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There were many studies in the 1960s, and a lesser number of later ones, for launch vehicles with nuclear-thermal upper stages. I have rarely seen mention of what emergency procedures were considered for launch failures.

Dangers of launching a nuclear thermal rocket suggests the hazard is not extreme - for the case of an NTR started in orbit. A nuclear upper stage has the possibility of running for some time but failing to reach orbit.

Even in the pre-Chernobyl era, there has to have been serious consideration of this. What studies were done, and is there any available summary of the results?

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    $\begingroup$ You may want to include studies of space-based reactors, which were more numerous (and were actually deployed!), into the consideration. Basically, robust reactor shielding and de-spinning (maintaining positive attitude control) are your best friends. $\endgroup$ – Deer Hunter Feb 14 '15 at 21:51
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    $\begingroup$ Remember that a nuclear-thermal engine doesn't have a huge mass of stuff just looking to go boom. While it certainly could crash it's not going to go up in an approximation of a tactical nuke. Furthermore, the real danger is used rods, not fresh ones. $\endgroup$ – Loren Pechtel Feb 14 '15 at 21:51
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    $\begingroup$ Nukes, schmukes. Real rocketeers use liquid fluoride and hydrazine. $\endgroup$ – Deer Hunter Feb 14 '15 at 23:42
  • $\begingroup$ A bit about "poison wires" to prevent criticality from water getting inside the pressure vessel: sciencemadness.org/lanl1_a/lib-www/la-pubs/00397413.pdf $\endgroup$ – Deer Hunter Feb 15 '15 at 0:01
  • $\begingroup$ There is some concern about an unused NTR core falling into a lake or ocean, which serves as a moderator and causes criticality (more a "meltdown, release of radionucleides" problem than a nuclear explosion.) $\endgroup$ – ikrase Aug 25 '20 at 6:20
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50 years old abort routines are hard to come by, but the NERVA-specs (unclassified 9/8/1970) clearly specify a malfunction mode in which the engine should be able to provide a minimum of thrust and impulse. The values stated (thrust of 30000 pounds, impulse of 10⁸ lb-seconds) are enough to direct the upper stage away from densely populated areas, towards a landing in the ocean. The engine should also be capable of operating with just one turbo pump
Normal procedure for saving the crew during a launch failure is separating the capsule from from the rocket, and fire a solid rocket escape tower to get away, followed by a normal descent with parachutes. The Mercury capsules, pre-dating the NERVA program, was equipped with escape towers.

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