NEEP 541 – Material Properties Fall 2003 Jake Blanchard

Outline Materials in Reactors Fission Fusion Material Properties Tensile tests Impact tests Creep tests

Materials in Reactors Fission Fuel Cladding Moderator Core structure Reflector Control rods Coolant Pressure vessel shielding Fusion Fuel Structure Tritium breeder Coolant insulators shielding

Fission Primary radiation damage is in fuel and cladding Cladding: Adequate strength (T, fluence) Corrosion resistance Thermal conductivity Neutronics (low absorption) Available resources Fabricability Inexpensive

Cladding Materials Low thermal absorption cross section Al Mg Zr Be High thermal absorption cross section Nb Mo Ta V Ti Steel

Some Numbers MaterialThermal - ZrFast - steel Tmax (C) CoolantWaterSodium Pressure (atm)130<1 Clad thickness (mm) Clad OD (mm) Life (dpa)20150

Fusion Structure Requirements Same as fission plus… Low swelling Low embrittlement Typical Materials Austenitic steel (316 SS) Ferritic steel (lately ODS FS) Refractory alloys composites

Radiation Effects Radiation hardening (increase in strength) Embrittlement (decrease in ductility) Swelling (volume increase due to voids) Irradiation creep

Tests Tensile tests (modulus, ductility, strength) Tube burst tests (creep) Impact tests (ductility, fracture toughness)

Tensile Tests

Understanding the Tensile Test A 0 =cross sectional area before test (in test section) A=cross sectional area during test (load=P) L 0 =section length before test L=section length during test

Tensile Tests Engineering stress=  eng =P/A 0 True Stress=  true =P/A Before necking, A~ A 0 Engineering strain=  =(L-L 0 )/L 0 True strain=

Stress-Strain Curve

True Stress – True Strain

Combined

When does necking start? Plastic Instability (dP=0) Volume is conserved

Plastic Instability Necking occurs when slope of true stress-true strain curve=true stress

Plastic Instability suppose

Hardening

Impact Testing Test for ductility Measure energy absorbed during fracture

Typical Results DBTT=ductile to brittle transition temperature T E (J) Upper shelf Lower shelf irradiated DBTT 40

Creep Tests Apply load and measure deformation as a function of time time Creep strain primarysecondarytertiary

Study creep rupture with a tube burst test p 2R L

Burst Test Analysis p Slice cylinder vertically

Burst Test Analysis Slice cylinder horizontally (picture is shown cut away vertically as well)

Burst Test Analysis Uniaxial (1-D tensile test) Constant stress

Burst Test Analysis

Negative radial strain means that wall gets thinner Zero axial strain means length doesn’t change Positive hoop strain means radius increases Analysis assumes small strain, constant stress For large strain, wall thins and stress increases, leading to rupture