1. Safety Issues Cryovessel, Refrigerators and Associated Equipment WBS 1
D. G. Haase
NC State University and TUNL

2. Components of WBS 1.3 Cryovessel Refrigerators
Outer volume
LN Shield
4.2 K Shield
300 l LHe Entrainment Volume
Associated pumps and instrumentation
Refrigerators
Helium Liquefier (long-lead time procurement)
Dilution Refrigerator (long-lead time procurement)
Liquid Nitrogen Services
Central Insulation Volume
Sensors and Controls

3. nEDM in FNPB

4. Cryovessel Neutron Beam LHe Entrainment Volume Intermediate Shield
4 K Shield
Outer
Vessel DR
Cryostat
Neutron
Beam
Helium
Insulation Volume

5. Cryovessel Design Criteria Overview
House, support and cool the magnet system, central volume and dilution refrigerator at 4.2 K for 180 days between warmups
Provide thermal grounding for appropriate electrical sensors and controls for other systems
Able to cool from room temperature close-up to full helium insulation volume at Toperating in 14 days
Appropriate safety devices and procedures

6. Cryovessel Components
Enclosure for all of cryogenic components of the nEDM experiment
Vacuum vessel
Intermediate heat shield
Liquid helium entrainment volume
4.2 K heat shield
Support structure
Associated vacuum system
Sensors and controls
Safety releases and vents

7. Helium Liquefier Design Criteria Overview
Provide 13 l/hr/48 watts of equivalent refrigeration/liquefaction to the cryovessel for 180 days between warmups
Closed cycle system
Meet appropriate safety standards and procedures
A LN storage and delivery system continuously cools the liquefier engine and traps, as well as the intermediate temperature shield of the cryovessel

8. Helium Liquefier - Components
Liquefier Engine (Linde L70 turbine compressor)
Compressor (Kaeser CSD 122, 75 kW, supplied through Linde)
Transfer Lines (Linde supplied bayonets)
LN Air Trap
Oil Removal System
Gas Purity Monitor
Moisture Meter
Pump Inlet Gas Reheater
40,000 Gallon Gas Storage Line (Quantum Technologies)
Gas Return Lines (locally fabricated)
Sensors and Controls (Linde, interfaced to EPICS system)
Piping to LN Supply (locally fabricated)
Installation and interfacing to Cryovessel

9. Dilution Refrigerator
Design Criteria Overview
Cooling power of 90 mW at T= 0.35 K
Continuous operation for 180 days
Adequate heat exchangers for liquid helium in insulation volume and 3He services system
Thermal grounding connections at 1.5 K, still and mixing chamber

10. Dilution Refrigerator
Components
External Gas Handling System
Pumping Stacks
Cryostat in Cryovessel
Separator
1.5 K Pot
Dilution Refrigerator
Thermal Grounds and Heat Exchangers
Sensors and Controls

11. Central Insulation Volume
Design Criteria Outline
Non-conductive, non-activated volume that will electrically insulate central detector components
Contains 1200 l of LHe at P = 1 atm and Toperating

12. Central Insulation Volume
Components
Barrel
End cap (for testing)
Seal and fasteners
Support structure
Cooling and pressurization
Sensors and controls

13. Sensors and Controls Design Criteria Outline
Monitoring of temperatures, pressures and liquid levels for normal operation of cryovessel, liquefier, dilution refrigerator and insulation volume
Appropriate thermal grounding and electrical shielding for all components that enter cryovessel
Electrical and mechanical control of WBS 1.3 processes
Thermal grounding points for mechanical and electrical devices from other subsystems
Safety issues - electrical

14. Classes of safety hazards
Large equipment
Electrical
Mechanical
Heights
Pressure vessels
Cryogenics
Cold
Displacement of oxygen
Enclosed cryogenic liquids

15. Cryogenic Safety Devices in FNPB
Oxygen Deficiency Monitors
Air handling system
Standard cryogenic safety clothing

16. Associated Documents WBS 1.3 Design Criteria Document
WBS 1.3 Engineering Document
nEDM Interface Document
nEDM Acceptance Criteria
Operation Manual for Cryovessel and Refrigerators
Hazards Analysis for Cryovessel, Refrigerators and Associated Equipment
Response to June 30, LLP Review

