Operational Experience Research Articles

AI Curriculum Design for Korea K-12 AI Education Through Analyzing AI Education Curriculum

This paper deals with the curriculum design of Korean K-12 AI education. AI is the core technology of 4th wave and it is impact is wide and strong. Therefore, every country has s strong nurture system for AI manpower. However, there are few materials about curriculum design and operation experience documentation because AI was an interest since 2016, and its education is very new. In Korea, they started a program for teacher manpower education in 2020. Therefore, there is no manpower that had an experience in the design and operation of the K-12 AI curriculum. The AI curriculum is a core parameter for AI manpower. So, AI-advanced countries try to develop AI education methods. This paper analyzes the K-12 AI curriculum of the advanced countries, and then designs and suggests Korea’s K-12 AI curriculum.

Analysis of predictors of the development of chronic heart failure in pa-tients after coronary bypass on a working heart

Тhe article analyzes the prevalence of coronary heart disease (CHD) and its surgical treatment by performing coronary bypass surgery off-pump. The purpose of the study was to investigate echocardiography parameters in patients with CHD after off-pump coronary bypass surgery, depending on the number of shunts and their origin. The study included 521 people (416 men, 105 women), their average age was (64.2±3.4). All study participants underwent coronary bypass surgery off-pump. The article analyzes single-, two- and multi-vessel lesions of coronary arteries, paying attention to the origin of shunts. What were used during the provision of coronary bypass surgery off-pump. Attention is paid to echocardiography indicators, which are indicators of heart failure – left ventricular ejection fraction and end-diastolic volume. It has been established that coronary bypass surgery off-pump allows for the elimination of structural features (left ventricular ejection fraction, end-diastolic volume) and there are no restrictions on the number of applied shunts (distal anastomoses). Coronary bypass surgery off-pump is possible in severe clinical conditions of the patient, presence of concomitant pathology and is performed only if the operating surgeon has extensive operational experience. His assistants and the entire hearth team. Thus, it is extremely important to substantiate the indications for performing coronary bypass surgery on a working heart, taking into account the patient's personal characteristics, his age, the number of affected vessels, the structural features of the vascular bed, the functional state of the cardiovascular system and other body systems, which will allow to increase the efficiency surgical treatment of coronary heart disease, extend the duration and improve the quality of life of patients. Keywords: perforation, bleeding, stenosis, penetration, vagotomy, gastric resection.

Smart filter aided domain adversarial neural network for fault diagnosis in noisy industrial scenarios

The application of unsupervised domain adaptation (UDA)-based fault diagnosis methods has shown significant efficacy in industrial settings, facilitating the transfer of operational experience and fault signatures between different operating conditions, different units of a fleet or between simulated and real data. However, in real industrial scenarios, unknown levels and types of noise can amplify the difficulty of domain alignment, thus severely affecting the diagnostic performance of deep learning models. To address this issue, we propose an UDA method called Smart Filter-Aided Domain Adversarial Neural Network (SFDANN) for fault diagnosis in noisy industrial scenarios. The proposed methodology comprises two steps. In the first step, we develop a smart filter that dynamically enforces similarity between the source and target domain data in the time-frequency domain. This is achieved by combining a learnable wavelet packet transform network (LWPT) and a traditional wavelet packet transform module. In the second step, we input the data reconstructed by the smart filter into a domain adversarial neural network (DANN). To learn domain-invariant and discriminative features, the learnable modules of SFDANN are trained in a unified manner with three objectives: time-frequency feature proximity, domain alignment, and fault classification. We validate the effectiveness of the proposed SFDANN method based on two fault diagnosis cases: one involving fault diagnosis of bearings in noisy environments and another involving fault diagnosis of slab tracks in a train-track-bridge coupling vibration system, where the transfer task involves transferring from numerical simulations to field measurements. Results show that compared to other representative state of the art UDA methods, SFDANN exhibits superior performance and remarkable stability.

