MASTER ASSIGNMENT
Project background:
Nuclear Power Plants and research reactors built during the mid-20th century require ageing management including a comprehensive set of material characteristics of their concrete structures. This is the basis for demonstrating safety during life extension projects or when specific modelling is necessary for portions of the plant when design regulations have been updated with new or revised requirements.
NRG has performed ongoing research to address this subject, which includes;
- Gathering of international information on civil structures’ ageing issues and management thereof.
- Testing of a proposed assessment methodology by application to a nuclear reactor and comparison with comparable PWR with a steel containment. Creating plant-specific Ageing Management Programs dealing with the relevant mechanisms at the various locations relating possible relevant locations with measures to be taken for ageing management.
- Developing damage modelling in concrete structures of a reactor due to ageing mechanisms, focusing on the material behaviour of structural concrete and practical assessment in finite element modelling techniques.
Current work:
In the most recent work of this ongoing research, a chlorine ingress model, calibrated to data obtained from a reactor chimney, was determined that allows for the rebar reduction to be calculated. The diffusion model was based on Fick’s Law.
Furthermore, the design properties of concrete were determined in line with NEN-EN 1992-1-1:2004 and NEN-EN 1990. The material properties and reduced rebar diameter were used to re-evaluate the FEA model developed to assess the impact of a large mass (transport container) on the HFR floor due to a handling mishap.
The altered material properties and reduced rebar diameter are displayed below together, with the revised FEA visual results.
Future work:
The foremost aim is to be capable of conservatively and realistically modelling reinforced concrete with the possible effects of ageing and degradation having been considered. The current work allows for an accurate FEA model that considers the degradation due to rebar corrosion through the reduction of material properties and rebar diameter.
It was noted that the chloride ingress model is strongly influenced by the surface chloride concentration and w/c ratio for concrete and that it is vital to have more accurate information on the actual w/c ratio of the concrete in question and a better understanding of the chloride concentration levels. It is evident from the modelling that it is crucial to have accurate material properties as the changes in material strength and modelled rebar diameter can significantly impact the FEA results. A lower concrete strength with reduced rebar will allow for a first conservative model that can be used to justify safety if the analysis results demonstrate that the modelled concrete meets the design requirements.
Further work is required to allow for the modelling of rebar corrosion within the concrete to predict internal pressure generation and possible delamination. Additionally, a suitable method to model the loss of bond between the concrete material and the reinforcement is required as it will likely influence the concrete's structural capacity.
Your contribution:
In the Masters project you will predict and model ageing of the concrete, which will contribute to the safe operation of our research reactors (producing medical isotopes for 30.000 patients a day:www.30000perdag.nl) and power reactors to keep the energy sustainable and available for future generations.
Contact persons:
