Monday, 27 May 2013 18:49

Innovative welding solutions for the Nuclear Industry

polycar torchThe design and manufacturing of welding equipment for nuclear power production is one activity among Polysoude’s wide range of applications. In this field, the company is involved from the first stage up to the very end.

Enrichment

Most of the piping must be installed and joined directly inside the plant under construction, which means restricted access to the welding areas and the necessity of all-position welding. These conditions are perfectly met by the orbital welding equipment. Mobile power sources are adapted to the harsh on-site conditions including humidity and unstable energy supply; with open orbital welding heads and low profile open carriage-type welding heads.

Nuclear fuel fabrication

The final processing of enriched solid uranium hexafluoride (UF6) is carried out in nuclear fuel fabrication facilities.

The thin-walled tubes which are used to produce these rods usually consist of a zirconium alloy. The extremities of the tubes are sealed gas-tight by means of welded end caps. The weld is carried out without the addition of filler wire.

Nuclear power plant

The components of the primary cooling circuit of a nuclear power plant belong to the Nuclear Island. The welding of the heavy components is carried out as far as possible during prefabrication in a workshop using stationary welding equipment. For example, the core barrel is placed on a turntable and rotates during the weld operation; two welding torches are installed opposite on column and boom devices and weld simultaneously. Narrow gap welding equipment and control devices for the synchronisation of the weld cycle and the different movements are designed and manufactured by Polysoude.

The inner surfaces of the reactor vessel and the steam generators are protected against the corrosive attack of the coolant by a resistant layer, the important surfaces are commonly coated in an economical manner by strip cladding.

Special attention needs to be paid to the construction of the reactor vessel head. In particular, the top and bottom parts are complex components with numerous nozzles for control instruments and the Control Rod Drive Mechanism (CRDM).

To connect one of the four CDRM tubes, in the first step carbon steel is welded on the outside of the vessel head until a flat circular surface is attained. During the second step a circular cladding operation with low alloy steel wire is carried out until the specified height of the stud is reached. During all operations none of the welds are in contact with the coolant and all carbon steel surfaces are protected.

The central element of modern steam turbines, the rotor with a length of up to 20 metres and a weight of up to 350 tons. To complete the heterogeneous joint, the rotor segments are super positioned and the buttered sides are then welded together using the TIG hot wire narrow gap technique.

Maintenance and repair

Preventive maintenance and professionally carried out repairs are essential for the safe and sustainable operation of nuclear power plants. The improved design of delicate constructions, helps to avoid unscheduled downtime. Mechanised, remotely operated welding equipment allows respect of the specified procedures and helps to maintain the man-rem exposure of the repair personnel at a low level.

Recycling of used fuel and sustainable nuclear waste disposal

Polysoude is involved in the development of methods to seal the huge transport canisters lastingly using specific welding procedures.

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