Innovative Fusion
Confinement Concepts
Matt Walsh
October 3, 2014
Presentation Overview
● PFRC will produce at least 100 times fewer neutrons than a
D-T burning reactor
● Neutron radiation is still damaging, but PFRC will require
much less shielding than a D-T Tokomak (less than a meter
compared to several meters)
● With adequate shielding:
o The materials in the PFRC reactor will be able to
withstand up to and over 30 years of continuous
operation
o Reactor operators can safely stand less than a meter
from the reactor for extended periods
Acknowledgements
● Thank you to Russ Feder and Jonathan Klabacha for
help, guidance, wisdom, and patience
● Thank you to Professor Cohen for guidance, back of the
envelope calculations, and assistance preparing this
presentation
● Thank you to Kevin Griffin, with whom I worked this
summer
Background
PFRC - fusion reactor operating with D-3He
reaction, generates all charged particles:
2D
+ 3He -> 4He + 1p + 18.3MeV
Charged particles can be contained in magnetic
field, so plasma is easier to confine
Source: Huba, J. D. NRL Plasma Formulary. Washington, DC: Naval Research Laboratory, 2009. Print.
Background
Some neutrons are produced from side fusion
reactions:
2D
+ 2D -> 3T (1.01MeV) + 1p (3.01MeV)
-> 3He (.82MeV) + 1n (2.45MeV)
2D
+ 3T -> 4He (3.5MeV) + 1n (14.1MeV)
(small quantities compared to pure D-T fusion)
Source: Huba, J. D. NRL Plasma Formulary. Washington, DC: Naval Research Laboratory, 2009. Print.
PFRC Neutron Production
PFRC reduces neutron production
by:
1. Burning D-3He
2. Being smaller
3. Removing produced tritons
4. Using a 3He rich fuel mixture
5. Operating at a different
temperature than the peak for D-T
Comparing the Neutron Wall Load of
Reactor Designs
Types of Neutron Radiation Damage
● Microscopic:
o Changes in the lattice
organization of the material
(displaces atoms, creates
interstitials)
o Excitation of atoms, heating
o Activation - can induce
radioactivity in materials
Source: "Neutron Radiation."
Examples of Defects in Lattice Structure
Types of Neutron Radiation Damage
● Macroscopic:
o Embrittlement
o Swelling - problem for ceramics, can complicate
coolant flows especially in small channels
o Neutrons can cause production of He, forming gas
bubbles
o Production of heat
Source: "Development of Radiation Resistant Reactor Core Structural Material."
Types of Neutron Radiation Damage
● Considered most dangerous type of
radiation to humans due to high kinetic
energy
● Up to 10x more damaging than gamma or
beta particles
● Activation causes release of gamma and
beta radiation
Source: "Neutron Radiation."
Background Summary
● Neutron production is a smaller problem for
the PFRC than in D-T burning reactors
● Some neutrons will be produced
● Neutrons are damaging to both materials
and nearby people
Reactor Materials
● Shielding: Boron Carbide (B4C), can use B-10 enriched
to reduce amount required
● Cooling Coils: Tungsten (cooled with helium), modeled
as inner VV layer
● Superconducting Coils: YBCO - superconductivity at
over 77K (liquid nitrogen temperature)
● RF Antenna: Copper
Neutron Shielding with B4C
The large absorption cross
section of boron makes B4C a
good potential shielding
material.
Naturally occurring Boron
mixture is about 20% B-10 and
80% B-11.
Enriched B4C, with higher
concentration of B-10, can
provide the same neutron
shielding with less material.
Absorption Cross Sections of B-10 (above) and B-11
(below)
Device Dosage Tolerances
Heating
● Nuclear heating small relative to
bremsstrahlung, synchrotron
(1% of energy compared to 40%)
● Possible concern for
superconductors (liquid N2
cooled, must be kept at low T)
DPA
● Maximum for strengthened
steels O(100) (Nature Materials)
● High-T superconductors - limit
not studied, but increase in
performance with small amounts
● Not well studied for many
materials, including B4C
Device Dosage Tolerances
Swelling
● Material swelling of even a few
% would increase lengthwise
dimension by several cm
● Ideally keep this << 1% in
shielding
● Also difficult to estimate
Flux
● Concern for superconductor
materials, human operators, can
be a form of ionizing radiation
● Fluence limit for YBCO of 6e+17
n/cm^2 (with KE > .1 MeV) for a
TC drop < 5%
● According to OHSA for 2.5 MeV:
limit of 3.7e+13 neutrons/m^2
per calendar quarter
Attila Generated 3D Mesh (113,000 Cells)
Attila
Particle simulation code that solves
problems in space, angle and
energy
● A model mesh is a refinement
in space
● The scattering order refines the
angles considered in particle
interactions.