Performance of the Cue COVID-19 point-of-care molecular test: insights from a multi-site clinic service model.

The COVID-19 pandemic highlighted the critical need for rapid and accurate molecular diagnostic testing. The Cue COVID-19 Point-of-Care Test (Cue POCT) is a nucleic acid amplification test (NAAT), authorized by Health Canada and FDA as a POCT for SARS-CoV-2 detection. Cue POCT was deployed at a network of clinics in Ontario, Canada with n = 13,848 patrons tested between 17 July 2021 and 31 January 2022. The clinical performance and operational experience with Cue POCT were examined for this testing population composed mostly of asymptomatic individuals (93.7%). A head-to-head prospective clinical verification was performed between 17 July and 4 October for all POCT service clients (n = 3,037) with paired COVID-19 testing by Cue and RT-PCR. Prospective verification demonstrated a clinical sensitivity of 100% and clinical specificity of 99.4% for Cue COVID-19 POCT. The lack of false negatives and low false positive rate (0.64%), underscores the high accuracy (99.4%) of Cue POCT to provide rapid PCR quality results. Low error rates (cancellation rate of 0% and invalid rate of 0.63%) with the current software version were additionally noted. Taken together, these findings highlight the value of accurate molecular COVID-19 POCT in a distributed service delivery model to rapidly detect cases in the community with the potential to curb transmission in high-exposure settings (i.e., in-flight, congregate workplace, and social events). The insights gleaned from this operational implementation are readily transferable to future POCT diagnostic services. IMPORTANCE This manuscript reports on the findings of a large asymptomatic population who underwent surveillance COVID testing on the Cue COVID-19 Point-of-Care Test (POCT). Review of test performance of this rapid molecular POCT, as compared to gold standard RT-PCR, is valuable to many audiences, including public health, emergency testing services, employers, and the general population of consumers who are seeking a user-friendly, accurate, cost-effective, and sustainable testing model for COVID screening. The findings from this operational experience also inform future models of POCT services beyond COVID.

Operational Experience in Degradation (Ageing Effects) and Implementation of Ageing Management Programmes for Dry Storage Systems in Ukraine

The Coordinated Research Projects (CRPs) of International Atomic Energy Agency (IAEA) is a power tool to engage simultaneously a lot of different countries that operate Spent Fuel Storage Facilities for solving important safety issues at a deep level of competence and expertise. One of the topics that needs thorough research is behavior and state assessment of spent fuel assemblies and fuel rods during long/very long term storage in spent fuel storage facilities. It is naturally that over a long period, special attention is drawn to degradation mechanisms, ageing effects and ageing management programs that should be implemented in order to avoid and mitigate the impact of degradation mechanisms on spent fuel elements. This article describes the first step of implementing new IAEA CRP project “T13019. Performance Assessment of Storage Systems for Extended Durations (PASSED)” with contribution from the State Scientific and Technical Center for Nuclear and Radiation Safety (SSTC NRS), which conducts research regarding the “Operational experience on degradation (ageing effects) of dry storage systems” during the first stage” at the first stage. The overall objective of the research proposed by the SSTC NRS is to strengthen technical knowledge, experience and understanding of the long-term behavior of the dry spent fuel storage systems, and of the currently applied inspection and monitoring technologies. At the same time, a specific objective of involving the SSTC NRS in this project was not only to present national experience and practices, but also to study the existing experience of the participating countries, which also joined the CRP proposed by the IAEA. The article considers the existing storage systems for spent nuclear fuel at the Chornobyl and Zaporizhzhya NPP sites, provides examples of the aging management system for components and structures, as well as examples of the issues that require development, implementation and maintenance of aging management programs.

