[en] Purpose: In magnetic particle imaging (MPI) and magnetic particle spectroscopy (MPS) the relaxation time of the magnetization in response to externally applied magnetic fields is determined by the Brownian and Néel relaxation mechanisms. Here the authors investigate the dependence of the relaxation times on the magnetic field strength and the implications for MPI and MPS. Methods: The Fokker–Planck equation with Brownian relaxation and the Fokker–Planck equation with Néel relaxation are solved numerically for a time-varying externally applied magnetic field, including a step-function, a sinusoidally varying, and a linearly ramped magnetic field. For magnetic fields that are applied as a step function, an eigenvalue approach is used to directly calculate both the Brownian and Néel relaxation times for a range of magnetic field strengths. For Néel relaxation, the eigenvalue calculations are compared to Brown's high-barrier approximation formula. Results: The relaxation times due to the Brownian or Néel mechanisms depend on the magnitude of the applied magnetic field. In particular, the Néel relaxation time is sensitive to the magnetic field strength, and varies by many orders of magnitude for nanoparticle properties and magnetic field strengths relevant for MPI and MPS. Therefore, the well-known zero-field relaxation times underestimate the actual relaxation times and, in particular, can underestimate the Néel relaxation time by many orders of magnitude. When only Néel relaxation is present—if the particles are embedded in a solid for instance—the authors found that there can be a strong magnetization response to a sinusoidal driving field, even if the period is much less than the zero-field relaxation time. For a ferrofluid in which both Brownian and Néel relaxation are present, only one relaxation mechanism may dominate depending on the magnetic field strength, the driving frequency (or ramp time), and the phase of the magnetization relative to the applied magnetic field. Conclusions: A simple treatment of Néel relaxation using the common zero-field relaxation time overestimates the relaxation time of the magnetization in situations relevant for MPI and MPS. For sinusoidally driven (or ramped) systems, whether or not a particular relaxation mechanism dominates or is even relevant depends on the magnetic field strength, the frequency (or ramp time), and the phase of the magnetization relative to the applied magnetic field

[en] Emergency operation procedures are documents that identify the equipment or systems to be operated and list the steps necessary to mitigate the consequences of transient and accidents that have caused plant parameters to exceed reactor protection system set points or engineered safety feature set points, or other established limits and to restore safety functions. Operational modes of specific systems or components are not provided in the emergency operation procedures. These operational modes should be determined with consultations on technical evaluation by technical support center which is one of the plant emergency organizations during the emergency operation. To determine the operational modes, plant status, accident evolution, equipment availability and radiological effects to environment should be considered. This study summarizes the emergency operation steps requiring technical evaluation in determining the operational modes and proposes the essential technical evaluation guidelines to determine the mode. The results can be profitably utilized in training experts of technical support center and developing the plant specific technical evaluation guidelines

[en] MMIS(Man Machine Interface System) of an integral reactor is composed of a Control Room, Plant Protection System, Control System and Monitoring System which are related with the overall plant operation. MMIS is being developed with a new design concept and digital technology to reduce the Human Factor Error and improve the systems' safety, reliability and availability. And CCS(component control system) is also being developed with a new design concept and digital hardware technology A fully digitalized system and design concept are introduced in the NSSS CCS

[en] Bayesian Nets (BNs) has been known as one of promising techniques in estimating reliability of safety-critical software. However there are some hard factors to consider in practical application of the BN. The most important one among them is quantification of qualitative data including experts' judgments for modeling. In this paper, we introduce a method which we used in the reliability assessment of the safety-critical software for a reactor protection system. Main quantification in a BN modeling occurs during the construction process of Node probability Tables (NPTs) in BNs. Some rules for the NPT construction are described, and examples of key NPTs are explained. Also a case study was carried out by using the proposed quantification method

[en] This article explores how to test analogue RPS components using digital control technology. It is urgent and necessary to improve the test method under the general environment that human cost is growing and there is a heavy pressure for project construction schedule. The test equipment utilizes DCS technology, bus communication and software technology. Based on the study of test method used before, this article promotes that the digital control technology should be adopt in analogue RPS components testing instead of testing by hand. Using the new method, the testing efficiency and accuracy could be improved highly, the testing workload could be reduced greatly, and the goal can be achieved that the testing schedule and quality of components passing the testing meet the requirements. (authors)

[en] A Korean project group, KNICS, is developing a new digitalized reactor protection system (RPS) and the developed system will be packaged into a cabinet with several racks. The cabinet of the RPS is used for the RPS function testing and monitoring by maintenance operators and is equipped with a flat panel display (FPD) with a touch screen capability as a main user interface for the RPS operation. This paper describes the human factors activities involved in the development process of the RPS: conceptual design, design guidance, and evaluation. The activities include a functional requirements analysis and task analysis, user interface style guide for the RPS cabinet operator module (COM), and a human factors evaluation through an experiment and questionnaires

[en] It is necessary to assure the reliability of software in order to digitalize RPS(Reactor Protection System). Since RPS causes fatal damage on accidental cases, it is classified as Safety 1E class. Therefore we propose the effective testing methodology to assure the reliability of embedded software in the DPPS(Digital Plant Protection System). To test the embedded software effectively in DPPS, our methodology consists of two steps. The first is the re-engineering step that extracts classes from structural source program, and the second is the level of testing step which is composed of unit testing, Integration Testing and System Testing. On each testing step we test the embedded software with selected test cases after the test item identification step. If we use this testing methodology, we can test the embedded software effectively by reducing the cost and the time

[en] The development work related to design of an I and C system is underway at the KNICS R and D Centre. This design follows the laid out criteria for APR 1400 I and C design. The advantage is that the APR 1400 design has already been certified by the national regulatory body, the Korea Institute of Nuclear Safety. In line with these existing policies, this system is being developed using the safety grade digital components and qualified software. Apart from this, the design also incorporates the insight obtained from the human factor design methods. The objective here is to primarily design a system using safety-grade programmable logic controller. However the non-safety grade distributed control system, which is being developed at the R and D centre, forms part of this design. In addition other components are being developed in-house also forms part of this design. This report describes the functional logic and high level design requirements for each of the I and C systems. This has been discussed through a case study on Korean Standard Nuclear Plant (KSNP) - a Westinghouse (ABB-CE) designed 1000 MWe PWR. The main focus of this report is, discussion of design details pertaining to control system, protection system, monitoring system, information processing system and process instrumentation system. It may be noted that design of control system is not within the scope of this work. It is expected that the experience gained on this developmental work and the insight obtained on the detailed logic design will provide vital input for the development of Integrated I and C system

[en] The study on the qualitative risk due to cyber-attacks into research reactors was performed using bayesian Network (BN). This was motivated to solve the issues of cyber security raised due to digitalization of instrumentation and control (I and C) system. As a demonstrative example, we chose the reactor protection system (RPS) of research reactors. Two scenarios of cyber-attacks on RPS were analyzed to develop mitigation measures against vulnerabilities. The one is the 'insertion of reactor trip' and the other is the 'scram halt'. The six mitigation measures are developed for five vulnerability for these scenarios by getting the risk information from BN

[en] Software configuration management (SCM) is an activity, which configures the form of a software system (e.g., design documents and programs) and systematically manages and controls the modifications used to compile the plans, development, and operations resulting from software development and maintenance. The SCM tool, NuSCM, has been specifically developed for the software life-cycle configuration management of developing the KNICS plant protection system (PPS). This paper presents the application of NuSCM to the KNICS project