## 1 Introduction  
Nuclear power plants (NPPs) are globally important sources of clean energy that do not emit greenhouse gases. According to the International Atomic Energy Agency (IAEA), global electricity consumption is increasing annually, and it is predicted that by 2050, it will be approximately double that of 2022 [1]. Nuclear power is expected to contribute to both the rapid increase in electricity consumption and the mitigation of global warming, and the construction of new NPPs is planned around the world [2]. While there are multiple types of NPPs, many use pressurized water reactors (PWRs), and most of the plants planned for future construction also use PWRs. Additionally, most of the small modular reactors (SMRs) currently being developed are also based on PWR technology. From an economic perspective, NPPs face the challenge of higher operation and maintenance (O&M) costs compared with other power sources such as coal, oil, and liquefied natural gas-fired thermal power. The O&M costs of nuclear power are approximately twice as high as those of thermal power generation [3]. Reducing the O&M costs of NPPs is a problem that needs to be solved for the planned expansion and stable operation of NPPs. In the United States, grants have been provided for research on using digital technology to reduce O&M costs to one-tenth of the conventional level, specifically targeting innovative reactors [4]. It is anticipated that the utilization of digital technology will be essential for reducing O&M costs. In this study, we focus on ex-core instrumentation systems (EISs), which are essential for PWR plants, both currently in operation and planned for future construction. An EIS monitors the state of the reactor core by detecting neutron leakage from the reactor core with neutron detectors installed outside the reactor and issuing trip signals in case of abnormal conditions, making it a crucial component for PWR operation. However, the digitalization of EISs has been lagging behind other instrumentation and control (I&C) systems. The advantages of digitizing the I&C system include the ability to replace multiple hardware components with software, enabling miniaturization, reducing the number of degraded parts, and facilitating easy replacement. Additionally, utilizing digital technology allows for self-diagnosis, where the system itself can detect faults, leading to significant improvements in maintainability and reliability. While existing I&C systems are being replaced with digital systems, many EISs still remain analog. This is believed to be due to the unique neutron measurement required in nuclear power, as well as the high-speed operation for a safety system. In particular, EISs require rapid response performance compared with other I&C systems [5]. There are several examples of digitalizing EISs. One example is the SPINLINE system developed by Rolls-Royce, which utilizes a calibrated pulse acquisition board with a microcontroller [6; 7]. The SPINLINE system processes pulse signals from the neutron detector by combining the calibrated pulse acquisition board with the UC25 N+ processor board [6]. Another example is the DWK250 system developed by Mirion Technologies, which incorporates the NI 21 module to discriminate pulse signals derived from neutrons from other signals such as gamma rays and electrical noise, as well as the NZ21 module for signal processing to generate the count rate [8]. These examples demonstrate the ongoing progress in digitalizing pulse signal processing for EISs. As previously mentioned, there are few examples of digitalizing pulse signal processing for EISs, all of which use multiple modules for pulse measurement and microprocessors. The IAEA mentioned that techniques utilizing microprocessors have replaced analog techniques used in NPPs because microprocessors have many advantages compared with analog devices. However, microprocessors now have short product life cycles, and applications may become obsolete in a relatively short time due to a lack of replacement parts and support [9].