Dust tracking techniques applied to the STARDUST facility: First results

Abstract

HIGHLIGHTS• Use of an experimental facility, STARDUST, to analyze the dust resuspension problem inside the tokamak in case of loss of vacuum accident.• PIV technique implementation to track the dust during a LOVA reproduction inside STARDUST.• Data imaging techniques to analyze dust velocity field: first results and data discussion. ABSTRACTAn important issue related to future nuclear fusion reactors fueled with deuterium and tritium is the creation of large amounts of dust due to several mechanisms (disruptions, ELMs and VDEs). The dust size expected in nuclear fusion experiments (such as ITER) is in the order of microns (between 0.1 and 1000 (im). Almost the total amount of this dust remains in the vacuum vessel (W). This radiological dust can re-suspend in case of LOVA (loss of vacuum accident) and these phenomena can cause explosions and serious damages to the health of the operators and to the integrity of the device. The authors have developed a facility, STARDUST, in order to reproduce the thermo fluid-dynamic conditions comparable to those expected inside the W of the next generation of experiments such as ITER in case of LOVA. The dust used inside the STARDUST facility presents particle sizes and physical characteristics comparable with those that created inside the VV of nuclear fusion experiments. In this facility an experimental campaign has been conducted with the purpose of tracking the dust re-suspended at low pressurization rates (comparable to those expected in case of LOVA in ITER and suggested by the General Safety and Security Report ITER-GSSR) using a fast camera with a frame rate from 1000 to 10,000 images per second. The velocity fields of the mobilized dust are derived from the imaging of a two-dimensional slice of the flow illuminated by optically adapted laser beam. The aim of this work is to demonstrate the possibility of dust tracking by means of image processing with the objective of determining the velocity field values of dust re-suspended during a LOVA.

Numerical Simulations as Tool to Predict Chemical and Radiological Hazardous Diffusion in Case of Nonconventional Events

“…This kind of accident can occur in Tokamaks, when a LOVA happens or when hazardous dust is accidentally or voluntarily exposed to the wind. It is clear from Figure 11 that almost the total amount of dust is resuspended in the first second after the air inlet in accordance with the peak of air velocities measured (see [19,54,57]) and the dust mobilized during the experimental campaigns (see [56,58,59]).…”

“…The experimental campaigns have been set at the beginning to collect data about the thermofluid dynamic behaviour in case of LOVA replications inside STARDUST and STARDUST-U. Together with these experimental campaigns the QEP research group carried out experiments to analyse the quantity of dust mobilized [56,57] and determine the velocities direction and modules by the use of optical techniques [58,59].…”

A novel integrated approach for the hazardous radioactive dust source terms estimation in future nuclear fusion power plants

“…Modeling of a fusion reactor vacuum vessel is crucial for accident analysis and to predict materials inventory and mobilization, both from the experimental and numerical point of view. For that reason, along with experimental facilities to reproduce source term mobilization phenomena [26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36] it is also very important to develop a numerical model [37, 38] in order to predict particles quantities, velocity and direction in case of accidents such as a loss of vacuum, and not referring just to administrative limits but to estimates based on a more accurate methodology.…”

First 3D numerical simulations validated with experimental measurements during a LOVA reproduction inside the new facility STARDUST-Upgrade

“…An fluid-dynamic conditions comparable to those expected inside the vacuum vessel of the next generation of experiments (such as ITER) in case of LOVAs due to small air leakage [4][5][6][7][8][9][10][11][12][13] and upgraded it in 2014 ("STARDUST-Upgrade") making it suitable to simulate LOCAs; increasing the field of view inside the chamber; and allowing to replicate LOVAs for more than one accidental configuration [14]). …”

“…The CFD study of LOVA scenario is a challenging task for today numerical codes and models because it involves 3D vacuum volumes, multiphase flows ranging from highly supersonic to nearly incompressible and heat transfer simultaneously [4][5][6][7][8][9][10][11][12][13][14][15][16]. Development of specific codes and additional validation of existing ones are required.…”