If it costs only €1 billion to extend the lifespan by 20 years, then nothing else can compete with it. The capacity is 1 GW.
OL3 will generate ~745 TWh over his life, from a total investment of ~€11bn.
Loviisa life extension will generate ~170 TWH, from an investment of ~€1bn.
Considering the capacity factor, we are comparing 6€/MWh for Loviisa against ~15€/MWh for OL3.
So, it is worth mentioning that extending the life of an existing power plant can be a really good investment.
Main difference is in initial setup/concrete installment!!
You can review all the maths using data from OL3 here: https://reactoratlas.com/en?y=2026&s=finland-olkiluoto-nucle...