51314-3984-Assessing Feasibility of Cathodic Protection for Nuclear Containment Liner

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Product Number: 51314-3984-SG

ISBN: 3984 2014 CP

Author: Joseph Fernandez

Publication Date: 2014

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Localized macrocell-aggravated corrosion of the nuclear reactor containment steel liners has taken place due to embedded foreign material in the concrete shell. Cathodic protection (CP) with externally placed anodes has been considered as a remedial measure but it is not known to what extent the presence of other embedded reinforcement may electrochemically shield the liner surface and lower the achievable protection. Finite element numerical modeling of the system was conducted to assess the feasibility of effective CP under those conditions. The model calculated as function of system parameters the potential and oxygen concentration distributions in a region approximating the macrocell conditions. The anodic current density (and therefore corrosion rate) can be derived from the integration of the output. The calculations were then extended by incorporating an external anode that delivered protective current as in a typical impressed current arrangement. The output in the form of the corrosion rate before and after protection was computed for a range of likely concrete parameters that included oxygen diffusivity and resistitivity amount of reinforcement as well as for a range of steel and anode polarization variables and of applied protective current density. The results indicated that under selected plausible circumstances CP may be a viable method of controlling liner corrosion. The relative improvements where the corrosion rate at the affected zone was lowered by a factor of about 100 were achieved in an envelope of conditions that included concrete oxygen diffusivity about 1.0E-8 m2/sec resistivity ~ 100 Ohm-m and a steel placement density ~ 1 m2 of steel per m3 of concrete.Impact of the findings could be significant. Determining the issues that need to be dealt with for cathodic protection practicality could allow design changes to current and new nuclear power plants to help implement CP.