Ice passport of a river icebreaker: propulsion ability

The work begins a series of publications summarizing the experience of long-term ice operation of shallow-seated river icebreakers of project 1191. This article is devoted to the analysis of full-scale data on the ice propulsion ability of the vessel.
 In tabular form, the speed characteristics of the icebreaker on the advancing, stern board and ramming icebreaking are given depending on various conditions and operating modes in solid ice and ice channel: thickness of the ice cover; the degree of its fragmentation, extent of destruction, concentration; height, density and humidity of the snow cover; depth of the water area; total power of thrusting electric motors.
 The procedure for using tabular data to evaluate the operational propulsion ability of a vessel in ices is shown in the article.

Innovation of metallurgical equipment by developing innovative winding method for hot rolled strip

At carrying out of researches the complex technique including analytical review of literary sources, review of experience of operation and output of finished products at strip winding by winders of industrial enterprises of Kazakhstan and foreign countries, from reporting and statistical data, theoretical researches of technical parameters of new design of winders, experimental researches of methods of winding were used. These data will give an opportunity to evaluate and highlight the main influencing factors that will allow to create an innovative and workable system of hot-rolled strips winding. Experimental studies were carried out on a new design of coiler with its binding to the laboratory rolling mill "DUO-100", and their results were processed by methods of mathematical statistics according to standard techniques. In the process of laboratory studies of the coiler model with combined coil formation as one of the main parameters was the force from the water and air jet on the surface of the drum or on the coiled strip.

Technology Suitability Assessment of Battery Energy Storage System for High-Energy Applications on Offshore Oil and Gas Platforms

Selecting a battery energy storage technology for application on offshore platforms or marine vessels can be a challenging task. Offshore oil and gas platforms (OOGPs) require battery energy storage systems (BESSs) with high volumetric density, high gravimetric density, high safety, a long life span, low maintenance, and good operational experience, amongst other BESS properties. No single battery chemistry can satisfy all these factors perfectly, which implies that there is a need for a method that determines the most suitable battery chemistry for a given application. To this end, this paper proposes an improved version of a 7-step procedure proposed in the literature to systematically and logically determine the most suitable BESS for high-energy applications on OOGPs. In order to implement the 7-step procedure, a review of the state-of-the-art of consolidated and emerging battery chemistry is done. As part of the 7-step procedure, the operational experience of the battery chemistry was also reviewed. The 7-step procedure was then applied to a case study (with two test cases) of a real OOGP in the North Sea. The first test case considers BESS for peak shaving, for which six battery chemistries were assessed in detail. A technology suitability assessment (TSA) weighted score is calculated, which is based on five attributes critical for the energy storage choice in the considered application, which are weight, space, safety, life cycle cost, and operational experience. Of the six battery chemistries assessed, lithium iron phosphate (LFP) has the highest technology suitability assessment (TSA) weighted score and is therefore deemed the most suitable battery chemistry for peak shaving. The second test case considers BESS for spinning reserve. Since this is a high C-rate application, only battery chemistry capable of high C-rate was evaluated. From the TSA evaluation, LFP and lithium nickel manganese cobalt have the joint highest TSA weighted score and are therefore deemed the most suitable battery chemistry for spinning reserve.

Informing Early Design Decisions Through Functional Analysis of Maintenance Drivers

Operational expenditures dominate the cost of long field-life systems, with maintenance comprising a significant proportion for many systems. However, engineers lack the tools to assess maintenance during conceptual design. Familiar systems mitigate this problem by providing historical maintenance data from which empirical models can be derived. Emerging technologies, like marine renewables, lack operational maintenance data. As a result, engineers must make decisions with no historical data and minimal, if any, operational experience. The high operations cost incurred from basic maintenance tasks, and the loss of energy production during maintenance, further highlight maintenance as a critical cost driver. This paper develops a data-driven model to estimate maintenance intervals of long field-life systems during conceptual design. The model links the elementary functions of a component to maintenance requirements. Relative maintenance considerations were determined by mining function and maintenance data from manuals of long field-life systems. Machine learning was applied to generate a function-maintenance model from the maintenance data. The model consisted of functions grouped into buckets of increasing maintenance demand. The machine learning model was applied to an exemplary long field-life system, a wave energy converter, to explore possible redesigns to reduce maintenance costs. This paper shows that maintenance costs, actions and intervals can be confidently accounted. The function-maintenance model offers two beneficial impacts: it reduces life cycle cost uncertainty, and allows engineers to make informed decisions during conceptual design when redesign costs are at their lowest.

