INTRODUCTION

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

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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

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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.

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