17. Helium Insulation Volume
Quantity
Specification
References/Comments
Volume
1200 liters
Volume is set by separations needed to avoid electrical breakdown in the high electric field in the experimental area.
Normal minimum and maximum operating pressures
1.5 atmospheres during testing and flushing at room temperature.
1.5 atmospheres during loading with liquid helium below 4.2 K
Rough vacuum during flushing and testing
Maximum allowable working pressure
2.0 atm
Selected to avoid unintended operation of the overpressure protection devices (OPD) due to operational transients. The OPD will be set to operate at not greater than 2.0 atm. The primary OPD connects directly to an overhead line that vents gas outside of FNPB
Design internal pressure
3.0 atm
Set by closed form calculations and FEA calculations

18. Cryovessel Vacuum Volume
Cryovessel - highest anticipated normal internal operating pressures
1.2 atmosphere during testing and flushing processes.
High vacuum during operation
Vacuum needed for effective thermal insulation of the components at Toperating.
Cryovessel - maximum normal external operating pressure
1 atmosphere
Interior of cryovessel at high vacuum, ambient pressure on outside
Cryovessel - design maximum internal pressures
80 psi = 5.3 atm
10 atm
Based on stress and FEA results of cryovessel without windows. Value determined by requirement that maximum deflection of the tee section limited to 1 mm or less under an external load of 24 psi (1.6 x atomospheric pressure)
Design pressure for zirconium window at upstream end of cryovessel
Cryovessel - maximum anticipated internal working pressure (MAWP)
1.5 atmospheres
Using 1.2 atmospheres as the highest anticipated normal internal operating pressure of the cryovessel. Primary overpressure protection devices (OPD) will set to operate at not greater than 1.5 atmospheres. Secondary OPD’s shall be installed on the cryovessel to operate at pressures with the lowest set at not less than 3 atm, and the highest set at no greater than 5 atm.
Cryovessel overpressure protection devices (OPD)
The main OPD will be set for 1.5 atm
The primary OPD connects directly to an overhead line that vents gas outside of FNPB Building

19. Cryovessel Entrainment Volume
Liquid helium entrainment volume
Nominal 300 l
The volume is chosen to allow time to react to temporary stoppages or malfunctions in the liquefier or refrigerator subsystems. Note that the liquefier system does not include an external liquid storage dewar. The static helium boiloff rate during a malfunction would be about 12 liquid liters per hour.
Liquid helium entrainment volume- normal anticipated internal operating pressure
1.2 atmosphere to rough vacuum during testing and flushing processes.
1 atmosphere during operation
Liquid helium entrainment volume- maximum anticipated internal operating pressure (MAWP)
1.5 atm
Using 1.2 atmospheres as the highest anticipated normal internal operating pressure of the cryovessel. Primary overpressure protection devices (OPD) will set to operate at not greater than 1.5 atmospheres.
Liquid helium entrainment volume- maximum anticipated external operating pressure
Set by MAWP for the cryovessel
Capacity requirements for the various OPD's described in this document, and the types of devices to be used shall be determined as part of the ongoing design process.
The design process will consider all credible hazards that would lead to overpressures of cryogenic liquids or gasses within the cryovessel or its enclosed subsystems.

20. Cryovessel OPD

21. Cryovessel OPD

22. Cryovessel OPD

23. Cryovessel OPD

24. Applicable Standards
Title 10 Code of Federal Regulation (CFR) Part 851, WORKER SAFETY AND HEALTH PROGRAM (February 9, 2006)
ASME Code Section VIII, Pressure Vessels
Spallation Neutron Source Quality Manual - SNS-QA-P01 Revision 5
Spallation Neutron Source Final Safety Assessment Document For Neutron Facilities ES0016-R01
SNS Mechanical Design Development Document - NFDD-ENG-003-R00
EDM_Hazard_Analysis_March_2007.pdf

25. Response to June 30, Review
Issues related to common volumes between components (ie. liquefier storage vessel and 300 l (entrainment volume) should be included in the safety analysis.
This has been completed for the December, 2008, review. The external liquefier storage vessel has been removed from the system design.
The design of the cryovessel should be communicated to the proper individuals at SNS to ensure they meet the SNS safety criteria.
We have had numerous face-to-face, phone and conversations on this matter with SNS operations and safety personnel.
Appropriate safety criteria and quality assurance should be incorporated into fixed cost bid documentation for each of these three items.
This will be done when the formal requests for bids are submitted to vendors.
There should be regular contact between project managers and individuals at the SNS responsible for ensuring the safe operation of the experiment.
We have had numerous conversations with SNS personnel and have established contacts with all personnel responsible for ensuring the safe operation of the experiment.

