WASHINGTON, April 6 (UPI) -- Japan's quake-hit Fukushima nuclear plant could face a number of new threats, some of which may continue indefinitely, U.S. engineers warn.
The warnings are contained in a confidential March 26 assessment by the Nuclear Regulatory Commission based on the assessment of U.S. engineers sent to Japan to help with the crisis. The document was obtained by The New York Times.
Among the new threats, the assessment said filling the plant reactors' containment structures with radioactive cooling water could increase the stress on them and cause them rupture from aftershocks that have been hitting the plant ever since the March 11 earthquake and tsunami, the Times said.
There are also threats of explosions inside the containment structures as seawater pumped into them can release hydrogen and oxygen.
The document also sheds light on how the partially melted fuel rods and salt buildup in the reactors are disrupting the flow of fresh water to cool the nuclear cores, the Times said.
Workers trying to bring the plant under control already have experienced some of the major threats, such as radiation burns to their colleagues and leakage of radioactive water into the ocean.
Some experts told the Times prolonged heating and melting as a result of ineffective cooling could also create a radioactive mass remaining in a molten state for a long time.
Union of Concerned Scientists' David A. Lochbaum, who was not involved in the preparation of the document, told the Times the issues raised in it were disturbing.
"I thought they were, not out of the woods, but at least at the edge of the woods," he said. "This paints a very different picture, and suggests that things are a lot worse."
One of the steps suggested by the NRC would be to inject nitrogen into the containment structures to remove any hydrogen and oxygen.
It also said engineers should continue to add boron to cooling water to help prevent the cores from restarting the nuclear reaction, even though it may not be an immediate threat.