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

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

nEDM in FNPB

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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.

Cryovessel OPD

Cryovessel OPD

Cryovessel OPD

Cryovessel OPD

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 - 102030102-ES0016-R01 SNS Mechanical Design Development Document - NFDD-ENG-003-R00 EDM_Hazard_Analysis_March_2007.pdf

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 email 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.

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

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.

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

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

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

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

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)

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)

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)

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)

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)

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

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

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

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.

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