SEOUL, South Korea — Like Japan, resource-poor South Korea has long relied on nuclear power to provide the cheap electricity that helped build its miracle economy. For years, it met one-third of its electricity needs with nuclear power, similar to Japan’s level of dependence before the 2011 disaster at its Fukushima plant.

Now, a snowballing scandal in South Korea about bribery and faked safety tests for critical plant equipment has highlighted yet another similarity: experts say both countries’ nuclear programs suffer from a culture of collusion that has undermined their safety. Weeks of revelations about the close ties between South Korea’s nuclear power companies, their suppliers and testing companies have led the prime minister to liken the industry to a mafia.

The scandal started after an anonymous tip in April prompted an official investigation. Prosecutors have indicted some officials at a testing company on charges of faking safety tests on parts for the plants. Some officials at the state-financed company that designs nuclear power plants were also indicted on charges of taking bribes from testing company officials in return for accepting those substandard parts.

Worse yet, investigators discovered that the questionable components are installed in 14 of South Korea’s 23 nuclear power plants. The country has already shuttered three of those reactors temporarily because the questionable parts used there were important, and more closings could follow as investigators wade through more than 120,000 test certificates filed over the past decade to see if more may have been falsified.