JPH0151158B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention quickly removes the radioactivity of unnecessary radioactive waste by converting radioactive waste containing long-lived radionuclides into stable nuclides or short-lived radionuclides through nuclear transmutation. This relates to a method of processing the disappearance process.

Due to the operation of nuclear reactors, large amounts of highly radioactive waste are generated and accumulated. At present, the final treatment and disposal method for this highly radioactive waste is to tightly seal it in vitrified or asphalt solidified materials, store it, and wait for its radioactivity to decrease as it decays. but,
Among highly radioactive wastes, those with long average lives such as ¹³⁷ Cs and ⁹⁰ Sr must be managed safely for many years, and as the amount of storage increases, the selection of storage locations becomes more difficult.・It becomes extremely difficult to secure.

Therefore, a processing method that rapidly reduces the radioactivity by converting these long-lived radionuclides into stable nuclides or short-lived radionuclides by some method, that is, an extinction processing method, is of great significance. As a method of extinction treatment, a method of transmuting the radioactive nuclide through a nuclear reaction and extinguishing the radioactivity in a short period of time can be considered.

Conventionally, methods using n, γ and n, 2n reactions using neutrons have been proposed as methods for annihilation using such nuclear reactions. The reason for using neutrons is that nuclear reactions using neutrons were thought to be suitable for annihilation treatment because they have a large reaction cross section and the energy of the neutrons used is small. but,
In order to effectively annihilate ¹³⁷ Cs, ⁹⁰ Sr, etc., a high neutron flux density is required, and there is currently no equipment that can generate this neutron, and even if one were to be developed, it would be large-scale and would be difficult to develop. It cannot be put into practical use. To date, nuclear reactors, fusion reactors, and high-energy proton accelerators have been considered as candidates for this neutron source. As a result, the neutron flux density of nuclear reactors is too low, and there are limits to increasing it.Fusion reactors are currently still in the experimental stage, and it will be difficult to put them into practical use in the short term. In addition, in order to use a high-energy proton accelerator for annihilation processing, a large-scale, high-intensity, high-energy proton accelerator must be manufactured, which requires a huge amount of cost and is not suitable for industrial use. ,
Each method has its own difficult problems, such as the fact that many problems still remain, and it is extremely difficult to put it into practice in the near future.Therefore, there is a strong desire for the development of some other method of extinction processing. There is.

The present invention has been made in view of the above-mentioned conventional circumstances, and its purpose is to facilitate the annihilation treatment of highly radioactive waste containing long-lived radionuclides without using neutron beams, which has been conventionally considered. The objective is to provide a method that can be implemented.

The present invention, devised to achieve these objectives, is configured to irradiate highly radioactive waste containing long-lived radionuclides with gamma rays having an energy of 10 to 25 M eV instead of neutron beams. .

To explain nuclear reactions caused by gamma rays, when gamma rays are applied to an atomic nucleus, normally only scattering of gamma rays is observed if the energy is low;
When a γ-ray with an energy of about eV or higher is applied to an atomic nucleus, γ, n, γ, p, γ, d, γ, α,
Phenomena called photonuclear reactions such as γ and f reactions are observed. The most common of these reactions are the γ,n and γ,p reactions, and when the energy of γ-rays reaches 10 to 25M eV, they become extremely easily absorbed, producing a reaction of several hundred megabytes called a giant resonance.
A resonance phenomenon is observed.

Cesium-137 causes a giant resonance phenomenon especially in the γ-ray energy range of 10 to 22 M eV, and strontium-90 causes a giant resonance phenomenon especially in the γ-ray energy range of 14 to 22 M eV, but the nuclide Generally speaking, the energy of gamma rays is 10
A giant resonance phenomenon occurs in the ~25 M eV region.

The present invention utilizes this giant resonance in the treatment of radioactive waste, thereby making it possible to efficiently transmute the waste.

FIG. 1 is a conceptual diagram of an apparatus for implementing the method of the present invention. As shown in the figure, the apparatus mainly includes an electron beam accelerator 1, an electron-gamma ray converter 2 provided opposite to the electron beam accelerator 1, and a cooling device 3 for cooling the converter 2. , and a shield 5 that can contain radioactive waste 4 and prevent leakage of γ-rays. The electron beam 6 generated by the electron beam accelerator 1 is converted into gamma rays 7 by bremsstrahlung in the electron beam-gamma ray converter 2. At this time, the heat generated by the electron beam-gamma ray converter 2 is cooled by cooling water flowing through the cooling device 3. Electron beam - γ
The gamma rays 7 produced by the radiation converter 2 irradiate the radioactive waste 4, and the long-lived highly radioactive nuclides existing inside the waste are converted into stable nuclides or short-lived nuclides through nuclear transmutation by gamma, n reactions, etc. It is converted into a radionuclide with a limited lifespan, and its radioactivity is quickly reduced, or eliminated. The shield 5 prevents leakage of γ-rays to the outside of the device.

