* IAEA mission to report back to June ministerial conference
* Countries differ on how to boost atom safety - diplomats
(Adds quotes, detail, background)
By Fredrik Dahl
VIENNA, May 17 (Reuters) - The U.N. atomic agency will send a fact-finding mission to Japan's crippled Fukushima power plant next week, as part of efforts to help boost global safety standards after the worst nuclear disaster in 25 years.
Nearly 20 experts from a dozen countries will take part in the May 24-June 2 visit to Japan to make a preliminary assessment of safety issues linked to the Fukushima accident, the International Atomic Energy Agency (IAEA) said on Tuesday.
The mission, headed by a senior British official, will then submit a report to a ministerial conference in Vienna on June 20-24, which the IAEA says will launch work on strengthening international safety related to operating nuclear power plants.
The move underlined the ambition of the IAEA, which was criticised for being slow in its early response when the massive earthquake and tsunami struck in March, to take a more active role to help ensure there is no repeat of the Fukushima crisis.
More than two months after a magnitude 9 earthquake and a deadly tsunami knocked out its power and cooling systems, causing fuel rods to melt, engineers are still trying to gain control of the plant and bring its reactors to a cold shutdown.
Japan's nuclear emergency -- the most serious since Chernobyl in 1986 -- has put the spotlight on how the Vienna-based agency is equipped to deal with an accident that has implications for other member states.
Although vested with powers to curb the proliferation of atomic weapons, the U.N. body does not have the ability to enforce any of its recommendations on the safety of nuclear plants.
DIVISIONS
Mike Weightman, Chief Inspector of Nuclear Installations of the United Kingdom, will lead the expert mission to Japan.
It will include IAEA and other experts under an agreement with Japan's government, which has been under fire at home for its handling of the crisis, as has the plant's operator.
"The mission will conduct fact-finding activities at Tokyo Electric Power Company's Fukushima Daiichi Nuclear Power Station site and in other locations," the IAEA statement said.
The experts' report will be "an important input in the process of reviewing and strengthening the global nuclear safety framework that will be launched" by the June meeting, it said.
Earlier on Tuesday, Japan unveiled new plans to contain the crisis at the nuclear plant after admitting it faced greater challenges than first disclosed, but kept its goal of bringing the reactors under control by January. [ID:nL4E7GH0U4]
Diplomats expect next month's ministerial meeting, to be hosted by the IAEA, to adopt an action plan on nuclear safety.
But they say there are disagreements among the IAEA's 151 member states on whether to make safety rules mandatory and whether to give the agency more powers in implementing them.
Such issues are now mainly the responsibility of national authorities, and that is expected to largely remain the case.
"That is a big divide (in opinions)," one diplomat from a developing country said."There will be a plan of action -- to look at, analyse and strengthen the international safety regime. But they won't make it mandatory."
(Reporting by Fredrik Dahl; Editing by Mark Trevelyan)
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