The objective of Project Agreement 22 was to determine the feasibility of covering the

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complete reactor neutron flux range from 1 x 10 to 5 x 10 nv in-core by using in-core or out-of-core ion chambers.

This report describes the analytical predictions and the experimental results of a nuclear instrumentation development program undertaken by General Electric to determine the feasibility of this approach. The program has been concerned with the development of a fujl-range reactor control system incorporating either in-core or out-of-core ion chambers, and the purpose of the program has been satisfied by the development of a full-range instrumentation system consisting of two electronics subsystems. Counting techniques are utilized for source and lower intermediate range neutron fluxes, and Campbell — or mean-square voltage — techniques are utilized for inter­mediate and power range fluxes.

Historically, power reactors have used out-of-core neutron detectors for source and inter­mediate range coverage during a plant startup. In present power reactors, an in-core neutron


source producing about 3×10 nv is attenuated by the water annulus surrounding the core so that the incident flux at the detector is approximately 0. 5 to 3. 0 nv. Larger power plants, especially those with internal steam separation, provide for much larger water annuli and neutron source


attenuations of perhaps 10 have been projected. Additionally, there is considerable interest in the in-core flux as opposed to the out-of-core flux, and consequently, it has become necessary to develop suitable in-core detectors for the source and intermediate range fluxes.

The development program has investigated the problems associated with the in-core counting detector, the in-core Campbelling detector, the in-core transmission lines, as well as those unique problems of a two-channel, full-range instrumentation system. In addition, the effort has been expanded to ensure a compatible system for either in-core or out-of-core applications. In this manner, flexibility of the developed hardware for a wide range of applications has been assured.