That is not a certainty. According to the NRC report on 3-mile Island (which I think is the worst in US history) the release was about 1 millirem. For comparison a x-ray is 6 millirem and normal background radiation is 100-125.
Western reactor designs are not like Chernobyl. They are designed to fail 'safe' and have over-designed containment vessels to prevent accidents from leaking into the community.
The reactor at Three Mile Island only had a containment vessel because it was on the flight path in/out of a nearby airport. Otherwise federal regulators were going to let it be built without a containment vessel.
The containment vessel at Three Mile Island was designed to survive a direct hit by a loaded 707 - because those flew over the reactor. They were NOT over-designed.
Edit: I designed the Feedwater Control System for the Lungmen Nuclear power stations going up in Taiwan.
Edit2: Reply to jibiki below; Yes, no containment was the absurd comment. I don't know the details but I can guess the builders strengthened the containment building to appease the eviros - it was probably completely unnecessary and only raised the costs. The enviros and the lefties have gotten away with such "stories" for years but now thanks to the internet, the truth shall set us free! See Clay Shirky on Thinking the Unthinkable.
"I want to mention that the reactor containment at Three Mile Island was actually thicker than most others, because citizen action, prior to the construction of the plant, demanded a thicker containment, because the Three Mile Island Unit 2 is right in the flight path of the Harrisburg Airport."--Harvey Wasserman
(Of course, nobody was ever planning to build it without a containment... I hope?)
Please don't lump us all together like that; this enviro-leftie is very pro-nuclear. Following political ideology blindly has never been limited to any particular viewpoint.
A single exception, no. But environmentalism takes a lot of forms: Greenpeace hippies, Sierra Club hunters and naturalists, and humanists interested in long-term sustainability (which is where I fall). Though there's still a strong residual echo of the (understandable) knee-jerk reaction to nuclear from the 70s, there are now many environmentalists who support nuclear as a lesser evil compared to coal.
Apologies for having an easily-struck nerve, re: implied "All X are Y" statements. :)
Western reactor designs are not like Chernobyl. They are designed to fail 'safe' and have over-designed containment vessels to prevent accidents from leaking into the community.