Because the nuclear energy industry is so tightly regulated and often state-owned (and because it is so feared by the general population, perhaps out of proportion to the actual risk), the potential for greedy company owners to recklessly sacrifice safety in the name of profit is much, much less than in oil or coal.
http://www.law.cornell.edu/uscode/html/uscode42/usc_sec_42_00002210----000-.html^ is government imposed cap on liability for the nuclear industry -- private liability for nuclear accidents is $375 million for an individual company, plus $12.6 billion from an industry liability pool. Any significant accident, even ones far less severe that Fukushima, would cost far more than that.
To help you cut though the legislative-ize
"Ensure adequate compensation to the victims of a nuclear power plant accident" = taxpayers are on the hook because the nuclear industry can't cover their risk
"to promote private industry's participation in the development of nuclear power by limiting its liability in the event of an accident." = reassure stockholders they can safely invest in nuclear because the taxpayer is going to pay clean up the mess
This is a huge subsidy to nuclear because investors see the industry as safe (artificially so), their insurance premiums are that much less, and the extraordinary catastrophic risks uniquely associated with nuclear become the government's problem.
Conclusion: Government interference at least in this aspect has made the nuclear company owners far more reckless and willing to take risks with a meltdown than they otherwise would be if there were no government subsidy.
Conceded: The government makes these kinds of get off the hook deals with oil and gas as well.