Operation Of Nuclear Power Plants Research Articles

Когда кристаллизованный интеллект может быть профессионально «нежелательным» личностным качеством операторов

Purpose: To discuss the case of oppositely directed influences of the indicators of crystallized and fluid intelligence in the decisive rule designed to predict the professional success of the nuclear power plants (NPPs) operators. Material and methods: This paper analyzes the results of psychodiagnostic examinations of operators of main control rooms (MCR) of NPPs that functioned under normal conditions. All individuals were administered the J. Raven’s “Progressive matrices”, the Russian language adaptation of the Minnesota Multiphasic Personality Inventory (MMPI) and the Sixteen Personality Factor Questionnaire (16PF, form A). A cross-expert review using the ranking method revealed two groups of operators with relatively higher and lower levels of professional success. The method of canonical correlation analysis has been used to obtain the best linear discriminator for predicting the professional success of MCR operators based on indicators of psychodiagnostic tests. Results: Based on the results of the expert assessment, two groups of operators with the highest and lowest professional success were identified. Decisive rule were obtained that make it possible to predict the professional success of operators based on a system of signs (values of the psychodiagnostic tests scales multiplied by coefficients) after the data processing using canonical correlation analysis. Unexpected result was that the high values of 16PF factor «B» turned out to be «undesirable» for the prediction of professional success, that is, these values increased the probability of assigning the operator to the group of the lowest successful specialists. Conclusion: Factor «B» of 16PF was considered as a tool for assessing predominantly crystallized intelligence, and the Raven’s test – for the fluid one. At the same time, there are no methods that allow measuring these indicators in their purest form. Taking this fact into account, the author believes that the true role of factor B in the decisive rule did not reflect the undesirability of advanced crystallized intelligence among MCR operators. It is most likely that its opposition to the «desirable» indicator (the number of correctly solved tasks of the Raven’s test) made it possible to single out the role of fluid intelligence (or some of its lower-level aspects) as a professionally important quality for the particular operator activity.

Rocking stiffness of electrical cabinets with tubular base in nuclear power plants

Safe operation of nuclear power plants during an earthquake requires continued operation of safety related electrical equipment as intended. Such equipment are mounted in electrical cabinets and are seismically qualified by using an in-cabinet response spectra (ICRS). Generation of ICRS requires a good understanding of the cabinet’s dynamic characteristics. Past studies have shown that the rotational stiffness associated with the cabinet base and the mounting arrangement plays a primary role in the dynamic behavior of the cabinet. This rotational stiffness is needed to evaluate and characterize the global rocking mode of cabinet vibration. Existing studies have developed formulations to calculate the rocking stiffness for a few mounting arrangements that are typically found in United States and some other western countries. However, existing formulations could not be applied to cabinets in South Korean nuclear plants due to the differences in cabinet mounting type. This study is focused on consideration of tubular mounting arrangement that is typically found in South Korean plants. First, closed-form formulations are developed using fundamental principles of mechanics for two separate cases of this mounting arrangement. Then, detailed nonlinear finite element (FE) analyses are conducted for different mounting arrangements corresponding to different properties and dimensions of the tubular base. The FE models are used to calibrate the proposed closed-form formulations for various different configurations and structural or geometrical properties of tubular members. The proposed formulations provide a simple and accurate estimation of cabinet rocking stiffness which otherwise is difficult to evaluate without a shake table test or a detailed finite element analysis.

Vibroconverter mathematical model based on the levitation effect

Modern requirements for the safe operation of nuclear power plants dictate the need to introduce systems for early reactor plants state diagnosis. Vibrations have always been a threat to the safe nuclear power plants operation, therefore, solving the issues of improving the nuclear power plants vibronoise diagnostics accuracy, especially in the field of ultra-low frequencies, is an urgent task. The most promising way to solve the problem of flexible guides in electromechanical vibration transducers is the levitation effect, which makes it possible to completely eliminate mechanical contact and, accordingly, reduce the sensitivity threshold of the transducer. The article presents an analysis of existing vibration transducers and offers analogue and digital mathematical models of the magnetic levitation system, taking into account the influence of the electromagnetic force nonlinearity. The characteristics of such a nonlinear system are studied using the method of harmonic linearization, which makes it possible to obtain an equivalent linear system. At the same time, the third order terms of the electromagnetic force expansion in the Taylor series are taken into account, which made it possible to obtain a more accurate analogue the vibration transducer model. For the developed vibration transducer digital model, using the z-form method, a system function and the corresponding difference equation were obtained. Expressions and graphs of transient, pulse and frequency characteristics are derived for both analogue and digital vibration converter models, which allow us to conclude about the accuracy and adequacy of the developed digital model. Using obtained vibration transducer digital models will make it easier to model its operation and reasonably select the vibration transducer initial parameters.

