Neutron Temperature Measurements in a Cryogenic Hydrogenous Moderator

The advisability of prototypic testing for space nuclear systems

“…In retrospect, those who had opposed the PBRCX on grounds that analytical tools were sufficiently advanced saw that unanticipated interactive effects of the design cannot always be effectively modeled. We discovered that the PBR rocket engine, while having a goal of a negative temperature coefficient in reality exhibited a positive temperature coefficient over a modest temperature range [5,6]. This was a completely unexpected event and resulted in a short stand down for safety purposes when it was discovered that the CX could exhibit a positive temperature coefficient, when all the safety documentation showed (from analysis) that the temperature coefficient would be negative [7].…”