RU2270488C2 - Method for radiation treatment of parts and materials by hard gamma-rays - Google Patents

Abstract

FIELD: radiation engineering and technology; physicochemical processes for treatment of materials with dosed ionizing rays to impart new useful properties to them.

SUBSTANCE: proposed method for radiation treatment of parts and materials with hard rays of fission products accumulated in closed loop of circulating-fuel nuclear reactors involves use of ultrashort-living gaseous products of fission accumulated in liquid-fuel homogeneous reactor core which are removed with gas flow from fuel solution and conveyed over closed loop to radiation chamber accommodating parts and materials to be irradiated wherein high-strength field of gamma-rays is built up due to disintegration of ultrashort-living products of fusion; then gas flow depleted with respect to fusion products as result of their radioactive disintegration is returned to reactor core.

EFFECT: enhanced operating safety at desired gamma-ray power level; enlarged functional capabilities.

3 cl, 1 dwg

Description

Technical field

The invention relates to the field of radiation engineering and technology, that is, to production operations associated with the implementation of chemical, physico-chemical processes under the influence of ionizing radiation on various substances in order to create new useful properties due to dosed irradiation.

State of the art

Radiation technology is a rapidly developing field of science and technology, which formed in an independent direction in the early b0s of the XX century. Nuclear reactors, electrophysical facilities (accelerators, neutron generators, etc.), as well as radionuclides, can be used directly or indirectly as sources of ionizing radiation.

Currently, around 70 radiation processes have been implemented around the world, considerable experience has been gained in the creation of radiation-technological installations [G.A. Cherevatenko, E.D. Chistov, V.M.Kodyukov "Radionuclide sources in radiation technology" M., Energoatomizdat , 1989]. The most common radiation-chemical installations associated with the initiation of various chemical processes in the irradiated material. The class of biological plants covers processes of a biological nature, such as, for example, sterilization, processing of agricultural products, etc. This may also include radiation technological installations intended for radiation therapy in nuclear medicine. The use of radiation modification processes is of interest in the production of synthetic materials, vulcanization of rubber products, ion-exchange and separation membranes.

In radiation technology, a wide variety of sealed sources of ionizing radiation is used, differing both in activity (in the range of 10 ⁶ -10 ¹⁵ Bq), and in designs and sizes: from point and small-sized to long blocks and assemblies. The most widely used pilot plants with a gamma radiation source of the ⁶⁰ Co radionuclide and electron accelerators.

The most powerful source of ionizing radiation is a nuclear reactor. Various processes have been developed using gamma radiation of fission products: irradiation devices with spent fuel elements of nuclear power plants, radiation circuits with circulating nuclear fuel.

A known method of obtaining a powerful source of gamma radiation based on a nuclear reactor with fuel circulation - gaseous uranium hexafluoride UF ₆ . ["The Efficiency of Uranium Radiation Circuits with Various Working Substances in High-Temperature Nuclear Reactors" - In the collection "Questions of Atomic Science and Technology". Ser. Atomic and Hydrogen Energy, 1977, Issue 2 (3), p.109, Authors: E.A. Borisov, A.Kh. Breger, E.S. Starizny and others]. The authors performed an analysis of various options for radiation contours. It is shown that the most powerful γ-radiation is generated in the radiation circuit of the reactor, the working substance of which is gaseous nuclear fuel - uranium hexafluoride UF ₆ .

The high efficiency of this variant of the radiation circuit is explained by the contribution to the total radiation power not only of long-lived fission products with a half-life (T _1/2 ) of several days to many years, but also of short-lived ones with T _{1/2 of} only a few seconds, and giving the most severe gamma radiation.

However, the use of gaseous uranium hexafluoride UF ₆ as nuclear fuel requires solving the complex problem of corrosion resistance of structural materials, because gaseous fuel, in itself like fluoride, all the more under the influence of intense ionizing radiation, is a chemically aggressive medium. Uranium hexafluoride UF ₆ in such reactor and, consequently, in the circuit of radiation-production apparatus is under a high pressure required for criticality of the reactor, which reduces the safety of the power plant during its operation. In addition, the presence of delayed neutrons in the circulating fuel can cause the activation of structural materials of the irradiation chamber, and also affect the controllability of the neutron characteristics of the reactor.

