The speech was Moon's followup on his presidential campaigns to cut coal and nuclear power.
Moon said plans for new power reactors will be cancelled and the operating periods of existing units will not be extended beyond their design life.
The new President of South Korea, Moon Jae-in has committed his country to phasing out all coal and nuclear power stations suggesting a major change in energy policy for the Asian state.
"So far, South Korea's energy policy pursued cheap prices and efficiency".
"The government will not extend the operational life cycle of nuclear reactors".
He noted that with the world's highest density of nuclear power plants, South Korea is no longer safe during earthquakes. "We will obtain a social consensus as soon as possible, taking into account the safety, construction progress rate, costs and spending as well as reserve power rate", Moon said.
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South Korea's oldest nuclear reactor Kori No.1 was permanently shut down at midnight on Sunday after reaching the end of its 40-year-lifespan, the first South Korean nuclear power plants to be closed permanently. Its nuclear power production from 25 nuclear plants in 2016 was the fifth-largest in the world, according to the World Nuclear Association. He said the seismic resistance of the country's nuclear power plants - which had been reinforced since the March 2011 Fukushima Daiichi accident in Japan - would be re-examined.
The former president Lee Myung-bak saw nuclear as an important source of clean energy, while Park wanted to increase the number of reactors to 36 by 2029.
The city of Busan on South Korea's southeastern coast said Monday it will strengthen cooperation with the Argonne National Laboratory, a research institute funded by the U.S. Department of Energy, on decommissioning nuclear reactors following the shutdown of a commercial nuclear reactor in the city.
To decommission the Kori 1 reactor, South Korea plans to invest developing its own decommissioning technology and experts in the area.
He hailed the shutdown of the reactor, calling it the start of the country's journey to becoming a nuclear-free nation and a safer South Korea.
At the same time, spent nuclear fuel will be cooled for 6 to 7 years and then transferred by December 2025 to a yet-to-built dry storage facility able to store a total of 1,391 spent fuel bundles. The decommissioning will take at least 15 years and cost 643.7 billion won ($569 million), the energy ministry said.