starting in the 1960s have been controversial for years. in the 1970 dale bridenbaugh and two colleagues became known as the ge-3 when they quit over safety concerns about the mark i reactors, which they feared were not large or strong enough to contain radiation in the event of a meltdown. in fact, ge specifically marketed the mark i as cheaper and easier to build. bridenbaugh is watching the events in japan fearfully. you know, it s frightening to me that we ve gotten into this situation where thousands of people may lose their lives as a result of this. reporter: after the ge-3 quit back in 1975, the mark i reactors here in the u.s. all underwent safety modifications. ge tells abc news the mark is have, quote, a proven track record of performing reliably and safely for more than 40 years. but is 40 years too long for a nuclear reactor to be in operation? some experts we spoke to said, yes.