Ukrainian President Volodymyr Zelenskiy, center, visits the "new safe confinement" shelter that spans the remains of the Chernobyl nuclear power plant's Reactor No. 4, in Chernobyl, Ukraine, Wednesday, July 10, 2019. A structure built to confine radioactive dust from the nuclear reactor at the center of the 1986 Chernobyl disaster was formally unveiled on Wednesday.(Ukrainian Presidential Press Office via AP)

Ukrainian President Volodymyr Zelenskiy, left, listens to an engineer as he visits the "new safe confinement" shelter that spans the remains of the Chernobyl nuclear power plant's Reactor No. 4, in Chernobyl, Ukraine, Wednesday, July 10, 2019. A structure built to confine radioactive dust from the nuclear reactor at the center of the 1986 Chernobyl disaster was formally unveiled on Wednesday.(Ukrainian Presidential Press Office via AP)

Ukrainian President Volodymyr Zelenskiy, center, poses for a selfies as he visits the "new safe confinement" shelter that spans the remains of the Chernobyl nuclear power plant's Reactor No. 4, in Chernobyl, Ukraine, Wednesday, July 10, 2019. A structure built to confine radioactive dust from the nuclear reactor at the center of the 1986 Chernobyl disaster was formally unveiled on Wednesday.(Ukrainian Presidential Press Office via AP)

Ukrainian President Volodymyr Zelenskiy, foreground, visits the "new safe confinement" shelter that spans the remains of the Chernobyl nuclear power plant's Reactor No. 4, in Chernobyl, Ukraine, Wednesday, July 10, 2019. A structure built to confine radioactive dust from the nuclear reactor at the center of the 1986 Chernobyl disaster was formally unveiled on Wednesday.(Ukrainian Presidential Press Office via AP)

A view inside the "new safe confinement" shelter that spans the remains of the Chernobyl nuclear power plant's Reactor No. 4, in Chernobyl, Ukraine, Wednesday, July 10, 2019. A structure built to confine radioactive dust from the nuclear reactor at the center of the 1986 Chernobyl disaster was formally unveiled on Wednesday. (Ukrainian Presidential Press Office via AP)

Ukrainian President Volodymyr Zelenskiy, right, signs a helmet as he visits the "new safe confinement" shelter that spans the remains of the Chernobyl nuclear power plant's Reactor No. 4, in Chernobyl, Ukraine, Wednesday, July 10, 2019. A structure built to confine radioactive dust from the nuclear reactor at the center of the 1986 Chernobyl disaster was formally unveiled on Wednesday.(Ukrainian Presidential Press Office via AP)

Ukrainian President Volodymyr Zelenskiy, foreground, visits the monument to the victims of the 1986 Chernobyl tragedy near the "new safe confinement" shelter that spans the remains of the Chernobyl nuclear power plant's Reactor No. 4, in Chernobyl, Ukraine, Wednesday, July 10, 2019. A structure built to confine radioactive dust from the nuclear reactor at the center of the 1986 Chernobyl disaster was formally unveiled on Wednesday.(Ukrainian Presidential Press Office via AP)

Ukrainian President Volodymyr Zelenskiy, centre, poses for photo with other officials as he visits the abandoned city of Prypyat some 3 kilometers (1.86 miles) from Chernobyl in Prypyat, Ukraine, Wednesday, July 10, 2019. A structure built to confine radioactive dust from the nuclear reactor at the centre of the 1986 Chernobyl disaster was formally unveiled on Wednesday.(Ukrainian Presidential Press Office via AP)

Ukrainian President Volodymyr Zelenskiy and other officials visit the abandoned city of Prypyat some 3 kilometers (1.86 miles) from Chernobyl in Prypyat , Ukraine, Wednesday, July 10, 2019. A structure built to confine radioactive dust from the nuclear reactor at the center of the 1986 Chernobyl disaster was formally unveiled on Wednesday.(Ukrainian Presidential Press Office via AP)

A playground is seen in the abandoned city of Prypyat some 3 kilometers (1.86 miles) from Chernobyl in Prypyat, Ukraine, Wednesday, July 10, 2019. A structure built to confine radioactive dust from the nuclear reactor at the center of the 1986 Chernobyl disaster was formally unveiled on Wednesday.(Ukrainian Presidential Press Office via AP)

Poject Durector of Novarka Cyrille Fatiguer (R) presents a symbolic key to General Director of Chernobyl Nuclear Power Plant Sergiy Kalashnyk (C) as Ukrainian President Volodymyr Zelensky a looks on during a commissioning ceremony for a new metal dome designed and built by French consortium Novarka encasing the destroyed reactor at Chernobyl plant on July 10, 2019, in Chernobyl. - Ukraine and its European partners on July 10 formally inaugurated a new metal dome encasing the destroyed reactor at the infamous Chernobyl plant, wrapping up a two-decade effort. Branded as the world's largest moveable metal structure, the so-called New Safe Confinement seals the remains of the fourth reactor at the nuclear plant that was the site of the massive Chernobyl disaster in 1986. (Photo by SERGEI SUPINSKY / AFP)

