No, the firefighters who responded to the Chernobyl disaster were not buried in concrete.
After the explosion at the Chernobyl nuclear power plant in April 1986, several firefighters were exposed to extremely high levels of radiation while battling the fire. They faced dangerous conditions, and many of them suffered from serious health issues as a result of their exposure.
While the site of the reactor itself was encased in a concrete sarcophagus to contain the radiation, the firefighters were not simply buried in concrete. Instead, they were treated in hospitals for their radiation sickness and were later laid to rest with dignity. The idea that they were buried under concrete likely stems from the confusion surrounding the containment efforts and the tragic circumstances of their service during the disaster.