The State Nuclear Regulatory Inspectorate of Ukraine is reporting on Feb 12, 2013 a partial collapse of wall fragments and lighting over turbine unit 4 due to heavy snowfall.  This area is not part of the containment structure and does not constitute an immediate risk. The radiation levels have remained steady and  there appears to be no risk of radiation leaks.   

The Chernobyl Reactor has been encased in a concrete sarcophagus since a tragic nuclear accident  in 1986.

Below is an image of the facility with the collapsed area highlighted.