1. Duy Phan, EN-STI-RBS

2. Description of the hazards  An Oxygen Deficiency Hazard (ODH) exists when the concentration of O2 ≤ 19.5 % (by volume)  Cold burns are burns that take place as the result of skin coming in contact with an object or a fluid that is extremely cold Why assessing these hazards?  Presence of a cryogenic installation involving helium inside the HIE-ISOLDE facility  Several people working in the vicinity of cryogenic fluids  Request from the HSE Unit to carry out a Risk Assessment How assessing these hazards?  Calculation tool provided by the HSE Unit and based on REFPROP (EDMS 1203283)1203283  Visits on site  Computational Fluid Dynamics simulations (CFD)

3. ODH ANALYSIS OF THE HIE-ISOLDE FACILITY 3

4. Main Objectives Determine the concentration of O2 that would remain in the atmosphere in case of accidental release of Helium (liquid or gas) Step 1 Define the location and the number of ODH equipment (sirens, alarms, etc.) to be installed in the areas subject to potential oxygen deficiency Step 2

5. Scope of the ODH analysis Bldg. 198 Compressor building Bldg. 199 Cold box building Bldg. 170 LINAC tunnel Case 1 Case 2 Case 3 [Acknowledgement: S. Maridor]

6. Methodology chosen Name: Safety Form OHS-0-0-7 – ODH Calculation (EDMS 1203283)1203283 Purpose: Preliminary analysis used to calculate the quantity of fluid that could be accidentally released in an installation and define, with the help of the HSE Unit, adequate control measures to mitigate the risks or reduce their consequences. Room properties Fluid properties O2 concentration and volume released

7. 1st case – bldg. 198 - compressor building NameStateVolumePressureTemperature Heliumgas 2*80 m 3 2 bars ≤ P ≤ 15 bars 300 K PROPERTIES OF THE FLUID SurfaceHeightVolumeFree volume 218 m²7.34 m1600 m 3 75 % PROPERTIES OF THE ROOM HYPOTHESIS CONSIDERED FOR THE ODH ANALYSIS The worst case scenario concerning pressure has been considered for the analysis  Pressure = 15 bars The ventilation system is not taken into consideration No interlock considered to stop the release of helium SCENARIO CONSIDERED Leak on the transfer line connecting the helium buffer tanks to the compressors Ground level Platform Helium compressor station Working platform Crane Outside Helium tanks [Acknowledgement: S. Maridor]

8. 1st case – bldg. 198 - compressor building RESULTS (cf. ODH Preliminary Assessment - Compressor building 198 – EDMS 1311170 )1311170 Case considered – Enriched gas layer Height of the gas layer = 5.31 m 7.34 m 5.31 m Necessity to install ODH detectors to alert operators working at height in case of accidental release of helium

9. 2nd case – bldg. 199 – cold box building PROPERTIES OF THE FLUID SurfaceHeightVolumeFree volume 190 m²4.5 m855 m 3 40 % PROPERTIES OF THE FIRST LEVEL HYPOTHESIS CONSIDERED FOR THE ODH ANALYSIS Loss of cold box content has been discarded  no impact on O2 concentration The ventilation system is not taken into consideration No interlock considered to stop the release of helium In case of helium flush all the helium would accumulate on the first floor NameStateVolumePressureTemperature Heliumliquid 1 m 3 1.3 bars4.5 K SCENARIO CONSIDERED Loss of helium from the Dewar through the safety valve due to loss of insulation vacuum First floor Ground level opening Dewar Cold box [Acknowledgement: S. Maridor]

10. Case considered – Homogeneous mixture Volume of gas discharged = 719 m 3 O2 after discharge = 0 % 1st floor 2nd case – bldg. 199 – cold box building RESULTS (cf. ODH Preliminary Assessment – Cold box building 199 (dewar) – EDMS 1311170 )1311170 Necessity to install ODH detectors to improve the efficiency of the evacuation of the building

11. 3rd case – bldg. 170 – LINAC tunnel NameStateVolumePressureTemperature Heliumliquid 0.16 m 3 1.3 bars4.5 K PROPERTIES OF THE FLUID SurfaceHeightVolumeFree volume 75.48 m²4 m301.92 m 3 86 % PROPERTIES OF THE LINAC TUNNEL HYPOTHESIS CONSIDERED FOR THE ODH ANALYSIS Other scenarios discarded  no release of helium inside the tunnel No interlock considered to stop the release of helium Natural ventilation is not taken into consideration SCENARIO CONSIDERED Loss of helium from one of the cryomodules due to an internal rupture of the insulation vacuum Cryomodules [Acknowledgement: S. Maridor]

