The FDA has in fact approved irradiation for pork as well as the USDA and FSIS; however it must be done in low-doses. Not all pork is irradiated, though some of it is.
Low doses or irradiation are used in order to effectively control trichina. Even treated pork is still considered to be dangerous and needs to be handled with proper care and all the necessary safety precautions taken.
Although the trichinella parasite may still be alive in the pork, it will not have the ability to reproduce whatsoever. Those packages of pork that are irradiated must be labeled appropriately as per USDA regulations.