Outside of the reactor building, six boilers (heat exchangers) have been installed during the operation period. Such devices were intended to transfer heat from carbon dioxide to water, and, therefore, generate the steam to move the turbines and produce electric energy.
Between 2019 and 2020, some preliminary activities for the demolition of boilers will be conducted. Among these, the most important demolishing the concrete panels, located outside the reactor building, which insulate the upper pipes of the primary circuit.
The panels to be dismantled consist of 2 concrete elements each: the upper horizontal element, with a weight of 126 tonnes, and the lower vertical element, weighing 51 tonnes. Both elements are placed at a height of 40 metres. The demolition operations planned for these elements will produce a negligible quantity of radioactive waste.
The technique of “controlled crushing” will be adopted for the dismantling, and the panels will be cut in smaller concrete blocks to ensure their safe handling.
This technique was selected for its low environmental impacts, both in terms of industrial powders and structure vibrations; moreover, it is the most appropriate technique for works at height.
Subsequently, between 2020 and 2023, the six boilers will be demolished, thus, significantly reducing the volume of the plant and the shape of the reactor building.
For the cutting operations on boilers, among several techniques, the diamond wire cutting was selected; this technique simultaneously allows the cutting of the boiler internal components (tie rods, spacers, shelves, steel sheets etc.), which are not reachable through hot cutting techniques.
The decommissioning project involves cutting the boiler in 9 parts: 2 caps and 7 sections containing the “tube bundles” of the systems used for the thermal exchange from carbon dioxide to water and the production of steam.
The top-down cutting operation will be implemented through a bridge crane and a specifically-created cutting device able to shift vertically along the boiler. The whole working area will be protected and statically confined from the weather by a set of panels, and it will be maintained slightly under pressure compared to the external environment, thus avoiding external dispersions.
After cutting, the parts obtained will be shipped to the treatment facility to be further split and decontaminated.