  Giant planet formation process is still not completely understood. The
current most accepted paradigm, the core instability model, explains several
observed properties of the solar system's giant planets but, to date, has faced
difficulties to account for a formation time shorter than the observational
estimates of protoplanetary disks' lifetimes, especially for the cases of
Uranus and Neptune. In the context of this model, and considering a recently
proposed primordial solar system orbital structure, we performed numerical
calculations of giant planet formation. Our results show that if accreted
planetesimals follow a size distribution in which most of the mass lies in
30-100 meter sized bodies, Jupiter, Saturn, Uranus and Neptune may have formed
according to the nucleated instability scenario. The formation of each planet
occurs within the time constraints and they end up with core masses in good
agreement with present estimations.
