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true	true		Neutronics Analysis of Fusion Systems	Presentation slides for the fusion energy neutronics workshop	Jonathan Shimwell	fusion,neutronics,neutron,photon,radiation,simulation,openmc,dagmc	.columns { display: grid; grid-template-columns: repeat(2, minmax(0, 1fr)); gap: 1rem; }, .columns3 { display: grid; grid-template-columns: repeat(3, minmax(0, 1fr)); gap: 1rem; }, h1 { text-align: center }

Prompt responses

Neutron wall loading

Energy carried by uncollided source neutrons incident on a unit area of first wall per unit time
Units typically used $MW m^{-2}$
Useful for estimating neutronics results and scaling or comparing results
For simple source distributions and geometry, can calculate analytically
Complex source distributions or geometries require more sophisticated methods (e.g Monte Carlo)

Significant poloidal variation of neutron wall loading occur in toroidal magnetic confinement fusion reactors

Energy deposition calculated from the flux using “Kinetic Energy Released in MAterials” (KERMA) factors
Energy lost by a neutron from a collision is assumed to be deposited locally
Gamma photons produced by neutrons are transported to determine where their energy is deposited (need coupled neutron-photon transport)
The power density distribution is used in thermal-hydraulics calculations and subsequent structural analysis (e.g. thermal stress)
Total heating is used for sizing cooling systems
Nuclear energy multiplication (Mn) is ratio of energy deposited by neutrons and gamma photons in the reactor to neutron energy incident on FW

At same location with same neutron flux, nuclear heating depends on material
High-Z materials usually yield higher nuclear heating than low-Z materials
Gamma heating represents ~85% of nuclear heating in high-Z materials and only ~40% in low-Z materials
Nuclear heating drops rapidly as we move away from FW