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Session Overview
3.02-3: Fast Neutron Reactors – Sodium Fast Reactors - III
Tuesday, 17/Mar/2020:
3:30pm - 5:00pm

Session Chair: Kazuya Ohgama, Japan Atomic Energy Agency, Japan
Location: L-1011

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Sketch Design of Fuel Sub-Assemblies for a SFR-150 MWe

Thierry Beck1, Victor Blanc1, Jonathan Chabassier1, Eric Deveaux1, Bruno Fontaine1, Thierry Lambert1, Benoit Perrin2

1CEA, DEN, DEC, Cadarache; 2Framatome

During the years 2018 and 2019 of the ASTRID program, a simulation program on SFRs has been prepared by the CEA and its industrial partners – EDF and Framatome – featuring sketch studies of a smaller-size SFR with extended experimental purposes. The power of the core has been reduced to 150 MWe to minimize investment costs while keeping the capacity to demonstrate the feasibility of Pu multi-recycling and to qualify designs and technologies expected for the future industrial SFRs.

These requirements led to an evolutive design for the core and the fuel sub-assemblies (S/A) over the reactor lifetime. At the beginning, the fuel pins will be similar to the one in former SuperPhénix SFR with UPuO2 fuel containing Pu from reprocessed PWR-UOX fuels. In the next step, Pu coming from reprocessed PWR-MOX fuels will be introduced. Then the concepts for the future industrial SFRs will be qualified: low void worth core, ASTRID-like large pin-small wire bundle, ODS cladding…

This paper presents sketch design studies of fuel S/A for a 150 MWe SFR at the end of 2019.

The hexagonal wrapper tube can host either a 169-SPX-type-pins bundle or 127-ASTRID-type-pins bundle. The thermomechanical behavior of the fuel bundle has been calculated with DOMAJEUR code. The lower gas plenum of the fuel pins has been reduced thanks simulations with GERMINAL fuel performance code, developed within the PLEIADES software environment, considering a nominal operation up to 87.5 dpa followed by an unprotected loss-of-flow transient. The upper neutron shielding is made of steel and B4C rings housed in a leaktight compartment to stay compatible with the washing process, while limiting the secondary sodium activation and the irradiation level of diversified absorber rods electromagnet. The overall S/A length of 4.20 m has been reduced by 30 cm compared to ASTRID-600 in the perspective of costs reduction.

Innovative Decay Heat Removal Systems in European Sodium Fast Reactor

Joel Guidez1, Antoine Gerschenfeld1, Konstantin Mikityuk2, Janos Bodi2, Enrico Girardi3, Jeremy Bittan3, Clément Bore3, Aleksander Grah4

1CEA; 2PSI; 3EdF Lab Paris-Saclay; 4JRC

A set of three decay heat removal (DHR) systems proposed for the European Sodium Fast Reactor (ESFR) concept in frame of the Horizon-2020 ESFR-SMART project is presented. The DHR capabilities of these systems are estimated using thermal calculations to verify that the proposed set corresponds to the safety rules to be respected by a Generation-IV reactor. The advantages of the proposed DHR systems are compared to other DHR systems used in SFRs. Finally, an overall assessment of ESFR DHR function is carried out.

Study of the Metal Corium Jet Impingement on the SFR Core-Catcher Material

Frédéric Payot1, Christophe Journeau1, Christophe Suteau1, Frédéric Serre1, Alexandre Lecoanet2, Michel Gradeck2, Nicolas Rimbert2, Xiaoyang Gaus-Liu3, Thomas Cron3

1CEA; 2University of Lorraine; 3KIT

Severe accidents (SA) are taken into account as early as the design phase for future sodium-cooled fast reactors. Among the mitigation processes considered for SA, there is the option of installing corium transfer tubes in the reactor core to remove the molten fuel and thus reduce its reactivity as early as possible. The objective of these tubes is to channel the UO2-PuO2-steel mixture towards a core-catcher located in the reactor vessel. Before it reaches the core catcher, the corium (T~3000°C) comes into contact with sodium (T~400°C), which causes the corium to fragment and the sodium to vaporise. If there is incomplete fragmentation of the corium jet when it exits the discharge tube, a coherent jet could induce significant ablation on the core-catcher tray due to the very high heat exchanges. The state of the art on ablation by jets shows that the protective materials would have to be very thick to protect the metal structures from the effect of the corium jets, in particular for the metallic jets. A few studies show that when the depth of the cavity created by the jet exceeds a few times its diameter, the ablation is slowed by the presence of liquid in the cavity created by the ablation of the material. This phenomenon is referred to as the "pool effect” and is currently poorly modelled. Two experimental facilities study this phenomenology in the European project ESFR-SMART:

- Water jet impingement on ice block, in HANSOLO facility at the University of Lorraine.

- Large-mass JIMEC tests, using high temperature prototypic steel impacting stainless steel block at KIT;

Two ablation regimes were evidenced throughout the jet impingement. A splashing regime was firstly identified with a constant ablation kinetics. Then, a large cavity in the block filled with liquid, “pool-effect”, was observed which reduces the ablation kinetics.

CFD and severe accidents relevant to Sodium-cooled Fast Reactors - Calculation of thermal ablation during corium-alumina interaction

Olivier Czarny, Adrien Collin de L’Hortet, Nicolas Goreaud


In a SFR design, corium relocation during a severe accident plays a significant role for the mitigation of the event ; the purpose is twofold : easing the corium heat removal, and limiting corium reactivity. A crucial issue is the demonstration that the SA mitigation devices are able to withstand the thermomechanical loadings induced by the corium interaction, components ensuring the relocation shall remain functional within the delay necessary for the corium to being fully displaced from the core to the debris tray. And the debris tray shall not be drilled after the total mass of corium has been relocated completely on its surface.

Using CFD and up-to-date physical and numerical modelling, the interaction between corium jets and the sacrificial material layer on the debris tray surface is analyzed, as well as the resulting ablation process.

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