There are 30,000 to 40,000 rods--composed of twenty tons of zirconium--in an average nuclear power plant.  (??)

From previous discussions and diagrams it appeared that a single reactor vessel had four assemblies of about 25 rods each. Treating all six reactors at Fukushima as "one plant" that gives 600 rods in the reactors at any one time. There may be a fraction of that number of new rods on site for replenishment at any given time. Even if these rods were changed every year for 40 years and were still on site that would only be 24,000 rods -- for six reactors.

However, those calculations are for the BWR designs by GE. Have any reactors been built that use substantially more rods per reactor, say 200 rods at any given time? If so, that should produce higher neutron flux densities and I don't know how that might impact the metallurgy, etc.

"It is not necessary to have hope in order to persevere."