Another method of obtaining intense ionizing radiation is implemented in a radiation circuit in which a liquid metal alloy (for example, an In-Ga alloy) is circulated through the active zone of a nuclear reactor [Atomic Science and Technology in the USSR, Moscow: Atomizdat, 1977, p. 96]. In this case, the source of radiation is radioactive nuclei formed as a result of neutron capture by indium and gallium in the reactor core. This method is convenient in operation, since due to the short half-life of the activated elements, access to the equipment is possible only a few days after the circuit stops. However, to create powerful sources of gamma radiation, reactors with high neutron flux densities are needed.

Of interest is a method for producing gamma radiation based on a high-temperature HTGR reactor with continuous circulation of ball fuel elements (TVEL) along the contour of a radiation-technological installation [Epiphany R.G. et al. Power nuclear reactor with circulation of ball fuel elements. Report at the All-Union Meeting on Applied Radiation Chemistry, Obninsk, November 1965]. The source of gamma radiation is the radiation of fission products accumulated in spherical fuel elements. Compared to spent fuel assemblies of nuclear power plants, this method allows increasing the source power through the use of short-lived fission products.

An irradiation facility based on the use of spent fuel elements of a nuclear power reactor as a source of intense gamma radiation from fission products was chosen as a prototype. The source of gamma radiation is the radioactive nuclei of fission products accumulated in the uranium fuel of the reactor during operation of the nuclear power plant. One of the variants of this method was implemented at the Leningrad NPP [A.G. Emelin, S.A. Nikolayev, I.E. Somov, V.G. Shevchenko, "Calculation and experimental justification of the irradiation plant from the spent RBMK reactor designs." Herald of Radtech-Euroasia, No. 1 (8), 1994, pp. 83-98]. During the operation of a large channel power reactor (RBMK), a significant amount of spent fuel assemblies (SFA) was accumulated. The described method is convenient in that the spent fuel assemblies, which are waste products, are used in irradiation devices, and when solving problems in the field of radiation technologies, part of the cost of storing SFAs and other technological needs of nuclear plants is compensated.

However, when implementing this method, technical and organizational measures must be taken to maintain the specified parameters of the irradiation installation, since the decay rate of the PD decreases in time, for which it is necessary to provide for the periodic replacement of the SFA.

Disclosure of invention

The task to which the invention is directed is to increase the level of safety of radiation processing of products and materials for radiation technologies while maintaining the level of gamma radiation power and expanding technological capabilities.

The problem is solved in that in the method of radiation processing of products and materials by hard gamma radiation of fission products accumulated in spent fuel elements of a nuclear power reactor, fission products - radionuclides accumulated in the active zone of a homogeneous nuclear reactor with liquid nuclear fuel - are used as fission products krypton, xenon and their daughter isotopes, which are removed from the fuel with a gas stream and sent in a closed circuit to the irradiation chamber, in which they place irradiated products and materials and where, as a result of the decay of gaseous fission products - radionuclides of krypton, xenon and their daughter isotopes, they create a gamma radiation source, and then the gas stream depleted in fission products as a result of their radioactive decay is returned to the nuclear core the reactor.

In a particular embodiment, an aqueous solution of uranium salts, for example, uranyl sulfate UO ₂ SO _4, is used as circulating fuel.

In another particular embodiment, compounds of uranium - 233, and / or uranium - 235, and / or plutonium - 239 are used as circulating fuel.

The possibility of using homogeneous liquid fuels in nuclear reactors was successfully demonstrated back in the 1950s and 1960s. According to publications of those years, it is known that more than 20 research reactors with fuel based on aqueous solutions of uranium salts operated in the world. These include reactors: HRE-1, HRE-2, LOPO, HYPO, SUPO, etc. [Tishchenko VA, Smirnov Yu.V., Raevsky II US Research Reactors: AINF Review, 588, M., Central Research Institute of Atominform, 1984]. All these reactors use an aqueous solution of uranyl sulfate UO ₂ SO ₄ with various enrichment in the ²³⁵ U isotope as fuel, graphite is a reflector, water is a moderator and a coolant.

