Neutronic Activation Analysis for ITER Fusion Reactor

Neutronic Activation Analysis for ITER Fusion Reactor Barbara Caiffi 100 Congresso Nazionale SIF 1

Outlook Nuclear Fusion International Thermonuclear Experimental Reactor (ITER) Neutronics Computational Tools Activation Analysis for ITER Reactor 2

Nuclear Fusion Q=17.6 MeV D + T 4He (3,5 MeV) + n (14,1 MeV) How much energy from... 1 g ( 21H,31H) 1 g 235U 1 g petrol 1 g coal 7*108 KJ 8*107 KJ 40 KJ 0.04 KJ 3

Fuel Availability on the Earth DEUTERIUM: natural abundance 0.0154 % of H reserve in the oceans 2 1016 Kg TRITIUM: β radioactive with 12 years half life, not available in large quantities What is available? LITHIUM: n+ 6Li t + α + 4.8 MeV n+ 7Li n + t + α -2.8 MeV from 1 kg of Lithium can be produced 0.43 kg of tritium Lithium reserve in Earth crust [1] 1.3 10 9 Kg, TRITIUM: 5.6 10 8 Kg Lithium reserve in the ocean [1] 2.3 1014 Kg TRITIUM: 1014 Kg 1kg of D-T fuel produces 7* 108 MJ 200 GWh Year World Energy Consumption: 145 Gwh[2] Fusion could fulfil energy supply for 1.5 billion years [1]U.S. Geological Survey, 2012, commodity summaries 2011: U.S. Geological Survey [2]IEA, Annual Report 2013 4

How to Achieve Fusion Inertial Confinement Iced DT pellet as a fuel Heating trough laser compression Works in pulse mode only Magnetic Confinement At temperature required for fusion to occur, plasma is completely ionized Charge particles can be confined using magnetic field Application of this concept are the Tokamak (like ITER) 5

Tokamak RESULTING FIELD LINES The plasma is a secondary winding of a transformer. The resultant toroidal plasma current provides for Ohmic heating and generates the poloidal magnetic field Bθ Poloidal coils generated an additional toroidal magnetic field Bφ for greater stability 6

Economy of a Tokamak nτe n : ions density τe : confinement time Ignition : fusion charge products compensate for energy loss ( α in the case of DT plasma). n τe> ~2 1020 m-3s ~2 1019 m-3s ~25 3T =F (T ) < σ v >ab (T ) f c, ab Qab Abr T 4(1+δab ) Break-even : Fusion energy released must exceed the energy supplied. E FU =Q p=1 ηin E IN 7

Where we are now? ITER parameters Maior radius Minor radius Volume Plasma current Toroidal field Density Peak Temperature Fusion Power Plasma Burn 6.2 m 2 m 830 m 3 15 MA 5.3 T 10 20 m-3 2*108 K 500 MW 300-500 s 8

ITER Project ITER SITE: Cadarache (France) MAIN GOAL: Q>10 CADARACHE 500 MW of fusion power from 50 MW input power TER TIMELINE: 2008: Site levelling 2010: Start Tokamak complex excavation 2013: Start Tokamak complex construction 2014: Arrival of first manufactured components 2015: Begin tokamak assembly 2019: Complete tokamak assembly 2020: First Plasma 2027: First D-T Operation 9

ITER Machine 30 m 28 m 10

ITER Machine VACUUM VESSEL 30 m 28 m 11

ITER Machine VACUUM VESSEL BLANKET 30 m 28 m 12

ITER Machine VACUUM VESSEL BLANKET 30 m DIVERTOR 28 m 13

ITER Machine VACUUM VESSEL BLANKET POLOIDAL FIELD COILS 30 m DIVERTOR 28 m 14

ITER Machine VACUUM VESSEL BLANKET POLOIDAL FIELD COILS TOROIDAL FIELD COILS 30 m DIVERTOR 28 m 15

ITER Machine VACUUM VESSEL BLANKET POLOIDAL FIELD COILS TOROIDAL FIELD COILS 30 m CENTRAL SOLENOID DIVERTOR 28 m 16

ITER Machine VACUUM VESSEL 30 m 28 m 44 openings ( ports ): 18 upper ports 17 equatorials ports 9 lower ports 17

