The sodium spillage phenomenon in large liquid-metal fast breeder reactors (LMFBRs) during highly energetic hypothetical accidents has been investigated. A parametric study of the spillage process was accomplished with the ICECO code employing a control-volume method. A 1000-MW(electric) reactor, with prescribed leak paths, is modeled and analyzed during the slug impact phase. Leak paths are assumed to exist as annular penetrations in the reactor cover and as a gap at the vessel-head junction. The behavior of sodium spillage was investigated under conditions of different accident energetics, various opening cross-sectional areas, and multiple leak paths, with both stationary and moving reactor covers. Highly energetic accidents were used as the initiating events for the spillage processes described. The intent is to evaluate the range of applicability of the spillage methodology derived. It is not the intent to imply that such energetic accidents have been identified in any LMFBR safety analysis. The behavior of spillage beyond the initial transient period has also been investigated. During the transient period immediately following slug impact, it was found that spillage from annular penetrations in the reactor cover is only weakly sensitive to changes in slug velocity. The same conclusion applies to spillage from a fixed gap at the vessel-head junction. Quantity of sodium spilled during a fixed time was seen to vary proportionally with opening size. Significant sensitivity of spillage to accident energetics was seen only in cases of spillage from the vessel-head junction when the reactor cover was movable. The influence of slug impact on the motion of the reactor cover leads to the conclusion that sodium spillage is most sensitive to accident energetics inasmuch as the area of the leak path is affected. Preliminary results from sodium fire calculations indicate that spray ejection from penetrations in the reactor cover will not cause significant pressurization of the secondary containment from sodium ejected during the initial transient.