A computer-based alarm processing system for nuclear power plants is being developed in a G2 expert system software tool. In the G2 environment, every alarm is treated as an object of alarm class. The attributes of each alarm object include activation status, alarm messages, process value, time, priority, acknowledgment state, and icon color. If an alarm is activated, its icon color, on an overview process mimic diagram changes corresponding to its priority which can be set initially or determined dynamically by reasoning rules and procedures. The process conditions, such as plant or equipment status and correlated alarms` states determine the priority of the activated alarm. The knowledge base of the system is constructed by process analysis of the plant and discussion with operators and nuclear plant experts. (author). 6 refs, 3 figs, 1 tab.