Hard chemical decontamination of steam generator tube bundles

Abstract

The work presented here concerns hard chemical decontamination of steam generator (SG) tube bundles removed from service subsequent to SG replacement operations. The aim of the program is to undertake an SG tube bundle decontamination operation that will facilitate the dismantling of an SG removed from service. The proposed decontamination method associates a combination of nitric acid and cerium nitrate, with regeneration of the Ce 3+ into Ce 4+, by injecting ozone into the decontamination solution during the operation. Decontamination is effected at low pH and at room temperature. The activity removed from the SG tube bundles is transferred into the decontamination solution, dryed, and immobilized in a solid, coated form for storage. The program goals are to obtain a high decontamination factor (DF > 1000) on the Inconel 600 SG tube material and to reduce the volume of the resulting secondary radwastes. This paper presents the results already obtained during the pilot decontamination of a regenerative heat exchanger at the Tricastin nuclear power plant and the approach that will be applied for decontaminating full-size steam generators in Sweden and France.