Dismantling/Remediation of a Highly Contaminated Sump in Running Plant Conditions

A sump in the RPE circuit in the EDF - Nuclear Power Plant of Cruas-Meysse, showed an extremely high radiation dose rate since 2007. Different attempts to decontaminate the sump did not have the desired effect. The sump is a so-called “gatte” where two flows of different fluida circulates. A chemical flow transverses the sump within stainless steel piping, the second flow which is (contaminated) residual water, flows through this sump in contact with the sumps walls. The dose rate was estimated at 20 Sv/h, and it was presumed being a single hotspot in the dead zone of the sump, where no chemicals from the chemical decontamination attempts and no high pressure water contact had been possible, or had any effect. To protect the maintenance and exploitation people from the radiation, the sump had been protected with a physical protection system, named a sarcophagus. The client asked to leave this protection system, which was modular, on place during the dismantling works to assure its radiation protection function. The paper describes the remote controlled dismantling of the sump within the particular running conditions of the power plant, the developments made to the equipment, and the conditions in which the works had to be carried out. Some lessons learnt and particular points of attention are revealed to complete this paper.