VIENNA (Reuters) - Conditions at a badly damaged Japanese nuclear power plant are grave but not deteriorating badly, the U.N. atomic agency said on Friday.
The International Atomic Energy Agency gave its assessment after Japanese engineers conceded that burying the plant in sand and concrete may be a last resort to prevent a large radiation release, the method used to seal leaks from Chernobyl in 1986.
"The situation at Fukushima Daiichi nuclear power plants remains very serious but there has been no significant worsening since our last briefing" on Thursday, Graham Andrew, a senior IAEA official, told a briefing.
"The situation at the reactors at units 1, 2 and 3 appears to remain fairly stable."
Japan still hopes to solve the crisis by fixing a power cable to two reactors to restart water pumps needed to cool overheating nuclear fuel rods, rather than resorting to Chernobyl-style containment.
"After the accident is over then there will be a whole range of issues in the post-accident phase that need to be considered very carefully," Andrew said.
"How to deal with the reactors that are left, to remove the fuel safely and as necessary to decommission (them) ...But you will appreciate that they are not the immediate priority of today."
Chernobyl was only fitted with its concrete cover -- also known as the "sarcophagus" -- six months after disaster first struck.
Working on cooling continued, Andrew said, describing the start up of diesel generators for this purpose at units 5 and 6 as a positive development.
He said officials were still concerned about pools holding spent fuel at reactor units 3 and 4. "Reliable, validated information is still lacking on water levels and temperatures at the spent fuel ponds," he said.
The IAEA was getting information on radiation levels in 47 Japanese cities and finding no health threats so far.
"Dose rates in Tokyo and other cities remain far from levels which would require action. In other words they are not dangerous to human health," Andrew said.
In Tokyo, IAEA Director General Yukiya Amano met Japan's prime minister, other senior officials and the vice president of plant operator Tokyo Electric Power Co (TEPCO).
"The director general stressed the importance of providing faster and more detailed information about the situation at the nuclear power plants, including to the international community," Andrew said, adding Japanese counterparts had agreed to this.
He said international organisations had found flight and maritime operations can continue normally into and out of Japan's major air and sea ports and there was no medical basis for imposing additional measures to protect passengers.
Editing by Jon Boyle