# Digitalization of the Ex-Core Neutron Flux Monitoring System for APR1400 Nuclear Power Plant
## 1 Introduction  
The analog Ex-core Neutron Flux Monitoring System (ENFMS) has been satisfactorily performing its functions but it was implemented using older technology, subject to obsolescence and aging as well as limiting the possibility of adding new capabilities that could be beneficial to the system. Obsolescence can make the system be less reliable, especially when it is left to degrade. It can also lead to reduced availability and a compensatory increase in operation and maintenance (O&M) costs in order to maintain acceptable performance while aging and environmental degradation can reduce performance. As the industrial base has largely been moving to digital-based systems, traditional analog instrumentation and control (I&C) systems for nuclear power plants (NPPs) have been replaced with digital I&C systems. In Korea, major I&C systems in nuclear power plants have been digitalized with programmable logic controllers (PLCs) and distributed control systems (DCSs) applied to the Advanced Power Reactor 1400 (APR1400) including Shin-Kori NPPs 3, 4, 5 & 6 and Shin-Hanul NPPs 1 & 2 in operation or under construction in Korea as well as Barakah NPP 1, 2, 3 & 4 under constructionin United Arab Emirates. However, the ENFMS is one of the few systems which has not yet been digitalized and which serves as the key motivation of this study. A digitalized ENFMS will eliminate the necessity for nuclear I&C systems to maintain extra signal processing electronics such as analog-to-digital (A/D) and digital-to-analog (D/A) converters, wires, cables, etc., for the signal communications between analog and digital systems. In addition, the digital ENFMS will be essentially free of drift that afflicts analog electronics so that it will maintain its calibration better aside from improving the performance in terms of accuracy and computational capabilities. Operating conditions can also be more fully measured and displayed since it has higher handling and storage capabilities. It can be easier to use and more flexible in application if properly designed. Indeed, it has the potential for improved capabilities, namely: fault tolerance, self-testing, signal validation, and process system diagnostics that could form the basis for entirely new approaches to achieve the required reliabilities. Specifically, when the preamplifier output of detector signal is directly digitized and processed to extract information of interest through digital signal processing. There are several significant advantages of digital signal processing compared to traditional analog signal processing. First are the analyses, which takes pulse-by-pulse differences into account, and can be used in development such as in making ballistic deficit compensations. Second, transient induced charge signals which deposit no net charge on an electrode can be analyzed to give information on the position of interaction within the detector. Third, dead times from transient overload signals are greatly reduced from tens of micro-seconds to hundreds of nano-seconds. Fourth, signals are easily captured so that more complex analyses can be postponed until the source event has been deemed interesting. Fifth, signal capture and processing may easily be based on coincidence criteria between different detectors or different parts of the same detector [1]. State-of-the-Art Technology for Digital Signal Acquisition, Processing Modules and the Digital ENFMS  
It is known that there have been several achievements on the digitalization of the data acquisition and processing system for radiation and neutron instrumentation and monitoring. XIA Corporation (formerly X-ray Instrumentation Associates, Hayward, CA 94544, USA), a digital data acquisition and processing systems supplier for X-ray, gamma ray and particle detectors in the USA, developed the DGF-4C, a model of the four-channel digital signal acquisition and processing module for nuclear applications. A block diagram of the DGF-4C is shown in Figure 1a.