Units 5 and 6 at the Kozloduy nuclear plant will keep running as long as they prove they are safe, Tsanko Bachiyski, head of Bulgaria's Nuclear Regulatory Agency, told reporters.

A program to extend the units' working life sets out timelines. Bachiyski said that, given their current condition and the work done so far, unit 5 could run until 2049 and unit 6 until 2051. But he stressed this is not a final deadline.

How much longer the reactors run depends on their condition, which is checked through a periodic safety review carried out to world standards. The review happens every ten years, and the plant's operators must prove the units are safe, Bachiyski explained. He added that the agency can also ask for shorter gaps between checks if it decides that's needed.

Bachiyski said the results of the ten-year review for unit 5 are expected by the end of this year, and for unit 6 a year later.

"If we find any shortfalls, we can change the deadline and shorten it. If there are shortfalls, a plan is drawn up with steps that can include replacing equipment, technical fixes, or studies to check certain safety aspects," Bachiyski explained.

He added that one of the checks looks at how the way the reactors are run — especially shutdowns — affects the equipment's remaining service life. All these factors should show the real level of safety for the years ahead, the head of the Nuclear Regulatory Agency said.