The present article is dedicated to analytical and numerical investigation of behavior of end elements of high-pressure casings for nuclear reactors. Nuclear energy generated inside the high-pressure casings will become an actual power-related choice of the human kind in the very near future. In this respect, development of methodology for proper calculation of axisymmetric plates resting against conical surface and bearing the evenly distributed load is becoming state of the art issue. In order to perform analytical calculation the authors used established concrete strength criteria and prerequisites assumed, while ANSYS WORKBENCH software package was applied to calculate the ultimate load value and stress state. Calculations were made considering a keyed connection between thick plate and load-bearing wall of the high-pressure casing and referring to considerably high, in one case, and low (variable), in the other case, plate stiffness. The article presents comparative analysis of calculation results that demonstrates calculation methods adequacy. The authors developed original methods of analytical and numerical calculations allowing to investigate stress state of end elements designed in the form of axisymmetric plates resting against conical surfaces. End elements behavior in load condition is characterized by formation of spheric vault where stress condition typical for concrete three-dimensional compression state occurs. Investigations presented show that sudden disintegration does not occur when concrete end elements are affected by cracks in the stretched area; instead, the spheric vault is formed. Strength of such spheric vault occurring in the element is rather depending upon load bearing wall stiffness, i.e. the lower the stiffness the smaller the strength and vice versa. The following scientific results have been obtained: – end elements shaped as thick axisymmetric plates in condition of ultimate load are characterized by spheric vault formation; -authors, based on assumptions and guided by approximate procedure have obtained the formula for spheric vault thickness calculation; – authors obtained original methods of analytical and numerical calculation to evaluate stress condition of high-pressure casings’ end elements shaped as thick axisymmetric plates resting against conical surface; – comparison of calculation results displays minor discepancies between analytical and numerical calculation models.