General Director of Chernobyl Nuclear Power Plant Sergiy Kalashnyk (L), Ukrainian President Volodymyr Zelensky, and Poject Durector of Novarka Cyrille Fatiguer pose with a symbolic key during a commissioning ceremony for a new metal dome designed and built by French consortium Novarka encasing the destroyed reactor at Chernobyl plant on July 10, 2019, in Chernobyl. - Ukraine and its European partners on July 10 formally inaugurated a new metal dome encasing the destroyed reactor at the infamous Chernobyl plant, wrapping up a two-decade effort. Branded as the world's largest moveable metal structure, the so-called New Safe Confinement seals the remains of the fourth reactor at the nuclear plant that was the site of the massive Chernobyl disaster in 1986. (Photo by SERGEI SUPINSKY / AFP)

General Director of Chernobyl Nuclear Power Plant Sergiy Kalashnyk (L), Ukrainian President Volodymyr Zelensky, and Poject Durector of Novarka Cyrille Fatiguer pose with a symbolic key during a commissioning ceremony for a new metal dome designed and built by French consortium Novarka encasing the destroyed reactor at Chernobyl plant on July 10, 2019, in Chernobyl. - Ukraine and its European partners on July 10 formally inaugurated a new metal dome encasing the destroyed reactor at the infamous Chernobyl plant, wrapping up a two-decade effort. Branded as the world's largest moveable metal structure, the so-called New Safe Confinement seals the remains of the fourth reactor at the nuclear plant that was the site of the massive Chernobyl disaster in 1986. (Photo by SERGEI SUPINSKY / AFP)

Ukrainian President Volodymyr Zelensky (R) presents an award to Chernobyl's hero during a commissioning ceremony for a new metal dome designed and built by French consortium Novarka encasing the destroyed reactor at Chernobyl plant on July 10, 2019, in Chernobyl. - Ukraine and its European partners on July 10 formally inaugurated a new metal dome encasing the destroyed reactor at the infamous Chernobyl plant, wrapping up a two-decade effort. Branded as the world's largest moveable metal structure, the so-called New Safe Confinement seals the remains of the fourth reactor at the nuclear plant that was the site of the massive Chernobyl disaster in 1986. (Photo by SERGEI SUPINSKY / AFP)

Ukrainian President Volodymyr Zelensky attends a commissioning ceremony for a new metal dome designed and built by French consortium Novarka encasing the destroyed reactor at Chernobyl plant on July 10, 2019, in Chernobyl. - Ukraine and its European partners on July 10 formally inaugurated a new metal dome encasing the destroyed reactor at the infamous Chernobyl plant, wrapping up a two-decade effort. Branded as the world's largest moveable metal structure, the so-called New Safe Confinement seals the remains of the fourth reactor at the nuclear plant that was the site of the massive Chernobyl disaster in 1986. (Photo by SERGEI SUPINSKY / AFP)

Ukrainian President Volodymyr Zelensky attends a commissioning ceremony for a new metal dome designed and built by French consortium Novarka encasing the destroyed reactor at Chernobyl plant on July 10, 2019, in Chernobyl. - Ukraine and its European partners on July 10 formally inaugurated a new metal dome encasing the destroyed reactor at the infamous Chernobyl plant, wrapping up a two-decade effort. Branded as the world's largest moveable metal structure, the so-called New Safe Confinement seals the remains of the fourth reactor at the nuclear plant that was the site of the massive Chernobyl disaster in 1986. (Photo by SERGEI SUPINSKY / AFP)

A picture shows a general view of a a new metal dome designed and built by French consortium Novarka encasing the destroyed reactor at Chernobyl plant on July 10, 2019, in Chernobyl. - Ukraine and its European partners on July 10 formally inaugurated a new metal dome encasing the destroyed reactor at the infamous Chernobyl plant, wrapping up a two-decade effort. Branded as the world's largest moveable metal structure, the so-called New Safe Confinement seals the remains of the fourth reactor at the nuclear plant that was the site of the massive Chernobyl disaster in 1986. (Photo by SERGEI SUPINSKY / AFP)

