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How did the containment vessel limit the release of radioactivity at Three Mile Island?

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nuclear engineering Installation of the dome of a containment structure at the Taishan nuclear power plant, Guangdong province, southern China, 2012.

During the Three Mile Island accident in 1979, the containment vessel served as the final fission product barrier, successfully preventing the vast majority of radioactive material from escaping into the environment.12

Following a partial core meltdown, a significant portion of the core's radioactivity—along with hydrogen gas generated by the reaction between superheated steam and fuel cladding—was released into the enclosure surrounding the reactor. Despite the occurrence of a hydrogen deflagration within the structure, the containment vessel maintained its integrity.13

By design, the containment is an airtight structure engineered to withstand internal pressure buildups and contain debris or radioactive releases resulting from severe accidents. Because the vessel effectively held these materials, only a very small amount of radioactivity was released, ensuring that the event did not pose a threat to the health of the surrounding population.413