With supply lines tripped up by sanctions and Moscow’s economy oriented toward its ongoing invasion of Ukraine, progress to replace these dinosaurs of the civilian nuclear age is plodding.

But continued reliance on aging technology made infamous by the world’s worst nuclear accident is also making Russia’s neighbors nervous.

“The extension of the operation of these reactors for five years raises concerns among neighboring countries, both regarding their own safety and the potential consequences for the Arctic,” Dmitry Gorchakov, a Bellona nuclear expert, said in Bellona’s January nuclear digest. All of Russia’s RBMK reactors are located within about 70 kilometers of European borders, he noted.

“However, in the context of Russia’s confrontation with the West, international dialogue and discussions to address concerns will be impossible, and the opinions of neighboring countries will not be a factor that the Russian government takes into account,” Gorchakov wrote.

At the beginning of the year, Rostekhnadzor, Moscow’s technical oversight agency, extended the operating license of the Leningrad Nuclear Power Plant’s Unit 3 reactor, an RMBK-1000 model that came online on 1979. Originally slated to run for 30 years, the unit was later extended for another 15 years before receiving its most recent permission to run until 2030.

The reactor is one of four at the Leningrad plant—and one of 11 nationwide—that was built on the RBMK 1000 design. Four others were built during the Soviet era in Ukraine at the Chernobyl nuclear power plant—including the one that exploded in 1986—and two similar RBMK-1500 reactors operated at the now-closed Ignalina nuclear plant in Lithuania, which where shut down for safety reasons.

The Russian technical agency has also said it plans to extend the operating license of the Unit 4 RBMK reactor at the Leningrad nuclear plant, the Units 3 and 4 RMBKs at the Kursk nuclear plant, and the first three RBMK units at the Smolensk nuclear plant. All of these reactors began operation in the late 1970s and early 1980s, and current extension plans envision running them until they reach 50-year operational lifespans.

The first two units at the Leningrad plant and the Unit 1 reactor at Kursk are the only RBMK’s in Russia that have stopped operation. While each of these RBMKs underwent comprehensive upgrades in the years following the Chernobyl catastrophe, no amount of remodeling was able to finesse their most deviling flaw as far as safe decommissioning and dismantlement are concerned—their graphite stacks.

A graphite stack is essentially bulky cylinder about 7 meters high and 11 meters across made of graphite bricks and weighing thousands of tons. Fuel is fed into the reactor via channels cut in the masonry, and the graphite acts as the moderator.

The concept originated in the late 1940s, when the Soviet Union and the United States began to build reactors to produce weapons plutonium—a time when considerations about how to dismantle them were not a priority. While most reactors in commercial operation around the globe are of the boiling water type, the Soviet Union’s first steps in civilian nuclear power were based on the unwieldy graphite moderated design.

And this, said Bellona nuclear expert Alexander Nikitin, presents big problems when it comes time to shut them down and disassemble them for environmentally safe storage. By the time the RMBKs are shut down, he said, the moderators represent some 3,800 tons of highly active graphite irradiated with Carbon-14 that takes 5,730 years to decay.

“No one—not just Russia—has yet found a safe technology to process and dispose of these stacks, but they are looking,” said Nikitin. Prior to the Russian invasion of Ukraine, robot dismantlement technology had made advances in stack dismantlement, but where those programs stand at present is unclear.

“Dismantling and burying these stacks is a major hemorrhoid,” Nikitin said.  

New technologies have allowed for RBMKs to run past their original runtimes, which partly side-steps that issue, Nikitin explained. But just how much punishment the graphite stacks can take remains unclear. Unit 1 of the Leningrad plant, for instance, was taken out of service in 2018 when it was discovered the reactor’s graphite stack had begun to swell and crumble into pieces.

For now, as Russia continues to extend the engineered lifespans of their RBMKs, both their ongoing operation, and what’s left of them when they shut down, pose troubling issues for the environment both inside and outside of Russia.