Six Inquiries Seek the Lessons of Three Mile Island
2d article in series on 3 Mile Island discusses 6 investigations that have been started into accident; probes are being conducted by Presidenial commission under Dr John G Kemeny, by Nuclear Regulatory Commission under Mitchell Rogovin, by Senate subcommittee under Gary Hart, by House subcommittee under Morris Udall, by state of Pennsylvania under Lt Gov William Scranton and by Nuclear Safety Analysis Center under Dr Edwin L Zebroski; comments by panel leaders and Dr Chauncey Starr, former president of Electic Power Research Institute, who is now developing utility industry's response to accident; illus of Dr Thomas V Malone of Essex Corp, which has built full-scale mock-up of Metropolitan Edison control room as part of NRC study (M)