Homogeneous liquid fuel reactors have several advantages over solid fuel reactors. They have negative temperature and power effects of reactivity, which ensures their high nuclear safety. The design of the core is greatly simplified: there are no claddings for fuel rods, spacing grids, and other parts that degrade the neutron characteristics of the reactor. The procedure for preparing the solution is significantly cheaper than the manufacture of fuel rods. Loading (pouring) mortar fuel is also much simpler, which allows you to change the concentration of fissile material in the fuel or the volume of the solution if necessary. In the active zone of the solution reactor, due to the good heat transfer conditions, the formation of local overheating is impossible due to the skewness of the energy-deposition fields. These reactors are simple and reliable in operation, do not require numerous personnel for maintenance.

Compared with other types of circulating homogeneous nuclear fuel, such as, for example, uranium hexafluoride UF ₆ , an aqueous solution of uranium salts has several of the following advantages:

low temperature of the fuel solution in the reactor (T <100 ° C);

high solubility of uranium salts in water, which makes it possible to create a compact reactor core;

low corrosiveness of the fuel solution and the presence of structural materials working in these conditions.

Today in Russia there are several reactors with solution fuel: IIN, VIR, IGRIK, HYDRA, ARGUS, operating both in stationary and pulse mode. The development of mortar reactors was carried out in the following two directions:

creation of pulsed solution reactors for studying dynamics, pulsed effects of radiation on materials and equipment, operating time of short-lived isotopes, activation analysis;

development and creation of research mini-reactors of stationary power of 20-50 kW.

It is known from the operating experience of the Argus stationary solution reactor that radioactive gases do not form stable chemical compounds in solution fuel and mostly leave the solution, remaining in the gas phase above the liquid surface [Loboda SV, Petrunin NV, Charnko V.E., Khvostionov V.E. Removal of fission products from the fuel of a solution reactor // Atomic Energy, vol. 67, issue 6, December 1989, pp. 432-433]. The mechanism of the removal of inert gases of fragmentation origin from the fuel solution is associated with the so-called "radiolytic boiling" in solution reactor systems, which involves the formation of gas bubble nuclei on the tracks of fission fragments. According to this model, first vapor bubbles form on the tracks of fission fragments, which, cooling and contracting, pass into gas bubbles containing the products of radiolytic decomposition of water - hydrogen and oxygen. Atoms of radioactive gases, falling into gas bubbles, are carried out from the fuel solution. The release time of the radiolytic gas bubbles is only a few seconds, which makes it possible to carry out relatively short-lived radioisotopes. Once in the gas envelope, the isotope “pops up” to the liquid-gas interface and passes into the free volume above the surface of the solution fuel.

The practical absence of iodine radioisotopes over the solution and the strong predominance of krypton and xenon isotopes are evidenced by the results of studies of gas samples taken from the internal volume of the VIR-2M pulsed solution reactor 2-3 minutes after its shutdown [Voinov AM, Kolosov V.F ., Matveenko A.S. et al. Water pulse reactor VIR-2M and its predecessors. // In the collection Questions of atomic science and technology. Ser. Physics of Nuclear Reactors, 1990, issue 3, pp. 3-15]. It was found that in radiation-significant quantities, only krypton and xenon isotopes are present in the samples, as well as daughter products of their decay - short-lived rubidium and cesium nuclides. The main radionuclides present in the air cavity of the reactor, whose half-lives exceed 1s, are given below:

^{85m, 85.87.88.89.90.90} Kr → ^{88.89.90m, 90} Rb → ^89.90 Sr

^{133.135m, 135.137,138,139,140} Xe → ^{137,138,139,140} Cs → ^{137m, 139,140} Ba.

