Fukushima Dai-ichi fuel debris retrieval: CFD calculations of aerosol dispersion and mitigation by spray systems in representative conditions of the 1F2 reactor pedestal

Thomas Gelain (1) , Emmanuel Porcheron (2) , Yohan Leblois (2) , Ioana Doyen (3) , Christophe Journeau (4) , Remi Delalez (5) , Damien Roulet (6)

1 IRSN/PSN-RES/SCA/LEMAC - Laboratoire d'expérimentations et de modélisation en aérodispersion et confinement
2 IRSN/PSN-RES/SCA/LPMA - Laboratoire de physique et de métrologie des aérosols
3 LTA - Laboratoire Technologie d'Assemblage
4 DEN/SMTA/LPMA
5 ONET Technologies
6 ONET

Introduction The general context of this study is related to demonstrate the feasibility of the use of the laser cutting technique for the fuel debris (or corium) retrieval on the damaged reactors of Fukushima Dai-ichi. IRSN is involved in a project led by ONET Technologies, in collaboration with CEA, to bring relevant elements to analyse the risk occurred by the dispersion of aerosols emitted by the dismantling operations and to propose and evaluate solutions to mitigate this risk. This article will present CFD simulations of aerosols dispersion and removal by spray during the laser cutting phase in representative conditions of Fukushima Daiichi unit 2 (1F2) pedestal. CFD simulations in representative conditions of 1F2 reactor pedestal of aerosol dispersion and removal by spray During the laser cutting operations for the fuel debris retrieval in air condition, particles will be produced, inducing a potential risk of dispersion into the environment. The role of IRSN, in the frame of this current project, is to contribute to evaluate the risk induced by the aerosol generation and dispersion during laser cutting operations, to propose a strategy of mitigation of this risk and to assess its efficiency. To do that, aerosol removal by spray was considered and tested experimentally and numerically in analytical and semi-analytical facilities in order to evaluate the spray removal efficiency and to optimize the spray parameters. Aware of the non-perfect representativeness of these tests in regard of the real configuration inside the reactor pedestal, more realistic CFD simulations were performed in a geometry representative of the 1F2 reactor pedestal. These simulations were performed with ANSYS CFX numerical tool (into which models for aerosols transport and deposition and for spray collection were implemented and validated at IRSN) for different cutting configurations depending on the materials to be cut and their location. Aerosol source term was implemented in calculations from experimental data during laser cutting of corium simulants. The scenario consists in injecting aerosols during the laser cutting operations associated to the spray activation and in following the aerosol concentration inside the pedestal in order to evaluate the efficiency of the spray removal depending on different configurations (laser cutting location, spray location, clutter, ventilation…). The full paper will present the numerical results regarding aerosols dispersion and removal by spray in the 1F2 reactor pedestal, and a comparison between the tested configurations. Acknowledgment This subsidized project is funded by the Japanese Ministry of Economy, Trade and Industry (METI) through the Eco Future Fund (EFF) and managed by the Mitsubishi Research Institute (MRI). The authors thank Mrs Christine Georges in charge of the general management of the project for the CEA.

Domaines: Sciences de l'ingénieur [physics]

Thomas Gelain, Emmanuel Porcheron, Yohan Leblois, Ioana Doyen, Christophe Journeau, et al.. Fukushima Dai-ichi fuel debris retrieval: CFD calculations of aerosol dispersion and mitigation by spray systems in representative conditions of the 1F2 reactor pedestal. International Conference on Decommissioning Challenges: Industrial Reality, Lessons learned and Prospects, DEM 2021, Sep 2021, AVIGNON, France. ⟨hal-03797584⟩