When decommissioning a nuclear power plant, it is difficult to make an appropriate plan to ensure sufficient space for temporary placement and conveyance operations of dismantling targets. This paper describes a system to support the temporary placement and conveyance operations using augmented reality (AR). The system employs a laser range scanner to measure the three-dimensional (3D) information of environment and a dismantling target to produce 3D surface polygon models. Then the operator simulates temporary placement and conveyance operations using the system by manipulating the obtained 3D model of the dismantling target in the work field. Referring to the obtained 3D model of the environment, a possible collision between the dismantling target and the environment is detectable. Using AR, the collision position is presented intuitively. After field workers evaluated this system, the authors concluded that the system is feasible and acceptable to verify whether spaces for passage and temporary storage are sufficient for temporary placement and conveyance operations. For practical use in the future, some new functions must be added to improve the system. For example, it must be possible for multiple workers to use the system simultaneously by sharing the view of dismantling work.