The radiation spectrum of these radionuclides contains hard gamma rays with an energy of 4 MeV and higher [N. G. Gusev, P. P. Dmitriev Quantum radiation of radioactive nuclides, M .: Atomizdat, 1977].

The drawing shows a diagram of a method of radiation processing of products and materials by hard gamma radiation.

The reactor core is an all-metal welded casing 1 of a cylindrical shape with a hemispherical bottom, which is connected to a gas circuit containing a circulation pump 2 and an irradiation chamber 3 for accommodating the irradiated products and materials. A cooling coil 4 and a fuel solution supply path 5 are also located inside the vessel. The reactor vessel is surrounded by a lateral and lower end graphite reflector (not shown). The gaseous products of radiolysis of the fuel solution are regenerated using a device comprising a catalytic recombiner 6, a heat exchanger 7 and a pipe 8, which together with the reactor vessel form a sealed system. To ensure remote control of gas flows, there are valves 9 with electromechanical actuators.

An example of the method

Solution nuclear reactor with a radiation circuit.

As a reactor designed for use in the field of radiation technology, the Argus research reactor with a closed gas circuit was selected.

The reactor fuel is an aqueous solution of uranyl sulfate, enriched in the ²³⁵ U isotope up to 90%, with a uranium concentration of up to 73.2 g / l. Volume, fuel solution 22 l. The maximum power of the reactor is 20 kW. Elements of the active zone in continuous contact with the fuel solution and the gas circuit are made of stainless steel 0X18H10T.

An aqueous solution of uranyl sulfate UO ₂ SO ₄ through the feed path 5 is poured into the active zone of a nuclear reactor, which is a housing 1 with a wall thickness of 5 mm and a diameter of 300 mm, in which the conditions of the fission chain reaction in solution fuel are maintained. Then the housing is sealed and connected to a loop gas circuit containing a circulation pump 2 and an irradiation chamber 3. As a result of the fission of uranium-235 or the nuclei of other fissile materials, radioisotopes are produced in the solution fuel, including gaseous ones, which, without entering into a chemical reaction with fuel or shrapnel elements enter the free space above the surface of the liquid due to the removal mechanism associated with radiolytic boiling. Heat is removed by means of a cooling coil 4. The gas fraction is removed from a free object above a liquid mirror by means of a circulation pump 2. With gas flows, the radioisotopes in a sealed circuit are sent to an irradiation chamber in which products and materials exposed to radiation are placed, and where, as a result of the decay of the radioactive nuclei of fission products, an intense gamma radiation field is created. Then the gas stream is returned to the reactor volume. In this case, the gaseous products of radiolysis of the fuel solution are regenerated using a device including a catalytic recombiner 6, a heat exchanger 7 and a pipe 8. Remote control of gas flows is carried out by valves 9 with electromechanical actuators.

The proposed method for the radiation treatment of the product and materials with hard gamma radiation using a research nuclear reactor with solution fuel, in comparison with others, is much easier to implement and operate, while ensuring the reliability of fulfilling the requirements of radiation and environmental safety. The irradiation chamber can be made depending on the configuration of the radiation treatment object in various versions, and the maintenance of the reactor and installation as a whole does not require numerous personnel.

Claims (3)

1. The method of radiation treatment of products and materials by gamma radiation of fission products accumulated in a closed loop of a nuclear reactor with circulating fuel, characterized in that as fission products use gaseous fission products accumulated in the active zone of a homogeneous nuclear reactor with liquid nuclear fuel, which are the gas stream is removed from the fuel and sent in a closed circuit to the irradiation chamber, in which the irradiated products and materials are placed and where, as a result of the decomposition of gaseous Recreatives Products division creating a source of gamma radiation and then a gas stream depleted of fission products as a result of radioactive decay is returned to the nuclear reactor core. 2. The method according to claim 1, characterized in that as the circulating fuel use an aqueous solution of uranium salts, for example, uranyl sulfate UO ₂ SO ₄ . 3. The method according to claim 1, characterized in that the compounds of uranium-233 and / or uranium-235 and / or plutonium-239 are used as circulating fuel.