Session: 03-02: Major facilities experience in handling accidents and D/D&D

Paper Number: 110133

110133 - Aerosol Characterization During Heating and Mechanical Cutting of Simulated Uranium Containing Debris: The Urasol Project in the Framework of Fukushima Daiichi Fuel Debris Removal 

One of the important challenges for the decommissioning of the damaged reactors of the Fukushima Daiichi Nuclear Power Station (1F) is the fuel debris retrieval. The generation and dispersion of radioactive aerosols during the cutting operations of fuel debris pose a significant radiation and health risk during the decommissioning process. Quantitative assessments of potential contamination with radioactive aerosols are fundamental to the development of a safety case for the decommissioning of 1F. Detailed studies on the generation of aerosols during cutting processes of inactive fuel debris simulants by various tools have been performed, underlining the influence of each cutting tool and its operating conditions, the chemical composition of cutting materials, and the environmental conditions of the dismantling, such as in air or underwater conditions. The size distribution, morphology and composition of particles released during cutting are equally significant when predicting their transport and deposition behavior through numerical simulations and assessing its radioactivity. Furthermore, quantitative characterization of radioactive aerosols is essential to develop and optimize technologies to capture and mitigate particulate contaminants.

In this context, the URASOL project (abbreviation for "Particle generation test using simulated uranium containing debris", a word coined from URAnium and aeroSOL), which is undertaken by a French consortium consisting of ONET Technologies, CEA, and IRSN for JAEA/CLADS, is dedicated to acquire basic scientific data on the generation and characteristics of radioactive aerosols from the thermal or mechanical processing of fuel debris simulant. Heating process undertaken in the VITAE (acronym for VITi-AErosols) facility simulates some representative conditions of thermal cutting by laser. For mechanical cutting, the core boring technique is implemented in the FUJISAN facility. Fuel debris simulants have been developed for inactive trials with hafnium and cerium content and for active trials with depleted uranium content.

The aerosols are characterized in terms of mass concentration, real time number concentration, mass size distribution, morphology, and chemical properties. The chemical characterization aims at identifying potential radioactive particles released and the associated size distribution, both of which are important information for assessing possible safety and radioprotection measures during the fuel debris retrieval operations at 1F.

This paper will present the main results regarding the characterization of aerosol generation emitted during heating and mechanical cutting process for inactive and radioactive fuel debris simulants in terms of particle size distribution, morphology and mass concentration. For inactive simulants, a comparison of the particle generation between URASOL results for heating process and for laser cutting will be also presented.

Acknowledgements: Most of this work has been carried out within the scope of contributions to the Japanese governmental subsidy program “Project of Decommissioning and Contaminated Water Management (Development of Analysis and Estimation Technology for Characterization of Fuel Debris)” funded by the Japanese Ministry of Economy, Trade and Industry (METI) and organized by the International Research Institute for Nuclear Decommissioning (IRID).

Presenting Author: Emmanuel Porcheron Inst For Radiological Protection and Nuclear Safety (IRSN)

Presenting Author Biography: Emmanuel Porcheron received his PhD in Fluids Mechanics in 1998 and his Habilitation to supervise research in 2014. He has been working for IRSN since 1999 leading research projects for nuclear safety applied to thermal hydraulics, hydrogen risk, instrumentation for multiphase flow, and D&D. He is deputy head of laboratory of Aerosols Physics and metrology and since 2015 in charge of R&D projects for radioactive aerosol issue during fuel debris retrieval at Fukushima Daiichi.