Neutron Radiography and Tomography

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Neutron Imaging Facility
: http://physics.nist.gov/MajResFac/NIF/index.html

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
: http://physics.nist.gov/MajResFac/NIF/index.html

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
: http://physics.nist.gov/MajResFac/NIF/index.html

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
: http://physics.nist.gov/MajResFac/NIF/index.html

Hydrogen Safety


Computational Fluid Dynamics modeling


Free software


NIST Fire Dynamics Simulator (FDS)


http://www.fire.nist.gov/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 air

1 g H
2

= 24 g TNT

Lower explosive limit by volume fraction

4%

Upper explosive limit by volume fraction

77%

Hydrogen Plume
22.4 lpm

Neutron Imaging Facility
: http://physics.nist.gov/MajResFac/NIF/index.html

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
: http://physics.nist.gov/MajResFac/NIF/index.html

Modeling Hydrogen Release in Reactor Confinement Building

Mass (kg/kg) x 10
-
4

Neutron Imaging Facility
: http://physics.nist.gov/MajResFac/NIF/index.html

Schematic of New Facility

Neutron Imaging Facility
: http://physics.nist.gov/MajResFac/NIF/index.html

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
: http://physics.nist.gov/MajResFac/NIF/index.html

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 case

Heavy concrete filled

Neutron Imaging Facility
: http://physics.nist.gov/MajResFac/NIF/index.html

Bismuth Filter


Bismuth crystal


Filters gammas and high
energy neutrons


Ideally single crystal


H

ere 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
: http://physics.nist.gov/MajResFac/NIF/index.html

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
: http://physics.nist.gov/MajResFac/NIF/index.html

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
: http://physics.nist.gov/MajResFac/NIF/index.html

Fast Exposure


Designed to ensure uniform fluence.


Beam is opened and closed in the
same direction

Neutron Imaging Facility
: http://physics.nist.gov/MajResFac/NIF/index.html

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
: http://physics.nist.gov/MajResFac/NIF/index.html

Shielding


Steel shot and wax
external to the reactor.


Inside reactor only
heavy concrete and
steel is used.

Neutron Imaging Facility
: http://physics.nist.gov/MajResFac/NIF/index.html

Schematic of New Facility

Neutron Imaging Facility
: http://physics.nist.gov/MajResFac/NIF/index.html

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
: http://physics.nist.gov/MajResFac/NIF/index.html

Real
-
Time Detector Technology


Amorphous silicon


Varian Paxscan 2520 high energy version


Cost is ~$100,000.00 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
: http://physics.nist.gov/MajResFac/NIF/index.html

New High Resolution Imaging Device


25 micrometer resolution available this fall.


An order of magnitude improvement in spatial resolution.


10 micrometer resolution expected in 2007.


Less than 10 micrometer???

Neutron Imaging Facility
: http://physics.nist.gov/MajResFac/NIF/index.html

Beam Properties

L

(m)

D

(cm)

L/d

Beam
Dia.

(cm)

Fluence
Rate

(s
-
1

cm
-
2
)

Fluence
Rate No
Bismuth

(s
-
1

cm
-
2
)

2

2

100

8

5.1x10
7

3.0 x10
8

3

2

150

13

3.4 x10
7

2.0 x10
8

4

2

200

17

2.5 x10
7

1.5 x10
8

6

2

300

26

1.7x10
7

1.0 x10
8

6

1.5

400

26

1.0x10
7

5.9 x10
7

6

1.0

600

26

4.3x10
6

2.5 x10
7

6

0.5

1200

26

1.0x10
6

5.9 x10
6

6

0.1

6000

26

4.3x10
4

2.5 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
: http://physics.nist.gov/MajResFac/NIF/index.html

Schematic of New Facility

Neutron Imaging Facility
: http://physics.nist.gov/MajResFac/NIF/index.html

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
: http://physics.nist.gov/MajResFac/NIF/index.html

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: 0
-
500 and 0
-
3000 sccm


N2: 0
-
2000 sccm


Air: 0
-
100, 0
-
500, 0
-
2000, 0
-
8000 sccm


O2: 0
-
500, 0
-
5000 sccm


He: 0
-
600, 0
-
6000 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
: http://physics.nist.gov/MajResFac/NIF/index.html

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.

Nitrogen

Hydrogen

Deionized
water

Hydrogen and
Oxygen Sensor
readout

Neutron Imaging Facility
: http://physics.nist.gov/MajResFac/NIF/index.html

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.