11.32. The number of assemblies discharged from a plant per year can be estimated from the average burnup, the mass of heavy metal per as­sembly, and the energy generated, as indicated in Example 11.1.

Example 11.1. Consider a typical lOOO-MW(el) PWR which discharges fuel assemblies with an average discharge burnup of 33,000 MW • d/t. If the thermodynamic efficiency is 32 percent, and each assembly contains 450 kg of total uranium, how many assemblies would be discharged an­nually? A plant factor of 0.7 may be assumed.

_ , , , [1000 MW(el)l(365)(0.7)

Thermal energy produced per year = a ——- = 7.98 x 105 MW • d.

Then

which may be rounded off to 54 assemblies per year.

Actually, the number discharged would depend on the core management scheme followed, but the approach is useful for estimating storage require­ments. For example, corresponding to the U. S. nuclear generating capacity of approximately 100,000 MW(el), about 5400 assemblies would be dis­charged per year before correcting for the BWR fraction of the assumed generating capacity. Of course, the adoption of longer operating cycles, which normally result in increased burnup, will reduce this estimate significantly.

11.33. On-site storage pool capacity prior to 1977, when reprocessing was deferred indefinitely in the United States, was designed to accom­modate approximately the number of assemblies that would be discharged in 5 years. Also, room in the pool must always be available to hold a full core should it become necessary to defuel the reactor. Even with the introduction of enhanced capacity measures, about one-half of the pres­ently operating nuclear units are expected to fill their existing storage capacity by 2000.