A picture shows a general view of a a new metal dome designed and built by French consortium Novarka encasing the destroyed reactor at Chernobyl plant on July 10, 2019, in Chernobyl. - Ukraine and its European partners on July 10 formally inaugurated a new metal dome encasing the destroyed reactor at the infamous Chernobyl plant, wrapping up a two-decade effort. Branded as the world's largest moveable metal structure, the so-called New Safe Confinement seals the remains of the fourth reactor at the nuclear plant that was the site of the massive Chernobyl disaster in 1986. (Photo by SERGEI SUPINSKY / AFP)

TOPSHOT A picture shows a general view of a a new metal dome designed and built by French consortium Novarka encasing the destroyed reactor at Chernobyl plant on July 10, 2019, in Chernobyl. - Ukraine and its European partners on July 10 formally inaugurated a new metal dome encasing the destroyed reactor at the infamous Chernobyl plant, wrapping up a two-decade effort. Branded as the world's largest moveable metal structure, the so-called New Safe Confinement seals the remains of the fourth reactor at the nuclear plant that was the site of the massive Chernobyl disaster in 1986. (Photo by SERGEI SUPINSKY / AFP)

An employee looks at monitors in the control room of the New Safe Confinement (NSC) new metal dome designed and built by French consortium Novarka encasing the destroyed reactor at Chernobyl plant on July 10, 2019, in Chernobyl. - Ukraine and its European partners on July 10 formally inaugurated a new metal dome encasing the destroyed reactor at the infamous Chernobyl plant, wrapping up a two-decade effort. Branded as the world's largest moveable metal structure, the so-called New Safe Confinement seals the remains of the fourth reactor at the nuclear plant that was the site of the massive Chernobyl disaster in 1986. (Photo by SERGEI SUPINSKY / AFP)

An employee looks at monitors in the control room of the New Safe Confinement (NSC) new metal dome designed and built by French consortium Novarka encasing the destroyed reactor at Chernobyl plant on July 10, 2019, in Chernobyl. - Ukraine and its European partners on July 10 formally inaugurated a new metal dome encasing the destroyed reactor at the infamous Chernobyl plant, wrapping up a two-decade effort. Branded as the world's largest moveable metal structure, the so-called New Safe Confinement seals the remains of the fourth reactor at the nuclear plant that was the site of the massive Chernobyl disaster in 1986. (Photo by SERGEI SUPINSKY / AFP)

An employee looks at monitors in the control room of the New Safe Confinement (NSC) new metal dome designed and built by French consortium Novarka encasing the destroyed reactor at Chernobyl plant on July 10, 2019, in Chernobyl. - Ukraine and its European partners on July 10 formally inaugurated a new metal dome encasing the destroyed reactor at the infamous Chernobyl plant, wrapping up a two-decade effort. Branded as the world's largest moveable metal structure, the so-called New Safe Confinement seals the remains of the fourth reactor at the nuclear plant that was the site of the massive Chernobyl disaster in 1986. (Photo by SERGEI SUPINSKY / AFP)

An employee looks at monitors in the control room of the New Safe Confinement (NSC) new metal dome designed and built by French consortium Novarka encasing the destroyed reactor at Chernobyl plant on July 10, 2019, in Chernobyl. - Ukraine and its European partners on July 10 formally inaugurated a new metal dome encasing the destroyed reactor at the infamous Chernobyl plant, wrapping up a two-decade effort. Branded as the world's largest moveable metal structure, the so-called New Safe Confinement seals the remains of the fourth reactor at the nuclear plant that was the site of the massive Chernobyl disaster in 1986. (Photo by SERGEI SUPINSKY / AFP)

An employee looks at monitors in the control room of the New Safe Confinement (NSC) new metal dome designed and built by French consortium Novarka encasing the destroyed reactor at Chernobyl plant on July 10, 2019, in Chernobyl. - Ukraine and its European partners on July 10 formally inaugurated a new metal dome encasing the destroyed reactor at the infamous Chernobyl plant, wrapping up a two-decade effort. Branded as the world's largest moveable metal structure, the so-called New Safe Confinement seals the remains of the fourth reactor at the nuclear plant that was the site of the massive Chernobyl disaster in 1986. (Photo by SERGEI SUPINSKY / AFP)

Visiters and journalists walk inside the New Safe Confinement (NSC) new metal dome designed and built by French consortium Novarka encasing the destroyed reactor at Chernobyl plant on July 10, 2019, in Chernobyl. - Ukraine and its European partners on July 10 formally inaugurated a new metal dome encasing the destroyed reactor at the infamous Chernobyl plant, wrapping up a two-decade effort. Branded as the world's largest moveable metal structure, the so-called New Safe Confinement seals the remains of the fourth reactor at the nuclear plant that was the site of the massive Chernobyl disaster in 1986. (Photo by SERGEI SUPINSKY / AFP)

