Session: OAC-07-01 OAC Ageing and Plant Life Management

Paper Number: 122236

122236 - Concrete Cracking Modelling Due to Reinforcement Bar Corrision 

NPPs and research reactors built during the mid-20^th century often have incomprehensive material characteristics for their concrete structures. This lack of quality records frequently leads to challenges when attempting to demonstrate safety during life extension projects or when specific modelling is necessary for portions of the plant when design regulations are updated with new or revised requirements.

In the framework of long-term operation, there is limited knowledge about ageing and the structural integrity of concrete structures. In order to increase the knowledge in the field of civil structures, this paper focuses on investigating the ageing mechanisms of civil structures at NRG, Petten, and using the previously calibrated chloride ingress model (PVP2023-105650) to determine expected internal pressure generation due to rebar corrosion within a FEA model to predict concrete cracking.

 In the most recent paper, PVP2023-105650, the modelling of ageing effects has been investigated by reduction of material strength properties and the development of a chloride ingress model calibrated to the HFR chimney. The model allows the predictions of rebar diameter reduction and internal pressure generation due to rust production. The FEA model developed under PVP2022-84008 was altered considering the reduced material properties and rebar diameter to gain a better insight into how it affected the determined concrete damage under a heavy drop impact.

The purpose of this research paper is to better understand the effect of internal pressure generation due to rust production and to allow the simulation of crack generation due to this degradation mechanism. The model has been calibrated to the results obtained from the HFR chimney. It is seen through the FEA simulation generated in Ansys that there is a close correlation to reality when modelling the calculated internal pressures using the chloride ingress model previously developed. The model is limited in its scope to the HFR chimney where the concrete information was obtained. Furthermore, the model has to be recalibrated for each time period as the contact stiffness varies over time. The modelling method is also sensitive to a reduction of mesh size which is contrary to the majority of FEA models.

In the future, core samples of affected HFR areas should be taken to determine the chloride concentration and rebar corrosion. This can allow for more data points for model calibration when simulating concrete cracking due to rebar corrosion.

Keywords: civil ageing management, long-term operation, chloride ingress model, concrete characteristics, concrete properties, concrete assessment criteria.

Presenting Author: Wesley Jarvis NRG

Presenting Author Biography: Wesley Jarvis is a South African Civil Engineer who has been working the Nuclear environment for 10 years. He began his career at the South African Nuclear Energy Corporation (Necsa) and now works at Nuclear Research and Consultancy Group (NRG). He has worked predominantly on structures with a focus on seismic engineering.

Authors:

Wesley Jarvis NRG
Kelvin Browning NRG
f.h.e. De Haan - De Wilde NRG