Modelling and assessment of the dispersion of particles in the ESS instrument hall
Author
Carini, Ettore
Term
4. term
Education
Publication year
2017
Pages
92
Abstract
This thesis, conducted in collaboration with the European Spallation Source (ESS), models and assesses a worst-case scenario in which potentially radioactive tungsten trioxide particles from the target area reach an instrument hall following a fire in the target concurrent with a fire in the connecting bunker. Using ANSYS Fluent CFD, a transient Large Eddy Simulation (LES) is applied for the airflow, coupled with a discrete phase of tungsten particles sized 0.1–2.3 μm following a Rosin–Rammler distribution. The bunker fire is represented by a simplified model focusing on the hot-air mass flow and is partially benchmarked against a validated pool-fire case. The scenario is first studied in a scaled-down geometry to examine the effect of heat release rate (330 kW–1 MW), showing that larger fires drive faster and larger particle releases, and then simulated for the full-scale instrument hall. In full scale, results indicate that after 20 minutes less than 11% of the particle mass has escaped, that escape occurs only through a ceiling-level outlet and not through ground-level openings, and that particles distribute across the hall’s full height with the smallest (~0.1 μm) most likely to escape. A qualitative risk assessment concludes that inhalation toxicity for personnel inside the instrument hall is the primary concern, while off-site environmental impact is smaller in magnitude but still relevant; the absence of ground-level outflow may also inform future rescue and evacuation planning.
Dette speciale, udarbejdet i samarbejde med European Spallation Source (ESS), modellerer og vurderer et worst-case scenarie, hvor potentielt radioaktive tungstentrioxidpartikler fra målområdet når en instrumenthal efter en brand i målet samtidig med en brand i den tilknyttede bunker. Ved hjælp af ANSYS Fluent CFD anvendes en transiente Large Eddy Simulation (LES) af luftstrømmen og en diskret fase af tungstenpartikler fordelt efter Rosin-Rammler i størrelsesintervallet 0,1–2,3 μm. Bunkerbranden repræsenteres med en forenklet model, der fokuserer på massestrømmen af varm luft og delvist benchmarks mod en valideret poolbrand. Scenariet undersøges først i en nedskaleret geometri for at studere effekten af varmeudviklingen (330 kW–1 MW), hvilket viser, at større brande medfører hurtigere og mere omfattende partikeludslip; derefter simuleres fuldskala-instrumenthallen. I fuld skala viser beregningerne, at efter 20 minutter er under 11% af partikelmassen undsluppet, at udslip kun sker via afkast i loftsniveau og ikke gennem åbninger i terrænniveau, og at partiklerne fordeles i hele hallens højde, hvor de mindste (~0,1 μm) har størst tilbøjelighed til at slippe ud. En kvalitativ risikovurdering peger på, at den primære fare er inhalationstoksicitet for personale i instrumenthallen, mens den eksterne miljøpåvirkning er mindre, men fortsat relevant; fraværet af udslip fra døre i terrænniveau kan desuden have betydning for fremtidige rednings- og evakueringsplaner.
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