People streamed into the central square of Slavutych in the early hours of Sunday, placing candles on a large radiation hazard symbol laid out on the ground as a midnight commemoration began for those killed in the Chernobyl disaster 40 years ago and the thousands who risked deadly radiation exposure to contain its aftermath.

Residents show up for the vigil each year despite wartime curfews and official warnings against large gatherings during Russia’s war on Ukraine.

The April 26, 1986 disaster shone a spotlight on lax safety standards and government secrecy in what was then the Soviet Union. The explosion was not reported by Soviet authorities for two days, only after winds had carried the fallout across Europe and Swedish experts had gone public with their concerns.

About 600,000 people, often referred to as Chernobyl’s “liquidators,” were sent in to fight the fire at the nuclear plant and clean up the worst of its contamination. Thirty workers died within months from either the explosion or acute radiation sickness. The accident exposed millions in the region to dangerous levels of radiation and forced a wide-scale, permanent evacuation of hundreds of towns and villages in Ukraine and Belarus.

The city of Slavutych, around 50 kilometres (32 miles) from the former plant, dates to this period. While most evacuees were resettled across nearby districts in Kyiv region, in late 1986 Soviet authorities began building what would become the city to house workers from the Chernobyl Nuclear Power Plant and their families. The first residents moved in around 1988.

Since then, the city has endured a brief Russian occupation during Moscow’s failed push to seize the Ukrainian capital in early days of the war, as well as harsh winters – especially the last one, when blackouts forced some residents to cook meals over open fires in the streets.