26. Cryogenic Hazards Event Loss of cryogenic refrigeration
Possible Consequences, Hazards
Pressure increases in all volumes containing liquid or gas. Slow conversion of liquids to gas.
Unmitigated consequences: Pressure increases in all volumes containing liquid or gas. Slow conversion of liquids to gas.
Potential Initiators
Loss of electrical power; stoppages in cryogen flow from liquefier, LN source or dilution refrigerator; operator error.
Hazard Mitigation
Method of Detection: Control panel alarms on refrigerator, dilution refrigerator and helium liquefier. Indicators include temperature, pressure and liquid level and gas flow sensors.
Preventive Features: Passive pressure releases vent liquid helium to room temperature storage volumes. Liquid nitrogen gas vents to atmosphere. 3He-4He mixture returns to dilution refrigerator storage tanks.
Mitigations/ Required Analyses: Documentation of relief device designs and relief line sizing calculations

27. Cryogenic Hazards Event
Loss of cryovessel insulation vacuum, inputting helium into vacuum space
Possible Consequences, Hazards
Rapid heating of the target and the internal parts of the cryostat above the normal operating temperatures, with accompanying increases in pressures. Collection of frozen air/nitrogen on inner surfaces of cryovessel and components.
Potential Initiators
Leak or break in cryovessel or its vacuum system; failure of external beam window; operator error
Hazard Mitigation
Method of Detection: Control panel alarms on refrigerator, dilution refrigerator and helium liquefier. Indicators include temperature, pressure and liquid level and gas flow sensors.
Preventive Features: Passive pressure releases vent liquid helium to room temperature storage volumes. Liquid nitrogen gas vents to atmosphere. 3He-4He mixture returns to dilution refrigerator storage tanks.
Mitigations/ Required Analyses: Documentation of relief device designs and relief line sizing calculations Proper design and installation of beam windows.

28. Cryogenic Hazards Event Large or medium fire in FNPB External Building
Possible Consequences, Hazards
Fire could stop operation of the nEDM cryogenic systems and affect the mechanical vacuum structures. The results would be the same as Events 1 and 3
Potential Initiators
Electrical shorts or motor malfunctions.
Hazard Mitigation
Method of Detection: Smoke detectors. Workers see and smell smoke.
See Events 1 and 3 for infrastructure impact indications.
Preventive Features: ORNL Fire Department response to fires. SNS combustibles control procedure. NEC requirements on wiring.
See Events 1 and 3 for relief devices that would become active.
Mitigations/ Required Analyses: Documentation of relief device designs and relief line sizing calculations

29. Cryogenic Hazards Event
Load from crane drops or collides with cryovessel, dilution refrigerator lines or gas handling system, LN transfer lines.
Possible Consequences, Hazards
A collision with the cryovessel may produce results the same as Events 1 and 2. A collision with the other components may produce results the same as Events 1 and 3. Possible massive spray of liquid helium or liquid nitrogen into the experimental room
Potential Initiators
Crane or sling failure. Rigger error.
Hazard Mitigation
Method of Detection: Workers see and hear collision or load drop. Dramatic changes in target parameters followed by Increase in concentrations of helium or nitrogen gas in experimental hall alarms.
Preventive Features: SMBS requirements on approval, conduct of lift, SMBS requirements on training of personnel doing lifts.
Hard limits on movement of lift during cryogenic operations.
Mitigations/ Required Analyses: Safety hardware

30. Cryogenic Hazards Event Seismic Event Possible Consequences, Hazards
Movement causes rupture of cryovessel and shearing of transfer and vacuum lines.
Potential Initiators
Earthquake.
Hazard Mitigation
Method of Detection: Would be immediately apparent to all workers on site since a PC-3 seismic event is a 2000-y earthquake.
Preventive Features: Passive pressure releases vent liquid helium to room temperature storage volumes. Liquid nitrogen gas vents to atmosphere. 3He-4He mixture returns to dilution refrigerator storage tanks.
Mitigations/ Required Analyses: Documentation of relief device designs and relief line sizing calculations

