1. Review of Helium Venting Analyses
Chris Tutt
AMS-02 Project Manager
Chris Tutt
AMS-02 Phase II Safety Review

2. AMS-02 Phase II Safety Review
Review of Hazard
Hazard to be addressed is release of asphyxiant gas into an occupied area.
Three major helium reservoirs within AMS-02 payload and GSE.
2500-liter main helium dewar inside the payload.
1000-liter master dewar used for filling main dewar.
1000-liter transfer dewar used for filling master dewar.
Venting analysis focused on main dewar as enveloping case, but results for all others are similar.
Chris Tutt
AMS-02 Phase II Safety Review

3. AMS-02 Phase II Safety Review
Main Helium Dewar
Main Helium Dewar has two major components
Helium Tank contains the cryogen itself
Vacuum Case provides vacuum space around the tank.
3 bar burst disk on helium tank defines the Maximum Design Pressure for the system.
Nominal operating pressure is ~16 mbar.
All hardware will be extensively tested prior to arrival at KSC.
Structural analysis shows high margins for MDP.
All welds will be inspected per MSFC-STD-504C.
Both items will be proof pressure tested.
Both items will be vacuum leak tested.
Chris Tutt
AMS-02 Phase II Safety Review

4. AMS-02 Phase II Safety Review
Main Helium Tank
Chris Tutt
AMS-02 Phase II Safety Review

5. AMS-02 Phase II Safety Review
Vacuum Case
Chris Tutt
AMS-02 Phase II Safety Review

6. AMS-02 Phase II Safety Review
GSE Dewars
Chris Tutt
AMS-02 Phase II Safety Review

7. Tank Overpressurization
Two mechanisms for overpressurization of tank.
Failure to remove nominal boil-off from tank.
Large external heat source increases boil-off beyond pump’s capability to remove.
First scenario requires weeks to reach burst pressure, so does not present safety hazard.
Only possible heat source for second scenario is ambient atmosphere and requires air leak into the dewar vacuum space.
Chris Tutt
AMS-02 Phase II Safety Review

8. AMS-02 Phase II Safety Review
Cause of Leak
Two leak scenarios were considered in analysis
Loss of Vacuum (LOV) – Total loss of vacuum caused by large breach of Vacuum Case. Requires major accident:
Forklift tine breaks through VC outer cylinder
Payload dropped during lifting operations
Large hardware falls on payload from significant height.
Maximum Credible Leak (MCL) – 3” leak through the double O-Ring seals in the VC upper and lower support rings.
Leak size defined by Payload Safety Review Panel and used for all payload bay leak analyses.
LOV can be prevented operationally, so following discussion will focus on MCL.
Chris Tutt
AMS-02 Phase II Safety Review

9. AMS-02 Phase II Safety Review
VC O-Ring Seals
Chris Tutt
AMS-02 Phase II Safety Review

10. AMS-02 Phase II Safety Review
CONICAL FLANGE
SUPPORT RING
O-RING TEST PORT
VACUUM SPACE
INTERFACE PLATE
Each sealing surface has double O-ring seals.
In MCL, both seals are assumed to have failed in the same location.
OUTER CYLINDER
Chris Tutt
AMS-02 Phase II Safety Review

11. AMS-02 Phase II Safety Review
MCL Defined Leak Size
Chris Tutt
AMS-02 Phase II Safety Review

12. Venting Analysis Overview
Venting Analysis consists of three basic steps
Calculation of time required for tank to reach 3 bar burst pressure after leak begins.
Calculation of mass rate of flow of helium leaving the main tank.
Calculation of oxygen levels in surrounding external space.
Only the third step is location dependent.
Chris Tutt
AMS-02 Phase II Safety Review

13. AMS-02 Phase II Safety Review
Time to Burst
Pre-burst pressure rise modeled as isochoric heating.
Heat flux from MCL calculated to be W.
Helium thermodynamic properties from NIST handbook.
Results driven by initial temperature and fill level.
Calculated times range from 54 min (1.9K, 95% full) to 86 min (1.7K, 80% full).
Chris Tutt
AMS-02 Phase II Safety Review

14. Typical Pressure Rise Profile
Chris Tutt
AMS-02 Phase II Safety Review

15. AMS-02 Phase II Safety Review
Time to Empty Tank
Mass flow out of the tank modeled as isentropic expansion through choked nozzle.
Results driven entirely by fill level.
The more helium in the tank, the longer it takes to empty.
Below 90% full, helium becomes two-phase prior to reaching 1 atm.
Calculated times range from 131 min after burst (80% full) to 239 min (95% full).
Chris Tutt
AMS-02 Phase II Safety Review

16. Typical Mass Flow Profile
Chris Tutt
AMS-02 Phase II Safety Review

17. AMS-02 Phase II Safety Review
Exterior Volume
Analysis done for four KSC spaces
Space Shuttle Processing Facility
Canister Rotation Facility
Canister
Payload Changeout Room
Results driven by three factors
Volume of external space
Air refreshment rate
Gas diffusion model
Chris Tutt
AMS-02 Phase II Safety Review

18. Original Gas Diffusion Assumption
Original discussions assumed that helium vapor would rise to the ceiling of external volume.
Chris Tutt
AMS-02 Phase II Safety Review

19. Current Gas Diffusion Assumption
At GOWG in November, GSRP requested analysis be redone assuming gas spreads evenly throughout the room.
Model used GSFC algorithm provided by SHOOT team.
Based on helium sensors measurements from Tevatron accident at Fermilab.
Venting memo describes results using second assumption.
Chris Tutt
AMS-02 Phase II Safety Review

20. AMS-02 Phase II Safety Review
GSFC Algorithm
Incoming Air
Ventilation
Exhaust
Incoming Helium
Helium enters control volume at R m3/s.
Ambient air removed by ventilation system at Q m3/s.
Chris Tutt
AMS-02 Phase II Safety Review

21. Oxygen Concentration Levels in PCR
Chris Tutt
AMS-02 Phase II Safety Review

22. Oxygen Concentration Levels in Canister
Chris Tutt
AMS-02 Phase II Safety Review

23. Oxygen Concentration Levels in SSPF
Chris Tutt
AMS-02 Phase II Safety Review

24. Oxygen Concentration Levels in CRF
Chris Tutt
AMS-02 Phase II Safety Review

25. AMS-02 Phase II Safety Review
Overall Trends
PCR falls briefly below 19.5%, but high ventilation rate allows rapid return to safe levels.
Canister’s small volume can be rapidly overwhelmed, but is not normally a manned volume when door is shut.
SSPF/CRF volumes are large enough and ventilation rates are fast enough that oxygen level never falls below 19.5%.
Chris Tutt
AMS-02 Phase II Safety Review

26. Proposed Safety Controls
GSE should be monitored for signs of temperature or pressure rise while AMS-02 is in manned area.
If leak observed, personnel should be removed from vulnerable areas.
Entire PCR
Elevated structures within SSPF and CRF
Oxygen sensors should be used to determine safety of atmosphere prior to reentering any area after venting event or opening Canister in the PCR.
Additonal vent lines and building modifications should not be necessary.
Chris Tutt
AMS-02 Phase II Safety Review