Application of BIM + VR Technology in Highway Design and Construction

The application of building information modeling BIM and virtual reality VR has become increasingly popular in highway design and construction aiming to improve the efficiency and quality of design and construction. BIM and VR technology enable the digital management of expressway design and construction facilitating a visual interactive and immersive operational experience. Using a highway construction project as a case study this paper illustrates the specific application of BIM + VR technology in highway design and construction. This provides digital intelligent and efficient solutions for highway construction ultimately enhancing the quality and efficiency of the design and construction processes.

Commercialization of Ceres SteelCell® Technology for Power Generation and Electrolysis

Ceres’ unique metal supported SOC technology is increasingly establishing itself as the global standard for SOC, combining robustness, efficiency and low manufacturing cost. The technology is rapidly moving from demonstration to true volume production, with Robert Bosch GmbH in Germany and Doosan Fuel Cell in South Korea both having licenses to manufacture Ceres SteelCell® cells and stacks at the hundreds of MW per year scale with factories under construction. Ceres currently have manufacturing plants making MW of stacks per year. Ceres SteelCell® technology has a wide range of applications in the power generation sector, with applications ranging from small scale <10kWe combined heat and power (CHP) systems to systems in the 100s of kW to MW range. An increasing area of interest for the application of SteelCell® technology is in the difficult-to-decarbonize marine sector, where the ability to operate efficiently on a range of fuels with much lower carbon emissions than the heavy diesel normally used for shipping. These include liquefied natural gas (LNG), methanol and liquid ammonia, as well as hydrogen. This is also driving development of higher-power systems in the MW range.An exciting new development is the application of Ceres SteelCell® technology to steam electrolysis. The inherent advantages of Ceres SteelCell® in terms of mechanical robustness, REDOX stability, low production cost and low-cost balance of plant are also applicable to electrolysis applications. In addition, there are potential thermodynamic advantages for integration of high temperature electrolysis with other industrial processes to utilize waste heat stemming from the lower temperature of operation of Ceres SteelCell® technology relative to competing SOC technologies as lower-grade heat is required. To demonstrate the capability of Ceres SteelCell® for electrolysis Ceres is developing a 1MWe-class steam electrolyzer demonstrator using a modular architecture of multiple smaller electrolysis cell modules (ECMs) which can operate standalone. Testing and validation of ECMs is currently ongoing prior to full system integration. These ECMs are built into a standard 40ft shipping container to form the complete system.Ceres has recently signed an agreement with Shell to operate one of these 1MW-class systems at Shell’s R&D center in Bangalore, India running for 3 years from 2023. In addition to gaining valuable experience in plant operation the hydrogen generated will be used for industrial processes on the site.

Development of Logistics Vietnam Services: Situation and Solutions

Through the method of document research, analysis, and synthesis, the article has reviewed the current situation of logistics services in Vietnam during the period of 2017 to 2022. Accordingly, this service is developing at a relatively high rate but still some limitations such as incomplete legal policies, desynchronized infrastructure or small-scale Vietnamese logistics enterprises, lack of human resources and international operational experience. The article also points out that the cause of the above existence is the lack of an overall development strategy, the lack of inter-sectoral coordination, and Vietnam's current weak logistics human resources. Based on the existence and identified causes, the authors have proposed a number of solutions to remove difficulties for logistics service activities in Vietnam. Completing institutions and policies, developing infrastructure in a synchronous manner and increasing connectivity, improving business capacity and service quality, and training and developing logistics human resources are the solutions that have been proposed given in the article. Through these solutions, the authors hope that Vietnam's logistics service will have a breakthrough development in the future.

