Not so sure about NERVA
Hi Mark
NERVA was a marginal design at best, expedited more for political expedience than technical quality. DUMBO was a better design, but not as far along in finished product terms as NERVA was when they were signing the funding forms.
Stephen Baxter wrote a chilling account of what might've happened if a nuclear 'Apollo' mission tanked in "Voyage". David Portree's Beyond Apollo post on NASA Nuke studies gives one serious pause for thought. He's read some pretty sobering assessments of the technical readiness for a NERVA style engine in space... for example, one real problem was just how to protect other vehicles from the x-rays coming off the reactor when it was shut-down and the Nuke Shuttle was being serviced between missions.