31. Operation Events Stoppage of flow in DR Stoppage of flow in 1.K pot
Stoppage of flow in separator
Pump failure
Loss of Electrical Power
Loss of Cryovessel Insulating Vacuum
Mitigations
Automatic - a
Passive - p
Electronic - e

32. Operation Event Stoppage of flow in DR (or DR pump failure) Effects
DR warms to 1.5 K (slow)
Mitigation
Move DR 3He/4He to storage volumes (a/p)
Stop data collection and 3He injection, flow and purification (a/e)
Open valve to allow insulation volume to SVP(a/p)
Open valve to allow target volume to SVP (a/p)

33. Operation Event Stoppage of flow in 1.5 K Pot (or 1.5 K pump failure)
Effects
DR warms to 4.2 K (slow)
Mitigation
Move DR 3He/4He to storage volumes (a/p)
Stop data collection and 3He injection, flow and purification (a/e)
Open valve to vent insulation volume to gas recovery system (a/p)
Open valve to allow target volume to gas recovery system (a/p)

34. Operation Event Stoppage of flow in helium separator (or pump failure)
Effects
DR warms to 1.5 K
Mitigation
Move DR 3He/4He to storage volumes (a/p)
Stop data collection and 3He injection, flow and purification (a/e)
Open valve to vent insulation volume to gas recovery system or atmosphere (a/p)
Open valve to allow target volume to gas recovery system (a/p)

35. Operation Event Loss of liquid helium in 300 l entrainment volume
Effects
DR warms above 4.2 K (slow)
Mitigation
Move DR 3He/4He to storage volumes (a/p)
Stop data collection and 3He injection, flow and purification (a/e)
Open valve to vent insulation volume to gas recovery system (a/p)
Open valve to allow target volume to gas recovery system (a/p)

36. Operation Event Loss of cryovessel insulation volume Effects
DR warms above 4.2 K (quickly)
Mitigation
Move DR 3He/4He to storage volumes (a/p)
Stop data collection and 3He injection, flow and purification (a/e)
Open valve to vent insulation volume to gas recovery system or atmosphere(a/p)
Open valve to allow target volume to gas recovery system or atmosphere (a/p)

37. Loss of Insulating Vacuum
Entrainment volume
Design/MAWP/Normal - 5 /1.3/1.0 atm
Heat flow dQ/dt = 6000 W
OPD at room temperature
30 in long by 2.87 in ID vent tube
P = 14.5 psi
Vents to 6/12 in ID tube to exterior of building

38. Loss of Insulating Vacuum
Central insulation volume
Design/MAWP/Normal - 3/2/1.2 atm
Heat flow dQ/dt = 6000 W
OPD’s at Toperating and room temperature
115 in long by 5.87 in ID vent tube
P = 4.0 psi
Vents to 6/12 in ID tube to exterior of building

39. Loss of Insulating Vacuum
Vent Stack
5.87 in ID x 152 in long adapting to 12 in ID x 520 in long to exterior of building
Combined flow from Entrainment Volume and Central Volume = .61 kg/sec
P = 1.6 psi

40. Dumping of LHe to Isolation Vacuum
Highly unlikely event
Possible causes
Spontaneous fracture of central insulation volume
Fracture analysis
Break in glue joint on window or valve operator
Continuing analyses of stresses
Scenario
Liquid flashes until Pgas = 1 atm
Liquid drips onto 4.2 K shield, magnets, through superinsulation, to 77 K shield, through superinsulation to outer aluminum vacuum wall
External wall should cool no more than 30 K. Aluminum does not embrittle.

41. Dumping of LHe to Isolation Vacuum
Gas expansion limited by heat input to liquid
5 in diam 1.2 atm OPD on cryovessel connected directly to 6/12 in vent line
Entrainment Volume will build pressure OPD opens at 1.3 atm
As Cryovessel pressure increases above 2.0 atm Central Insulation Volume OPD opens to 6/12 in vent line
Detailed analysis is not complete