a nuclide having a thermal neutron capture cross section of less than 1b (burn), ⁹⁰
Sr (15.3 mb: half-life 29 years) and ¹³⁷ Cs
(0.25b: half-life of 30 years). On the other hand, the second group, the second fission product, is a nuclide having a thermal neutron capture cross section of 1b or more, and is ⁹³ Zr (less than 2b: half-life 1.5 × 10 ⁶ years), ⁹⁹ Tc (19b: Half-life 2.1
× 10 ⁵ years, ¹²⁹ I (18b: half-life 1.6 × 10
⁷ years) and ¹³⁵ Cs (5.8b: half-life 2 × 10 ⁶⁾
Years).

Examples of TRU contained in the radioactive waste include ²³⁷ Np, ^241,243 Am, ²⁴⁴ Cm and ^{238 to 242} Pu.

In the present invention, these radioactive wastes, fission products and TRUs, are placed around the muon-catalyzed fusion reaction gas target in the order of the first fission products, TRUs, and the second fission products. As a result, the 14MeV neutrons generated by the fusion process first annihilate the first fission product by the (n, 2n) reaction,
Next, the neutrons leaking from the first fission product cell are TR
U is extinguished by a fission reaction (n, f), neutrons leaking from the TRU cell are heat-treated by a D ₂ O moderator, and the second neutron capture-dissociation reaction of a second fission product by the heated neutrons ( The extinction process can be performed by n, γ).

In particular, in the present invention, the thermal energy generated by the fission reaction of TRU is converted into electric energy and used as the electric energy source of the deuteron accelerator, so that self-sufficiency without external energy is required. It is possible to bring.

[0018]

The present invention will be described in detail below with reference to the embodiments shown in the drawings. FIG. 1 is a conceptual diagram of the present invention, in which a negative pion (π ⁻ ) of 1.5 is generated by irradiating a beryllium (Be) target with a 4 GeV-25 mA high-energy deuteron beam produced by a deuteron accelerator. × 10
It is generated at a rate of ¹⁷ s ⁻¹ . These pions spontaneously decay into muons (μ ⁻ ), which are used for muon-catalyzed fusion reactions. The muon beam focused by the beam concentrator is applied to the gas target located at the center of the annihilation furnace. The gas target contains D ₂ , T ₂ and (D-T) molecules compressed to a pressure of 1000 atm, and the muon in the gas target induces a muon-catalyzed nuclear fusion reaction to generate a 14 MeV neutron. Is generated.

Assuming that one muon is generated at 4.5 GeV deuteron beam energy and 20% of the muon beam is lost in the window of the gas target, the muon-catalyzed fusion reaction causes the muon to enter into the gas target. Each time it will be repeated 175 times.
Based on this assumption, if the efficiency of the accelerator from electric power to deuteron beam energy is 50%, one 14Me
The electrical energy required to generate V neutrons is 64 MeV. The yield of 14 MeV neutrons is
When using a 4 GeV-25 mA deuteron accelerator, 3.1
× ^{10 19} s ^- is ^one.

FIG. 2 shows an rz cross section of an embodiment of an extinction furnace used in the present invention. The center of the extinction furnace is made of 1 cm thick stainless steel with an inner radius of 2.5 cm and an inner length of 34 c.
A cylindrical gas target of m is placed, and 1000 atm of DT gas is compressed and accommodated therein. Around the gas target, a first fission product cell (hereinafter abbreviated as “first FP cell”) containing ⁹⁰ Sr, which is a typical first fission product, is installed.
The first FP cell has an inner radius of 19 cm and an inner length of 34 cm,
It is made of stainless steel having a thickness of 1 cm, and 114 kg of ⁹⁰ Sr metal having a density of 2.6 g / cm ³ is contained therein. This ⁹⁰ Sr is transmuted to ⁸⁹ Sr mainly by (n, 2n) reaction by 14 MeV neutrons. According to a preliminary investigation by the inventors, ⁹⁰ Sr (n, 2
n) The probability that the ⁸⁹ Sr reaction will occur is reduced by about 12% due to scattering from a 1 cm thick stainless steel. ⁸⁹ Sr produced in the 1st FP cell has ⁸⁹ Y with a half-life of 50 days.
(Stable nuclide).

Around the first FP cell accommodating ⁹⁰ Sr, a TRU accommodating a TRU composed of ²³⁷ Np, ^241,243 Am, ²⁴⁴ Cm and ^238-242 Pu is accommodated.
A cell is placed and ⁶ LiAl is placed around the outer circumference of this TRU cell.
A ⁶ Li inner cell containing ⁶ T is arranged, and ⁹⁹ T, which is a typical second fission product, is formed on the outer periphery of the ⁶ Li inner cell.
A second fission product cell containing c (hereinafter abbreviated as “second FP cell”) is installed. A moderator filling portion is provided around the second FP cell to fill D ₂ O as a moderator,
Around the moderator filling portion is surrounded by ⁶ Li outer cell containing ⁶ LiAl. These cells are the first FP
Like the cell, it is made of 1 cm thick stainless steel.

