Bugey 1 : le démantèlement du réacteur UNGG se fera sous eau
Dismantling of Bugey UNGG Reactor
1
EDF/CIDEN (France)
2
VT Nuclear Services, (United Kingdom)
EDF déconstruit actuellement 9 centrales, dont 6 de technologie Uranium Naturel-Graphite-Gaz (UNGG). Construites dans les années 60 et 70, détenues et exploitées par EDF, ce sont dans l’ordre de mise en service, Chinon A1, A2 et A3, Saint-Laurent A1 et A2 et enfin Bugey 1. Ces réacteurs sont tous définitivement arrêtés.
En 2001, EDF a décidé de démanteler complètement et sans attendre l’ensemble de ces centrales. A ce jour, les parties conventionnelles ont été globalement démolies, les parties nucléaires hors réacteur sont en cours de démantèlement, avec un avancement variable en fonction des centrales, et des études détaillées ont été menées pour le premier réacteur qui sera démantelé : Bugey 1. Viendront ensuite les réacteurs de Saint-Laurent A, enfin ceux de Chinon A.
Les méthodologies et techniques qui seront développées et mises en oeuvre sur le réacteur de Bugey 1 seront reproduites, autant que possible, sur les autres UNGG.
Abstract
Bugey 1 was the last in the line of the natural uranium fuelled, gas cooled, and graphite moderated reactors known as UNGG, to be built in France. Constructed between 1965 and 1972, it operated successfully until closure in May 1994. With an output of 540 MWe it was the largest of the fleet of UNGG reactors in France.
EDF strategy for these reactors, decided in 2001, is to achieve final stage III decommissioning, i.e. reactor vessel and internals removed, without any deferral period. Consequently EDF is moving ahead with the detailed plans for the dismantling works. Bugey 1 is intended to be the first of the UNGG reactors to be dismantled, followed by St Laurent A1-A2 and finally Chinon A1-A2-A3. The methodologies and techniques being developed for Bugey 1 are intended to be applied across the other reactors where practicable to do so.
The decision was taken that the dismantling works would be done underwater.
Following flooding the top cap of the caisson will be opened using a combination of coring and diamond wire sawing, similar to the methodology used at Fort St Vrain. A dismantling platform is installed during this operation in order to proceed to the reactor internals removal.
Following the opening of the top cap the dismantling of the reactor internals can proceed, the sequence being:
- Guide tubes,
- “Pavés de lestage” (steel bricks which sit on top of the graphite core),
- Steel links which tie the “corset” structure together,
- Graphite core, corset bricks and corset support tubes coincidentally.
After removal of the sidewall activated concrete down to approximately 3 m above the core support floor, the water level in the caisson will be lowered, and the platform lowered to just above the water level. The core support structure will then be dismantled.
Therefore it is intended to drain the caisson and perform the dismantling of all the lower internal structures manually.
The waste facilities include assay, box lidding, grouting and concrete capping. At present the intention is to grout the graphite wastes.
A new water treatment facility will be provided, located in the basement of the reactor building for treatment of the approximately 7000 cu.m. of water required to fill the reactor caisson. This water will be recirculated through filters and ion exchange equipment to maintain water clarity and to remove dissolved activity leached from the graphite. Secondary wastes from this plant will be treated in line with current practice on all other EDF operational plants in France.
© SFEN 2008