More than 1,000 firefighters are working to contain blazes around the site of the Chernobyl power plant, which 34-years ago this week became the site of the worst civilian nuclear disaster in history.

The fires have burned since the beginning of April, causing minor spikes in radiation as they churned through decades-old fallout, though the amounts released are not dangerous to human health, the UN’s atomic energy agency said on Sunday.

While the main fire has been extinguished, according to Reuters, it had advanced far into the 30-kilometer exclusion zone around the plant, which bore the brunt of the 1986 disaster. Smaller fires continued to burn on Friday evening, the plant’s administration said.

But the fires rekindle solemn memories, and raise uncomfortable questions about whether the land scorched by radiation more than three decades ago will ever be safe again.

A memorial at the entrance to the Chernobyl nuclear power plant. Photo: - Credit: Nils Bøhmer/Bellona

“On this day we bow our heads to the blessed memory of those heroes who saved the future from the danger of radiation,” President Volodymyr Zelensky, who visited the firefighters on Sunday, said in a statement to mark the anniversary.

He also expressed “deep respect” for the firefighters and others currently working in the zone to protect the lands from new disasters.

The fires began in the western part of the exclusion zone on April 3, spreading through nearby forests and raising columns of smoke that environmentalists worried could contain radiation. Although radiation levels at the site are only a quarter of what they were in the immediate aftermath of the disaster, trees and moss can absorb radiation from the soil and spread it into the atmosphere when burned.

Ukrainian officials offered contradictory accounts of ration measurements within the exclusion zone during the early days of the blazes. The head of Ukraine’s ecological services first said on Facebook that radiation had increased to 16 times normal levels. But he later retracted that statement. Officials now insist radiation levels are “within normal limits.”

The Vienna-based International Atomic Energy Agency, which both advocates for nuclear power and promotes its peaceful use, said it based its assessment on data provided by Ukraine.

A 2,600-kilometer area surrounding the April 26, 1986 disaster has been uninhabitable for decades. Following the explosion at the plant’s number 4 reactor, 116,000 people were forced to evacuate. The reactor itself continued to burn for 10 days, issuing clouds of poisonous radiation and contaminating three quarters of the European continent. Belarus, Ukraine and Russia were hit especially hard.

A view of the New Safe Confinement structure. Photo: - Credit: Nils Bøhmer/Bellona

Moscow was sluggish to admit to the catastrophe, but finally acknowledged it when Western European countries began reporting spikes in radiation levels.

To contain the fallout, 600,000 liquidators – comprised of police, fire fighters, medical workers, soldiers and engineers – were rushed to the site to create an ad-hoc containment structure of cement and steel over the ruins of the reactor. The conditions were chaotic and dangerous, and liquidators often worked without protective gear.

The sarcophagus, as the containment structure was called, trapped 200 tons of uranium and squelched the outpouring of radiation. But at the time, liquidators were concerned the structure would eventually give way. In 2005, it did.

Finally, in 2016, a 36,000-ton steel structure called the “New Safe Confinement” was placed atop the sarcophagus, with the goal of trapping the number 4 reactor’s radiation for the next 100 years. Within that time, technicians expect to dismantle the reactor’s remains and isolate the nuclear fuel that melted down during the 1986 disaster.

The project received more than $2billion in funding from 45 donor nations through funds managed by the European Bank of Reconstruction and Development.

Still, the vast expanse of the exclusion zone is growing more prone to wildfires. In the three plus decades since the disaster, the zone has been left more or less untouched, and deadwood and debris have accumulated. Researchers have been concerned for years that this lack of forest management – combined with higher temperatures and droughts brought on by climate change – are combining to make the Chernobyl exclusion zone a tinder box.

The influx of tourists to the site, which recently spiked thanks to the HBO miniseries Chernobyl, could make matters more precarious.

Ukrainian officials are investigating whether the recent spate of wildfires was deliberately set, and say they have a 27-year-old man in custody.