Abstract
This article presents the development and application of a modelling approach based on quantities obtained from mechanical and electrical tests to assess the aging of low voltage cable insulation for nuclear applications. In order to obtain experimental data needed for the establishing of the models, accelerated aging is performed on coaxial cables. The first part of this paper focuses on the development of a predictive modelling for mechanical properties; this allows the evaluation of the Dose to Equivalent Damage (DED) as a function of the aging stress (dose rate). However, the use of mechanical tests for cable aging assessment presents some problems, being such tests destructive for the insulation and potentially affected by local defects. The novelty of this work lays on the introduction of a new model, allowing the definition of the end-of-life point in terms of electrical non-destructive tests. The second part of this article presents the development of aging modelling of cable insulation and correlation with experimental data obtained at different stresses, which allow the estimation of the expected life of the cable under test to be derived from diagnostic measurements of electrical properties like, e.g, tan δ. Finally, the application of the proposed life model to two typical real-condition nuclear environments is presented and discussed.
Highlights
Current nuclear power plants (NPPs) were mainly built during the ‘70s and ‘80s and, since their designed life is supposed to be about 40 years, they are approaching their designed end-of-life [1,2,3,4]
In this article, the modelling of the mechanical and electrical response, together with an aging modelling approach, has been presented and discussed for LV cables used in nuclear environment
First focus has been paid on a life predictive modelling of mechanical quantities, from which Dose to Equivalent Damage (DED) values has been obtained as a function of dose rate
Summary
Current nuclear power plants (NPPs) were mainly built during the ‘70s and ‘80s and, since their designed life is supposed to be about 40 years, they are approaching their designed end-of-life [1,2,3,4]. For this reason, nowadays, the chosen end-of-life criterion is usually based on mechanical tests and, on EaB, which must be higher than 50%, in order to guarantee the delivering of communication of data signals and the equipment power supplying in case of accidental conditions. The reason for that could be related to the fact that high dose rates bring to abrupt variation of the absorbed dose with little variations of the mechanical response, resulting into higher DED values This method permits the evaluation of polymer behavior with aging at very low dose rates. Once DED values are obtained through the method described in Section III.A, it is possible to graphically acquire the tanδ end-of-life points, providing the values of dielectric losses corresponding to the material failure.
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