Large atmospheric refrigerant collapse - Numerical simulation challenges

With the advent of new generation nuclear power plants, the dimensions of structures are constantly increasing. Natural draught cooling towers, one of the largest structures in power plants, reach heights exceeding 200 metres and their size becomes a critical factor for their installation on site. This is all the more critical for nuclear power plants, which are subject to special safety provisions. In fact, by virtue of its height, the cooling tower becomes an item of equipment that can create a significant risk in the event of collapse, either by direct impact or by generation of a significant shock wave.

Our numerical simulation engineering team collaborated with one of its oldest partners in the study of ground acceleration induced by tower collapse. The objective was to measure the spectrum of acceleration of the shock wave at the level of the nuclear island, located 300 metres from the structure.

Our teams took part in the studies carried out as part of the technical assessment of the world's largest refrigerant.

The objectives of this analysis were to:

• Quantify the shock wave resulting from the collapse of the cooling tower.
• Compare the acceleration spectra obtained with the reference response spectrum of buildings subject to nuclear security criteria.
• Validate the location of the tower, in particular the distance separating it from critical buildings or, if necessary, impose a safety distance.

With the efficient collaboration of our teams, several non-linear dynamic analyses, requiring significant computer resources, were carried out using the finite element method and an explicit solver. The purpose of these numerical simulations was to numerically determine the maximum amplitudes of the shock waves generated by the collapse of the tower.