A major concern associated with Chernobyl style nuclear reactors is that:

The concern regarding Chernobyl-style nuclear reactors primarily revolves around the potential for accidental radioactive releases into the atmosphere. This type of reactor design, particularly the RBMK reactor used at Chernobyl, has specific vulnerabilities and can lead to catastrophic failures under certain conditions, resulting in the uncontrolled release of radioactive materials. Such accidents can have devastating environmental and health consequences, spreading radioactive isotopes far beyond the immediate vicinity of the reactor.

These reactors often lack the robust safety systems found in more modern designs that would help contain or limit the release of radiation during an incident. Factors like the use of graphite moderators in conjunction with water cooling can lead to scenarios where fires can escalate into significant radioactive contamination. Thus, the concern is not only about the occurrence of accidents but also about the direct impact these accidents can have on atmospheric contamination, which affects air quality, ecosystems, and public health on a broad scale.