I found some explosion commands either in command.h or define.h and also looked at some examples in FO2 script source some time ago. Then I tried scripting explosions using those methods and the game kept crashing. Not sure why, but you can find examples of scripted explosions in the FO2 script source. Look for traps on stuff like doors.
Also, you can make new weapons with damage type explosion, and min/max damage to whatever value you want, in 30 seconds in the mapper.