MADRID (Reuters) - Spain's oldest nuclear plant Garona is shutting down on Sunday ahead of new taxes included in a government energy reform that would render the plant unviable.

Spain is introducing higher taxes on electricity generation as a measure to address an over 24 billion euro ($31 billion)energy tariff deficit after years of selling power below costs.

The energy reform would add 153 million euros of taxes on Garona in 2013, its operator Nuclenor said in a statement, adding this would "increase current economic losses to the point of sending Nuclenor into bankruptcy."

The nuclear matter at Garona - which opened in 1970 and produced about 1.4 percent of annual Spanish electricity output - will be transferred to a storage pool at the plant on Sunday night.

Spain's industry ministry had wanted to keep Garona open to assure a mix of energy options for the country, but Nuclenor said it would need to invest around 120 million euros in order to keep the plant running, while also facing higher taxes.

Spain relies on imports to cover its energy needs, with nuclear energy providing 20 percent of domestic electric demand in 2011.

(Reporting by Tracy Rucinski; Editing by Mark Potter)