Transcript MUSIC Members - Nc State University

UCN Source at the
NCSU PULSTAR Reactor
Bernard Wehring and Albert Young
North Carolina State University
International Workshop on Neutron-Antineutron
Transition Search with Ultra Cold Neutrons
13-14 September 2002
Bloomington, Indiana
Outline
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NCSU PULSTAR Reactor
Desirable Attributes
NCSU UCN Source
Conceptual Designs
Conclusion
NCSU PULSTAR Reactor
NCSU PULSTAR Core
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5 x 5 array of fuel
assemblies
5 x 5 array of pins
Sintered UO2 pellets
4% enriched
1-MW power
Graphite, Be reflected
Light water moderated
and cooled
Desirable Attributes
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Properties
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Heavy loading of U-235 -- 12.5 kg
Low ratio of H to U-235 atoms
High ratio of fast to thermal flux in the core
Benefits
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High fast-flux leakage
High sensitivity to reflector material
Long core lifetime
PULSTAR Flux
1-MW TRIGA Mark II
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U-ZrH fuel
19.7% enrichment
3.5 kg U-235 mass
~ 64 liter core volume
1013 n/cm2s core avg
thermal flux
6.4 x 1012 n/cm2s core
avg. fast flux
Thermal flux
UCN Source at PULSTAR
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Parametric design calculations
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CN fluxes in the UCN converter and heating rates
by MCNP simulations of the PULSTAR reactor, CN
source, and UCN converter.
UCN production rates by integrating the converter
CN energy spectrum with the UCN production
cross sections.
UCN intensity at end of an open UCN guide using
lumped-parameter and UCN-transport calculations.
NCSU UCN Source Details
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UCN Converter
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Solid ortho D2
4-cm thick
18-cm diameter
CN Source
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Solid methane
1-cm thick
Cup shape around
UCN converter
Conceptual Design I
(top view)
CN Flux (MCNP)
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Averaged over UCN
converter
Integrated, 0 to 10 meV
CN energies
φ = 1.0 x 1012
CN/cm2-s
Neutron and Gamma Heating
Rates (MCNP)
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UCN converter, 86 g
UCN converter chamber, 484 g
CN source, 408 g
CN source chamber, 1164 g
0.7 W
2.1 W
4.0 W
4.4 W
UCN Production Rate
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P = N<σ>φ V
<σ> = <σsingle> +
<σmulti>
<σsingle> = 5 x 10-7 b/D
<σmulti> = 1 x 10-7 b/D
V = 1000 cc
P = 3.6 x 107 UCN/s
UCN Intensity at End of Open
Ni-58 Guide
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Io = f P
f = absorption leak / (absorption + leak)
absorption = 50 ms
leak = 4 V / (S<v>) = 4 t /<v> = 32 ms
f = 0.6
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Io = 2.2 x 107 UCN/s
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Conceptual Design II
(side view)
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CN flux averaged over
UCN converter
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4-cm thick x 18-cm
diameter
φ = 1.0 x 1012
CN/cm2-s
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UCN intensity at end of
open Ni-58 guide
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50-cm rise, 2-m level
Io = 1.2 x 107 UCN/s
Conceptual Design III
(side view)
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CN flux averaged over
UCN converter
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4-cm thick x 18-cm
diameter
φ = 1.2 x 1012
CN/cm2-s
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UCN intensity at end of
open Ni-58 guide
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50-cm rise, 2-m level
Io = 1.5 x 107 UCN/s
N-N Bar Experiment
Conclusion
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UCN intensity at bottle entrance (2 MW)
Io = 3 x 107 UCN/s
Bottle equivalent radius, R = 150 cm
Avg. chord length, L = 4/3 x R = 200 cm
L / (avg. UCN speed), t = 0.5 s
Bottle lifetime,  = 300 s
Discovery potential, coherent free path > 2L
> Io x (/2t) x (2t)2 = 9 x 109 s (> 6 ILL)