Neutronics in Fusion Technology DT Fusion Reaction QDT=17.6 MeV NEUTRON 14.1 MeV 80% of total energy PFUSION=500 MW Φn=1014 n/cm2s on the First Wall Neutrons: induce radioactivity in the structural materials as well as in the coolant damage materials through atom displacement, affecting mechanical and electric properties. produce hydrogen and helium, which make welding difficult if > 1 appm heat superconducting coils reducing their effectiveness These effects must be studied! 18

Shutdown Dose Rate The safety on a fusion plant requires a deep knowledge of the radiation map due to: prompt neutron and γ γ produced by activated material, in particular after the shutdown, when maintenance is planned. Three step procedure: Monte Carlo calculation of the spectral neutron flux in the materials Deterministic calculation of the radioactivity induced by neutrons as a function of irradiation or decay time Monte Carlo γ transport and calculation of the dose rate in the region of interest 19

Rigorous 2 Steps (R2S) Method 1) Monte Carlo neutron transport 2) Deterministic activation calculation 3) Monte Carlo γ transport INPUT MCNP Input File (3D geometry, materials, cross section libraries, neutron source) CODE OUTPUT MCNP5 - N Neutron flux and spectra map Material Irradiation Scenario Decay Time FISPACT Activity map γ source 23

Direct 1 Step (D1S) Method Substitute Capture with activation-induced radiative decay. Neutron and decay γ transport treated in a single run. Special, ad hoc generated, capture cross section data. (n,γ prompt) (n,γ activation decay) Cons: Ad hoc libraries should be produced for the activation dose relevant nuclides, so an a priori decision has to be made. Each set of libraries is suitable just for 1 cooling interval. 25

Shutdown Dose Rate Benchmarks Shutdown Dose Rate Benchmark at FNG[3] Mock-up of ITER First Wall (Water & Steel IG) Max diff < 25% Shutdown Dose Rate Benchmark at JET[4] In JET benchmark agreement is worse because of the lack of information about the technical drawing ( geometry, impurity content) Agreement between a factor 2-3 Good experimantal vs calculated data agreement [3] P. Batistoni, M. Angelone, L. Petrizzi, M. Pillon, Benchmark Experiment for the Validation of Shut-Down Activation and Dose Rate in a Fusion Device, J. Nucl. Sci. Techn., Suppl. 2, p. 974-977 (2002) [4] PETRIZZI, L., et al, Benchmarking of Monte Carlo based shutdown dose rate calculations for applications to JET, ICRS-10, Madeira, 2004 26

Shutdown Dose Rate in the ITER European TBM Port BIOSHIELD P IN ORT TE RS PA CE PIPE FOREST 3m TBM FRAME 4m 2m PO R PLU T G TBM 2 TBM 1 ITER project goals: 100 μsv/h 106 s after the shutdown in the Port Interspace Region [ ϕ~107 n/ (cm2s)] where maintenance is planned 27

European Test Blanket Module (TBM) Port Modules for tritium production tests, containing: Breeder (lithium) Neutron multiplier to improve efficiency n+ 6Li t + α + 4.8 MeV n+ 7Li n + t + α -2.8 MeV Helium Cooled Pebble Bed (HCPB): Breeder: lithiated ceramic pebbles (Li4SiO4 or Li2TiO3 ) HCLL Breeder Unit Neutron Multiplier: beryllium pebbles Helium Cooled Lithium Lead (HCLL): Breeder & Neutron Multiplier: PbLi eutectic (liquid at operating temperatures) HCPB Breeder Unit Inlet LiPb Pipe Helium cooled plates Outlet LiPb Pipe Helium cooled Lithiated pebbles + plates beryllium pebbles 28

