A nuclear reactor system including a nuclear reactor vessel housing a nuclear core in which fission reactions take place and a nuclear instrumentation system for monitoring the fission reactions, with the nuclear reactor vessel and at least a portion of the nuclear instrumentation system situated within a radiation shielded containment, the nuclear instrumentation system comprising: a nuclear detector responsive to the number of fission reactions within the nuclear core to provide an electrical output indicative thereof; a detector cable connected at one end to the electrical output of the nuclear detector, with the detector cable extending between the electrical output of the nuclear detector and a termination location within the containment; an amplifier situated at the termination location within the containment and having an input connected to the detector cable for receiving the electrical output of the nuclear detector and operable to amplify the electrical output of the nuclear detector to provide a nuclear detector amplified output signal (60, 66, 68); a field cable connected at an input location of the field cable to an output of the amplifier, with the field cable extending from the input location through a penetration in the containment to a field cable output at a processing location outside the containment; and a Nuclear Instrumentation System Signal Processing Assembly located outside the containment at the processing location and connected at the field cable output and operable to receive the nuclear detector amplified output signal and from the nuclear detector amplified output signal measure neutron radiation emitted within the core to determine a power level of the nuclear reactor system, characterized in that the amplifier is a vacuum micro-electronic device low noise amplifier having a vacuum micro-electronic device input, the detector cable is an integrated mineral insulated cable, and the field cable is a quadax-copper cable a nuclear detector responsive to the number of fission reactions within the nuclear core to provide an electrical output indicative thereof; a detector cable connected at one end to the electrical output of the nuclear detector, with the detector cable extending between the electrical output of the nuclear detector and a termination location within the containment; an amplifier situated at the termination location within the containment and having an input connected to the detector cable for receiving the electrical output of the nuclear detector and operable to amplify the electrical output of the nuclear detector to provide a nuclear detector amplified output signal (60, 66, 68); a field cable connected at an input location of the field cable to an output of the amplifier, with the field cable extending from the input location through a penetration in the containment to a field cable output at a processing location outside the containment; and a Nuclear Instrumentation System Signal Processing Assembly located outside the containment at the processing location and connected at the field cable output and operable to receive the nuclear detector amplified output signal and from the nuclear detector amplified output signal measure neutron radiation emitted within the core to determine a power level of the nuclear reactor system, characterized in that the amplifier is a vacuum micro-electronic device low noise amplifier having a vacuum micro-electronic device input, the detector cable is an integrated mineral insulated cable, and the field cable is a quadax-copper cable