Investigation method of radiation behaviour of nuclear reactor minute particles

FIELD: power engineering.

SUBSTANCE: invention refers to nuclear power engineering, and namely to investigation methods of minute particles of high-temperature gas cooled reactors. Investigation method of radiation behaviour of nuclear reactor minute particles consists in radiation of samples with high energy ions with subsequent isothermal annealing at temperature of 1500°C and more and analysis of samples prior to and after radiation. Samples made in the form of minute particle simulators with protective coverings and hemispheres prepared therefrom are pressed into matrix coal graphite composition thus forming a disc. Samples are located in the disc as a monolayer in a near-surface layer. Simulators of minute particles contact one of two flat disc surfaces. Hemispheres are led as equatorial sections to the same surface. Carbon microspheres containing stable isotopes of fission products and calcium phosphates are used as simulators of minute particles. Analysis of radiation damages is carried out by comparing structures of protective coverings on simulators of minute particles and protective coverings on hemispheres of simulators of minute particles.

EFFECT: invention allows improving informativity of investigation, determining accumulation mechanism of radiation defects in coverings and diffusion processes dealing therewith, determining physical and chemical transformations restricting corrosion resistance of the main power and diffusion barriers that are made from carbidic, nitrided and the like materials and included in the composition of minute particles.

The invention relates to the field of nuclear energy, in particular to methods of research microtalon high temperature gas cooled reactors (HTGR).

MICROTEL (MT) nuclear reactor is the fuel microsphere (TM) of the fissile material (UO₂, PuO₂, ThO₂and others) with protective coatings. As protective coatings on TM using pyrocarbon (Rus) of different density (1.0 to 2.0 g/cm³), silicon carbide (SiC), zirconium carbide (ZrC) and other ceramic materials (Degalan YG, Ponomarev-Stepnoi, N.N., Kuznetsov V.F., the high-temperature Behavior of nuclear fuel during irradiation, M., Energoatomizdat, 1987, 208 S.).

The number of layers of protective coatings MT may be different, but each of them part of the MT performs its specific functions:

the first TM layer, as a rule, is highly porous (in MT most HTGR this Rus), easy volume for containment of gaseous fission products (GPA) and reducing the total pressure of gases under high-density shell layers;

the second layer consists of high-density isotropic eng, which is the first diffusion barrier with respect to the GPA;

- further layers, for example, SiC or ZrC are the main force and diffusion barriers in relation to increasing in the process of combustion of fuel DAVLENIYa and solid products division (TPD), respectively.

- outer layer composed MT HTGR is a high-density isotropic eng.

Of the many, sometimes contradictory requirements of MT HTGR, the main factor is their ability to retain fission products at nominal operating conditions and possible emergency situations (overheating of the fuel entering the oxidant in the reactor core and the like). This requirement is due to the security environment in the loss of coolant and the operating conditions of the primary circuit equipment during operation and repair operations. Emissions into the environment limit the presence of coolant¹³¹I, and the operating conditions limit the additional flow in the circuit nuclides¹³⁴Cs¹³⁷Cs¹¹⁰Ag⁸⁹Sr⁹⁰Sr. All these conditions determine the requirement of relative leakage of fission products (PD) of MT-level R/B ≤10^-4÷10^-5where R is the rate of release of PD, the rate of formation of PD.

The radiation behavior of microtalon investigated irradiation in reactors: in Germany - in reactors AVR, FRJ; in the United States - in the FSV reactor, MTR, HFTR, TRIGA; in Japan in the JMTR reactor; in Belgium - in the BR2 reactor; in Sweden in the reactor R2; Britain in reactors DRAGON, DFR. The objects of research are MICROTEL placed in a special irradiation device.

For IP is to study radiation behavior of MT use their free filling in special containers (ampoules) or formed into patterns of microflow and carbon-graphite matrix composition. To maintain the constant temperature of the vials, which were loaded MT, in the gap between the walls of the capsules and irradiation device is a mixture of helium and nitrogen. The temperature measured W-Re or Ni-Ni/Cr thermocouples. To measure the fluence of thermal and fast neutrons in graphite shell of each of the irradiated vials are placed two or three Co - or Fe - monitor; sometimes use the monitors on the basis of silicon carbide. Each of the vials has an Autonomous system of internal cooling helium, which makes possible the determination of gaseous fission products in each ampoule separately.

