A new in-core startup system with combined source range and intermediate range flux monitoring function

A neutron flux monitoring system covering the whole startup range of a power reactor has been developed and extensively tested. A single miniature fission chamber is used for pulse mode as well as for variance mode measurements, giving a linear range of ten decades of flux. The drive mechanism for the retractable detector is of a completely new design using a flexible cable which is stored in a magazine when the detector is withdrawn from the in-core position. The new mechanism is thus very compact and makes a well-protected signal path between detector and preamplifier possible, at the same time improving the maintainability. The test programme includes three full years of full-scale tests in a BWR power reactor. The stability of both detector and electronics have been excellent during all tests. (author)