Relieved to arrive intact at the site's security gate, I was greeted by a calm American who shepherded me around the daunting complex over the next couple of days.

Thousands of people then worked at the site to ensure its continuing safety, but the atmosphere was eerily quiet. All the time the great hulk of the reactor building's temporary shelter loomed as a haunting reminder of the heroic response to the disaster and its terrible consequences.

Within weeks of the April 1986 explosive destruction of reactor number four, Soviet engineers began work on the building’s enclosing "sarcophagus," completing it later that year with 400,000 metric tons of concrete and 7,000 metric tons of steelwork.

Of some 200,000 people who worked at the Chernobyl site after the accident, 90,000 were involved in the shelter's construction, according to the operator. Around 50 later reportedly died through radiation exposure. Many thousands more deaths were estimated over the wider region.

I had covered the Chernobyl disaster from London for nearly six years after the disaster when plans for the sarcophagus emerged. 

Numerous studies and conferences followed, leading to the 2007 contract with the French-led Novarka joint venture to build a 150-m-long steelwork vault to span 257 m and rise 105 m. It was built at one side of the reactor building and slid over the sarcophagus in 2016. 

At the time of my visit, Novarka was only just beginning to set up and the existing management team took me though the safety procedures. While that involved rigorous technical safeguards, the advice to keep off potentially radioactive grass made the greatest impact.

Hearing about the reactor building’s uncertain condition and viewing its darkened interiors occupied most of the visit. But it was peripheral activities that brought home the scale of the disaster.

Walking alone with my guide through the nearby town of Pripyat, signs of the hasty evacuation by some 40,000 residents confronted us. Discarded toys, a rusting Ferris wheel and abandoned preparations for a children's festival stood among buildings threaded with spreading vegetation.

At the end of my visit's first day, we all boarded a train for the 55-km journey to Slavutych, where the workforce lived. We passed through a large, wooded exclusion zone, which had become dangerously contaminated. 

Older people, less concerned about long-term effects of radiation, were moving back in, I was told. Colonies of wolves, boars and even bears also were said to be thriving in the human-free zone. 

In an optimistic footnote, those Chernobyl wolves are developing resistance to cancer, according to new findings published this year by researcher Cara Love at Princeton University's Dept. of Ecology & Evolutionary Biology.