Presentation on theme: "Presentation Overview"— Presentation transcript:
0Innovative Fusion Confinement Concepts Matt WalshOctober 3, 2014
1Presentation Overview PFRC will produce at least 100 times fewer neutrons than a D-T burning reactorNeutron 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 operationReactor operators can safely stand less than a meter from the reactor for extended periods
2AcknowledgementsThank you to Russ Feder and Jonathan Klabacha for help, guidance, wisdom, and patienceThank you to Professor Cohen for guidance, back of the envelope calculations, and assistance preparing this presentationThank you to Kevin Griffin, with whom I worked this summer
3BackgroundPFRC - 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, Print.2D + 3He -> 4He + 1p MeV
4Background 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.
5PFRC Neutron Production PFRC reduces neutron production by:Burning D-3HeBeing smallerRemoving produced tritonsUsing a 3He rich fuel mixtureOperating at a different temperature than the peak for D-TComparing the Neutron Wall Load of Reactor Designs
6Types of Neutron Radiation Damage Microscopic:Changes in the lattice organization of the material (displaces atoms, creates interstitials)Excitation of atoms, heatingActivation - can induce radioactivity in materialsSource: "Neutron Radiation."Examples of Defects in Lattice Structure
7Types of Neutron Radiation Damage Macroscopic:EmbrittlementSwelling - problem for ceramics, can complicate coolant flows especially in small channelsNeutrons can cause production of He, forming gas bubblesProduction of heatSource: "Development of Radiation Resistant Reactor Core Structural Material."
8Types of Neutron Radiation Damage Considered most dangerous type of radiation to humans due to high kinetic energyUp to 10x more damaging than gamma or beta particlesActivation causes release of gamma and beta radiationSource: "Neutron Radiation."
9Background SummaryNeutron production is a smaller problem for the PFRC than in D-T burning reactorsSome neutrons will be producedNeutrons are damaging to both materials and nearby people
10Reactor MaterialsShielding: Boron Carbide (B4C), can use B-10 enriched to reduce amount requiredCooling Coils: Tungsten (cooled with helium), modeled as inner VV layerSuperconducting Coils: YBCO - superconductivity at over 77K (liquid nitrogen temperature)RF Antenna: Copper
11Neutron 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.
12Device Dosage Tolerances HeatingNuclear 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)DPAMaximum for strengthened steels O(100) (Nature Materials)High-T superconductors - limit not studied, but increase in performance with small amountsNot well studied for many materials, including B4C
13Device Dosage Tolerances SwellingMaterial swelling of even a few % would increase lengthwise dimension by several cmIdeally keep this << 1% in shieldingAlso difficult to estimateFluxConcern for superconductor materials, human operators, can be a form of ionizing radiationFluence 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
14Attila Generated 3D Mesh (113,000 Cells) Particle simulation code that solves problems in space, angle and energyA model mesh is a refinement in spaceThe 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
15Heating for Model with 20cm of B4C Maximum Heating by Region (W/cc)cm of B4CSuperconductorsShieldingInner VVRF Antenna201.05E-031.79E-011.24E-013.44E-04
16Heating 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
17DPA for Model with 20cm of B4C Maximum DPA/year by Regioncm of B4CSuperconductorsShieldingInner VVRF Antenna207.61E-041.68E-023.00E-025.56E-03
18Neutron 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^2Maximum Flux in Superconductorscm of B4CFlux (n/cm^2*s)30 year Fluence (n/m^2)201.24E+102.21E+21301.25E+092.22E+20401.20E+082.15E+19Trend Equation: Fluence = 2.1e+23*e^(-.229*thickness (cm)) (n/m^2)
20Flux Hand Calculation % stopped = e^(thickness/mean free path) mean free path = 1/((atomic density)*(cross section)Take into account expansion of areaEstimate: ~90% of neutrons absorbed with 32.85cm of shielding (actual: ~99.9%)
21Helium ProductionHe Production for Model with 20cm of B4CThe majority of He production occurs in B4C. With proper channeling, this amount could be easily removed from the shieldingMaximum He Production by Region (ppm/year)cm of B4CSuperconductorShieldingInner VVRF Antenna201.06E-035.90E+015.18E-09
22ConclusionsNeutron Flux, nuclear heating, DPA, and helium production are at least 100 times less in the PFRC than in a D-T reactorThe materials in the PFRC could withstand at least 30 years of operationEnriched B4C would decrease the amount of shielding needed but is not essential
23Future Areas of Research Examine activation of materialsHow do results change with addition of 14MeV neutrons from D-T reactions?Investigate effects of neutron irradiation on new materials (enriched B4C, YBCO)
24Sources"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.