● Energy groupings split different
energy neutrons into groups
that are evaluated together.
Illustration of Ray Effects from a Coarse Mesh
Heating
Heating for Model with 20cm of B4C
Maximum Heating by Region (W/cc)
cm
of
B4C
Superconductors
20
1.05E-03
Shielding
1.79E-01
Inner VV
1.24E-01
RF Antenna
3.44E-04
Heating Hand Calculation
Theoretical Heating = (Energy per Reaction)*(Reaction Rate)
Reaction Rate = (Neutron Flux)*e^(thickness/mean free path)
Theoretical Heating = 33.5 kW (considering only B4C and W)
Attila Calculated Heating = 40 kW
Discrepancy may be due to neglecting other materials,
secondary reactions, gamma heating
*In Attila, reaction rate refers to frequency of particle interaction
DPA
DPA for Model with 20cm of B4C
Maximum DPA/year by Region
cm of
B4C
20
Superconductors
7.61E-04
Shielding
1.68E-02
Inner VV
3.00E-02
RF Antenna
5.56E-03
Neutron Flux
With 38.87cm of natural or 32.85cm of
enriched shielding, 30 year fluence in
superconductors > 6e17 n/cm^2
log(Flux) for Model with 20cm of B4C
Maximum Flux in Superconductors
cm of B4C
Flux
(n/cm^2*s)
30 year Fluence
(n/m^2)
20
1.24E+10
2.21E+21
30
1.25E+09
2.22E+20
40
1.20E+08
2.15E+19
Trend Equation: Fluence = 2.1e+23*e^(-.229*thickness (cm)) (n/m^2)
Neutron Flux Regulations
OSHA Regulations2.5 MeV neutrons: 3.7+e13 neutrons/m^2 per calendar quarter
Flux Hand Calculation
% stopped = e^(thickness/mean free path)
mean free path = 1/((atomic density)*(cross
section)
Take into account expansion of area
Estimate: ~90% of neutrons absorbed with
32.85cm of shielding (actual: ~99.9%)
He Production for Model with
20cm of B4C
Helium Production
The majority of He production
occurs in B4C. With proper
channeling, this amount could be
easily removed from the shielding
Maximum He Production by Region (ppm/year)
cm of
B4C
20
Superconductor
1.06E-03
Shielding
5.90E+01
Inner VV
RF Antenna
0
5.18E-09
Conclusions
● Neutron Flux, nuclear heating, DPA, and
helium production are at least 100 times less
in the PFRC than in a D-T reactor
● The materials in the PFRC could withstand
at least 30 years of operation
● Enriched B4C would decrease the amount of
shielding needed but is not essential
Future Areas of Research
● Examine activation of materials
● How do results change with addition of 14MeV
neutrons from D-T reactions?
● Investigate effects of neutron irradiation on
new materials (enriched B4C, YBCO)
Sources
"Development of Radiation Resistant Reactor Core Structural Material." International Atomic Energy
Agency (n.d.): n. pag. Web.
Grimes, Konings, and Edwards. “Greater Tolerance for Nuclear Materials.” Nature Materials issue 7
(2008): 683-685. Web.
Huba, J. D. NRL Plasma Formulary. Washington, DC: Naval Research Laboratory, 2009. Print.
"Ionizing Radiation." Occupational Safety and Health Standards: Toxic and Hazardous Substances.
OSHA, n.d. Web.
"Neutron Radiation." Wikipedia. Wikimedia Foundation, 13 July 2014. Web. 21 July 2014.
Yvon, P., and F. Carré. "Structural Materials Challenges for Advanced Reactor Systems." Journal of
Nuclear Materials 385.2 (2009): 217-22. Web.