Implementation and Validation of an Aerosol Collection Model by a Spray in a CFD Code: Application to the Scavenging of Aerosols Released During Laser Cutting Operations of Fuel Debris for the Dismantling of the Damaged Reactors of Fukushima Dai-ichi

The general context of this article is related to the dismantling of the damaged reactors of Fukushima Dai-ichi and, more specifically, to the implementation of the laser cutting technique for the fuel debris retrieval. IRSN is involved in a project led by ONET Technologies and in partnership with CEA, to bring relevant elements in order to analyze the risks induced by the dispersion of aerosols released by the dismantling operations. During the laser cutting operations in air or underwater conditions, particles will be produced, involving a potential risk of dispersion into the environment. Hence, in order to prevent this situation, their collection is one of the safety key issues in the in-situ dismantling actions. For that, IRSN performed CFD simulations of aerosol scavenging by a spray to evaluate the collection efficiency by this technique. These simulations, conducted with the ANSYS CFX code, use an Eulerian method for the continuous phase, and a Lagrangian method for the spray for which a collection model detailed by Plumecocq [1] or Marchand [2] was implemented. Aerosols are modelled by a DQMOM population balance implemented by Gelain et al. [3] (already used for recent simulations in the same context), and enriched with a deposition model developed by Nerisson et al. [4]. At first, CFD simulations were performed with the geometry of the IRSN TOSQAN facility [5], comparatively to experimental results presented in a previous paper [6]. This step enables the validation of the collection model implementation and to study the sensitivity to the aerosol size. Then, CFD simulations were conducted with the geometry of the pedestal of Fukushima Dai-ichi reactors, to be more representative of a realistic case. For this configuration, sensitivity studies are described, highlighting both the influence of a multispray and of thermal-hydraulic conditions (temperature) on aerosol scavenging efficiency.

Aerosol Dispersion During Mastoidectomy and Custom Mitigation Strategies for Otologic Surgery in the COVID-19 Era

Objective To investigate small-particle aerosolization from mastoidectomy relevant to potential viral transmission and to test source-control mitigation strategies. Study Design Cadaveric simulation. Setting Surgical simulation laboratory. Methods An optical particle size spectrometer was used to quantify 1- to 10-µm aerosols 30 cm from mastoid cortex drilling. Two barrier drapes were evaluated: OtoTent1, a drape sheet affixed to the microscope; OtoTent2, a custom-structured drape that enclosed the surgical field with specialized ports. Results Mastoid drilling without a barrier drape, with or without an aerosol-scavenging second suction, generated large amounts of 1- to 10-µm particulate. Drilling under OtoTent1 generated a high density of particles when compared with baseline environmental levels ( P < .001, U = 107). By contrast, when drilling was conducted under OtoTent2, mean particle density remained at baseline. Adding a second suction inside OtoTent1 or OtoTent2 kept particle density at baseline levels. Significant aerosols were released upon removal of OtoTent1 or OtoTent2 despite a 60-second pause before drape removal after drilling ( P < .001, U = 0, n = 10, 12; P < .001, U = 2, n = 12, 12, respectively). However, particle density did not increase above baseline when a second suction and a pause before removal were both employed. Conclusions Mastoidectomy without a barrier, even when a second suction was added, generated substantial 1- to 10-µm aerosols. During drilling, large amounts of aerosols above baseline levels were detected with OtoTent1 but not OtoTent2. For both drapes, a second suction was an effective mitigation strategy during drilling. Last, the combination of a second suction and a pause before removal prevented aerosol escape during the removal of either drape.