Durability of Concrete in French Nuclear Power Plants

Concrete is the most widely used construction material in the world. This material is combined with passive reinforcements (reinforcement) and sometimes active reinforcements (prestressing tendons). The composite material thus formed can be used to build resistant structures with complex shapes, making it the material of choice for construction.

This material is widely used in the nuclear industry, both in nuclear power plants and downstream of the fuel cycle for nuclear waste storage.

The basic components of concrete are water, cement and aggregates of various sizes (sand, pebbles). The aggregates used are generally local, due to transport costs. As a result, formulations are not homogeneous either in time or space. Every concrete is different.

What's more, each concrete structure is exposed to different environmental conditions, depending on whether it's in a hotter or cooler region, more or less humid, by the sea, subject to frost and de-icing salts, and in contact with different types of soil.

Assessing the service life of concrete structures is therefore a difficult task, requiring an overall view of the pathologies and physical phenomena that can affect concrete, and of the loads (mechanical and environmental) imposed on a given structure.

Finally, in the nuclear context, some of the concrete structures that make up a nuclear power plant play an important role in safety. In addition to the economic impact of plant unavailability, failure of these structures would have consequences for the risk of radioactive releases into the environment in the event of an accident. This is the case, for example, with containment structures.

As a result, nuclear operators are studying the pathologies affecting the concrete of their structures, so as to be able to assess the residual lifespan of structures, and the appropriate maintenance operations to extend that lifespan.

This article begins by presenting the concrete structures for which durability issues have been identified and studied, such as containment vessels, cooling towers, fuel storage pools, reinforced concrete pipelines, water intake structures and vessel shafts. For each of these structures, the relevant ageing mechanisms are briefly described.

Secondly, the material concrete is presented in greater detail: the main characteristics of its constituents, in particular cement, are explained, as well as the principle of the hydration reaction which enables concrete to harden when cement is placed in the presence of water. Metallic materials frequently used in conjunction with concrete, such as reinforcing bars, prestressing tendons and metal liners, are also described....