Chris Tutt AMS-02 Phase II Safety Review 1

Review of Helium Venting Analyses

Chris Tutt

AMS-02 Project Manager

Chris Tutt AMS-02 Phase II Safety Review 2

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

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

Main Helium Tank

Chris Tutt AMS-02 Phase II Safety Review 5

Vacuum Case

Chris Tutt AMS-02 Phase II Safety Review 6

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

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

VC O-Ring Seals

Chris Tutt AMS-02 Phase II Safety Review 10

Each sealing surface has double O-ring seals.

In MCL, both seals are assumed to have failed in the same location.

CONICAL FLANGESUPPORT RING

O-RING TEST PORT

VAC

UU

M S

PAC

E

INTERFACE PLATE

OUTER CYLINDER

Chris Tutt AMS-02 Phase II Safety Review 11

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

Time to Burst

Pre-burst pressure rise modeled as isochoric heating. Heat flux from MCL calculated to be 655.5 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

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0 500 1000 1500 2000 2500 3000 3500 4000 4500

Time (sec)

Pre

ssu

re (

MP

a)

Lambda Point

Tank Filled

Burst Pressure

Chris Tutt AMS-02 Phase II Safety Review 15

Time to Empty TankMass 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

0.001

0.01

0.1

1

10

100

0 2000 4000 6000 8000 10000 12000 14000 16000 18000 20000

Time (sec)

Mas

s F

low

(kg

/s)

Burst Pressure

Pressure EqualizesHelium Goes Two-Phase

Helium Fully Vapor

Tank Empty

Chris Tutt AMS-02 Phase II Safety Review 17

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

GSFC Algorithm

Helium enters control volume at R m3/s.Ambient air removed by ventilation system

at Q m3/s.

Incoming Helium

Ventilation Exhaust

Incoming Air

Chris Tutt AMS-02 Phase II Safety Review 21

Oxygen Concentration Levels in PCR

18.50%

19.00%

19.50%

20.00%

20.50%

21.00%

4000 6000 8000 10000 12000 14000

Time (sec)

Oxy

gen

Lev

el (

%)

Pressure Equalizes

Helium Fully Vapor

Tank Empty

Chris Tutt AMS-02 Phase II Safety Review 22

Oxygen Concentration Levels in Canister

3.00%

6.00%

9.00%

12.00%

15.00%

18.00%

21.00%

4000 6000 8000 10000 12000 14000

Time (sec)

Oxy

gen

Lev

el (

%)

Pressure Equalizes

Helium Fully Vapor

Tank Empty

Chris Tutt AMS-02 Phase II Safety Review 23

Oxygen Concentration Levels in SSPF

20.80%

20.85%

20.90%

20.95%

21.00%

4000 6000 8000 10000 12000 14000

Time (sec)

Oxy

gen

Lev

el (

%)

Pressure Equalizes

Helium Fully Vapor

Tank Empty

Chris Tutt AMS-02 Phase II Safety Review 24

Oxygen Concentration Levels in CRF

20.50%

20.60%

20.70%

20.80%

20.90%

21.00%

4000 6000 8000 10000 12000 14000 16000

Time (sec)

Oxy

gen

Lev

el (

%)

Pressure Equalizes

Helium Fully Vapor

Tank Empty

Chris Tutt AMS-02 Phase II Safety Review 25

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.