The surveys of the bearing and enclosing civil structures damaged after the Chornobyl Unit 4 accident that were conducted by the State Research Institute of Building Structures and Institute for Safety Problems of Nuclear Power Plants from 1995 to 2012 showed that a number of structures were in unstable condition. They include a group of structures that are especially dangerous in terms of the bearing capacity and are very likely to collapse. To ensure safe operation, immediate stabilization measures were developed and successfully implemented at the Shelter in 2005—2008. The justifying calculations show that the structures will comply with nuclear and radiation safety requirements (in terms of stability, bearing capacity etc.) over 15 years. The most unstable structures have to be dismantled by 2023, which is one of the conditions in the strategic plan for further transformation of the Shelter into a safe system. Two stages of safety measures have been defined for the unstable structures to be dismantled. The functional purpose of and climatic impacts on the bearing structures and, as a consequence, the Shelter lifetime are subject to change after stabilization of the unstable structures and installation of the New Safe Confinement (NSC) into the designed position. The paper analyzes scenarios for dismantling of unstable structures, stabilization measures and the probability of failure after implementation of the stabilization measures. A list of structures subject to early and deferred dismantling is provided. Shelter safety criteria and radiation protection objectives are considered.
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