Experimental and Mathematical Simulation Techniques for Determining AN In-Situ Response Testing Method for Neutron Sensors Used in Reactor Power Plant Protection Systems.

An analytical neutron sensor response model and methods for transient response measurements of neutron sensors (Compensated Ionization Chamber), including possible in-situ techniques have been developed and evaluated to meet the provisions of Draft Standard ISA Sd67.06, IEEE 338-1977, and NRC Guide 1.118. One in-situ method requires the perturbation of the high voltage detector (sensor) power supply and measurement of the sensor response. The response to a perturbation of the power supply is related to the response of the sensor to a transient change in neutron flux. Random signal analysis is another in-situ technique to monitor the neutron sensor response. In this method the power spectrum of the inherent fluctuations from the neutron sensor output (Current in CIC) are measured and evaluated. Transient response techniques (including in-situ methods) are experimentally and analytically evaluated to identify the mechanisms which may cause degradation in the response of the neutron sensors. Response time degradation was investigated through a change in sensor and signal cable response time in a predictable manner (through changes in the detector fill gas and use of a delay box for signal cable). Sensors and attached cables having different response times are evaluated using power supply perturbation, transient change in radiation flux (both x-ray and neutron flux), and analysis of the random signals from neutron sensors. The objective of the experimental evaluation was to correlate the measured response time using transient radiation flux changes and power supply perturbation. The objective of the analytical model of the different sensor response was to predict response time and degradation mechanisms. Completion of this work contributed to improved understanding, monitoring, and the response time verification of neutron sensors. As a consequence improved and safer nuclear power plant operation may be attained.