Continuous temperature monitoring at periphery of nuclearly hazardous clusters (NHC) in Chernobyl NPP оbject “Ukryttya” southeast quadrant of room 305/2 was being carried out from November 1988 to 2015 with using “Finish” Information and Measurement System. During previous years, some attempts were made to analyze accumulated databank and to assess the parameters of heat source concentrated within NHC area. The creation of New Safe Confinement (NSC) of ChNPP Unit 4 has made prerequisites for changes in temperature-humidity regime within the оbject “Ukryttya”, and, consequently, in NHC status. This work was carried out in order to clarify earlier conclusions concerning regularities of thermal regime formation around the NHC until NSC creation. This work was aimed at creating initial dataset for further evaluation of NH state within NSC conditions. The methods of statistical analysis of data on temperature of sub-reactor slab (elevations +8.00 - +9.30) were used, in reactor shaft (elevation limits. The research period has covered the time interval from November 1988 before December 2015. To make a comparative analysis of time dependences of concrete temperature at different distances from NHC boundaries, mean annual values were given (normalized) to the values calculated for 1991 year. Analogously normalized data for temporary characterization of fuel afterheat and environmental mean annual temperature values were overlapped on obtained picture. The results obtained in this work made it possible creating an integral picture of temperature dynamics at different distances from NHC boundaries in room 305/2 during survey period from 1991 to 2015 years. Earlier obtained values of temperature gradients and its change’s trends at NHC periphery, which were observed before the NSC was installed in its design position, were refined. More accurate data were obtained on degree of impact of additional internal heat source onto total heat release from the NHC area (not more than 0.071 kW/t of uranium in 2016 year) and uranium mass concentrated in deep burn-through place of sub-reactor slab (up to 18 ± 5 tons). Based on the data obtained and design value of spent nuclear fuel afterheat (0.208 kW/t), total rate of heat source hidden under the layers of black lava-like fuel-containing masses and 1986 year concrete in southeast quadrant of room 305/2 was estimated at 5.1 ± 1.4 kW/h (as of November 2016).
Keywords: accident at the Chernobyl NPP, fuel-containing mass, nuclearly hazardous clusters, temperature, heat sources, residual afterheat.
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