Radiolytic decomposition of water on the coolant side ofzirconium cladding is generating a pressure of H2 of 10-4 bar withthus a similar surface concentration of H2. Hydrogen, H2, is thusdiffusing into the zirconium, which can in fact contain aconsiderable amount of dissolved hydrogen. Using the data andassumptions below, and other information you may need to gatherfrom other sources, and assuming
ï‚· The cladding is uniformly at 400 degrees C
ï‚· PWR reactor pressure is 1800 psi
ï‚· The cladding is pure Zr
ï‚· The cladding is 1 mm in thickness
ï‚· There is a sink for hydrogen at the inner clad thus the H2pressure is negligible
ï‚· The diffusion coefficient is described by
ln D = ln A – Ea/RT
where
D = diffusion coefficient
A = pre-exponential factor (7.9 x 10-3 cm2/s)
Ea = activation energy for diffusion (44900 J/mol)
R = ideal gas law constant
T = absolute temperature
a. Compute the flux of hydrogen into the cladding at steadystate
b. Sketch the concentration profile across the cladding
c. More realistically, zirconium can react with hydrogen to formzirconium hydride, ZrH2. Determine whether we will see hydrideformation in the cladding.
