Materials of alternative nuclear power plants of the fourth generation :: SPE RESST

Materials of alternative nuclear power plants of the fourth generation

The reduction in the hydrocarbon resource base prompted the world's leading countries to propose for the energy market a new class of nuclear installations - modular high-temperature gas-cooled nuclear reactors (HTGR) capable of effectively producing both electricity (with an efficiency ~50%) and in the nuclear-technological complexes - liquid synthetic fuel from coal (the nearest perspective), and in the future - hydrogen for use in hydrogen power. Their important advantages are the modularity and extremely short (2 years) commissioning period from the beginning of construction. For the introduction of nuclear power systems of a new generation in the nuclear power industry of Ukraine, it is important to increase the effectiveness of scientific research, in particular, in the development of radiation-resistant reactor materials. The prediction of the change in the properties of structural and fuel materials caused by neutron irradiation and charged particles in large doses is the main requirement in the development and operation of the newest power reactors, which also include the fourth generation high-temperature gas-cooled reactors (HTGR).

Simulation experiments by determination of corrosion resistance of reactor graphites in the oxygen environment.

Simulation tests were carried out on the samples of perspective reactor graphites of the MPG, GSP and ARV brands.

A research method has been chosen and a multipurpose unit for oxidizing graphite samples in oxygen has been modernized (see Figure 1).

Figure 1 - Scheme of the unit for oxidation and saturation of samples oxygen: 1 - vacuum chamber, 2 - annealing furnace, 3 - forvacuum chamber, 4 - samples holder, 5 - rod of input of the holder, 6 - gas supply pipelines, 7 - gas accumulator, 8 - gas flow indicator, 9 - gas purifier heating furnace, 10 - quartz tube with copper shavings, 11 - balloon O₂, 12 - samples, 13 - valves

The kinetics of graphites oxidation in oxygen at temperatures 400, 600 and 800 ° C for 50, 10 and 3 hours, respectively, was determined. It has been confirmed that the process of graphite materials oxidation in oxygen happens to loss of weight.

The mass loss of graphite materials samples is characterized by the formation of a gaseous corrosion product and the absence of oxide films on the surface. Since the samples are made of powder materials, graphite materials have a significant porosity, the value of which depends on the technology of their production. The oxidation process can occur not only on the surface of the samples, but also in the pores, and, therefore, in the volume of material. This explains the significant corrosion rates, which are shown in a decrease of mass of samples.

The appearance of the samples (see Figures 2 - 4) demonstrates that at temperatures around 400 °C process of corrosion goes with a low speed and the samples retain their shape. At 600 °C, corrosive manifestations are observed after 10 hours on samples (except for samples of GSP graphite with a density of 1,77-1,9 g/cm³). Therefore, it should be expected that during further oxidation these samples will be destroyed.

Figure 2 - Appearance of the original samples: a) MPG; b) GSP-1,52; c) ARV

Figure 3 – The appearance is model after tests in the oxygen environment at 400 °C for 50 hours: a) MPG; b) GSP-1,52; c) ARV

Figure 4 – The appearance is model after oxidation in the oxygen environment at 600 °C for 10 hours: a) MPG; b) GSP-1,52; c) ARV

The most intensive process of destruction of the investigated samples of graphite materials is observed during oxidation from 800 °C (see Fig. 5). At the same time, there is not only a significant rate of mass loss, but also an accelerated reduction in size and forming of samples. At this temperature, the material is not corrosion-resistant.

Figure 5 - Appearance of samples after testing at 800 °C for 3 hours: a) MPG; b) GSP-1,52; c) ARV

Simulation experiments to determine the corrosion of reactor graphites in an oxygen environment under the action of electron irradiation.

To carry out experiments to study the corrosion of graphite samples in an environment oxygen during electron irradiation, an ELIAS electron accelerator of the NSC KIPT with an electron energy (2-3) MeV and a beam current (1-1000) ?A was used (see Fig. 6).

Figure 6 - Generator of a bunch of primary electrons of the ELIAS NSC KIPT

A camera was designed and manufactured to irradiate the samples (see Figure 7-8).


Figure 7 - Camera for irradiating specimens in assembly		Figure 8 - Appearance of an installed chamber for irradiating samples on an ELIAS electron accelerator

Simulated corrosion tests of various graphite types in the environment oxygen at a temperature of 600 °C and an oxygen pressure of 0.1 MPa were carried out under the action of 2.5-MeV electron fluxes and a beam current of 230 μA (see Fig. 9). It is shown that under the irradiation the oxidation process and oxidation speed of graphites increase by (5-10) times.

Figure 9 - Inside the irradiation chamber with mounted samples and thermocouples

It is shown that the oxidation speed under irradiation depends on the position of the sample in the irradiation chamber - and thus on its temperature - and for samples with identical initial characteristics can differ approximately twice.

It is determined that among the samples considered, the graphite of GSP with density (1.77-1.9) g/cm³ has the greatest corrosion resistance, under the same conditions of the simulation experiment.