Systematic control of high-temperature and high-dose radiation of materials in active zones of nuclear reactors is one of the most important and acute tasks of experimental radiation materials science. The monitoring is especially necessary for power reactors because construction materials of such objects should accommodate high doses (more than 1023 neutron/cm2) and high temperatures (up to 1500 K).
Usually local conditions of reactor internal radiation of materials (temperature, dose) are defined by calculation or passive methods with the usage of different radiation monitors – constructions made of special materials. The simplest temperature monitors are melting monitors. These are different alloys with known melting points. Their disadvantage is the impossibility to define temperature of radiation in case of short-term temperature overshoots exceeding melting points.
Considering the experience of nuclear reactors’ exploitation and having conducted a series of research, MEPhI specialists of Department № 60 “Physics of extreme states of matter” together with their colleagues from Obninsk and JSC VNIINM have offered to use high-temperature dielectric materials which have necessary wide temperature range with well-measured radiation changes of structure and physical properties, as new monitors of temperature of reactor internal radiation. In such materials (compounds like Al2O3, MgO, MgAl2O4, BN, Si3N4, SiC, with melting points from 2000 K (silicon nitride) to 3000 K (boron nitride)), as a rule, chemical temperature annealing range of radiation structural damage turns out to be much wider in comparison with metals, for example, and can reach melting points of monitor materials. It is connected with the fact that irradiation leads not only to appearing of different crystalline defects as in metals, and to the creation of local areas of nonstoichiometry and inclusion of phases with changed crystal structure.
The second type of monitors includes materials, radiation properties of which, including isotopic composition, are reliably measured. The research of radiation changes of structure of such materials and physical properties, connected with them, allow to get characteristics of conditions (temperature, dose) of the radiation. The method of definition of conditions of internal reactor radiation is in the research of radiation-guided changes of structure (radiation-induced defects of different kind) and properties of materials dependent on conditions of irradiation.
The possibility of usage of ceramic monitors for detection of radiation temperatures in nuclear reactors in temperature range from 400 K to 1900 K has been shown at the example of monitors from materials on the basis of Al2O3 and BN as the result of conducted research. Temperature conditions of irradiation are defined with the help of measuring of intensity of optical absorption or line displacement in X-ray ranges of irradiated materials from the temperature of further post-radiational annealing.
Nowadays the offered method has found its successful application for defining conditions of internal reactor radiation of materials in material research assemblies in fast power reactors (for example, BN-600). The measurings have confirmed the possibility and reliability of definition of radiation temperature with the help of ceramic monitors.
Dr. Phys.-Math.Sci., Professor V.M. Chernov said about the plans of the Department of Physics of extreme states of matter: “We plan to additionally verify the method of detection of neutron doses of material radiation with the help of measuring of concentration (burnout) of B-10 isotope in monitors of temperatures on the basis of BN, giving them additional function of dose monitors”.
