High-temperature corrosion tests of carbonic materials of nuclear power systems generation IV under irradiation on the electrons accelerator :: SPE RESST

High-temperature corrosion tests of carbonic materials of nuclear power systems generation IV under irradiation on the electrons accelerator

Safe exploitation perspective concerning implementation in power industry of Ukraine the 21st century of modular high-temperature gas-cooled reactors (HTGRs) with low specific power for electricity producing and alternative hydrocarbon fuels and hydrogen from available mineral resources is expected to require the resource forecasting of carbon reactor materials at regular (up to 1300 °C) and hypothetical emergency (up to 1600 °C) operating conditions HTGR. Careful attention should be paid to estimating the radiation-induced corrosion degradation of the reactor graphites properties in chemically aggressive oxidizing environment under reactor irradiation.

For accelerate and reduce tests cost on reproduction of radiation effects for materials the charged particle accelerator can be used.

The researches purpose was to reproduce keyword parameters of temperature and corrosion loads for the materials applied in HTGR generation IV. In particular, a research in the conditions of standard maintenance (temperature of 1250 °C) of materials in a radiation environment of the target modular HTGR generation IV.

Preparation of samples

Experimental samples from different grades reactor graphites (GSP, ARV, MPG) and CCCM with a size of 40×2×3 mm were made and the production of the spherical elements Ø 45 mm and Ø 60 mm from these graphites.

Testing equipment

The modular device for carrying out researches on carbonic materials samples oxidation in the air and steam environment which was tested in the temperature range (400 … 1250) °C and pressure 0,1 MPa is prepared.

The modular device showed satisfactory results on working capacity.

Technique of carrying out experiments

Based on the executed tests and the set operability parameters of the modular device the technique of experiments for a research of samples corrosion resistance of carbonic materials irradiated with electrons in the air and steam environment at temperatures of 1000 … 1250 °C (local standard NSC KIPT 067:2014) was developed. The technique is recommended for use in researches related to the study carbonic materials corrosion resistance which are used in reactor building.

The research of samples carbonic materials corrosion resistance is carried out under the influence of an electron beam at a temperature 400 … 1250 °C (according to the experiment plan) in the air and steam environment for 30, 60 and 80 minutes.

Parameters of the electron beam during irradiation: electron energy in the 2.5 MeV beam; beam current up to 300 μA.

Results of experiments

Experiments on the carbon materials oxidation were carried out at a temperature 1250 °C in an air- steam environment at a pressure of ˜0.1 MPa (20% steam) and flow rate of an air and steam compound (7.0 ... 10.0) m/s (was calculated for each experiment) for 30, 60 and 80 minutes without irradiation and irradiation with 2.5 MeV electrons in the range of electron beam currents (10 ... 300) μA. Samples from graphite grades of GSP, ARV and PGM were used.

Results of graphites oxidation researches in the air and steam environment without irradiation are given in Table 1.

Table 1 – Mass losses of samples graphites of different grades in the air and steam environment in case of 1250 °С

Graphite grade	T, min.	Δm/m, %
GSP	20	16.8
	40	32
	64	45.6
	84	60
ARV-2	30	33,6
	58	52
	74	61,6
MPG-7	30	27,2
	64	46,4
	80	56,8

It is determined that, in the absence of irradiation, the corrosion resistance in air and steam environment is same for all investigated graphites grades.

The total oxidation rate 0.15 mg/g per second without irradiation is also independent of the chemical composition of the oxidants studied-air or air with 20% water steam. Steam adding significantly changes the nature of the time dependence of the oxidation rate.


Figure 1 – Dependence of oxidation rate in the air and steam environment from time for GSP graphite at a temperature 1250 °C without irradiation		Figure 2 – Dependence of oxidation rate in an air environment from time for GSP graphite at a temperature 1250 °C without irradiation

In case of electrons irradiation the situation changes cardinally.

At a temperature (1200 ... 1250) °C and an electron beam current less than or equal to 10 μA, irradiation with electrons does not affect the graphite materials oxidation rate.

At the same temperature at a beam current 30 ?A and 300 μA, the oxidation rate increases substantially. At the same time, the highest corrosion resistance was found in GSP graphite with the density of 1.84 ... 1.90 g/cm³ manufactured using the technology of NSC KIPT.

The received results, first of all, are important for implementation of a systematic approach to the selection of graphite materials that can be used in fuel elements and absorbing elements of nuclear reactors' core, as well as in the components of advanced IV generation nuclear power systems.