Surgénération

Résumé

La surgénération ou surrégénération est la capacité d'un réacteur nucléaire à produire plus d'isotopes fissiles qu'il n'en consomme, en transmutant des isotopes fertiles en isotopes fissiles. Le seul isotope fissile disponible en tant que ressource naturelle sur Terre est l'uranium 235, directement exploitable dans le cycle du combustible nucléaire. La surgénération permet théoriquement de valoriser en tant que combustible nucléaire l'ensemble des matières fertiles tels l'uranium 238, qui représente plus de 99 % de l'uranium naturel, et le thorium, lui-même trois fois plus abondant que l'uranium. Historique vignette|Enrico Fermi. Le concept de surgénérateur a été développé dès les débuts de l'énergie nucléaire. Aux États-Unis, Enrico Fermi propose le concept de surgénérateur dès 1945, et en 1946 est construit le petit réacteur rapide américain Clementine (refroidi au mercure). En 1951 se produit la première réaction nucléaire du premier réacteur américain refroidi au sodiu

Source officielle

https://fr.wikipedia.org/wiki/Surg%C3%A9n%C3%A9ration

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The general license application (RBG) for the Swiss deep geological repository will be submitted in 2024. Furthermore, the decommissioning of the nuclear power plants (NPPs) is coming soon, with the Mühleberg NPP (KKM) scheduled to shut down in 2019. In support of the associated analyses and planning, availability of accurate descriptions of the nuclear waste streams is of paramount importance. The work described in this thesis represents a significant improvement of Nagra's most important radioactive waste characterization methodologies: for spent fuel, NPP decommissioning waste, and reactor waste. The resulting high-fidelity nuclide inventories will decisively support the future waste disposal research and development, as well as serve the NPP decommissioning planning in general. The spent fuel characterization demonstrated is based on Polaris. This approach is compared against the code sequence used in the industry (Studsvik CMS), in order to confirm that, when the necessary fuel data is available, either one of these codes can be used to provide detailed nuclide vector for the spent fuel. Afterwards, possible ways to produce the desired nuclide vectors in the future are identified. For decommissioning waste, every step of the old characterization methodology has been further developed and improved upon. This includes a new, detailed, fully three-dimensional approach to NPP modeling and the development of a new activation sequence (based on the ORIGEN depletion solver), which outputs a highly-resolved component-wise activation distribution and visualization. Additionally, the methodology is extended to apply the method's results for algorithm-optimized packaging concepts and waste volume minimization through decay storage and free release analyses. At the end, recommendations for the future improvements are presented. The decommissioning waste characterization methodology is then expanded to accommodate reactor waste, and the more complex nature of the non-stationary components of this waste stream (such as the control rods). A systematic general approach, based additionally on the component dose rate measurements, allows for a more efficient and flexible characterization of all reactor waste. These developments serve as an important foundation in the ongoing transition from a conservative approach towards a best-estimate plus uncertainty (BEPU) waste characterization, which is vital for accurate safety analysis studies, as well as waste and cost minimization. The results produced by these methodologies will form the basis for the next version of MIRAM (the Swiss Model Inventory of Radioactive Materials), MIRAM2020, which is to be used for the RBG. They will also be used as part of the next Swiss NPP decommissioning cost study, KS2021. At the same time, the obtained results are already being provided to the Swiss NPPs planning their decommissioning, specifically KKM and Beznau (KKB), allowing detailed component-wise segmentation strategies and packaging concepts decision making, finally leading to notable cost reduction for the utilities.

EPFL2019

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Aqueous effluent treatment system

Lionel Bertschy, Frédéric Edouard Juillard, Jeremy Luterbacher, Gaël Peng

Aqueous effluent treatment system (2) including a separation reactor (4) having a reactor chamber fluidly connected to an aqueous effluent source (3), connected via a pump (5) to an inlet (34) of the reactor chamber, a fluid extraction system (6) connected to a liquid effluent outlet (38) at a top of the reactor chamber, and a solid residue extraction system (8) connected to a solid residue outlet (36) at a bottom of the reactor chamber. The separation reactor is operable to generate pressures exceeding 22 MPa and temperatures exceeding 300°C in the reactor chamber configured to generate a supercritical zone (40) in an upper portion of the reactor chamber to which the liquid effluent outlet (38) is connected, and a subcritical zone (42) in a lower portion of the chamber within the reactor chamber to which the solid residue outlet (36) is connected. The solid residue extraction system comprises an output circuit (10) comprising a collector (18) coupled to the solid residue outlet via a collector input valve (V1) and to a water output tank (32) via a filter (26) and a collector liquid output valve (V4) operable to be opened to cause a pressure drop at the solid residue outlet to draw solid residue out of the reactor chamber, the solid residue extraction system further comprising a gas feed circuit (14) connected via a gas supply valve (V5) to the collector, the gas supply valve operable to be opened to extract solid residues in the collector to a solids output tank (20) connected to the collector via a collector solids output valve (V6) .

2020

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A new calculational scheme has been developed for the accurate assessment of gamma heating in fast reactors, its special feature being the determination of the gamma source distribution that is formulated in a near-to-exact manner. The improved methodology, which has been implemented into the ERANOS (European Reactor Analysis Optimized System) code package, is currently validated for Puburning configurations, for which gamma-heating target accuracies are particularly high. This has been accomplished through comparisons with new integral measurements conducted at the MASURCA facility, as well as with reevaluated earlier experiments. In the new measurements, absolute gamma-heating rates were determined in PuO2/UO2-fueled cores surrounded by a steel/sodium reflector, mainly using TLD-700 thermoluminescent dosimeters. Thereby, a considerable effort was undertaken to minimize systematic errors. The calculation/experiment values determined from the analysis of the critical experiments are 0.90 for the PuO2/UO2 core region, 0.84 for the steel/sodium reflector, and 0.89 for an internal steel/sodium diluent zone. The most plausible causes for the observed discrepancies have been identified to be data related, i.e., too low fission gamma energies and too low capture cross sections for the structural elements. The transferability of the current validation findings to a modified Superphenix configuration, in which the radial fertile blanket is replaced by a steel/sodium reflector, and to the 1500 MW(electric) Pu-burning CAPRA 4/94 reference design has been demonstrated.

American Nuclear Society2001

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EPFL2019