As result of accident occurred on April 26, 1986 at ChNPP Unit 4, silicate fuel melt, which solidified in the form of lava-like fuel-containing masses (FCM), originated in sub-reactor space. In their origination epicenter, in the places of deep fusion penetration in sub-reactor slab concrete, FCM clusters representing nuclear hazard (NHC), were localized. The objective of current work was to estimate the characteristics of NHC material environment as a product of corium with concrete interaction (MCCI) that is typical for the aftermath of NPP severe accidents with escape of core melt materials in sub-reactor space. There was an assumption that corium formation, under heat transfer crisis, begins from uranium dioxide melting in over-heated pellet part inside fuel element shells. Dilution in melt of zirconium and zirconium dioxide produces UO2-Zr-ZrO2 initial system. The estimate of physical characteristics of corium being diluted at the MCCI start by negligible amount of steel structures iron was carried out with using well-known model of multi-component solution with considering functional dependence of temperature of melt liquid components’ density. Geometrical and physical characteristics of MCCI end product (corium diluted by concrete degradation products) were calculated for several options differing in initial corium composition and initial MCCI temperature. Element content of NHC silicate matrix was estimated under condition of availability in their content of uranium with 45 - 55 % mass share. Timeframes were indentified of their origination in the places of deep fusion penetration in sub-reactor slab concrete. The results obtained in this work were compared with published data, including those previously used in model calculations and estimates of possible consequences of self-sustaining nuclear chain reaction.
Keywords: severe accident at NPP, RBMK-1000, corium, spent nuclear fuel afterheat, MCCI products, nuclearly-hazardous clusters, fuel-containing masses.
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