2 DGS-SEE SEMINAR ON FIRE PROTECTION FOR PHYSICS RESEARCH FACILITIES OCTOBER 2015 CERN FIRE SIMULATIONS IN THE PS ACCELERATOR TUNNEL TO DEFINE A SMOKE EXTRACTION STRATEGY TRISTAN HEHNEN

3 Table of contents Introduction Aim of the study Tunnel description Proposed model General information Model overview First results Smoke propagation Near field of the fire Possible Improvements

4 Introduction

5 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 to Nov Supervisor: Saverio La Mendola Supervisor: Armin Seyfried Lukas Arnold Introduction

6 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

7 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

8 Data on ventilation system taken from EDMS and EDMS (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

9 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: m³/h Section TR 3 –TR 4: m³/h Proposal: Three simulations for exploration of the scenario – Wooden panals stay in place – No wooden panels – Panels will disapear gradually Tunnel description

10 Tunnel description Tunnel cross section and illustration of the RVS air flow Cable trays Magnets Wooden panels

11 Proposed model

12 Simulations conducted with Fire Dynamics Simulator (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

13 Gaps RVS inlet RVS extraction Magnets Wooden panels Cable trays Model overview Upper tunnel Trench

14 Gasburner RVS inlet RVS extraction Magnets Wooden panels Part of the tunnel at the centre Cable trays Model overview

15 RVS inlet RVS extraction Magnets Wooden panels Cable trays Model overview

16 ~ 200 m FAVS inlet FAVS extraction Model overview

17 10 cm cubes 20 cm cubes Two Meshes with different cell size to save computational time Model overview

18 Opend tunnel ends Opend tunnel endings (upstream end shown here) Model overview

19 First results

20 Smoke distribution ~417 s after ignition – Roughly 100 m propagation in the upper part – Roughly 60 m propagation in the trench Smoke propagation

21 Flow through the gap Velocity profile, ~417 s after ignition Near field of the fire

22 Temperature profile, ~417 s after ignition Near field of the fire

23 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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