No, as far as I know, it isn't. If you do get a radio app, it won't work since the S4 does not have an antenna/receiver for FM radio. It was built that way, so your only option is Internet radio.
Once again many thanks for the advice. I remember reading that the phone did not have the hardware but I wondered if there was a way round it. It's a shame that they did not include it since it gives more options.