According to the Arka news agency, the 376 MW reactor at the Metsamor NPP (pictured) was taken offline on 20 September for maintenance and refuelling.
At the same time, the first phase of a scheme to prolong the plant’s operational lifetime until 2026 was implemented by Russia’s Rosenergoatom.
The Soviet-built VVER-440 light water reactor came online in 1980 and provides 31 per cent of Armenia’s power. The plant was initially planned to be shut down this year, but its operators have applied to the country’s nuclear regulator to extend its lifetime through a scheme financed by a $270m grant and $30m in loans from Russia.
The Metsamor reactor has been the subject of scrutiny due to its location in an earthquake-prone region and lack of a containment vessel. The European Union has termed the reactor the "oldest and least reliable" and a 2011 report in National Geographic called it "the world's most dangerous" nuclear plant.
Earlier this month the International Atomic Energy Agency (IAEA) conducted a safety review of the plant, with a report to be published within three months.
Accoding to the World Nuclear Association, a six-month shutdown is planned for 2017 to implement safety upgrades as well as turbine modernization designed to increase the plant’s output by 15-18 per cent.
The plant’s other reactor, which came online in 1976, was shut down in 1989 after an earthquake raised safety concerns. The currently functioning reactor was restarted in 1995.
A second Armenian reactor with a capacity of 1060 MW is planned to be operational by 2023.