Immersion ultrasound improves the repeatability of shear-wave elastography for measuring median nerve elasticity

ObjectiveTo study the factors that influence the measurement of median nerve elasticity, to provide a more reproducible test for the assessment of median nerve elasticity using shear wave elasticity (SWE), and to reduce operator empirical dependence. To compare the repeatability of the median nerve elasticity measurement using immersion SWE with that using contact SWE, analyze the factors affecting SWE measurement, and provide a more repeatable method for doctors without SWE operation experience.MethodsTwo doctors without SWE operation experience measured the median nerve mean elastic modulus (Emean) at the same position and at different time points on the right wrist of 58 healthy volunteers using immersion and contact ultrasound methods. The intraobserver and interobserver repeatability of measurements was assessed using the interclass correlation coefficient (ICC), while the repeatability was assessed using the Bland–Altman diagram.ResultsThe intraobserver and interobserver repeatability of the median nerve elasticity measured via contact SWE by inexperienced operators were classified as good, with ICCs of 0.633 (95% CI 0.380–0.783) and 0.552 (95% CI 0.243–0.735), respectively. The intraobserver and interobserver repeatability of the median nerve elasticity measured by immersion SWE were very good, with ICCs of 0.975 (95% CI 0.958–0.985) and 0.942 (95% CI 0.902–0.966), respectively. The intraobserver and interobserver Bland–Altman diagram of median nerve elasticity measured by immersion SWE showed that 98% of the points fell within the 95% limits of agreement. The intraobserver and interobserver Bland–Altman diagram of median nerve elasticity measured by contact SWE showed that 94% of the points fell within the 95% limits of agreement.ConclusionImmersion ultrasound can improve the repeatability of median nerve elasticity measurements by inexperienced operators.

Operational experience with a liquid organic hydrogen carrier (LOHC) system for bidirectional storage of electrical energy over 725 h

Hydrogen storage in liquid organic hydrogen carriers (LOHC) enables the utilization of renewable energy in different sectors. In this paper, we describe the operational experience with one single LOHC system for bidirectional electrical energy storage at the kW scale. The system includes a reactor for the hydrogenation and dehydrogenation of LOHC, as well as a fuel cell and an electrolyzer based on polymer electrolyte membrane (PEM) technology. The LOHC used is the substance pair dibenzyltoluene/perhydro-dibenzyltoluene. For dehydrogenation, the upflow operation with common discharge of liquid and gaseous product was found to be the preferred mode of operation. For hydrogenation, it was shown that stable operation is possible also with fluctuating hydrogen production from the electrolyzer. After operating the reactor for 725 h in the hot state, i.e., at temperatures above 150∘C, samples of the catalyst and LOHC were taken and analyzed. These showed no signs of serious degradation.

The FIRE-IN project: Tsunami-risk related practitioner challenges and 3rd cycle overall results.

This article summarizes the methodology for the identification of practitioners' challenges, in the context of the H2020 funded project FIRE-IN (Fire and Rescue Innovation Network) activities. The project consisted of five thematic areas or "Thematic Working Groups", as they are called, i.e., Search and Rescue Emergency Response, Structure Fires, Landscape Fires Crisis Mitigation, Natural Hazard Mitigation and Chemical Biological Radiological Nuclear and Explosives, and three iterations, each one including the identification of capability challenges, the screening for solutions, that can potentially address these challenges, and the request for ideas regarding future innovations that will complement already existing ones and will assist in covering capability gaps. This article focuses on the natural hazard mitigation working group and tsunamis in the Mediterranean region as a case study for the 3rd and last iteration of the project. The scenario of a tsunami occurrence in the Mediterranean is the basis for the FIRE-IN 3rd cycle workshop, as an indicative example of a high impact - low probability event, which aims to identify practitioners' Future Common Capability Challenges in Europe. The current status of the tsunami hazard in Europe, national and international tsunami risk mitigation measures and procedures and operational experience from recent events are also discussed. Focus is provided on the natural hazard mitigation and tsunami related practitioners' challenges, while results from the FIRE-IN request for ideas process and the interaction between practitioners, researchers and industry are also discussed. The aim is to present practitioners' current and future capability challenges , one of the main outcomes of the FIRE-IN project, and to provide further guidelines to stakeholders of disaster management towards a safer Europe, mainly, through preparedness and adaptation for stronger and resilient societies.