12. Case considered – Homogeneous mixture Volume of gas discharged = 117 m 3 O2 after discharge = 11.6 % 3rd case – bldg. 170 – LINAC tunnel RESULTS (cf. ODH Preliminary Assessment – HIE-ISOLDE tunnel building 170 – EDMS 1311170 )1311170 Necessity to install ODH detectors due to the small volume of the tunnel and the significant quantity of LHe released in case of an accident

13. LocationScenario Hypothesis adopted concerning helium behaviour Hazard acceptability Presence of ODH detectors Compressor building (bldg. 198) Leak on the transfer line Stratification due to warm helium Potentially unsafe Requested due to the presence of operators at height Cold box building (bldg. 199) Release of helium through the safety valve of the Dewar Homogeneous mixture due to effect of cold helium convection Potentially unsafe Requested due to the short time needed to create an ODH in the area LINAC tunnel (bldg. 170) Release of helium through the rupture disk of a cryomodule Homogeneous mixture due to effect of cold helium convection Potentially unsafe Requested due to the short time needed to create an ODH in the area Summary of the results of the ODH analysis

14. Outputs from the visit of the HIE-ISOLDE facility – Bldg. 198 CONTROL MEASURES TO BE IMPLEMENTED 2 ODH detectors connected to: 2 flashing lights located inside the building 1 evacuation siren Ground level Platform ODH flashing lights ODH detectors

15. Outputs from the visit of the HIE-ISOLDE facility – Bldg. 199 CONTROL MEASURES TO BE IMPLEMENTED 2 ODH detectors connected to: 4 flashing lights located inside the building 1 evacuation siren 1 dynamic extraction system with an extraction flow of 14 000 m3/h (11 ACH) to avoid any accumulation of helium ODH flashing lights ODH detectors First floor

16. Outputs from the visit of the HIE-ISOLDE facility – Bldg. 170 CONTROL MEASURES TO BE IMPLEMENTED 2 ODH detectors connected to: 4 flashing lights located inside the building 2 flashing lights near the entrances of the tunnel 1 flashing light on the working platform located above the tunnel ODH flashing lights ODH detectors

17. CFD OF A RELEASE OF HELIUM INSIDE THE LINAC TUNNEL 17

18. Why carrying out a CFD in the LINAC tunnel? Is access possible during steady state? 6 Cryomodules Internal rupture of the insulation vacuum of one of the cryomodules Scenario considered for the simulation [Acknowledgement: Y. Leclercq]

19. Hypothesis considered for the simulations Volume available in the tunnel ~ 260 m3 Set pressure of the burst disk: 1.5 bar absolute Masse of helium released = 20 kg (0.16 m3) Leak temperature: Tmin = 15 K, Tmax = 40 K Mass flow through the burst disk: Qmin = 5 kg/s, Qmax = 8 kg/s 90° orientation of the burst disk

20. ‘REFERENCE-CASE’ Volumetric concentration of O 2 [%] 5 m Evolution of the concentration of O2 - 2.5-20 s [Acknowledgement: E. Da Riva] 5 m

21. ‘REFERENCE-CASE’ Temperature [K] Evolution of the temperature - 2.5-20 s [Acknowledgement: E. Da Riva] 5 m Technical solutions still under discussion Routing of the safety relief device of the vacuum vessel outside the tunnel Emptying of the cryomodules before intervention (steady-state only) Listing and prioritisation of the interventions to be carried out in the tunnel

22. CONCLUSION 22

23. 23 Essential information The study has confirmed the presence of ODH in all the locations assessed (bldg. 198, 198 and LINAC tunnel) Different scenarios leading to an oxygen deficiency atmosphere have been identified but only some of them have been considered for the ODH analysis ODH analysis is a process that should be carried out in several steps… …and can require additionnal studies for complex installations (CFD) A layout of an ODH installation has been proposed following a collaboration between EN/STI, GS/FB, GS/ASE, EN/CV and TE/CRG The implementation of the ODH layout has been done in such a way that operators working in areas subject to ODH would be quickly alerted in order to evacuate in the most efficient way

24. THANK YOU FOR YOUR ATTENTION… 24 Acknowledgements A-P. Bernardes (EN/STI), E. Da Riva (EN/CV), G. Camplone (EN/CV), G. Lindell (DGS/SEE), N. Delruelle (TE/CRG), N. Broca (GS/ASE), Y. Leclercq (TE/CRG), S. Maridor (EN/MEF), M. Dole (GS/ASE) Contact: duy.phan@cern.chduy.phan@cern.ch