While the core temperature continues to drop, thus significantly lowering the likelihood of a meltdown or second explosion, the radiation emitting from the ruins of Unit Four still pose a long-term threat to much of the USSR and Eastern Europe. To contain the radiation, Slavsky proposes building a giant sarcophagus around Unit Four. It is not enough to simply bury the reactor in concrete; the commission must build a structure allowing for ventilation and continued monitoring of the core’s remains. On June 5, Gorbachev gives Slavsky less than four months to complete the sarcophagus.

Because the radiation levels around Unit Four are so high, cranes and robots must build the structure. But even robots can’t function properly when affected by the high levels of gamma rays emitted from the graphite fragments that still litter the roof of the adjacent Unit Three, a zone nicknamed by Major General Nikolai Tarakanov as “Area Masha” or “Area M.” In Area M, the radiation levels reach 10,000 roentgen, enough to cause a fatal dose in three minutes. After trying and failing to use a Soviet lunar rover to clear the roof, Tarakanov resorts to using what he calls “bio-robots”—human beings.