When citizen science meets radon building diagnosis: Synthesis of a French pilot project developed in the framework of the European RadoNorm research project.

As part of the European RadoNorm research project, citizen science pilot projects focusing on the management of radon risk in houses have been implemented in four countries. This article describes the methodological basis, the development and the results of the French pilot project. Building on an initial review of existing literature, the pilot project aims to frame a 'participatory approach' aligned with the standards and recognized practices of citizen science. Particular attention was given to the management of data and the inclusion of ethical considerations. The focal point of the project was the process of radon building diagnosis which is supposed to be carried out whenever (high) radon concentrations are measured and should be prerequisite to mitigation works. As experience shows, however, this diagnosis is hardly implemented in France. To help remedy this situation, the pilot project recruited citizens already aware about radon from Pays Vesoul Val-de-Saône (East of France) to test an existing online self-evaluation guide for radon diagnosis, report on their operational experience and meet with radon/building experts. This enabled citizens to contribute to improvements in form and content to the guide and to ensure that it would be better fit for purpose. Comparison of the guide with experts' practices offered additional perspectives on what building diagnosis should entail. The pilot project produced rich and high-quality data that will nurture the evolution of the guide. The project demonstrated both the viability and the utility of applying the citizen science approach to radon post-measurement phases, with measurable benefits in bridging knowledge gaps and in encouraging behavioural changes. The results of using a citizen science approach in the field of radon management and research are encouraging, and they far outweigh the challenges involved in the implementation.

Operational and engineering experiences of gas injection to JET for TT and DT operational campaigns

Following the first deuterium–tritium experiment (DTE1) at UKAEA, modifications were investigated to the Joint European Torus’ (JET) gas introduction (GI) systems to increase the gas feed capabilities of the JET facility to better support future campaigns. The GI systems comprise the GI and gas distribution system in the Active Gas Handling System (AGHS), and neutral beam injection and the tritium injection modules on the torus. During DTE1 about 100 g of tritium was supplied from AGHS to JET users. During the second deuterium–tritium experiment (DTE2) and the tritium–tritium experiment (TT) just over 373 g and 630 g of tritium respectively was supplied to JET users for the campaigns. The tritium and deuterium gas supply systems of the fuel cycle can be underestimated as having fewer technical or scientific challenges based on the mechanical simplicity of equipment that they consist of. However, operational experience has shown these systems have the potential to bottleneck a campaign programme. This publication outlines the upgrade requirements foreseen, following DTE1, for operations in the DTE2 and TT campaigns, how these changes impacted the gas supply operations, and where limitations were encountered. The areas discussed include—challenges of upgrading and maintaining equipment designed for a short operating life; the impact of having differences between user requirements and gas supply capabilities; the logistics of gas supply involving multiple control room locations; communication routes between gas supply systems and teams; and safely controlling and tracking tritium gas movements. The latest JET tritium campaigns highlighted a number of challenges for future facilities looking to operate in both batch and continuous gas injection operational modes. The recommendations from this publication intend to provide a starting point for how to address these challenges and optimise gas supply in support of future fusion programmes. This work has been carried out within the framework of the contract for the operation of the JET Facilities and has received funding from the European Union’s Horizon 2020 research and innovation programme. The views and opinions expressed herein do not necessarily reflect those of the European Commission.