ITER Model MCNP Model XZ SECTION 6m XY SECTION 8m B-Lite: Official Model for ITER neutronic analysis Represents 40 sector of the reactor Contains only main components TBM Port represented as an homogenized watersteel block Contains 21216 cells, 27920 surfaces, 26 materials Run 57 histories per second per core (10 9 histories take 24h using 250 cores) CAD drawing of the TBM Port PORT PLUG PORT INTERSPACE 29

ITER Model VERTICAL CUT PORT PLUG z[cm] HORIZONTAL CUT PORT INTERSPACE y[cm] 300 PORT PLUG PORT INTERSPACE BLANKET 350 TFC 250 MESH1 200 MESH2 MESH1 100 150 50 0-50 -100-150 -200 BIOSHIELD TFC -250-300 CRYOSTAT 900 MESH2 TFC 1000 1100 1200 1300 1400 1500 x[cm] TBM1 TBM2 TFC CRYOSTAT VACUUM VESSEL 900 1000 BIOSHIELD 1100 1200 1300 1400 1500 x[cm] 30

Neutron Flux Map PORT INTERSPACE PORT PLUG 2 z[cm] NEUTRON FLUX[n/cm s] z[cm] 1E14 215 165 1E12 115 65 NEUTRON FLUX[n/cm2s] 250 150 1E10 50 1E8-50 1E6-150 15-35 -85 875 1014n/cm2s 975 1075 106n/cm2s 1175 x[cm] 108n/cm2s Calculation performed on rectangular mesh 5.6E7 imposed over the geometry (voxel 3.2E7 dimensions 10*10*10 cm3) 1.8E7 Jobs run on 600 cores 1.0E7 with MPI capability (ENEA cluster CRESCO), time 24 h 109 histories x[cm] required variance reduction techniques (Weight Windows) 1.0E8 1200 108n/cm2s 1300 1400 1500 1600 107n/cm2s 31

Shutdown Dose Rate in the Maintenance Area Model ACTIVATION GAMMA SOURCE[γ/cm3s] Impurity content of Steel 316 IG : - Co60 0.05% wgt 70% dose -Ta182 0.01% wgt -22% dose 12 days after the shutdown Shutdown Dose Rate [μsv/h] Shutdown Dose Rate [μsv/h] LIMIT Shutdown Dose Rate exceeds the limit imposed by the ITER project (100 μsv/h 12 days after the shutdown) close to cryostat and Pipe Forest structure. Gaps and other experimental ports are the main responsible of the dose Optimization of the gaps and of the experimental port cross talk is currently under investigation 32

Shutdown Dose Rate in the Maintenance Area Model Monte Carlo Model Neutron Flux in Port Plug z[cm] n/(cm2s) 1E14 215 165 1E12 115 65 1E10 15 1E8-35 -85 Port Port Plug Interspace UPPER PORT EQ. PORT 1E6 875 1014n/cm2s 975 1075 106n/cm2s 1175 x[cm] LOWER PORT 108n/cm2s Shutdown Dose Rate exceeds the limit imposed by the ITER project (100 μsv/h 12 days after the shutdown) close to cryostat and Pipe Forest structure. Gaps and other experimental ports are the main responsible of the dose Optimization of the gaps and of the experimental port cross talk is currently under investigation 35

Conclusions The worldwide efforts in fusion technology aim at developing, in the long-term, power reactors which can contribute substantially to the supply of electricity. The construction and operation of the experimental fusion device ITER ( International Thermonuclear Experimental Reactor ) is an essential next step towards this long-term goal. The availability of qualified computational tools and nuclear data for the neutron transport simulation and the calculation of activation and material damage is a pre-requisite to enable reliable design calculations for these facilities. An automated R2S shutdown dose rate calculation tool was made and used to evaluate the actual design European TBM Port. From preliminary results, the shutdown dose rate in the region of maintenance is higher that 100 μsv/h. The main contribution is due to the cross-talk with the other experimental ports, which must be better described in the MCNP model and further investigated. 36

Thank You! 37