exposure. When the first government commission group returned to Moscow, Legasov was asked to stay by Scherbina but was replaced by his scientific rival Evgeny Velikhov in the formal hierarchy. The team began to be concerned with small areas of reactor activity, as well as the integrity of the concrete pad. Velikhov in particular was concerned that the reactor remains could melt deep into the ground, as shown in the US film The China Syndrome. Water in the lower barboteur was drained but Legasov was convinced that an explosion was not possible, in contrast to what some scientists and politicians feared. He also considered the possibility of ground water contamination to be extremely low, but precautionary work was initiated to cool the reactor using an underground system. Legasov considered these containment steps to be excessive but understandable, while also provided the infrastructure for the eventual construction of a shelter sarcophagus over the reactor. He opposed a plan to extend the underground cooling system outside the reactor 4 building, as well as other projects he considered to be redundant. Legasov was impressed by the operation of the KGB in the area but considered the Civil Defence group to be in shambles. He was also concerned at the lack of safety literature distributed to the population. Legasov thought people worked together efficiently and this put them in good spirits. On 5 May, Legasov was summoned to meet with the Politburo in Moscow, including Mikhail Gorbachev, to report on progress. Legasov and Anatoly Alexandrov described the meltdown scenarios, and Legasov agreed with the plan to tunnel under the reactor to provide cooling. After the meeting, Scherbina told him that he could work from Moscow but was quickly ordered back to Chernobyl. Legasov reassured Gorbachev by phone that scale of contamination was understood and the reactor was not a continuing threat to other countries. Legasov developed a plan to extinguish the reactor fire using nitrogen gas pumped throughout the plant's pipe network but the pipes were too badly damaged to be effective. Around 9–10 May, Gorbachev requested a chronology of events and the cause of the accident in preparation for an interview, which Legasov provided in writing with a few edits from other investigators. After 10 May, the situation had somewhat stabilized and Legasov was able to spend less time at the accident site but still frequently visited. Upon returning from Chernobyl for the