To produce energy, the nuclear site uses a fuel placed in the reactor core. The fuel assemblies, new or used, are cooled into a nuclear pool. They are stored in storage racks of 17 or 12 tons, immersed underwater. The fuel must be unloaded all the 12 to 18 months of the reactor.
Project and constraints
On some sites, the fuel storage racks must be changed.
REEL, supplier of racks and lifting systems, developed an innovative solution that moves the unreachable racks by the auxiliary bridge. A project on which the company faced various constraints :
- use of the bridge deck for controlled horizontal movement,
- the weight of the 17-ton racks to lift facing the 2-ton footbridge,
- a water depth of 14 meters to move a rack 5 meter in height,
- surface limited to the footprint of the rack (2.5 x 2 m),
- and the radiating and contaminated environment.
The equipment that could be decontaminated, simple, and quick to deploy, with easy storage in a 20 ’IP2 container. REEL turned to us for the production of nuclear lifting cushions (inflatable balloons). Indeed, Pronal is recognized for its high-quality products which are quick to deploy.
The Pronal solution, the nuclear lifting cushions
After many exchanges, REEL and Pronal resulted in OMPB (Outillage de Manutention Par Ballon) equipment. Based on the Archimedes’ buoyancy, this innovation function thanks to our nuclear lifting cushions. 3D woven, this technicality gives them very high dimensional stability and great rigidity.
This dimensional stability was essential to avoid the balloons’ volume increasing when the rack is raised. It also allowed stacking several cushions while keeping a rigid set. Otherwise, theses cushions were usually used for heavy loads lifting like planes (see PARC).
The nuclear lifting cushions provided for the design of OMPB had for characteristics:
- a dimension of 3000 x 2040 mm for the top cushions,
- a dimension of 3000 x 1500 mm and 3000 x 1000 mm for the bottom cushions,
- PMUC tridim fabric,
- a height of 450 mm inflated (20 mm flat),
- a lifting force of 14 tonnes,
- and an inlet on the side for air supply.
The equipment thus produced, is composed of 2 plates under which 2 groups of balloons come to bear. First, the group of 3 balloons under the lower plate, keeps the tools vertical once the rudder is clamped under the rack. Then, the upper plate is detached and then lifted to tension the chains. The upper cushions are then inflated one by one starting from the upper cushion.
The first plate remains connected to the footbridge of 2 T via a spring box. This maintains a controlled load of around 300 kg. So, during lifting, it is possible to move the rack horizontally and with great precision.
Advantages and conclusion
The stability and the rigidity of our inflatable nuclear balloons allowed at the system to achieve its goals. Thank the Archimedes’ buoyancy, our inflated air balloons lifted their own weight and floated the entire system. In addition, once deflated, the cushions allowed the system to fit into an ISO 20 ‘container. In this way, it could be transferred to other sites and reused.
The concept was first validated in early 2018 in the REEL nuclear pool in Nantes, 12m deep, with a load of 17 tonnes. Later, REEL once again used it in the CETIC pool, to move 2 racks of 12-ton.
REEL’s concept received the award of the EDF Challenge Innovation, in 2019 in Paris!
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