TOKYO, JAPAN (CBS) - Scientists in the U.S. are warning that workers at Japan's damaged Daiichi nuclear complex must solve a mind-boggling set of problems before any real promise of safety is in sight.
A confidential survey prepared for the U.S. Nuclear Regulatory Commission and obtained by the New York Times says many early measures used to prevent a meltdown at Daiichi are now threatening its stability.
The report warns of fresh threats. Gallons of seawater initially used to keep the reactors cool are leading to new worries over the corrosive effects of salt on the reactors, and containment pits now filled with high levels of water are leading to fears over their structural safety.
American scientists are also worried about more hydrogen explosions at the plant, which has released dangerous amounts of radiation into the air.
The plant's operator, Tokyo Electric, says it will add nitrogen into reactor No. 1 to force out the hydrogen and prevent further blasts. The measure satisfies at least one Tokyo nuclear expert.
"Of course we have to avoid [a] hydrogen explosion," said Yoshiaki Oka, a professor in the department of engineering at Waseda University. "But in my view, most radioactivity is already released in the first three explosions."
One 8-inch crack that was leaking radioactive water straight into the Pacific Ocean has been plugged using a combination of liquid glass and gravel.