WASHINGTON -- A U.S. nuclear industry official says there is evidence that the primary containment structure at one of the stricken Japanese reactors has been breached, raising the risk of further release of radioactive material.

Anthony Pietrangelo of the Nuclear Energy Institute said Tuesday that falling pressure inside the suppression pool at the No. 2 reactor at Fukushima Dai-ichi and reports of rising radiation levels there raise the possibility that at the reactor's containment has been breached. He said the breach of the primary containment structure could lead to the release of more radioactive materials.

Pietrangelo, chief nuclear officer of the institute, also praised Japanese authorities, saying that they were doing a "heroic" job of dealing with the damage to several nuclear plants in the wake of last week's earthquake and tsunami.