Since the loss of vital alternating current power and the residual heat removal system (RHRS) during shutdown at Vogtle Unit 1 on March 20, 1990, much attention has been focused on the need to evaluate system performance following such an event in a light water reactor. To evaluate system response following loss of the RHRS, a simplified, transient, nonequilibrium methodology was developed to provide early insights into the accident consequences and identify key phenomenological and system behavior in need of further, more detailed studies. During shutdown, with the reactor coolant system (RCS) at reduced pressure and temperature, inventory reductions are achieved through the introduction of nitrogen into the system. On removal of the man way entries, air can then enter the system. If the RHRS fails under such conditions, the steam generators may be able to be used as an alternate means of decay heat removal provided RCS integrity can be ensured. Moreover, once boiling initiates, RCS pressure increases because of the presence of noncondensable gases in the system. As a consequence, there is a need to assess the RCS pressure response since the success of this strategy depends on whether the peak pressure is sufficient to cause failure of any of the RCS temporary boundaries used during plant refueling outages. If there is insufficient time to close an open RCS and boiling initiates, a source of coolant makeup is needed to prevent core uncovery and fuel damage. Should boiling persist for several hours, an appreciable amount of boric acid accumulates in the reactor vessel. The subsequent restoration of the RHRS may result in the inadvertent precipitation of the boric acid in the RHRS lines, preventing its further use for decay heat removal. The methodology serves as an analytical tool to assess the RCS peak pressure when attempting to utilize the steam generators following a loss of the RHRS during shutdown and the consequences of borated water addition for long-term core cooling in the event the RCS is open to the containment. The analyses demonstrate that the steam generators could be used for heat removal from reduced inventory conditions at shutdown provided the RCS integrity can be ensured. If the RCS cannot be closed and loss of the RHRS results in boiling, the simple action of adding borated water to the RCS to prevent core uncovery poses a potential boric acid precipitation concern during the long term. The results of the evaluation in which the steam generators are used as an alternate means of decay heat removal are pertinent to pressurized water reactors utilizing U-tube steam generator designs. Further research is being conducted to assess behavior in plants utilizing once-through steam generators. Peak pressures are not expected to differ significantly from that for the U-tube design.