Neutron Imaging Facility: Neutron Radiography and Tomography Facilities at NIST to Analyze In-Situ PEM Fuel Cell Performance Facility Staff David L. Jacobson Daniel S. Hussey Elias Baltic Muhammad Arif Physics Laboratory Project Design Engineer James LaRock Center for Neutron Research National Institute of Standards and Technology Technology Administration U.S. Department of Commerce Fuel Cell Partners Jon Owejan Jeffrey Gagliardo Thomas Trabold General Motor Fuel Cell Activities

Neutron Imaging Facility: Old Facility Began operation in 2003 Located at BT-6 Facility was small –Volume 3 m 3 Basically no support for fuel cell experiments other than –Hydrogen gas 1.2 slpm –Nitrogen from bottle –Air from bottle Ceased operation in December of 2005

Neutron Imaging Facility: New Facility First users February 27, 2006 Located at BT-2 Much bigger 30 m 3 House gases/fluids –Hydrogen (18.8 slpm) –Oxygen (11.1 slpm) –Nitrogen –Air –Deionized water –Chilled water Freeze chamber for low temperature testing (-40 o C) available early 2007 Fuel cell test stands available and supported by NIST staff

Neutron Imaging Facility: Hydrogen Safety Computational Fluid Dynamics modeling –Free software –NIST Fire Dynamics Simulator (FDS) – Release point in reactor confinement building Extremely high buoyancy turbulently mixes hydrogen resulting in low concentrations throughout room Diffusion coefficient at STP in air= 0.61 cm 2 s -1 Diffusion velocity at STP in air  2 cm/s Buoyant velocity at STP in air= (1.9 m/s to 9 m/s) Explosive equivalent at 28% H 2 in air1 g H 2 = 24 g TNT Lower explosive limit by volume fraction4% Upper explosive limit by volume fraction77% Hydrogen Plume 22.4 lpm

Neutron Imaging Facility: Modeling the Release Point Lower flammability limit Upper flammability limit Maximum release modeled for 22.4 liters per minute (2 g H 2 ). Very seldom is this release rate actually required. Above release point a maximum of 68 mg of hydrogen is expected to be within the range of 77% to 4% and so an unlikely detonation of such a mixture is expected to have a maximum explosive yield similar to a few firecrackers. Conclusion: for our system it is safe to release hydrogen to the room.

Neutron Imaging Facility: Modeling Hydrogen Release in Reactor Confinement Building Mass (kg/kg) x 10 -4

Neutron Imaging Facility: Schematic of New Facility

Neutron Imaging Facility: Design of Neutron Collimation Primary collimator tapers beam Bismuth filter –15 cm long –Liquid nitrogen cooled Apertures –5 positions Local shutter –Heavy concrete filled –60 cm in length –3 through tubes for additional collimation Fast exposure control –Allows < 1 second exposure control Primary collimator Apertures Bismuth filter Fast exposure Local shutter

Neutron Imaging Facility: Primary Collimator Hollow steel frame Filled with heavy concrete 10 cm long steel rings taper beam down to 2 cm maximum aperture size Borated aluminum discs are used throughout to reduce long term activation Steel rings taper beam from reactor Steel caseHeavy concrete filled

Neutron Imaging Facility: Bismuth Filter Bismuth crystal –Filters gammas and high energy neutrons –Ideally single crystal –Here we have several large single crystals 5 cm reduces thermal neutrons by 57 % 15 cm reduces neutron fluence to 19 % Banjo Dewar –Provides insulated liquid nitrogen jacket –Sealed and evacuated during operation Banjo Dewar (named after the musical instrument) Super insulation/liquid nitrogen jacket 10 cm dia. hole for bismuth to sit

Neutron Imaging Facility: Aperture Assembly Can be any material that fits 5 positions Largest aperture diameter is 2 cm due to primary collimation Easily changed without major shielding manipulations 5 apertures (2 cm, 1.5 cm, 1.0 cm, 0.5 cm, 0.1 cm)

Neutron Imaging Facility: Rotating Drum Rotates to 1 of 4 positions –Position 0 beam is blocked –Position 1 beam is collimated for 1 cm effective aperture –Position 2 beam is collimated for 2 cm effective aperture –Position 3 no collimation currently Filled with heavy concrete 60 cm long

Neutron Imaging Facility: Fast Exposure Designed to ensure uniform fluence. –Beam is opened and closed in the same direction

Neutron Imaging Facility: Fast Exposure Designed to ensure uniform fluence. –Beam is opened and closed in the same direction Time for each motion is about 0.1 seconds. Can be set for fixed times and manually operated Can be operated by computer control.

