Phase Composition of Non-irradiated Nuclear Fuel from 4th Unit of Chornobyl Nuclear Power Plant

S. V. Gabielkov, I. V. Zhyganiuk, V. G. Kudlai, P. E. Parkhomchuk,
S. A. Chikolovets

Institute for Safety Problems of Nuclear Power Plants, NAS of Ukraine,
36a, Kirova st., Chornobyl, 07270, Ukraine

DOI: doi.org/10.31717/2311-8253.19.2.3

Abstract

It is necessary to assess the state of unirradiated nuclear fuel 32 years after the accident in order to assess the nuclear, radiation and environmental safety of the New Safe Confinement complex — the Shelter object. Standards samples are required for conducting studies of the crystalline phases’ composition of fuel-containing materials for uranium oxides determination and its oxidation level by X-ray diffraction.
The objectives of the work were: 1) to study the phase composition of unirradiated nuclear fuel of the 4th unit of the Chornobyl Nuclear Power Plant (NPP); 2) to determine the possibility of using samples of unirradiated nuclear fuel as standards in determining the content of uranium oxides in fuel-containing materials by X-ray diffraction methods. The phase composition of the unirradiated nuclear fuel of the 4th unit of the Chornobyl NPP was determined by X-ray diffraction. We used a diffractometer “Dron-4” upgraded for θ–θ scheme, Cu Кα radiation. The “Dron-4” was calibrated by basic diffraction line of alpha Quartz. We held determining lines by X-ray method in wide range of angle. At the same time, we determined lines with highprecision in the narrow range of angle. Data processing was carried out by a New Profile 3.5 program. The New Profile 3.5 program developed in the National Technical University “Kharkiv Polytechnic Institute”. For identification of phases the diffraction database from ASTM was used.
It is shown that the sample of non-irradiated nuclear fuel is represented by uranium oxide UO₂ with cubic structure. It has been established that samples of unirradiated nuclear fuel can be used as standards in the study of fuel-containing materials using X-ray qualitative and quantitative phase analysis methods. The increase in the interplanar distance for the main reflection of unirradiated nuclear fuel may indicate that in the 32 years that have passed since the accident in the fuel, the process of additional oxidation of uranium oxide UO₂ began.

Keywords: non-irradiated nuclear fuel, diffractometer, uranium oxide, X-ray phase analysis, X-ray quantitative analysis, phase composition.

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