Figure 2 shows the processing speed of radioactive waste when annihilating radioactive waste using the above-mentioned equipment, using ¹³⁷ Cs as an example. is the case of no processing. The processing speed is expressed as the time T (unit: seconds) until the number of atoms of the radioactive nuclide is halved by irradiation as follows.

T=0.693/(σ・φ・10 ^-24 ) Here, σ is the cross-sectional area of the nuclear reaction due to γ-rays (unit:
burn), and φ is the number of γ-rays incident per unit time on a unit cross-sectional area of radioactive waste (unit: cm
^-2 s ^-1 ).

In the case of σ of ¹³⁷ Cs, the energy of the γ ray is especially
The maximum value is 0.32 barns in the region of 10 to 22M eV.

As the gamma ray for irradiating this, an electron beam with an intensity of 100 mA/cm ² and an energy of 30 M eV is obtained from the electron beam accelerator 1, and 10% of it is converted into a platinum electron beam-gamma ray converter. If ¹³⁷
It will be 2018. This means that the half-life of ¹³⁷ Cs due to β-decay is
Considering that it is 30 years, this means that it has been shortened to 1/15. Moreover, regarding nuclear transmutation of ¹³⁷ Cs, it reacts as follows: ¹³⁷ Cs (γ, n) ¹³⁶ Cs ↓β ^- 13.5d ¹³⁶ Bas st , and turns into a more stable substance. Even if this is taken into account, no new long-lived radioactive materials will be created, and radioactive waste can be effectively disposed of.

The effective nuclide other than ¹³⁷ Cs when the method of the present invention is applied is ⁹⁰ Sr, and its nuclear transmutation is ⁹⁰ Sr (γ, n) ⁸⁹ Sr ↓β ⁻ 50.4d ⁸⁹ Y st . In addition, it is also effective to apply the method of the present invention to the actinide group ( ²⁴¹ Am, ²⁴³ Am, ²⁴⁴ Cm, etc.), which are waste materials with a longer life.

As is clear from the above explanation, an electron beam with an energy of about 30M eV generates gamma rays with energy capable of causing a giant resonance phenomenon, so the electron beam accelerator 1 can be implemented in a small size. be. Since the particles irradiating the radioactive waste 4 are gamma rays, the electron beam -
There is no need to evacuate the equipment on the right side of the γ-ray converter 2. Therefore, the electron beam-γ-ray converter 2 can be easily cooled, and the radioactive waste 4 can be easily handled.

Additionally, in general, the lighter the nuclide with the smaller mass number, the more
Nuclear reactions tend not to occur unless the energy of irradiation is high. By utilizing this property and limiting the energy of the irradiated gamma rays,
It becomes possible to selectively annihilate only the nuclide that is desired to be annihilated in the substance to be treated, which was impossible with the conventional neutron annihilation treatment method. Moreover, by utilizing such properties, if a low atomic number (element with low mass number) is used as the shielding body 5 in the apparatus shown in FIG. It is possible to make it difficult for nuclear reactions to occur even when irradiated, and as a result, it is possible to reduce the generation of secondary radioactivity.

In this way, with conventional technology, long-lived radioactive waste had to be stored for a long time while waiting for it to naturally reduce, but with the method of the present invention, radioactivity can be artificially reduced in a short time. Furthermore, unlike the conventional nuclear reaction using neutrons, it is easy to carry out, and therefore, it can have a very large effect on the safety management of highly radioactive waste.

[Brief explanation of drawings]

FIG. 1 is a conceptual diagram of an apparatus for carrying out the method of the present invention, and FIG. 2 is a graph showing the effectiveness of the method of the present invention. 1... Electron beam accelerator, 2... Electron beam-gamma ray converter, 4... Radioactive waste, 5... Shielding body.

Claims (1)

[Claims] 1. Radioactive waste containing long-lived highly radioactive nuclides is irradiated with gamma rays with an energy of 10 to 25 M eV to convert long-lived radionuclides in the waste into stable nuclides or short-lived nuclides. A method for disposing of radioactive waste characterized by converting it into a long-lived radionuclide. 2. Long-lived highly radioactive nuclides contained in waste 1
The method according to claim 1, wherein the species is cesium-137. 3. The method according to claim 2, wherein the gamma ray has an energy of 10 to 22 M eV. 4 Long-lived highly radioactive nuclides contained in waste 1
Claim 1 in which the species is strontium-90
The method described in section. 5. The method according to claim 4, wherein the gamma ray has an energy of 14 to 22 M eV.