With such a structure, the first floor
Neutrons leaking from the P cell induce a fission reaction (n, f) and a neutron capture reaction (n, γ) in the TRU cell, and the TRU is extinguished by the fission reaction (n, f). Further, the neutrons leaking from the TRU cell are heat-treated by the D ₂ O moderator, and the second FP is heated by the heat-treated neutrons.
⁹⁹ Tc in the cell is mainly neutron capture reaction (n, γ)
Is transmuted to ¹⁰⁰ Tc. The resulting ¹⁰⁰ T
c decays to ¹⁰⁰ Ru (stable nuclide) with a half-life of 16 s.

FIG. 3 shows in the first FP cell containing ⁹⁰ Sr,
In the TRU cell containing the TRU and in the second F containing the ^{9 9} Tc
The neutron spectrum in the P-cell is shown, which allows us to understand the annihilation reactor performance. As can be seen from this figure, in the first FP cell containing ⁹⁰ Sr, 14 MeV
There is a strong neutron peak. Further, it can be seen that the neutron spectrum in the TRU cell is similar to that of the fast reactor, and high thermal energy can be obtained.

The main function of the ⁶ Li inner cell is to prevent the thermalized neutrons from re-entering the TRU cell. When the thermalized neutrons enter the TRU cell, they also enter the first FP cell, and in the first FP cell, (n, 2
Since the ^{8 9} Sr converted by the (n) reaction is returned to ⁹⁰ Sr by the (n, γ) reaction, it becomes impossible to perform an efficient annihilation process. In this ⁶ Li inner ^{cell 6}
The Li (n, α) T reaction is also triggered to produce tritium.

[0025] The main function of the ⁶ Li outside the ^cell, 6 Li
Although it is to produce tritium by the (n, α) T reaction, it also has a function of reducing leakage of neutrons to the outside of the annihilation reactor.

As a material for incorporating ⁶ Li, ⁶
LiAl alloys can be preferably used, which makes it possible to achieve a high density of ⁶ Li and enable a compact extinction furnace design. According to the annihilation reactor design shown in FIG. 2, the probability of tritium production is 0.98 per 14 MeV neutron,
Almost all tritium consumed by the muon-catalyzed fusion reaction can be produced and self-sufficient in the method of the present invention.

In the annihilation reactor design shown in FIG. 2, the number of fission reactions is 1.08 per 14 MeV neutron, which corresponds to a thermal energy of 210 MeV. This heat energy can be converted to electric energy of 70 MeV when the conversion efficiency from heat to electricity is 1/3. As described above, since the electric energy required to generate one 14 MeV neutron is 64 MeV, only the thermal energy generated by the fission reaction in the annihilation reactor can supply the electric energy required for the annihilation treatment according to the present invention. Therefore, it can be said that the present invention is energetically self-contained.

For each nuclide in the annihilation furnace of FIG. 2, 14
(N, 2n) reaction per MeV neutron, (n, f)
Table 1 shows the results of calculating the probability of reaction and (n, γ) reaction, and the elimination half-life.

The MCNP Monte Carlo neutron transport code [JF Briesmeister, "MCNP: A General Pu" is used for this calculation.
rpose Monte Carlo Code for Neutron and Photon Tran
sport ", Version 3A, LA-7369-M, Los Alamos National
Laboratory (1986)] was used. The elimination half-life for each nuclide was calculated from the following three quantities. 1) Inventory of each nuclide in the annihilation reactor shown in the second column of Table 1. 2) 14 MeV neutron production rate; ie 3.1 × 10
¹⁹ n / s. 3) Sum of reaction probabilities for each nuclide shown in the sixth column of Table 1.

In calculating the half-life of fission products, fission products due to the (n, f) reaction of TRU are not taken into consideration. For reference, structural material (stainless steel)
The elimination half-life of the element is also shown. TRU (n, γ)
Alternatively, in the (n, 2n) reaction, the amount of TRU cannot be effectively reduced because TRU is produced. Therefore, the TRU extinction half-life calculated using only the (n, f) reaction rate is shown in brackets in the eighth column of Table 1. From Table 1, the elimination half-lives of ⁹⁰ Sr, ⁹⁹ Tc and TRU are about 1.6 years, 1.6 years and 0.6 respectively.
You can see that it is the year.

[0031]

Table 2 shows the amount of each nuclide that can be eliminated by one year by the present invention. From this table, ⁹⁰ Sr,
^The amount of ⁹⁹ Tc and TRU extinction processed is about 4 each year.
It can be seen that they are 0 kg, 96 kg and 245 kg. When this invention is implemented using a 100 MW (electrical) drive, the annual release of radioactive waste emitted from almost one 3000 MW (heat) light water reactor can be treated.