During irradiation in a nuclear reactor are determined by the following integral for the whole population of microtalon parameters:

- duration of exposure;

- the temperature in the center of the ampoule, graphite and metal shell of the capsule;

- the fuel burnup;

- flux density of thermal and fast neutrons;

- the heat and the intensity of the division.

The dismantling of the irradiation devices division of structural elements and vials microvilli and subsequent materials research MT is carried out in hot cells.

Irradiation of microflow in a nuclear reactor main goal is the definition of marginal operational capabilities of protective coatings on the retention of PD within the particles is under specified test parameters. At the stage of post-irradiation tests in hot cells are determined by changes in the structural, strength and other characteristics of coatings in comparison to their original state on samples-witnesses. The detecting defects in coatings and study their evolution as a set of neutron fluence is one of the main tasks of the reactor materials. Unfortunately, due to the high radioactivity conducting materials research MT can be performed only with the use of special manipulators and devices (hardware), placed in hot cells. However, not all equipment necessary for the study of subtle mechanisms of physical-chemical, thermal and radiation-chemical transformations, can be placed in these conditions. For these purposes, developed and used an intermediate system between the hot chamber and equipment abroad. All this increases the cost of qualifying fuel and does not always give the true result of the mechanisms of formation and evolution of defects in coatings MT.

For example, the total cost of works to justification of the choice of microtool for very high temperature reactor (VHTR) in terms of their tests on pre - and in-reactor stage is ~77 million dollars. USA. The costs of post-irradiation studies, including high temperature of the jig in the hot cell, make up 31% of the above amount. (Screening Tests for Selection of VHTR Advanced Fuel. PC-000510, Revision O. " Issued by General Atomics for the Department of Energy. Contract No.DE-AC03.01S F22343).

Ceramics, for example, on the basis of pyrocarbon and SiC, ZrC, TiC, Al₂About₃and others, belongs to the class of subactivities materials. Therefore, neutrons and high-energy ions, in addition to radiation damage, the evolution of which is a subject of study, additional sources of radiation is not formed. This allows almost any stage of irradiation to extract samples from the vials and conduct research of their characteristics using equipment outside the hot cell.

For MT, the last irradiation in a nuclear reactor, because of the formation of a large number of high-level radioactive isotopes such a procedure of studies characteristics of coatings outside the hot cell is virtually impossible.

In the irradiation process in the protective coatings MT significant changes occur. For Rus coatings characterized by shrinkage, which grows replaced secondary swelling. Shrinkage in the Russo-coatings is caused by growth stresses in them, which when reaching a certain fast neutron fluences relax with the formation of radial cracks in the layer.

Formed in the Russo-layer through cracks form channels for direct access of iPod is tov division, in particular metal, which cause the radiation-chemical corrosion carbide layers MICROTEL. Formed during the combustion of fuel GPA creates tensile stresses in power carbide layer and in conjunction with corrosive TPD significantly increase the probability of fracture coatings MT, i.e. limit resource use.

The above-described one of the possible mechanisms of depressurization of microtalon during irradiation. However, even this simplified approach to the analysis of processes in the MT shows that for the correct choice of a multilayer protection TM microtalon necessary choices, such characteristics of protective layers (PyC,SiC, ZrC, SiC+PyC, ZrC+PyC, TiC, NbC, TaC, ZrN, TiN, and others), both macro - and microstructure, crystal structure, phase composition, the condition of the interface between the layers, physico-mechanical, thermal and diffusion properties, the value of the density and thickness of the layers, finally, the sequence of layers in the composition of the MT, and so on. The important fact is that all the characteristics of the layers it is necessary to study the composition of the real structure MT, i.e. in those conditions, when implemented stress-strain state of the pavement because of growing inside MT GPA pressure.

