Quote from Yahoo Nesw by Associated Press:
Concerns about radiation were at the forefront of other countries' worries as the situation at the Fukushima Dai-ichi nuclear plant appeared to worsen. Surging radiation levels forced Japan to order emergency workers to temporarily withdraw from its crippled nuclear plant Wednesday, losing time in a desperate operation to cool the overheating reactors.

Tokyo, which is about 170 miles (270 kilometers) from the stricken nuclear complex, reported slightly elevated radiation levels Tuesday, but officials said the increase was too small to threaten the 39 million people in and around the capital. - end of quote.

Please don't get alarmed too much....
But knowing ahead of time won't hurt any.
I have the following charts of spreading of radiation that escaped or may escape into the atmosphere.

You can see below some scientific analysis on how radiation spread through Europe after Chernobyl, and also how wind currents could possibly spread radiation from Japan to the rest of the world.
Compared to Chernobyl, Japanese situation may be much different as it involves the global Jet Stream.

Chernobyl Fallout Chart



The Wind Chart and estimated direction of the spread
of the Japanese Fallout

Please remember, this is only the wind chart,
not the actual radiation spread !!
The darn thing seems to be heading to Southern California (higher wind with red color) and then it (lower wind with yellow color) turns to north heading for the west coast to Seattle and then into Canada. Then the final tail may end up in New York (not shown in the picture though). However this Jet Stream will and may change it's direction at any time.

An accidental radiation leak in Japan can easily fall down in your backyard in New York.
Just imagine how small the world is !!
We shall realize that the world and it's people are just "One".
We are fatefully "Together". There's no escape from it.

A thought by SNUMA WM in the morning of March 16, 2011