Transcript MICE AFCSWG Safety Review Summary Mary Anne Cummings Dec. 17, 2003 MICE Video Conference.

MICE AFCSWG Safety Review Summary
Mary Anne Cummings
Dec. 17, 2003 MICE Video Conference
The Review
Last week (Dec 9-10) we had our first formal review of the safety
issues involved in the MICE experiment at LBL
The Review Committee:
D. Allspach (FNAL)
G. Benincasa (CERN)
M. Seely (Jlab)
L. Starritt (NASA/WSTF)
J. Weisend (SLAC) Chair
J. Wells (RAL)
MICE AFC Safety Issues:
Hydrogen:
RF cavities:
Magnets:
Flammability, detonation, low temperature, O2 cryopumping,
large liquid-gas expansion ratio
Dark currents, Be windows
Large fringe fields, quenching
Topics:
Magnets
LH2 Absorber
LH2 System
RF System
M. Green
M. A. Cummings
E. Baynham
D. Li
Detectors
A. Bross
Magnetic forces
J. Rochford
R & D, testing, certification W. Lau
Hazard Summary
E. Baynham
The LH2 Issues
Compact structure of the cooling channel means the absorber and LH2 system have
to be designed with all other components and safety hazards in mind
•For safe operation, have designed with the redundant requirements:
1) LH2 and O2 separation
2) The avoidance of any ignition sources in contact with hydrogen.
• The four key features of the design with respect to safety are:
1) Window thicknesses specified based on safety factors of 4.0 for the absorber
and vacuum windows at maximum allowable working pressure (MAWP).
Vacuum windows required to withstand 25 psi outside pressure without
buckling.
2) Two layers of shielding between the outside atmosphere and the LH2; the outer
surface at room temperature to minimize the freezing of O2 on the absorbersystem windows.
3) Separate vacuum volumes provided for the RF cavities, magnets, and LH2
absorbers.
4) Hydrogen evacuation systems using valved vents into external buffer tanks.
Accommodating LH2
RAL safe LH2 operation
1.
2.
3.
4.
Sufficient clearance for LH2 venting into evacuation tanks (21 liters liquid 
17000 liters at STP)
RF: Window provides spark barrier; vacuum between RF and LH2 vacuum
vessel
LH2-Air flammability limits: 4-75% ; detonability limits 18-59% 
conventional seals and vacuum vessels can provide sufficient barriers
between them.
All safety interlocks mechanical – based on expeditious venting of LH2 into
evacuation tank
Absorber coil system
Ambient temperature on vacuum shields and outer channel wall
Quench force on windows is small
Static forces are decoupled from the LH2 absorber
Heat from quench and static sources are insufficient to cause boil-off
Clearance for possible LH2 rupture into vacuum volume sufficient to
prevent cascading window rupture
L-H2
IN/OUT
C-He IN
C-He OUT
Absorber Vacuum Volume:
Magnet bore
Large end plate
GATE VALVE
24-M4
4-M6
Absorber Window:
Vacuum Window:
24-M8
He inlet:
Outer wall
MLI
LH2 System
Ventilated Hood
Absorber vacuum
Outside
Safety and design considerations:
Lab
Hydride bed storage option
Safety containment/Hydrogen Zones
Pipework and implementation
Interlocks: evacuation system and burst disks
Heat and temperature
Experiment certification
LH2 absorber
Coil assembly
Transverse absorber/coil
removal from channel
Metal hydride beds
with buffer tanks
Window certifications
Absorber pre-assembly and testing
Absorber/coil assembly, testing and certification
Assembly into MICE cooling channel and certification
Hydrogen fill
Off-normal conditions
Exception handling for LH2:
Expeditious H2 evacuation (relief valves, pumping)
MICE shut-down
Hydride bed temperature regulation
Magnets: passive shielding; restricted access; forces analysized and
structurally accommodated
RF: shielding of beamline, cryo equipment and detector electronics;
water valve interlock; restricted access
Safety design based on recovery from 2 independent system failures
Off-normal conditions, LH2:
1)
2)
3)
4)
5)
6)
7)
8)
9)
RF cavity vacuum or detector vacuum air leak
Absorber vacuum window leak
Absorber leak
Hydrogen freezing
Large heat leak to the absorber
Loss of refrigeration or loss of electrical power
Quench of the focusing solenoid
Rupture of the hydrogen window
Rupture of both hydrogen and safety windows
Review Outcome
Unqualified success:
Positive first review: no show-stoppers or omissions
Excellent advice and feedback
Detailed suggestions for development in three areas:
Gas-handling and venting
R & D of the metal hydride system
Windows development (seals, monitoring)
Good discussion on interlocks and monitoring
Instructive discussion of “instrinsically safe” and proper
response thresholds for off-normal conditions
Can now proceed with the technical design