According to an assessment prepared by the Nuclear Regulatory Commission, U.S. engineers are warning that Japan's troubled nuclear plant is facing a wide array of fresh threats that could persist indefinitely, The New York Times reports.

Among the new threats are the mounting stresses placed on the containment structures as they fill with radioactive cooling water, making them more vulnerable to rupture in aftershocks.

The document also cites the possibility of explosions inside the containment structures due to the release of hydrogen and oxygen from seawater pumped into the reactors. In addition, the document raises new questions about whether pouring water on nuclear fuel in the absence of functioning cooling systems can be sustained indefinitely.