Twice a year between 2011 and 2015, Belgian filmmakers Yves Degryse and Bart Baele and French journalist Cathy Blisson travelled to Zvizdal, a small Ukrainian village whose inhabitants had been almost entirely evacuated after the nuclear disaster of Chernobyl in 1986.

Still technically a forbidden zone due to the threat of radioactive infection, it took some negotiation to actually reach Zvizdal.

“The strange thing is, once you are there, the nature of the place is amazing,” says Degryse, one of the founding members of the theatre group Berlin. “It is strange to have that image of Chernobyl on the one hand and on the other hand this natural paradise.”

The regular trips to the village begun after the French journalist Cathy Blisson – who used to write reviews of Berlin’s theatre productions – asked Degryse and Baele to collaborate on a film based around the only two remaining citizens of Zvizdal; the elderly couple Nadia and Pétro Opanassovitch Lubenoc. Even their daughter had long since relocated.

“They were the only ones in the area who refused to leave,” says Degryse. “Pétro mentioned a lot that you should stay in the place you are living, the place you are born.”

The result of four years spent building trust with the couple, Zvizdal will be screened at the Brighton Dome Corn Exchange from 23-25 May; 30 years and one month since the Chernobyl nuclear reactor exploded.

Without electricity, running water and any means of communication to the outside world, Pétro and Nadia’s shared life is one of self-sufficiency and pragmatism. Degryse knew he and Baele had to follow the couple’s “rhythm” whilst filming and interviewing, “not the inverse.”

“You have to build up a relationship over time; we worked very slowly for the standards of film. If you are living in an isolated way for over 25 years, naturally you are very reflective. They never knew when we were coming over because we had no way to tell them. Each time we had to hope they were still alive. They have this urge for communication, but also when we had been with them for more than three days we had to go somewhere else and leave them be.”

Degryse talks of the issue of intervention, and to what extent he, Bart and Cathy should involve themselves in the lives of their subjects; a pertinent dilemma for every filmmaker, but all the more pronounced in such an extreme, intimate atmosphere. They brought goods for the couple on every visit, and offered to help with the couple’s work in the fields, which was refused. A recurring question was whether Nadia and Pétro should move to Kiev, like many other former residents of the village, or stay in Zvizdal.

As Degryse recalls: “after a few years of visiting, the issue begun to be raised about what one of them would do if something happened to the other. He was more convinced about moving than she was. It was this question of: at what point should you change?”

Despite these fleeting thoughts of relocation, there is also the hope – expressed particularly in the first days of filming – that Zvizdal’s ex-citizens will one day return to the village. “They saw the possibility that people could come back,” says Degryse. “They even proposed to us that we should live there, and bring our families!”

And yet part of Petro and Nadia’s insistence on staying over these decades is an intriguing, if scientifically unproven, theory. “Pétro claimed that the people who had moved away from the infected areas had since died, whereas those that stayed – like he and Nadia – had survived because their bodies had adapted.”

In the sole company of each other for such a vast amount of time, the couple’s relationship is, as Degryse asserts, “microscopic” in its intensity. “They really need each other,” says the filmmaker. “But they quarrel, too, like all people can quarrel. There is a lot of humour, hard humour. But survival is the main issue, so they are very pragmatic.”

It was understandably difficult for Degryse, Baele and Blisson to reacclimatise upon returning home to Antwerp and Paris after every Ukrainian excursion, and an inevitable sadness met the filmmakers after the final trip last winter. Now that Zvizdal is ready for its UK premiere in Brighton, though, Degryse is excited, and complimentary to the festival’s audience.

“It’s always a very open crowd, which I like, and that is probably connected with the way the festival runs its programme. There is a lot of openness, a lot of curiosity.”

Zvizdal

Brighton Dome Corn Exchange, Church Street, Monday, May 23, to Wednesday, May 25.

Mon and Tue, 8pm, Wed, 6pm and 8pm, from £15. Call 01273 709709.