The next generation of nuclear reactors will need to be financed by taxpayers because private investors aren’t willing to bear the risks associated with building new plants.

That was the warning from bankers at a meeting of industry and government officials in Prague this week. The Nuclear Energy Agency event underscored the hard decisions Western economies soon need to make to keep one of their biggest clean energy sources going. While the public have warmed to nuclear in recent years, spiraling project costs have made private equity cautious.

Officials have estimated that the world needs to spend $5 trillion to triple nuclear-power generation over the next 25 years. The problem is that years of delays and billion-dollar budget overruns at European and the U.S. projects are spooking investors, and scores of reactors already running on borrowed time will need to be replaced. No private investors want to take on construction risks, said Simon Taylor, a financier at the Cambridge Nuclear Energy Center.