[0033]

FIG. 4 shows the results of calculating the multiplication factor k _eff of the annihilation reactor by the MCNP Monte Carlo neutron transport code using fission neutrons as an initial input of neutrons instead of 14 MeV neutrons as a function of TRU inventory. The TRU inventory of an extinguishing furnace having the dimensions shown in Fig. 2 is about 348 kg (see Table 1), so 0.6
It can be seen that the extinction furnace can be operated under subcritical conditions with ak _eff of 8 and much less than the critical k _eff value of 1.0. The TRU inventory has a critical _keff value of 1.0
To be smaller than 1800 kg should not be exceeded. However, reducing the plutonium fraction in the TRU will reduce the k _eff value, allowing a larger TRU inventory.

As for the amount of heat generation, a high heating density is expected.
Calculated in ⁹⁰ Sr and TRU cells. The average heat density in the ⁹⁰ Sr cell was produced primarily by β and γ heating, but was only 0.23 kW / cm ³ . The average heat density in the TRU cell was 2.6 kW / cm ³ mainly produced by the fission reaction.

In the above embodiment, ⁹⁰ Sr was used as the first fission product having a thermal neutron capture cross section of less than 1b.
Are treated with ⁹⁹ Tc as the second fission product having a thermal neutron capture cross section of 1b or more, but other first fission product ¹³⁷ Cs is used as the first F instead of ⁹⁰ Sr.
Processing in a P-cell, or other second fission product ⁹³ Zr, ¹²⁹ I instead of ⁹⁹ Tc or
It is also possible to process ¹³⁵ Cs in the second FP cell.

[0037]

As can be seen from the above description, according to the present invention, 14 MeV produced by muon catalyzed fusion is produced.
Neutrons can be used to efficiently extinguish both fission products and TRU contained in radioactive waste.

In particular, by arranging the TRU in the annihilation reactor, the TRU nuclide can be extinguished by the fission reaction and thermal energy can be produced, and this thermal energy is converted into electric energy and necessary for the production of 14 MeV neutrons. By using such a source of electrical energy, it is possible to design a system that does not require external energy.

Further, since the annihilation furnace can be operated efficiently under subcritical conditions, the safety is higher than that in the nuclear fission reactor operated under critical conditions.

Furthermore, tritium is produced by transmutation of ⁶ Li in the annihilation furnace, and by using this tritium as the source of tritium consumed in the muon-catalyzed fusion reaction, tritium self-sufficiency in the system is also achieved. It will be possible.

[Brief description of drawings]

FIG. 1 is an explanatory view showing the concept of the present invention.

FIG. 2 is a zr sectional view showing an example of an extinction furnace used in the present invention.

3 is a graph showing a neutron spectrum in a first FP cell (including ⁹⁰ Sr), a TRU cell (including TRU) and a second FP cell (including ⁹⁹ Tc) in the extinction furnace of FIG. 2.

4 is a graph showing the relationship between the multiplication factor k _eff of the extinction furnace of FIG. 2 and the TRU inventory.

Claims (2)

[Claims] 1. A muon is generated by spontaneous decay of negative pions generated by irradiating a beryllium target with a high-energy deuteron beam from a deuteron accelerator; a cylindrical gas target containing a high-pressure mixed gas of deuterium and tritium. Around ⁹⁰ Sr or ¹³⁷ C
a first fission product cell containing a radioactive first fission product selected from s, and a transuranium element cell containing a transuranium element around the first fission product cell; disposed to ⁶ Li inner cells containing ⁶ LiAl ^{around, 93} Zr around the 6 Li inner ^cells, 99 Tc,
^A second fission product cell containing a radioactive second fission product selected from ^{12 9} I or ¹³⁵ Cs is provided, and a moderator filling section is provided around the second fission product cell to add D ₂ O to the moderator. As a filling material, and ⁶ LiAl around the moderator filling portion.
The muon-catalyzed nuclear fusion reaction is generated in the gas target by irradiating the gas target of the extinction furnace surrounded by a ⁶ Li outer cell containing 14 MeV to generate 14 MeV neutrons; Eliminates the first fission product in the first fission product cell by the (n, 2n) reaction, and the neutrons leaking from the first fission product cell cause the fission reaction of the transuranium element in the transuranium element cell. Neutron capture reaction (n, f) of the second fission product in the second fission product cell by neutrons that have been extinguished by (n, f), leaked from the transuranium element cell, and have been heat-treated by the D ₂ O moderator. γ) is used for annihilation treatment; the thermal energy generated by the fission reaction of the transuranium element is converted into electric energy to convert the electric energy of the deuteron accelerator. Use as Energy supply; annihilation method for treating a radioactive waste using nuclear fusion, characterized in that. 2. A ⁶ in the _{D 2} O ⁶ Li inner cells by neutrons thermalized by a moderator and ⁶ Li outer cell
Li is converted to tritium by a ⁶ Li (n, α) T reaction, and the obtained tritium is used as a source of tritium consumed in a muon-catalyzed fusion reaction in the gas target. The extinction processing method according to item 1.