Actinide compounds are the major constituents of general radioactive waste produced by nuclear power plants and special radioactive waste called "fuel debris" generated from power plant accidents such as those that occurred in the Fukushima-Daiichi Nuclear Power Plant. Comprehensive understanding of the properties of actinide compounds is important for separating and reusing the actinides from the radioactive waste or to decommission Fukushima Daiichi Nuclear Power Plant safely. However, actinides are artificially synthesized elements (except for uranium) and are inherently hazardous due to their radioactive nature, leading to enormous constraints in experiments aimed at elucidating their properties. For safety and feasibility, it is desirable to perform quantum chemical calculations of actinide compounds to understand their basic electronic structures. However, accurate descriptions of their electronic states require highly precise relativistic treatment and electron correlation treatment on the same footing. Particularly, static electron correlation may be more pronounced due to the involvement of actinide's 5f and 6d orbitals in chemical bonding, because these orbitals are located energetically close to each other.