Abstract: An enclosure for confining radio-active products or waste comprising a fluid-tight underground rigid supporting outer shell of reinforced concrete opening to the outside through a reinforced concrete chimney, an innermost vessel for containing said radioactive products or waste, surrounded by said shell and made from thin corrugated stainless steel sheet material, an intermediate vessel made from thin corrugated stainless steel sheet material, located between said shell and innermost vessel and surrounding the latter, means for cooling said vessels through fluid flow circulation by natural convection within ducts adjacent to at least one of said vessels and means for feeding and/or discharging said radio-active products or waste into or from said innermost vessel.