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:

Charged particles can be contained in magnetic field, so plasma is easier to confineSource: Huba, J. D. NRL Plasma Formulary. Washington, DC: Naval Research Laboratory, 2009. Print.

2D + 3He -> 4He + 1p + 18.3MeV

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-3He2. Being smaller3. Removing produced tritons4. Using a 3He rich fuel mixture5. 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, heatingo Activation - can induce

radioactivity in materialsSource: "Neutron Radiation."

Examples of Defects in Lattice Structure

Types of Neutron Radiation Damage

● Macroscopic: o Embrittlemento Swelling - problem for ceramics, can complicate

coolant flows especially in small channelso 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

AttilaParticle 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.

Attila Generated 3D Mesh (113,000 Cells)

Illustration of Ray Effects from a Coarse Mesh

Heating

Maximum Heating by Region (W/cc)

cm of B4C

Superconductors Shielding Inner VV RF Antenna

20 1.05E-03 1.79E-01 1.24E-01 3.44E-04

Heating for Model with 20cm of B4C

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 kWDiscrepancy may be due to neglecting other materials, secondary reactions, gamma heating

*In Attila, reaction rate refers to frequency of particle interaction

DPA

cm of B4C

Superconductors Shielding Inner VV RF Antenna

20 7.61E-04 1.68E-02 3.00E-02 5.56E-03

Maximum DPA/year by Region

DPA for Model with 20cm of B4C

Neutron Fluxlog(Flux) for Model with 20cm of B4C

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

With 38.87cm of natural or 32.85cm of enriched shielding, 30 year fluence in superconductors > 6e17 n/cm^2

Maximum Flux in Superconductors

Trend Equation: Fluence = 2.1e+23*e^(-.229*thickness (cm)) (n/m^2)

Neutron Flux RegulationsOSHA Regulations- 2.5 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%)

Helium Production

The majority of He production occurs in B4C. With proper channeling, this amount could be easily removed from the shielding

cm of B4C

Superconductor Shielding Inner VV RF Antenna

20 1.06E-03 5.90E+01 0 5.18E-09

Maximum He Production by Region (ppm/year)

He Production for Model with 20cm of B4C

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.