The New Safe Confinement (NSC) structure built over the old sarcophagus covering the damaged fourth reactor of the Chernobyl nuclear power plant, photographed on April 20, 2018. #

Widows of Chernobyl victims hold portraits of their husbands, who died following the clean-up operations for the 1986 Chernobyl nuclear explosion, at Chernobyl's victim monument in Ukraine's capital Kiev, on April 26, 2018. #

Vera Toptunova caress the tomb of her son Leonid, who was an engineer at the Chernobyl nuclear plant, at Mitino Memorial in Moscow, Russia, on April 26, 2018, on the 32nd anniversary of the disaster. About 600,000 people, often referred to as Chernobyl's "liquidators," were sent in to fight the fire at the nuclear plant after an explosion on April 26, 1986. #

A woman touches a portrait at the monument to Chernobyl victims in Slavutich, the city where the power station's personnel live, some 50 kilometers (30 miles) from the accident site, during a memorial ceremony early on April 26, 2018. #

A radiation-warning sign stands near the check-point "Maidan" of the state radiation ecology reserve inside the 30-kilometer exclusion zone around the Chernobyl nuclear reactor, some 370 kilometers ( 231 miles) southeast of Minsk, Belarus, on April 11, 2016. #

Graffiti on a building on the main square in the town of Pripyat, which was abandoned following the Chernobyl nuclear accident, on November 29, 2016, in Pripyat, Ukraine. #

A central square in the deserted town of Pripyat on April 5, 2017. Once home to more than 40,000 people whose lives were connected to the Chernobyl nuclear power plant, Pripyat was hastily evacuated one day after a reactor at the plant three kilometers (two miles) away exploded on April 26, 1986. #

A tree grows out of the door of an abandoned barn inside the exclusion zone around the Chernobyl nuclear reactor, in the abandoned village of Krasnoselie, Belarus, on February 17, 2016. #

In this aerial view, a partially constructed and now abandoned cooling tower stands as the new enclosure, built over stricken reactor number four, is seen in the distance behind at the Chernobyl nuclear power plant on August 19, 2017. #

Tourists take pictures of a building in the ghost village of Kopachi near Chernobyl nuclear power plant on April 23, 2018, during their tour to the Chernobyl exclusion zone. #

Stray puppies play in an abandoned, partially completed cooling tower inside the exclusion zone at the Chernobyl nuclear power plant on August 18, 2017. An estimated 900 stray dogs live in the exclusion zone, many of them likely the descendants of dogs left behind following the mass evacuation of residents in the aftermath of the 1986 nuclear disaster. Volunteers, including veterinarians and radiation experts from around the world, are participating in an initiative called Dogs of Chernobyl, launched by the nonprofit Clean Futures Fund. Participants capture the dogs, study their radiation exposure, vaccinate them against parasites and diseases including rabies, tag the dogs, and release them again into the exclusion zone. #

Anna Sovtus, a Ukrainian veterinarian working with the Dogs of Chernobyl initiative, tends to a stray puppy she had just washed in the bathroom sink at a makeshift veterinary clinic inside the Chernobyl exclusion zone on August 17, 2017, in Chornobyl, Ukraine. Some released dogs are being outfitted with special collars equipped with radiation sensors and GPS receivers, in order to map radiation levels across the zone. #

An aerial view of a Soviet-era hammer and sickle on top of an abandoned apartment building in the ghost town of Pripyat, not far from the Chernobyl nuclear power plant on August 19, 2017, in Pripyat, Ukraine. #