ABSTRACT
Sizewell C nuclear power station is currently in the development phase. EDF as designer of this project is in charge of the cooling seawater circuit design.
The cooling system is similar to the Hinkley Point C project and comprises of 3 offshore tunnels: 2 intake and 1 outfall tunnels. These hydraulics tunnels are subject to specific loadings due to the operation of the nuclear power plant.
Pre-dimensioning studies of the tunnels in particular for the design of the concrete segments were carried out by Tractebel. The difficulties identified during the structural design of the hydraulic tunnels at the Concept Design stage are mainly linked to the ground conditions in which the tunnels are positioned, the internal pressure in the cooling circuit and the objective to be perfectly watertight.
In fact, the tunnel cross section is composed of a ring of segments and not a continuous structure. Due to this configuration, the relative pressure applied at the intrados can lead to an opening at the weak points of the structure, usually the joints. Hence, verification shall be made focusing on the capacity of the joint equipped with gaskets to stay water tight under the worst combination of loads .
This article presents the studies carried out by Tractebel to determine the admissible relative pressure for hydraulic tunnels lined with concrete segments, beyond which the tightness of the concrete segment joints -equipped with gaskets - or the structural strength may not be maintained. Several sensitivity analyzes were carried out taking into account different parameters as deconfinement rate, internal pressure, three-dimensional effect, etc.
