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0 Innovative Fusion Confinement Concepts
Matt Walsh October 3, 2014

1 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: The materials in the PFRC reactor will be able to withstand up to and over 30 years of continuous operation Reactor operators can safely stand less than a meter from the reactor for extended periods

2 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

3 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 confine Source: Huba, J. D. NRL Plasma Formulary. Washington, DC: Naval Research Laboratory, Print. 2D + 3He -> 4He + 1p MeV

4 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, Print.

5 PFRC Neutron Production
PFRC reduces neutron production by: Burning D-3He Being smaller Removing produced tritons Using a 3He rich fuel mixture Operating at a different temperature than the peak for D-T Comparing the Neutron Wall Load of Reactor Designs

6 Types of Neutron Radiation Damage
Microscopic: Changes in the lattice organization of the material (displaces atoms, creates interstitials) Excitation of atoms, heating Activation - can induce radioactivity in materials Source: "Neutron Radiation." Examples of Defects in Lattice Structure

7 Types of Neutron Radiation Damage
Macroscopic: Embrittlement Swelling - problem for ceramics, can complicate coolant flows especially in small channels Neutrons can cause production of He, forming gas bubbles Production of heat Source: "Development of Radiation Resistant Reactor Core Structural Material."

8 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."

9 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

10 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

11 Neutron Shielding with B4C
Absorption Cross Sections of B-10 (above) and B-11 (below) 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.

12 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

13 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

14 Attila Generated 3D Mesh (113,000 Cells)
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

15 Heating for Model with 20cm of B4C
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

16 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

17 DPA for Model with 20cm of B4C
Maximum DPA/year by Region cm of B4C Superconductors Shielding Inner VV RF Antenna 20 7.61E-04 1.68E-02 3.00E-02 5.56E-03

18 Neutron Flux log(Flux) for Model with 20cm of B4C
With 38.87cm of natural or 32.85cm of enriched shielding, 30 year fluence in superconductors > 6e17 n/cm^2 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)

19 Neutron Flux Regulations
OSHA Regulations- 2.5 MeV neutrons: 3.7+e13 neutrons/m^2 per calendar quarter

20 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%)

21 Helium Production He Production for Model with 20cm of B4C 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 Superconductor Shielding Inner VV RF Antenna 20 1.06E-03 5.90E+01 5.18E-09

22 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

23 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)

24 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): Web. Huba, J. D. NRL Plasma Formulary. Washington, DC: Naval Research Laboratory, Print. "Ionizing Radiation." Occupational Safety and Health Standards: Toxic and Hazardous Substances. OSHA, n.d. Web. "Neutron Radiation." Wikipedia. Wikimedia Foundation, 13 July Web. 21 July 2014. Yvon, P., and F. Carré. "Structural Materials Challenges for Advanced Reactor Systems." Journal of Nuclear Materials (2009): Web.

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