Neutron Imaging Facility: Shielding Steel shot and wax external to the reactor. Inside reactor only heavy concrete and steel is used.

Neutron Imaging Facility: Schematic of New Facility

Neutron Imaging Facility: Flight Path and Sample Position 6 meters from aperture to sample position. Aluminum flight tube evacuated. Short sections can be made into a shorter tube for closer positions. Closest position is 1 meter.

Neutron Imaging Facility: Real-Time Detector Technology Amorphous silicon Varian Paxscan 2520 high energy version –Cost is ~$100, US –No longer produced as of 2006 –However, if you are willing to void the warranty you could convert a low energy detector (still produced) to a high energy detector. Radiation hard High frame rate (30 fps) 127 micron spatial resolution No optics – scintillator directly couples to the sensor to optimize light input efficiency –Standard green Li6ZnS scintillator 0.3 mm thick We experienced a failure of the readout electronics in July of 2006 –Failure is believed to be due to radiation damage –We were able to quickly fix by swapping the guts of a spare low energy panel with this detector frame. Data rate is 42 Megabytes per second (160 gigabytes per hour) Neutron beam scintillator aSi sensor Side view Readout electronics Scintillator aSi sensor Front view

Neutron Imaging Facility: New High Resolution Imaging Device 25 micrometer resolution available this fall. An order of magnitude improvement in spatial resolution. 10 micrometer resolution expected in Less than 10 micrometer???

Neutron Imaging Facility: Beam Properties L (m) D (cm) L/dBeam Dia. (cm) Fluence Rate (s -1 cm -2 ) Fluence Rate No Bismuth (s -1 cm -2 ) x x x x x x x x x x x x x x x x10 5 At 6 m A factor of 2 in beam fluence rate can be gained by removing 5 cm of bismuth

Neutron Imaging Facility: Schematic of New Facility

Neutron Imaging Facility: Beam Stop With most intense beam the field is less than 0.2 mrem hr -1 or 2  Sv Magnesium is used instead of aluminum to avoid harsh 7 MeV gamma from aluminum Box of boron carbide 15 cm thick absorbs majority of beam The rest is wax and steel shot 90 cm 45 cm

Neutron Imaging Facility: Hydrogen Systems State of the art, custom-built, PEFC test stand Flow control over H2, Air, N2, He, O2 with accuracy of 1 % full scale: –H2: and sccm –N2: sccm –Air: 0-100, 0-500, , sccm –O2: 0-500, sccm –He: 0-600, sccm Users can create custom gas mixtures for anode and cathode in the stand Measurement of high current densities with boost power supply allowing voltage control of the cell to a minimum of 0.01 V Heated Inlet gas lines Built-in humidification of anode and cathode gas streams for all flow rates Graphical User Interface Logs and stores files of all cell parameters during operation Multiple thermocouple inputs Interfaced with facility hydrogen safety system All users of the NIST NIF have access to the stand

Neutron Imaging Facility: Hydrogen Systems Continued Piping manifold appears in back. Nitrogen gas supplied from liquid nitrogen dewar. Hydrogen generator provides 18.8 liters per minute. Deionized water for the hydrogen generator and test stand humidifiers. NitrogenHydrogen Deionized water Hydrogen and Oxygen Sensor readout

Neutron Imaging Facility: Final Remarks Facility is accepting proposals through the NIST user proposal system as well as proprietary requests directly to NIST staff. Users from both industry, national laboratories and academia use the facility for both proprietary and non- proprietary research. Reactor cycle is 290 days per year currently all have been utilized.