There is a method of investigation of the radiation behavior of microtalon the venom of the aqueous reactor, involves the pressing of a mixture of microtalon with pyrocarbon coatings and matrix carbon-graphite composition of flat disks, heat-treated disk at 1800°C, irradiation in a nuclear reactor and the analysis of radiation damage coatings on output through defects gaseous products divisions. (Zoller P. Das Transportverhalten der Spaltprodukte Cäsium und Strontium in beschichteten Brennstoffteilchen für Hochtemperaturreaktoren under Bestrahlungen: JüL-1324, Jülich, 1976).

The disadvantage of this method lies in the fact that, for the study of radiation resistance of coatings (number and types of defects formed, the shrinkage values when the swelling of the protective layers, the structure and phase composition of the interface between the layers, etc.) you must extract microtalon from a matrix of flat disks, which can only be performed in the hot cell, and the characterization of the coatings can be carried out by a limited number of techniques. According to this method it is not possible to conduct research on the kinetics of accumulation of radiation defects and their evolution in layers of protective coatings and especially in the boundary layer directly on the samples prepared from irradiated microtalon, for example by transmission electron microscopy, electron microprobe analysis of high-resolution method to determine the local with the touch of a given chemical element (in our case TPD) in any aggregate state - EXAFS(Extended X-Ray Absortion Fine Structure), the methods of electron paramagnetic resonance (EPR), a method of optical microscopy in the ultraviolet and visible spectral regions and other

This ultimately leads to the fall of informative researches and it is impossible to establish the true mechanism of physical-chemical transformations in the protective coatings microtalon under the simultaneous effect of layers on the internal gas pressure (GPA together with CO and CO₂and radiation defects in the material.

There is a method of investigation of the radiation behavior of microtalon nuclear reactor, which consists in pressing a mixture of microtalon with pyrocarbon coatings and matrix composition of flat disks. MICROTEL the disks are arranged orthogonal to the axis of the drive section in two concentric circles, are heat-treated disk at 1800°C, irradiated in a nuclear reactor and analyze radiation damage to the coating on the release of gaseous fission products from microtool by passing helium through the disks and subsequent γ-spectrometrybased (Fürthmann R. Bestrahlungsverhalten von beschichteten Brennstoffeilchen mit spaltproduktbindenden Kernnadditiven. JüL-1620, Jülich, 1979).

The disadvantage of this method, like the previous one, is the low level of information content studies and, as a consequence, the lack of opportunity in which Stanovlenie kinetic (dynamic) parameters physico-chemical transformations in the process of diffusion interaction of fission products with coating material, additionally stimulated the formation and development of radiation defects.

Investigations of the radiation behavior of microtalon nuclear reactor should allow testing in a wide temperature range (1000-2000°C)and heating the samples shall be carried out in irradiation devices to provide the ability to periodically retrieve samples from the irradiation device and the analysis of the structural transformations in layers at different dose rate, etc. For carrying out the above studies, the samples subjected to radiation and chemical exposure, should not be radioactive. At the same time samples (simulators microtalon) should allow to model close to in-situ stress-strain state of protective coatings due to internal gas pressure in the sample-simulator microtalon.

As noted above, carbide and nitride layers, for example, SiC, ZrC, NbC, TiN, ZrN, NbN, etc. are the main power coatings and diffusion barriers in relation to TPD in the composition of microtalon. Therefore, the study of their radiation behavior of neutrons and high-energy ions is given the most attention.

There is a method of studying the parameters of the crystal structure of SIC samples in plates with RA the measures of 0.6×0,1×0,01 cm after neutron irradiation to a dose of 2.0·10 ²¹4.2·10²¹n/cm²at temperatures between 460 and 1040°C. (R.J.Price, Effects of fast-neutron irradiation on pyrolytic silicon carbide, J. Of Nucl. Mater., 33, 1969, p.17-22).

