In addition to its interventions in the sectors of chemistry and pharmacy, Ducroux is also, as a special industrial valves manufacturer, invested in the research and development of a comprehensive range of devices for application to liquid sodium, sought by the nuclear industry.
The liquid sodium is used in nuclear reactors of fourth generation because it has several advantages: it does not slow down the neutrons (reactors are so-called "fast neutrons"), it is a very good heat transfer, and it remains liquid between 98°C and 890°C.
This technology of sodium cooled reactors has emerged in the 70’s with several projects in France (Rhapsody in 1967 and Phoenix in 1973, developed by the Commissariat à l'Energie Atomique), and another industrial prototype called Superphénix, developed in 1985 by a Franco-Germano-Italian consortium, before meeting a slowdown between 1997 and 2007.
Ducroux participated in development of this sector in its area of expertise: the special valves. Since the late 60’s and until 2009, the company supplied more than a thousand valves for loop tests at the CEA in France, but also for South Korea (KAERI) and India (IGCAR). These valves have been developed and designed to run on sodium to a temperature of 550°C; temperature which is reached at the output of the heart of the reactors of this sector.
Ducroux also provided valves for the Superphenix prototype reactor, including all of the valves of DN equal to or less than 40mm (more than 300 devices).
Two technologies exist for this very special application that is liquid sodium.
The first is called the solidified gasket. It is an adaptation from high temperature valves with cooled packing gland. The principle is simple and ingenious: the liquid sodium fits in a space provided between the stem and an extended bonnet. It is cooled by fins arranged on the bonnet until solidification when the temperature drops below 98°C. The seal so created guaranties tightness and allows the opening / closing of the valve through a very particular specification of the control stem. A packing gland with multiple O-rings provides a safety function.
The bellow valvesThe second technology used is the bellow valves. A metal bellow (Inconel, 316Ti, Hastelloy ...) is welded on the low side of the stem and under the bonnet. It completely isolates the gland packing from the fluid, ensuring a perfect safety.
Each technology has its advantages and disadvantages. The technique is simple in solidified gasket, has no wearing parts, but imposes significant sodium purity to prevent crystallization along the control stem. The bellow valves technology doesn’t have those defaults, but the bellow is a wearing part and a sufficient temperature (150 ° F minimum) must be ensured to operate the valves.
Each technology can be provided in on/off valves or in control valves (for this last case, we will prefer the bellow technology), operated manually or by pneumatic actuators.
Under the revival of the sector (objective of an industrial demonstrator Astrid 2020), the CEA charges Reg Technology, through its range of valves Ducroux, to improve the design of those sodium valves. The objectives are multiple: save space, cost, and dependability.
This 3-year project should result in the birth of a new generation of valves or in an improved technology to optimize the current valves by the addition of a new manufacturing process.