Primary and Secondary Circuits of French Nuclear Power Plant Chemistry

France's nuclear fleet comprises 58 PWR (pressurized water reactor) units, with electrical outputs ranging from 900 to 1,450 MWe, spread over 19 sites.

The operating life of a PWR-type nuclear unit, summarized in a box (§ 1 ), is reviewed every 10 years. It is currently estimated at 40 years. In order to estimate this lifespan, it is necessary to know the main modes of degradation of reactor components from the outset, and to ensure that they are maintained in good working order or replaced whenever possible. Corrosion phenomena in the metal parts of the primary and secondary circuits are responsible for most of the damage observed. In addition to the direct effects of corrosion on materials (risk of cracking, embrittlement, loss of mass), there are indirect effects which contribute to the appearance of phenomena in which the corrosion products released are responsible for deposits in sensitive areas, fouling and clogging of steam generators (SGs) on the secondary side, and are also the source of radioactivity deposited in the primary circuit.

To control the various phenomena, several levers of action are necessary. Whether it's the continuous improvement of component manufacturing processes, or optimized operating modes, the choice of the right chemistry is ultimately one of the main tools for keeping circuit components in good condition. As water is the main carrier of elements in solution, controlling chemical parameters during all phases of operation helps to control most degradation phenomena.

More recently, developments in the chemical industry have had to take into account the various issues raised by the TSN law, codified in the French Environment Code, which places the various interests protected by the law (safety, radiation protection, environmental protection, health and safety) on an equal footing.

The first part of the article is devoted to the primary circuit and the second to the secondary circuit of French PWR power plants. In each part, the main degradation modes and associated issues are presented, followed by the choice of chemical conditioning for each circuit. Finally, new avenues for optimization are proposed.