Nerva Nuclear Reactor Instrumentation

The environmental conditions existing at many of the points at which measurements are required in the ground testing of the NERVA reactors are beyond the capabilities of commercially available transducers. The measurement of the temperatures inside the reactor core was accomplished by pushing thermocouples to the high temperature limit of this sensing means. Tungsten and tungsten alloys have shown the capability of surviving a reactor test at these temperatures in the presence of carbon and high pressure hydrogen. Vibration and pressure transducers have been developed which can operate in an ambient of cryogenic hydrogen with internal temperatures of over 500°F degrees generated by gamma and neutron heating. The measurement of strain with gages subjected alternately to cryogenic and maximum high temperatures for this type sensor was accomplished with weldable gages. The problem of bringing electrical signals from the sensors in the severe environments to the data recording system was solved by using magnesium oxide insulated conductors in stainless steel sheaths. In future testing, measurements are desired at locations in the core where temperatures and radiation levels are even higher than those which have already been experienced. Development continues on thermocouples to measure 5000°R, on vibration and acoustic pressure transducers to operate at radiation heating levels of four watts per gram and on methods of connecting magnesium oxide insulated sheathed cable to strain gages bonded with ceramic cements.