Equipped with two 510MW units, the facility had been operating since 1977.
It had supplied around 13% of the country's total power mix last year by generating a total of 8.47 terawatt hours (TWh) of atomic power.
The planned investments will lead to the renewal of the facility's automation system and upgrade of its turbine generators.
It will also involve installation of the backup cooling system at the plant, in order to ensure that the facility remains functional until 2030.
Loviisa Power Plant deputy director Thomas Buddas said: "The investment programme currently being carried out at the Loviisa nuclear power plant is the most extensive in the plant's history.
"The programme aims to secure safe, reliable and profitable energy generation for the duration of the operating licenses, i.e. until 2027 and 2030."
The backup cooling system is expected to ensure plant safety, and is independent of seawater and the diesel fuel storage and distribution system.
Buddas said: "As a carbon dioxide-free production form, nuclear energy curbs climate change,
which improves energy security of supply for society and supports the increase of renewable energy in the energy system."
"The Loviisa power plant contributes with steady and reliable base-load electricity,
