Not Just Fusion: Exploring TWDEC
Technology for Fission Fragment Direct
Energy Conversion
A. G. Tarditi
Electrical Power Research Institute, Knoxville, TN
Introduction
•  Fission fragments direct energy conversion has been
considered in the past for increasing power plant
efficiency [1-4] and for space propulsion [5-6]
•  These concepts were focused on the direct conversion
of the charged fragments utilizing high-voltage DC
electrodes.
__________________________________________
[1] S. A. Slutz et al. ,Phys. Plasmas 10, 2983 (2003)
[2] P. V. Tsvetkov, et al., Trans. American Nucl. Soc., 91, 927 (2004)
[3] http://www.ne.doe.gov: 2003 and 2004 annual reports
[4] R. Clark and R. Sheldon, AIAA 2005-4460 (2005)
[5] G. Chapline and Y. Matsuda, Fusion Technology 20, 719 (1991)
[6] P. V. Tsvetkov, et al., AIP Conference Proceedings 813.1, 803, (2006)
Introduction (II)
•  Considering a different approach: direct energy
conversion of charged fission fragments kinetic
energy into alternating current via a traveling wave
coupling
•  This approach was first conceived application to
fusion reactions (Traveling Wave Direct Energy
Converter, TWDEC [7-9])
_________________________
[7] Momota H. et al. Fusion Technology, 35, 60 (1999)
[8] Momota, H., Miley, G.H., AIP, Conf. Proc., 608, 834, (2002)
[9] Yasaka Y. et al., Nucl. Fusion 49, 075009 (2009)
Previous Work on Fission DEC
Previous Work on Fission DEC
•  Fission fragments direct energy conversion has been
considered in the past for increasing power plant
efficiency [1-4] and for space propulsion [5-6]
•  These concepts were focused on the direct conversion
of the charged fragments utilizing high-voltage DC
electrodes.
__________________________________________
[1] S. A. Slutz et al. ,Phys. Plasmas 10, 2983 (2003)
[2] P. V. Tsvetkov, et al., Trans. American Nucl. Soc., 91, 927 (2004)
[3] http://www.ne.doe.gov: 2003 and 2004 annual reports
[4] R. Clark and R. Sheldon, AIAA 2005-4460 (2005)
[5] G. Chapline and Y. Matsuda, Fusion Technology 20, 719 (1991)
[6] P. V. Tsvetkov, et al., AIP Conference Proceedings 813.1, 803, (2006)
Previous Work on Fission DEC
Figure 2. Schematic of proposed Fission Fragment
Rocket. Fissile dusty plasma fuel is confned to dust
chamber, where RF induction coils heat the plasma.
Fission fragments are collimated by the magnetic field
either to collection electrodes for power, or exit the reactor for thrust.
Previous Work on Fission DEC
Previous Work on Fission DEC
Early JPL work: http://archive.org/details/nasa_techdoc_19670002490
Comparison w\Fusion Design
Momota-Miley Design [8] : Direct Energy Converter D-3He IEC
fusion core (several units, each 10 MW/6,000 kg) : D-3He IEC
units: power=10 MW, weight=6,000 kg
•  TWDEC (pair) total weight=35,000 kg
•  TWDEC power in=250 MW, power out=150 MW (h=0.6)
•  Length=150 m, Diameter=6.6 m
•  Heat removal 100 MW radiator panel 50x140m, temperature
600 K
•  Specific mass: a=0.14 kg/kW
TWDEC Fission Conceptual Design
•  Exploring of DEC configurations that could be
implemented within a nuclear fission core
•  Collecting and collimating a beam of charged fission
fragments (e.g. thin solid core for optimal fragment
extraction, [1])
•  Consider application to gas core (e.g. vortex
confinement, [7])
___________________________
[7] Sedwick, AIAA Journal of Propulsion and Power, Vol 23, No.
1, Jan-Feb 2007.
TWDEC Fission Conceptual Design
•  Charged fission fragments (positively charged, about
20 electron charges) are magnetically collected and
focused
•  Fission fragment beam of relatively low density, to
avoid significant space charge effects.
TWDEC Fission Example
•  235U => 140Xe + 94Sr + 2n
•  Consider a 100 MeV 140Xe fragment with a +20e
charge
•  140Xe fragment speed vXe=1.17·107 m/s
•  For a inter-electrode TWDEC distance of d=1 m the
frequency of the AC power is f0=vXe/2d=5.85 MHz
Alternating-gradient
beam focusing TWDEC Fission Example
•  Solenoidal magnetic field B0= 0.5 T:
-  140Xe fragment gyroradius= 1.71 m
B
Collimated
Fragment
Beam
Fragment at reduced
drift speed into TWDEC •  Side injection can reduce drift speed and TWDEC
frequency
•  Bunching can provide the non-adiabatic injection
required to capture the ions.
TWDEC Fission Example
•  235U => 140Xe + 94Sr + 2n
•  Consider a 100 MeV 140Xe fragment with a +20e
charge
•  140Xe fragment speed vXe=1.17·107 m/s
•  Consider a magnetic field B0= 0.5 T:
-  140Xe fragment gyroradius= 1.71 m
•  For a inter-electrode TWDEC distance of d=1 m the
frequency of the AC power is f0=vXe/2d=5.85 MHz
•  In “real life” multiple products must be considered
TWDEC Fission Challenges
•  In “real life” multiple fragment products (different
masses and energies) must be considered
•  Multiple channels may be required for efficiency
•  Electron flow must be dealt with
Summary
•  Fission fragments leave thin
fissile fuel elements
•  Fragments carry large positive
charge (≈20 e) and are collimated
into a beam by a magnetic field
•  Traveling Wave DEC converts
fragment energy into AC electric
power