Reference no: EM133028000

Question 1. The operating temperature of a plasma-facing component in a fusion tokamak reactor is limited from above by the recystallization temperature of the material, which is -1200°C for tungsten, -400°C for copper, and -700°C for iron. The coolant temperature, on the other hand, is likely going to be close to 100°C. Estimate the maximum value of stationary heat flux from the plasma to the coolant that can be conducted through a 1cm-thick plate of (a) tungsten, (b) copper, and (c) iron. What is the maximum thermal flux, per unit area, that can be transferred through a 1cm thick tungsten-copper plate consisting of a 0.5cm plate of tungsten joined to a 0.5cm thick plate of copper? The thermal conductivity of copper is 400 W/(m-K), for tungsten it is 170 W/(m-K), and for iron is it 80 W/(m-K).

Question 2. Small (millimetre size) samples of Fe are exposed to mono-energetic 14 MeV neutrons with 14 the flux of 10 neutrons/(cm².$). Provide a rough estimate of how many defects, in percent per lattice site, are going to be accumulated in the samples over (i) one hour, (ii) one day, (iii) one year. The average total cross-section of scattering of a neutron by a Fe nucleus is -2.10 cm².

The orientation-average threshold defect formation energy In Fe it Is ~40 eV. Assume that approximately 30% of all the energy of atomic recoil events Is absorbed by electronic excitations and does not contribute to defect production. Compare the result with the total number of atoms per unit volume. Note that the maximum number of defects that can possibly accumulate in a material is -2% per lattice site.

Question 3. Why are radiation-induced phenomena sensitive to temperature, and what is the name of the scientist who discovered the law of thermally activated reaction rate and diffusion? Assuming that the temperature-dependent diffusion coefficient of a defect in iron is given by equation D(T) = Do.exp(-Ea/k₈T); where D₀ = 10¹³ (nm)²/s, k₈ =8.62-10^-5 eV/K, T is the absolute temperature, and E_a=1.3 eV, and that a defect perform three-dimensional random Brownian motion, estimate the volume of space V, in nm3 units, that a defect is able to explore over the time interval of one second at temperature (a) 20°C, (b) 300°C, and (c) 700°C.