Accident management activities at nuclear power plants require concurrent communication, information sharing, team based decision-making and collective actions under tactical and dynamic environments. Team effectiveness under such environments can be characterized as the performance of team situation awareness with hierarchically distributed information and knowledge susceptible to organizational characteristics and communication quality. This paper proposes a team performance model, called a team crystallization model comprising of four elements: state, information, organization, and orientation and its quantification method using a communication process model based on a receding horizon control approach. The team crystallization model is a holistic approach for evaluating team effectiveness in conjunction with team situation awareness considering physical system dynamics and team behavioural dynamics for a tactical and dynamic task at a nuclear power plant. This model provides a systematic measure to evaluate time-dependent team effectiveness or performance affected by mufti-agents such as plant states, communication quality in terms of transferring situation-specific information and strategies for achieving the team task goal at a given time, and organizational factors. To demonstrate the applicability of the proposed model and its quantification method, a case study was carried out using the data obtained from a full-scope power plant simulator for 1000 MW(e) pressurized water reactors with four on-the-job operating groups and one expert group who knew accident sequences. (C) 2005 Elsevier Ltd. All rights reserved.