Abstract
Owing to the consumption of the resources of energy increases exponentially and the conventional topic of nuclear safety becomes more important to be taken into account than before, there is a tendency that nuclear power plants all over the world and their nuclear instruments are in the beginning of being digitalized. In addition to being enough to take over the nuclear technology precisely which makes the calibration of the whole instrumentation and control system becomes easier, the fully-developed technology of semiconductor reduces the errors from experiments with its characteristic of stability. As a result of the instrumentation and control system plays an important role in wide-range reactor power monitoring and reactor period estimation, digitalization of the wide-range neutron monitoring system is conducted in the nuclear field. A new digital monitoring system is developed based on Field Programmable Gate Array (FPGA) technique according to reports of characteristics of modules and online measurement results through the analysis of the wide-range neutron monitoring system (WRNM) in Tsing-Hua Open-Pool Research Reactor (THOR), with the study of digitalizing methods included. The specification of the self-developed digital 12-bits resolution monitoring prototype is consist of two ADC channels with different gains, a 488.2 kHz sampling frequency, a 16.7 milliseconds sampling time interval, zero dead time and two counters. In order to improve the accuracy of measurement, the front part of the digital circuit includes two ADC channels with no hand-shake during data transfer, which makes the designed FPGA digital monitoring system achieve the criteria of zero dead time and full scale of reactor power measurement successfully, almost same as the original analog monitoring system. Compared with the dead time more than 96% by using the oscilloscope and more than 80% by using the Photon II data acquisition card, wave observation through the FPGA based digital system prototype is better owing to its characteristic of zero dead time. It is proved that the real time data calculated by the self-developed digital system is approximately equal to the result from the analog system. In the study, a real time reactivity meter is also established according to the dynamic property of nuclear reactor, which works normally in THOR daily operation. Campbell theorem is applied to the real time power data calculation in the front digital circuit to realize the digital Campbell algorithm, which is compiled by the FPGA commercial board. On the other hand, the reactivity meter is accomplished by the phenomena of point kinetics and delayed neutron precursors in nuclear reactor dynamics, which means the reactivity can be obtained by the variation of the power data versus time under appropriate sampling time interval and known operating parameters. Moreover, a verification is compiled in the program to make a comparison of the calculated data and the data from the original monitoring system, and it can enhance the safety of reactor operation. In addition, an intuitive human-machine interface is developed for the digital wide-range neutron monitoring system by LabVIEW belongs to National Instruments. With dynamic history graph, the display panel can provide operators more information of a nuclear reactor. It is observed that the coefficient of variance (COV) between the data smoothed by 60-points moving average and the output power data of the analog system is up to 0.9992. Similarly, the period calculated by 60-point least square fitting is also matched with the data collected by the original NM-1000 system. It is concluded that not only the precision but also the system response time of the self-developed digital monitoring system has a good agreement with the original analog one installed in THOR.