Abstract
The impact of an aircraft is widely known to be one of the worst events that can occur during the operation of a plant (classified for this reason as beyond design). This can become much more catastrophic and lead to the loss of strength of/collapse of the structures when it occurs in the presence of ageing (degradation and alteration) materials. Therefore, since the performance of all plant components may be affected by ageing, there is a need to evaluate the effect that aged components have on system performance and plant safety. This study addresses the numerical simulation of an aged Nuclear Power Plant (NPP) subjected to a military aircraft impact. The effects of impact velocity, direction, and location were investigated together with the more unfavorable conditions to be expected for the plant. The modelling method was also validated based on the results obtained from the experiments of Sugano et al., 1993. Non-linear analyses by means of finite element (FE) MARC code allowed us to simulate the performance of the reinforced concrete containment building and its impact on plant availability and reliability. The results showed that ageing increases a plant’s propensity to suffer damage. The damage at the impact area was confirmed to be dependent on the type of aircraft involved and the target wall thickness. The greater the degradation of the materials, the lower the residual resistance capacity, and the greater the risk of wall perforation.
Highlights
Impact Effects on an Aged Nuclear Power Plant (NPP).The need to investigate the effects caused by an aircraft impact on nuclear installation [1,2,3]) is of primary importance and assumes further importance for existing plants that have undergone ageing phenomena or for which an extension of operation (or long-term operation (LTO)) is expected.Ageing could become an Achilles’ heel for the resistance capacity of structures in such severe accident conditions
The plant ages too; this means that the cumulative effects of ageing and obsolescence on the safety of nuclear power plants must be re-evaluated periodically to verify that the performances of the single components and the whole plant are within acceptable limits
A proper analysis has to be performed to ensure that the effects of ageing will not prevent structures, systems, and components (SSCs) from being able to accomplish their required safety functions
Summary
The effects of physical ageing, degrading SSC performance, and non-physical ageing (their obsolescence) have to be considered in safety assessments. As for the latter point, it is important to remark that obsolescence occurs when nuclear equipment becomes out of date in comparison with current codes, requirements, regulations, and technology. An assessment of the plant reliability—in whole or in part—that accounts for ageing degradation is necessary to determine the point in time where profitable operation is no longer possible (IAEA, 2018) This will help defining the optimum preconditions for achieving safe long-term operation (LTO) and Materials 2021, 14, 816. The method to approach aircraft impact is described at length in [2]
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