A High Temperature Remote Pulse Preamplifier System for Reactor Startup Channels

Source and startup-range pulse instrumentation for large reactor plants in general impose severe environmental conditions on the design of preamplifiers and pulse coupling networks. Space or size limitations electrical noise fields, high ambient temperatures, and lack of accessibility for maintenance all adversely affect signal-to-noise ratio and reliability. An additional problem was present in the design of the startup preamplifier system for the Hallam Nuclear Power Facility (HNPF) because the detector was located in a high gamma field, making some special precautions necessary to prevent small-signal pileup. This paper describes the design of a preamplifier system which overcomes these problems and yields high stability and long term, maintenance-free service at ambient temperatures up to 100°C. The installed system shows at least a 35 db improvement in signal-to-noise ratio over conventional instruments in the same application. Remote location of the preamplifier (up to about 100 feet) from the detector is possible so that the preamplifier itself is out of both the radiation field and the highest temperature locations. The system consists of the chamber and transformer coupling network (between chamber and preamplifier,) and a reliable, high stability preamplifier.