The plant splits hydrofluoric acid into hydrogen and fluoride. The hydrogen then gets scrubbed and released into the atmosphere and fluorine goes into the process. If the hydrogen and fluorine recombine, it can be very reactive and cause a non-radioactive hydrogen explosion. On Saturday, hydrogen was accidentally recombined with fluorine causing a massive explosion that could be heard a mile away and leading to the plant being temporarily shut down.
Looks like the IAEA isn't doing their job here in the USA!