On Monday the two submitted reports to the Finnish Radiation and Nuclear Safety Authority STUK on the readiness of their nuclear facilities to withstand extreme natural conditions.
These self-published reports are part of a system of nuclear stress tests ordered by the EU after last spring's Fukushima disaster in Japan. They are intended to reconsider the effects of possible earthquakes, floods and severe weather conditions on plant operations.
TVO, which operates two reactors at Olkiluoto in Eurajoki on the west coast and is building a third there, was the first to release its own safety assessment on Monday morning. It says that its studies do not indicate the need for any major immediate changes.
However the company says it will continue to improve its readiness for a loss of power supply as well as its seawater cooling systems.
TVO says that about 20 people have been working on its report since last summer.
In its own assessment, Fortum also promises to beef up the seawater cooling system at its nuclear power station in Loviisa on the south coast. It also says it will study how to ensure the cooling of fuel rods during exceptionally protracted emergency situations.
A new consortium, Fennovoima, plans to build its first nuclear reactor at Pyhäjoki on the west coast.