It will never be as bad as Chernobyl. If a complete meltdown occurs, it will be very localized and emit radioactivity levels that are lower than what the Soviets had. This event is still controllable to an extent too, whereas the one at Chernobyl was just fiery explosive chaos.
http://english.chosun.com/site/data/html_dir/2011/03/17/2011031701085.html