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While the US has claimed only sending one nuclear reactor (SNAP 10-A) into space, Russia has sent many. Here on earth we've adopted a Defense in Depth strategy to design for safety controls. Though, everything in space is different...

What special design considerations are needed for nuclear reactors in space?

What have we learned from the number of nuclear reactors already in orbit?

What are the dangers of these reactors in orbit and can existing reactors be safely sequestered?

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  • $\begingroup$ Avoidance of moving parts is rather important... (yes, I know there are control drums) . $\endgroup$ – Deer Hunter Jul 31 '15 at 4:51
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There is no universally accepted design criteria for fission reactors launched into orbit, mostly because until recently only the U.S. and the Soviet Union had the capability and both countries employed vastly different design and operation philosophies. Most of the existing standards in the west are likely to be based on the U.S. DOE policy for the use of radioisotope systems which looks at statistical failure models and their effects on radioisotope dispersal and their effects on the health of affected populations.

Fission reactors have some aspects that make launch inherently safer, and in some aspects more dangerous. When launched, fission reactors have yet to fission a single atom and therefore have no radioactive fission products built up, making dispersal of fuel a lesser health concern. However, there is a concern that enriched fuel materials could land in countries attempting to acquire nuclear weapons. Also, the majority of earth is covered by water, which is a great neutron reflector and also softens the neutron spectrum to a region where an unintended criticality event becomes more likely. Finally, to date there has been little work to define a minimum safe orbit for fission operations. Obviously, the primary concern is that radiation could have negative effects on manned space operations, but to be honest, any gamma, neutron or beta radiation, would be negligible to what already exists due to our own star and other stars. The bigger concern, is how it could affect scientific instruments in orbit.

While this is a lengthy response, the quick answer is that there are few existing guidelines, because at present nobody is launching nuclear reactors. However, there are a few areas of concern that have to be addressed when procedures are put in place.

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    $\begingroup$ Would not call reactor neutron flux negligible. Aren't there any NRC/joint documents on design and operations? Could you please provide a few bullets related to e.g. ground handling, launch abort modes, mechanical reliability, risk of neutron embrittlement, debris avoidance, disposal? Wouldn't say your answer is lengthy, it could gain a lot by explicitly treating those subjects - even if it increased its overall length, it would also make the post much more lucid. $\endgroup$ – Deer Hunter Aug 6 '15 at 21:57
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    $\begingroup$ I'd agree, this isn't a particularly lengthy response for this stack exchange and references/links are always appreciated. Neutron flux would be negligible because it falls off based on the inverse square law and space is big - you're not likely to be close enough for it to matter if you're not rendezvousing with the reactor. $\endgroup$ – 1337joe Aug 6 '15 at 22:16
  • $\begingroup$ Deer Hunter, to address your points is not possible. The point i am making is that there are currently NO standards for these topics for the simple reason that we are not making nor launching these systems now. DOE will not entertain spending money on this topic unless a serious program exists. The companies who partook in 20th century programs no longer exist and the standards were far less rigid the last time this country did this kind of work. In short, there are only opinions, but no standards as to how this work should proceed. $\endgroup$ – Jon Aug 7 '15 at 22:54

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