Thesis presented October 30, 2018

Abstract:
Biotechnology with microorganisms able to survive high radiation doses and concentrate radionuclides is an attractive technology to decontaminate nuclear effluents with low waste volume. By using two direct and complementary analysis methods, metagenetics and metaproteomics, the complete inventories of microorganisms present in a French nuclear reactor cooling pool (during operation and at shutdown) and in a radioactive ⁶⁰Co sources storage pool have been performed. The microbiota from the two pools were extremely different, with a majority of Cyanobacteria in the sources storage pool, and Proteobacteria in the reactor pool. Depending on the pools’ conditions a change in the microbiota had been observed. Variovorax was the main genus identified during the reactor’s operation. Some strains of Variovorax are able to use H₂ as an energy source, conferring them an advantage in nuclear pools. Several microorganisms have been isolated from the reactor pool. Among them 46 bacteria were identified. Their abilities to resist ionizing radiations and to accumulate specific radionuclides were determined. Several genera studied in this work had never been described concerning their ability to resist radiations or accumulate radionuclides. Six strains could entirely remove uranium from a 5 μM solution and up to 50 μM for two strains. This work presents the first complete inventory of a working nuclear reactor cooling pool. This PhD work opens interesting industrial perspectives as the isolated strains could be implemented in a new nuclear effluents decontamination process and fundamental perspectives as their resistance and radionuclides accumulation pathways could be deciphered.

Keywords:
Microorganisms, nuclear facilities pools, radionuclides

On-line thesis.