$4\mathrm{.}1.$ The reason for the different corrosion thicknesses at points A and B in the plot below is:

a$.$ The periodic variation in chemistry as the coolant reaches different locations in the fuel rod.

b$.$ The decrease in corrosion with decreased coolant temperature after mixing vanes.

c$.$ The fact that there are variations in coolant density at different cladding locations.

d$.$ The neutron flux varies periodically within the fuel rod and that causes corrosion to change.

e$.$ These are mid pellet and interpellet regions with corresponding variations in heat flux.

$4\mathrm{.}2.$ Stress Corrosion cracking can occur if:

a$.$ a tensile stress is applied to an existing crack

b$.$ the material has been previously sensitized

c$.$ the environment contains aggressive chemistry

d$.$ all the above conditions are needed for SCC$.$

$4\mathrm{.}3.$ During an $x-$ray diffraction experiment, taken with $Cu$ Ka radiation $($wavelength $=1\mathrm{.}5405),$ coherent scattering from a $Zr$ sample is achieved at $2=36\mathrm{.}15.$ The corresponding lattice parameter for this plane is approximately"

a$.5\mathrm{.}22$

b$.2\mathrm{.}94$

c$.1\mathrm{.}23$

d$.2\mathrm{.}46$

e$.$ None of the above