The disadvantage of this method is the impossibility of accounting for the stress-

deformed state of the SiC, actually existing in the spherical geometry of the particles, i.e. microtube. An additional disadvantage is the fact that irradiation of only neutrons flat samples of SiC according to this method does not take into account the impact on the structure parameters of silicon carbide radiation-chemical effects of the TPD and WITH that in structure MT may be significant.

There is a method of study of crystal structure parameters, types of generated defects, etc. of SIC samples in plates under irradiation by neutrons and ions of silicon (Si⁺²) at elevated temperatures: the neutron - fluence of fast neutrons (4,5-7,7)·10²¹n/cm²(E>0.1 MeV) at 300 and 800°C, ions Si⁺²to 5.1 MeV to about 200 dpa (displacements per one atom). (Y.Katon, N.Hashimoto, S.Kondo, L.L.Shead, A.Kohyama, Microstructural development in cubic silicon carbide during irradiation at elevated temperatures, J. Of Nuclear Materials, 2006, in press).

The disadvantages of this method, like the previous one, are:

the inability to take into account the effective stress-strain state of SiC, which is implemented as part of MICROTEL;

- does not teach is by radiation-chemical effects on the SiC-layer TPD and CO, which part of the MT at certain stages of exposure can have a significant impact on the integrity of the multilayer coatings;

- type SiC samples used in this way, it is not possible to estimate the radiation-dimensional stability "constrained" carbide layer, as implemented in the structure of the multilayer coating MT.

The closest analogue is the prototype of the proposed technical solution is the way to study radiation behavior of flat samples the silicon carbide material after irradiation with high-energy ions and subsequent isothermal annealing at a temperature of 1500°C or more. (Heather J.Maclean, Roland G.Ballinger, Silver ion implantation and annealing in CVD silicon carbide: the effect of temperature on silicon migration. Proceedings of the Conference on High Temperature Reactors, Beijing, China, September, 22-24, 2004, Paper B23, International Atomic Energy Agence, Vienna (Austria). Samples for testing were a flat plate CVD SiC with a thickness of 0.3 mm production Coorstek Inc., the density of the material is 3.21 g/cm³the grain size of 3-10 μm, the preferred orientation of grains is perpendicular to the sample surface. X-ray diffraction analysis (RDA) polished SiC sample was confirmed that the material was crystalline β-SiC with orientation (111). Each sample for ion implantation had a size of 5×5×0,3 see One surface of the sample was polished to a surface roughness RA of 0.005 μm, which was measured is camping on the interference microscope (Zygo.

The irradiation of the samples of β-SiC with silver ions was performed using the ATLAS accelerator at Argonne national laboratory. Ion beams with energies 93, 161 MeV was used for the formation of precipitates with peak concentrations at depths of 9 and 13 μm, respectively. Samples after implantation were annealed in order at 1500°C for 210 and 480 hours. For analysis of samples before and after annealing methods used XPS, SEM, TEM, SPEM and optical microscopy.

The disadvantages of this method are

- SiC samples are flat and do not reproduce the stress-strain state, such state MICROTEL, which leads to a distortion of the profile of the real diffusion of silver in the spot irradiation;

- introduced in the SiC silver ions leads to the amorphization of the crystalline structure of the carbide and registered migration routes of silver cause uncertainty in the interpretation of results to determine the diffusion parameters of the barrier of SiC;

the structure of SiC on flat samples and structure of SiC as part of microtool may differ significantly, which will result in incorrect data, for example, the diffusion coefficients.

The authors proposed technical solutions had the task of increasing the explanatory studies of radiation behavior of microtalon nuclear reactor.

Task d is highlighted by the fact that a method for investigation of the radiation behavior of microtalon nuclear reactor, which consists in the irradiation of the samples with high-energy ions, subsequent isothermal annealing at a temperature of 1500°C or more and the analysis of samples before and after irradiation, samples in the form of simulators microtalon with protective coatings and cooked them hemispheres are pressed in a graphite matrix composition, forming a disk in which the samples have a monolayer in the surface layer so that the simulators microtalon relate to one of the two flat surfaces of the disc, and go hemisphere Equatorial sections on the same surface, and as imitators of microtalon use carbon microspheres containing stable isotopes fission products and calciopoli and analysis of radiation damage carried out by comparing the patterns of protective coatings on the simulators microtalon and protective coatings on the hemispheres simulators microtalon.

