Official Saudi media confirmed that Park had arrived in Riyadh.
"We'll have some framework agreement" on technical cooperation, research and development and the exchange of personnel in the nuclear field, said Jungho Lee, head of the political section at Seoul's embassy.
He told AFP the agreement would be reached between King Abdullah City for Atomic and Renewable Energy (K.A.CARE) and South Korea's science, ICT and future planning ministry.
Saudi Arabia is the world's biggest petroleum exporter and entirely dependent on oil and gas for its electricity production.
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Park's visit is the first by a South Korean president since 2012.
The two nations enjoy "traditional friendly relations" but this is a chance to strengthen ties and discuss "topics of common interest" after King Salman acceded to the throne in January after Abdullah's death, Lee said.