Radiation Damage Effects in Solids. Los Alamos National Laboratory. Materials Science & Technology Division

Transcription

1 Radiation Damage Effects in Solids Kurt Sickafus Los Alamos National Laboratory Materials Science & Technology Division Los Alamos, NM Acknowledgements: Yuri Osetsky, Stuart Maloy, Roger Smith, Scott Lillard, Peter Hosemann, Eric Pitcher

2 Outline 1. Background on Radiation Effects (relationship to accelerators) 2. Introduction to Solids and Solid-State Defects 3. Introduction to Microstructural Evolution in Crystalline Materials 4. Introduction to Ion-Solid Interactions (the two-body collision)

3 1. Background on Radiation Effects (relationship to accelerators)

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6 Data for a 1200 MW PWR Uranium enrichment : 3.2% U 235 Fuel :UO 2 clad in Zircaloy Core layout :Fuel pins, arranged in clusters, are placed inside a pressure vessel containing neutron moderator and coolant -light (ordinary) water with outlet temperature 324 o C. Heat extraction : The water in the pressure vessel at high pressure (154 atm) is heated by the core. It is pumped to a steam generator where it boils water in a separate circuit; the steam drives a turbine coupled to an electric generator. Thermal efficiency :32% Core dimensions : 3.0m dia. x 3.7m high

7 In reactors, nuclear chain reactions produce lots of energy. High energy (~MeV) neutrons also cause significant structural damage to reactor materials. U 235

8 Nuclear reactions Šsource of energy Fission (heavy elements) 92 U235 (fissile) + n 92 U 236 (unstable) 56 Ba Kr n MeV Comparison with coal cycle: C + O 2 =CO 2 +4eV 1 ton of U = 2.7x10 6 tons of coal!! Fusion (light elements) 1 H2 + 1 H 2 2 He 4 + n + 17 MeV

9 Radiation Effects Each fission reaction produces 2 to 3 neutrons of high energy 1MeV Neutrons can react not only with fuel, e.g. U, but also with the surrounding component materials. The path of fast neutrons in materials is rather long and depends on the atomic mass of the material (e.g., it is shorter in heavy materials the probability of reaction with atoms, i.e., the crosssection, is higher in dense materials). The reactor core, which is source of fast neutrons, experiences important alterations: -radiation damage of reactor components -activation of materials due to nuclear reactions this leads to unstable products (radioactive waste)

10 Radiation Effects Atomic and microscopic changes in structure lead to macroscopic changes in properties (swelling, embrittlement, etc.). The scientific discipline of radiation damage research involves revealing mechanisms responsible for atomic and microstructural changes produced by irradiation and predicting macroscopic property changes.

11 Stress/Strain Curves showing increases in yield stress and decreases in elongation in 316L Stainless steel after irradiation 1000 T t =Tirr= 50C dpa Stress (MPa) dpa 1.1 dpa 0.09 dpa Unirradiated Strain (%)

12 Why Accelerators? 1. To simulate neutron radiation damage effects (often without the difficulties associated with producing and handling radioactive samples) 2. To produce neutrons (e.g., spallation neutron sources) 3. To perform novel specialized studies such as fission or corrosion experiments

13 Accelerator Irradiations Materials testing in a nuclear reactor can be costly and time consuming. Ion beam accelerator experiments have the advantage of allowing fast and inexpensive materials irradiations without activating the sample.

14 The Materials Test Station (MTS): A Fast Spectrum Irradiation Facility proposed for Los Alamos National Laboratory

15 The MTS target consists of two spallation target sections separated by a flux trap Beam current will be 1.25 ma (after LANSCE Refurbishment) Availability is expected to be 4400 hours per year Dimensions in cm. fuel rodlets in flux trap Beam pulse structure: 1.5 spallation target µs 7.6 ms ma Delivered to: left right left right target target target target proton beam spots (800 MeV, 1.25 ma)

16 Target Assembly Exploded View Fuel Module Material Sample Module (2x) Backstop Beam Spots Target Modules

17 Spatial distribution of the fast neutron flux shows uniformity over the dimensions of a fuel pellet Fast (E>0.1 MeV) neutron flux

18 MTS neutron spectrum is similar to that of a fast reactor with the addition of a high-energy tail flux per lethargy (a.u.) fast reactor MTS neutron energy (MeV) 6% of neutron flux is >10 MeV Effect on fuel is negligible Potential effects on cladding from additional He production Embrittlement Creep rupture Reduced incubation dose to void swelling

19 The Influence of Radiation on Corrosion Problem: Fission reactors (zircalloy cladding, stainless cooling) Waste (tanks, cooling ponds, processing, ) Accelerators. spallation neutron sources Mechanisms: Water radiolysis Physical damage to the passive film Electronic damage to the passive film

20 Water Radiolysis γ p n 1. Particles irradiate water e - γ γ + Primary species: e _ aq, H 2O 2, OH, H, O 2. Radiolysis/Ionization Meta/oxide e _ + e _ H 2 +2 OH _ aq aq e _ + H + H aq + H H 2 + OH _ e _ aq e _ aq + OH OH _ e _ aq + H 2 O 2 OH _ + OH H + H H 2 OH + H H 2 O H+ H 2 O 2 H 2 O + OH OH + OH H 2 O 2 H 3 O + +OH _ H 2 O k dm 3 /mol/s 3. Diffusion/Recombination 4. Corrosion?

21 Stainless Steel 316 Corrosion Rate as a Function of Position Relative to the Beam* *In DI water