As a protective coating using coating selected from the group comprising pyrocarbon and SiC, SiC+C, ZrC, ZrC+C, TiC, TiC+C, AlN, Si₃N₄, TiN, ZrN, TaN, NbN, NbC, TaC, Ti₃SiC₂Si₃Al₃O₃N₅.

Here is an example of the method, illustrating the causal link between essential features and technical achiev what tatom:

imitators of microtalon manufactured using ion-exchange resins by multiple impregnation solutions containing cations of metals (Ag, Pd, Eu, Rh, Sr, Ba, Cs and the like), and calcium phosphate gels, carrying out heat treatment in an inert or reducing environment and deposition on the obtained microspheres pyrocarbon coating density of 1.0-1.6 g/cm³;

- using the obtained simulators microtalon conduct the deposition in a fluidized bed coating, for example, from among: eng of different density and structural state, SiC, SiC+C, ZrC, ZrC+C, TiC, TiC+C, AlN, Si₃N₄, TiN, ZrN, TaN, NbN, NbC, TaC, Si₃Al₃About₃N₅, Ti₃SiC₂. The number of additional protective coatings and their combination is selected depending on the specific research objectives;

- made so the samples are placed on a horizontal surface, for example, in the form of concentric circles alternately at a distance from each other of 0.2-0.5 outer diameter of the simulator MICROTEL hemisphere (made in advance by grinding up the middle slice) and the simulators microtalon and are pressed in a graphite press composition consisting of a graphite powder and a binder on the basis of phenol-formaldehyde resin; the final stage of prototyping - high temperature ~1800°C) treatment in an inert atmosphere;

irradiation with high-energy ions (protons, carbon, oxygen, silicon, nitrogen, helium and the like) is carried out in the cell cyclotron equipped with a heater control system, gas, energy ions, etc.;

- used irradiation, Supervisory and regulatory systems of the cyclotron irradiation and cells allow us to interrupt the test, remove the samples and send to relevant research;

samples that have passed non-destructive testing, return to subsequent irradiation with high-energy ions;

- the proposed solution allows to study how the accumulation of radiation-chemical defects in the layers of protective coatings, staying in close to in-situ stress-deformed state, and a comparative study with loose layers in the structure of the hemispheres simulators microtalon.

The resulting set of comparative experimental data on the simulators microtalon hemispheres and allows you to set the mechanism of accumulation of radiation defects in coatings, and related diffusion processes GPA and TPD, to determine the rate-limiting step in the formation of micro - and macro defects in the layers, and, most importantly, to identify the physico-chemical processes, limiting the corrosion resistance of the basics of the s as part of microtalon power and diffusion barriers of carbide, nitride and other materials.

1. The method of investigation of the radiation behavior of microtalon nuclear reactor, which consists in the irradiation of the samples with high-energy ions with subsequent isothermal annealing at a temperature of 1500°C or more, the analysis of samples before and after irradiation, characterized in that the samples in the form of simulators microtalon with protective coatings and cooked them hemispheres are pressed in a graphite matrix composition, forming a disk in which the samples have a monolayer in the surface layer so that the simulators microtalon relate to one of the two flat surfaces of the disc, and go hemisphere Equatorial sections on the same surface, and as imitators of microtalon use carbon microspheres containing stable isotopes of fission products and calciopoli and analysis of radiation damage carried out by comparing the patterns of protective coatings on the simulators microtalon and protective coatings on the hemispheres simulators microtalon.

2. The method according to claim 1, characterized in that the protective coating using coating selected from the group comprising pyrocarbon and SiC, SiC+C, ZrC, ZrC+C, TiC, TiC+C, A1N, Si₃N₄, TiN, ZrN, TaN, NbN, NbC, TaC, Ti₃SiC₂Si₃Al₃O₃N₅.