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DGS-SEE SEMINAR ON FIRE PROTECTION FOR PHYSICS RESEARCH FACILITIES 07-08 OCTOBER 2015

CERN

FIRE SIMULATIONS IN THE PS ACCELERATOR TUNNEL TO DEFINE A SMOKE EXTRACTION

STRATEGYTRISTAN HEHNEN

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Table of contents

• Introduction• Introduction• Aim of the study• Tunnel description

• Proposed model• General information• Model overview

• First results• Smoke propagation• Near field of the fire

• Possible Improvements

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Introduction

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• Member of the Doctoral Student Programme at CERN

• Work supported by the Wolfgang-Gentner-Programme of the German Federal Ministry of Education and Research (BMBF)

• Doctoral student at the Bergische Universität Wuppertal

• Department: Computer Simulation for Fire Safety and Pedestrian Traffic

Duration of the doctoral programm: from Nov. 2014 to Nov. 2017

Supervisor: Saverio La Mendola

Supervisor: Armin SeyfriedLukas Arnold

Introduction

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Aim of the study

• Aim: Estimate the amount of radioactive material within the smoke in case of fire.

• Study devided in two parts:– Part I: Fire simulation (by Tristan)

– Part II: Estimate amount of radioactive material in the smoke and possible environmental impact (by Joachim)

• This presentation is on Part I– Aim: Create an envelope case of the fire scenario to further

explore the conditions

– Provide mass release over time, based on heat of combustion, as input for Part II

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TR 4

TR 3

TR 2

Tunnel description

• Simulation of cable fire in trench• Simplified part of the tunnel,

represented as straight section

• Roughly a quarter of the ring (TR 2 to TR 4)

• No fire propagation over combustible items simulated

• Burnable gas injected into the domain (gasburner)

• Smoke detection after 9 min – ventilation system stopped

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• Data on ventilation system taken from EDMS 1296553 and EDMS 1224638 (CFD study of PS ventilation system)

• Injection and extraction air volume fluxes are equal

• Representation of Fresh Air Ventilation System (FAVS) and Recirculation Ventilation System (RVS) by according volume fluxes

• Nozzles of RVS represented by larger surface – similar to previous CFD study

Tunnel description

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• Volume fluxes:– FAVS 2500 m³/h (1250 m³/h in each direction) in

the middle of tunnel segment (TR 3)

– RVS • Section TR 2 – TR 3: 40000 m³/h

• Section TR 3 –TR 4: 35000 m³/h

• Proposal: Three simulations for exploration of the scenario

– Wooden panals stay in place

– No wooden panels

– Panels will disapear gradually

Tunnel description

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Tunnel description

• Tunnel cross section and illustration of the RVS air flow

Cable trays

Magnets

Wooden panels

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Proposed model

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• Simulations conducted with Fire Dynamics Simulator 6.1.2 (FDS)

• Fire simulated with αt²-approach: slow α, progress to 10 MW• Grid resolution changes:

– Two meshes

– Top mesh with 20 cm cubes

– Buttom mesh with 10 cm cubes

• Both tunnel ends opend to account for leakage• Flow through these openings is monitored

General information

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Gaps

RVS inlet

RVS extraction

Magnets

Wooden panels

Cable trays

Model overview

Upper tunnel

Trench

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Gasburner

RVS inlet

RVS extraction

Magnets

Wooden panels

• Part of the tunnel at the centre

Cable trays

Model overview

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RVS inlet

RVS extraction

Magnets

Wooden panels

Cable trays

Model overview

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~ 200 m

FAVS inlet

FAVS extraction

Model overview

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10 cm cubes

20 cm cubes

• Two Meshes with different cell size to save computational time

Model overview

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Opend tunnel ends

• Opend tunnel endings (upstream end shown here)

Model overview

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First results

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• Smoke distribution ~417 s after ignition– Roughly 100 m propagation in the upper part

– Roughly 60 m propagation in the trench

Smoke propagation

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Flow through the gap

• Velocity profile, ~417 s after ignition

Near field of the fire

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• Temperature profile, ~417 s after ignition

Near field of the fire

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• Possible improvements of the model:– Behaviour of the ventilation system not modelled:

• No duct network, no fans, no dampers ...

• Just fixed volume flux for inflow/outflow

• Turned off after 9 min

– Finer resolution for gap between magnets and trench

– Fire propagation prescribed, no propagation over combustible material

– Leakage of the PS tunnel not known, modelled as openings in the tunnel ends

– No leakage in the ceiling of the trench

– Tunnel modelled as straight section and not in the full extend - change in air volume available

Possible improvements

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Thank you for your attention!

Do you have any questions?