The Financial Times reports that Trump and the US want Ukraine's nuclear power plants for the same reason they want Ukraine's rare earth minerals -- they are valuable, and if the US owned them, rather than Ukraine, it might discourage Russia from attacking them. According to the article:

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https://www.ft.com/content/06d9949f-3cd8-42c2-873f-af2acdee0f42

The Trump administration could seek to use the plant to help power the extraction of rare and critical minerals that Ukraine holds, according to two senior Ukrainian officials involved in drawing up an agreement with Washington on rare earths and other raw materials. That deal was meant to be signed earlier this month when Zelenskyy and Trump met in the White House, but the signing ceremony was called off when the two leaders clashed in the Oval Office. The US president’s latest proposal for Ukraine to transfer control of its power plants mirrors that earlier minerals deal. Trump officials have suggested that US stakes in crucial assets in the country could serve as a form of protection. But Kyiv remains wary as this falls short of the security guarantees it is seeking from the US.