Assessment of the reliability of a concrete cask shell of the dry storage of the spent nuclear fuel

Abstract

Exploitation of NPP is accompanied by the accumulation of spent nuclear fuel, which is classified as highly active nuclear wastes. Application of modern technologies of dry long term storage of fuel in the conditions of NPP requires the estimations of reliability of equipment, in particular, sealed basket shell from the point of view of their degradation in course of time. Research aim is to consider possibility of probabilistic estimation of reliability of concrete shell of the cask for dry storage of spent nuclear fuel. Storage of spent nuclear fuel envisages creation of depositories of long term storage. Nuclear fuel storage is examined as nuclear installation and on the Law of Ukraine “About use of nuclear energy and radiation safety” needs estimation of his reliability on all term of exploitation, duration of that must be no less 50 years. Implementation of such estimation maybe based on construction of flow diagram of elements of flowsheet and them probabilistic calculations. Research is built on the analysis of structural features of elements of equipment, probabilistic calculations of reliability of construction on the whole and comparing of them to the state of equipment that worked a certain term. A calculated lifetime of
the ventilated cask has been fulfilled, taking into account the conditions of its operation, has proved that it does not exceed 33 years. The visual and approximate assessment of the surface of the concrete of the cask shell for different storage term showed that during the storage period of 7...9 years, there is a significant cracking that exceeds a similar figure of natural breeds in 3...5 times. The dependence of the reliability of the shell on the completeness of the construction of the functional structural scheme, as well as on the possibility of a calculated estimation of the period of reliable operation of the cask shell is proved. We observed degradation of the surface of the casks shells for a period less than the estimated. The reference value of reliability of concrete shell of the ventilated cask is calculated. Violation of superficial monolithic nature of concrete shell is appraised depending on shelf-life to the spent nuclear fuel cask. Expediency of systematic reviews and modernisation is well-proven with the surfaces of shells.