Design of a new kind of chemical experiment container with virtual reality fusion

BackgroundAt present, the teaching of experiments in primary and secondary schools is affected by cost and security factors. Existing research on virtual experiment platforms has alleviated these problems. However, the lack of real experimental equipment and use of a single channel to understand user intentions weaken these platforms operationally and degrade the naturalness of interactions. MethodsTo solve these problems, we propose an intelligent experimental container structure and a situational awareness algorithm, both of which are verified and applied to a chemical experiment involving virtual-real fusion. First, the acquired images are denoised in the visual channel using the maximum diffuse reflection chroma to remove overexposure. Second, container situational awareness is realized by segmenting the image liquid level and establishing a relation-fitting model. Then, strategies for constructing complete behaviors and making priority comparisons among behaviors are adopted for information complementarity and independence, respectively. A multichannel intentional understanding model and an interactive paradigm that integrates vision, hearing, and touch are proposed. ResultsThe experimental results show that the accuracy of the intelligent container situation awareness proposed in this paper reaches 99%, and the accuracy of the proposed intention understanding algorithm reaches 94.7%. The test shows that the intelligent experimental system based on the new interaction paradigm also has better performance and a more realistic sense of operation experience in terms of experimental efficiency. ConclusionThe results indicate that the proposed experimental container and algorithm can achieve a natural level of human-computer interaction in a virtual chemical experiment platform, enhance the user′s sense of operation, and achieve high levels of user satisfaction.

Debris Management in Turkey Provinces Affected by the 6 February 2023 Earthquakes: Challenges during Recovery and Potential Health and Environmental Risks

On 6 February 2023, southeastern Turkey was struck by two major earthquakes that devastated 11 provinces. Tens of thousands of buildings collapsed and more were later demolished. During post-event field surveys conducted by the authors, several disposal sites set up in the most affected provinces were detected and checked for suitability. Based on field observations on the properties of sites and their surrounding areas as well as on the implemented debris management activities, it is concluded that all sites had characteristics that did not allow them to be classified as safe for earthquake debris management. This inadequacy is mainly attributed to their proximity to areas, where thousands of people reside. As regards the environmental impact, these sites were operating within or close to surface water bodies. This situation reveals a rush for rapid recovery resulting in serious errors in the preparation and implementation of disaster management plans. In this context, measures for effective debris management are proposed based on the existing scientific knowledge and operational experience. This paper aims to highlight challenges during earthquakes debris management and related threats posed to public health and the environment in order to be avoided in future destructive events.

Possibility of misleading readings of water level in VVER steam generator during severe accidents with account for the Fukushima lessons

The severe accident at Fukushima Daiichi in 2011 has emphasized the importance of keeping instrumentation reliable in the course of a severe accident, for successful diagnosis of current state of the reactor and adequate decision making. After the electrical current was partially restored several hours into the accident at Unit 1, the readings of the water level in the core have been for a long time misleading. Given the conditions at the Unit, they were clearly contradicting the analytical estimates of coolability and degradation level of the reactor core. In the post-accident investigations this contradiction was explained by TEPCO by the effect of water evaporation in the reference leg due to heat up of the drywell atmosphere around. The water level instrumentation in different vessels of the VVER NPPs like steam generator, pressurizer is very similar to that at Fukushima BWR. Although the VVER and BWR designs are different in many aspects, it is important to verify if the lessons learnt from the Fukushima accident are applicable in case of severe accidents at VVER.This paper presents the results of numerical study for the possibility of misleading readings of water level in VVER steam generator during hypothetical severe accidents. These results demonstrate the importance of learning the lessons from the accidents that have happened at structurally similar NPPs, and their consideration in safety analyses of NPP units in operation and under design process. Accumulation of lessons learnt from previous operation and emergency experience is a very important advantage of nuclear fission technology that allows enhancing the safety of new designs of nuclear reactors.