Japan raced to avert a catastrophe on Wednesday after an explosion at a quake-crippled nuclear power plant sent radiation wafting into Tokyo, prompting some people to flee the capital and others to stock up on essential supplies. The crisis escalated late on Tuesday when operators of the facility said one of two blasts had blown a hole in the building housing a reactor, which meant spent nuclear fuel was exposed to the atmosphere. Prime Minister Naoto Kan urged people within 30 km (18 miles) of the facility -- a population of 140,000 -- to remain indoors, as Japan grappled with...