Session: 02-02 Risk Assessment and Waste Optimization

Paper Number: 108743

108743 - Assessment of the Airborne Release Fraction in Case of Dried and Particulate Contaminations 

                Several nuclear facilities are currently dismantling in France, namely in CEA's and EDF's sites. Decommissioning, dismantling, cutting operations and nuclear waste management can significantly affect worker risks. In this context, this work aims to better assess the internal exposure to radionuclides risks of such operations, in which the removal and airborne release fraction of radioactive substances from contaminated materials play an essential part on the uncertainties. For that purpose, understanding the behavior of contamination (i.e. possible removal by contact and airborne particle release) during a smearing procedure and under aeraulic stress is necessary to optimize the choice of Personal Protective Equipment during nuclear dismantling operations.
                Based on a previous study, most of the parameters influencing the removal and the resuspension of labile contamination were identified. Particularly, considering a dried liquid contamination, the role of the drying temperature, the relative humidity, the roughness of the contaminated surface and the swiping pressure were highlighted on the assessment of the labile contamination and the removal factor (Rf=Activity of the first swipe/Total labile Activity) [1]. Thus, considering a contamination presenting as a dried liquid on a stainless-steel surface, the surface roughness was determined as the most influencing parameter on the amount of labile contamination and the removal factor.
                Nonetheless, on the worksite, both dried liquid and particle deposit contaminations have to be considered. It is legitimate to admit that they behave differently under external stress. Consequently, a current study is being performed to better understand and compare these two types of surface contaminations against external stresses such as the smearing process to estimate the labile contamination and airflow. Fluorescein (solubilized in water or directly deposited as solid particles) is used as a simulant because it can be detected at very low quantities with high accuracy using fluorimetry analysis.
                For that purpose, the study is divided into two distinct parts:
                -     contamination resuspension process simulated by CFD (Computational Fluid Dynamics);
                -     laboratory experiments.

                The CFD approach is employed with the “Rock’n’Roll” (RNR) resuspension model to predict the airborne release fraction of particles. To compare our results with real data, a realistic aeraulic stress comparable to one induced by the walk of an operator is used. Note that these numerical simulations can give information only for spherical particles. This is why the laboratory approach is necessary to observe the behavior of dried liquid contamination.
                For that, a specific device is used to blow a controlled airflow on a stainless-steel surface leading to the resuspension of radioactive substances deposited on contaminated surface. The resulted aerosol is collected on a HEPA (High-Efficiency Particulate Air) filter, allowing the measurement of the contamination resuspended by a given airflow. On the first hand, we did not measure resuspension of contamination during the experiment with liquid-dried contamination of fluorescein. On the other hand, experimental methodology to study resuspension of particles is under improvement. Meanwhile, we estimated and compared the labile contamination and the removal factor of both; dried liquid and particle deposit contaminations by swiping method. We identified that, the change of contamination from liquid-dried contamination to particulate one induces a rise of 230 % of the removal factor.

                This new study will present the experimental and numerical approaches to assess the airborne release fraction in case of liquid dried and particulate contaminations. Analysis and associated discussions of these results will allow us to identify key parameters and ways of improvement for airborne release fraction assessment during dismantling operations.

[1] P. Agullo, A. Gossard, G. Ranchoux, E. Porcheron, F. Petitot, “Relevant parameters influencing the labile contamination and the removal factor”, Journal of Nuclear Engineering and Radiation Science, ICONE-29, Submitted.

Presenting Author: Pierrick Agullo French Alternative Energies and Atomic Energy Commission

Presenting Author Biography: I am graduated from Ecole Nationale Supérieure de Chimie de Montpellier, one of the French Grandes Ecoles from Montpellier focused on chemistry. During my studies, I had the privilege of going to China to learn more about the nuclear field at the French-Chinese Institut of Nuclear Energy (IFCEN) located in Sun Yat-Sen university and also visiting Oak Ridge National Laboratory in Tenessee, USA.

I am currently a Ph.D. student working on the development of a new method for assessing the risk of internal exposure to optimize the use of Personal Protective Equipment during nuclear dismantling.