There is a nuclear power plant in Loviisa, some 50 miles east from Helsinki (https://en.wikipedia.org/wiki/Loviisa_Nuclear_Power_Plant), so this option is within possibilities and has been evaluated.

However the two existing units in Loviisa will reach the end of their 50-year lifetime by 2030, so using them would depend on getting a lifetime extension (uncertain) or building a new reactor (very slow, as shown by the delays with the Olkiluoto unit 3 mentioned in another comment above).