TOPSHOT Visiters and journalists walk inside the New Safe Confinement (NSC) new metal dome designed and built by French consortium Novarka encasing the destroyed reactor at Chernobyl plant on July 10, 2019, in Chernobyl. - Ukraine and its European partners on July 10 formally inaugurated a new metal dome encasing the destroyed reactor at the infamous Chernobyl plant, wrapping up a two-decade effort. Branded as the world's largest moveable metal structure, the so-called New Safe Confinement seals the remains of the fourth reactor at the nuclear plant that was the site of the massive Chernobyl disaster in 1986. (Photo by SERGEI SUPINSKY / AFP)

Visiters and journalists walk inside the New Safe Confinement (NSC) new metal dome designed and built by French consortium Novarka encasing the destroyed reactor at Chernobyl plant on July 10, 2019, in Chernobyl. - Ukraine and its European partners on July 10 formally inaugurated a new metal dome encasing the destroyed reactor at the infamous Chernobyl plant, wrapping up a two-decade effort. Branded as the world's largest moveable metal structure, the so-called New Safe Confinement seals the remains of the fourth reactor at the nuclear plant that was the site of the massive Chernobyl disaster in 1986. (Photo by SERGEI SUPINSKY / AFP)

An employee stands inside the New Safe Confinement (NSC) new metal dome designed and built by French consortium Novarka encasing the destroyed reactor at Chernobyl plant on July 10, 2019, in Chernobyl. - Ukraine and its European partners on July 10 formally inaugurated a new metal dome encasing the destroyed reactor at the infamous Chernobyl plant, wrapping up a two-decade effort. Branded as the world's largest moveable metal structure, the so-called New Safe Confinement seals the remains of the fourth reactor at the nuclear plant that was the site of the massive Chernobyl disaster in 1986. (Photo by SERGEI SUPINSKY / AFP)

Employees stand inside the New Safe Confinement (NSC) new metal dome designed and built by French consortium Novarka encasing the destroyed reactor at Chernobyl plant on July 10, 2019, in Chernobyl. - Ukraine and its European partners on July 10 formally inaugurated a new metal dome encasing the destroyed reactor at the infamous Chernobyl plant, wrapping up a two-decade effort. Branded as the world's largest moveable metal structure, the so-called New Safe Confinement seals the remains of the fourth reactor at the nuclear plant that was the site of the massive Chernobyl disaster in 1986. (Photo by SERGEI SUPINSKY / AFP)

Employees stand inside the New Safe Confinement (NSC) new metal dome designed and built by French consortium Novarka encasing the destroyed reactor at Chernobyl plant on July 10, 2019, in Chernobyl. - Ukraine and its European partners on July 10 formally inaugurated a new metal dome encasing the destroyed reactor at the infamous Chernobyl plant, wrapping up a two-decade effort. Branded as the world's largest moveable metal structure, the so-called New Safe Confinement seals the remains of the fourth reactor at the nuclear plant that was the site of the massive Chernobyl disaster in 1986. (Photo by SERGEI SUPINSKY / AFP)

A stray dog lays in front of the New Safe Confinement (NSC) new metal dome designed and built by French consortium Novarka encasing the destroyed reactor at Chernobyl plant on July 10, 2019, in Chernobyl. - Ukraine and its European partners on July 10 formally inaugurated a new metal dome encasing the destroyed reactor at the infamous Chernobyl plant, wrapping up a two-decade effort. Branded as the world's largest moveable metal structure, the so-called New Safe Confinement seals the remains of the fourth reactor at the nuclear plant that was the site of the massive Chernobyl disaster in 1986. (Photo by SERGEI SUPINSKY / AFP)

A picture shows a monument near the New Safe Confinement (NSC) new metal dome designed and built by French consortium Novarka encasing the destroyed reactor at Chernobyl plant on July 10, 2019, in Chernobyl. - Ukraine and its European partners on July 10 formally inaugurated a new metal dome encasing the destroyed reactor at the infamous Chernobyl plant, wrapping up a two-decade effort. Branded as the world's largest moveable metal structure, the so-called New Safe Confinement seals the remains of the fourth reactor at the nuclear plant that was the site of the massive Chernobyl disaster in 1986. (Photo by SERGEI SUPINSKY / AFP)

A picture shows the New Safe Confinement (NSC) new metal dome designed and built by French consortium Novarka encasing the destroyed reactor at Chernobyl plant on July 10, 2019, in Chernobyl. - Ukraine and its European partners on July 10 formally inaugurated a new metal dome encasing the destroyed reactor at the infamous Chernobyl plant, wrapping up a two-decade effort. Branded as the world's largest moveable metal structure, the so-called New Safe Confinement seals the remains of the fourth reactor at the nuclear plant that was the site of the massive Chernobyl disaster in 1986. (Photo by SERGEI SUPINSKY / AFP)