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The design of the nuclear instrumentation system for the Pluto series of nuclear ramjet test reactors is an attempt to provide a very flexible nuclear sensing system that will be adequate for Tory II-C and following test reactors. The nuclear detectors will be exposed to the leakage neutron flux from the reactor during operation. Since the leakage flux is proportional to reactor power, the neutron detectors will give a measure of reactor power. A difficulty in providing nuclear instruments for this reactor is the uncertainty in the neutron energy spectrum of the leakage flux at the detectors. Since detector response varies with neutron energy, a large margin of flexibility is desirable. A difficulty which may be encountered is a significant shift in neutron energy spectrum at high power and temperature. This would make indicated nuclear power nonlinear with calorimetric power. A difficulty in insufficient instrument overlap was encountered with the Tory II-A experiment where a large margin of flexibility would have been useful. The detector placement for the Tory II-A experiment had the power range detectors in line with the reactor and main air pipe. At high air flows there was a much greater mass of air between the detectors and the reactor, allowing fewer neutrons to reach the detectors per unit reactor power. This is the reason for the power range detectors being placed off to the side of the Tory II-C test vehicle. Not all difficulties can be foreseen, but provision is made where possible to overcome them.