Calculation of radiation fields in the VVER-1000 concrete biological shield using Monte Carlo code Serpent

To calculate radiation fields in the concrete biological shield (CBS) of the VVER-1000 reactor in this work, we have developed and applied the Monte Carlo code Serpent simulation framework based on the variance reduction technique. We have quantified the radial, axial, and azimuthal variation of neutron and gamma-ray fluxes and the absorbed dose rate in the CBS. Using the calculation results, we estimate maximum neutron fluence and maximum absorbed dose in the VVER-1000 CBS over the period of 60 and 80 years of the reactor operation and localize the domains of highest radiation exposure. The obtained results are in good agreement with the available data on the VVER-1000 and other pressurized water reactors. We show that the fluence of neutrons with energy above 0.1 MeV decreases by half at a depth of 4 cm of concrete, and the gamma-ray absorbed dose decreases by 40 % at a depth of 13.5 cm. The outcomes from this research will help to assess the effects of prolonged irradiation of the VVER-1000 CBS, which is required for reliable risk assessment for extended operation of nuclear power plants.

ECOC-based integrated learning method for fault diagnosis in nuclear power plants

Abstract The fault diagnosis system of nuclear power plants plays an important role in ensuring the safety and economy of nuclear power plant operations. This paper first analyzes typical faults of nuclear power plants and their phenomena, and fault samples are obtained. A comprehensive study of the structure of the nuclear power plant system, its working mode and the association between each subsystem is carried out to analyze the monitoring parameters and fault characteristics and establish the fault data set. Secondly, an IFWA (Improved Fireworks Algorithm - Integrated Learning) algorithm is proposed to assess the severity of faults in the first circuit of a nuclear power plant. Finally, the fault diagnosis module is divided into three units according to the functional logic, i.e., condition monitoring unit, fault identification unit, and fault severity assessment unit. The results show that the diagnostic accuracy of the IFWA algorithm is 94.25% for SGTR in the single-fault diagnosis experiment and 96.25% for SGTR-LOCA in the multiple-fault diagnosis experiment. It shows that the IFWA algorithm proposed in this paper has the optimal performance capability when applied to nuclear power plant fault diagnosis and effectively assists managers in diagnosing faults and giving maintenance recommendations.

Critical review of nuclear power plant carbon emissions

Nuclear power plays a crucial role in achieving the target of carbon neutrality to build a sustainable society. However, it is not “carbon-free” when considering its entire life cycle. Therefore, accurate accounting and monitoring of its generated carbon emissions are required to avoid miscalculations of nuclear energy as a clean energy source. In this study, the life-cycle carbon emissions of nuclear power plants (NPPs) with different reactor types are reviewed. In addition to the characteristic differences among different reactors, disparities in the review results originate from the varying emissions at the respective stages of the nuclear fuel cycle, technology choices at each stage and accounting methods and boundaries. The carbon emissions resulting from NPP construction and operation are underestimated due to the limited data and methods, which creates uncertainty in the evaluation of NPP carbon emissions. An integrated framework for carbon emissions accounting considering the construction and operation of NPPs (CACO-NPP) is proposed. This integrated framework aims to improve the accounting accuracy for carbon emissions originating from NPPs. An emerging Generation III NPP with the latest technology, HPR1000 (an advanced pressurized water reactor), was adopted as a case study. The results show that the total emissions resulting from vegetation loss, equipment manufacturing and labor input during construction and operation are 1232.91 Gg CO2 with a carbon intensity of 1.31 g CO2/kWh, indicating the notable mitigation capability of Generation III NPPs. By combining the maturity of HPR1000 technology with successive design improvements, the carbon emissions of such reactor types could be further reduced. This development is very important for realizing China’s carbon neutrality target.

DETERMINATION OF TRITIUM IN VEGETATION IN THE OBSERVATION AREA OF REACTOR WWR-K IN KAZAKHSTAN

In assessing the impact of radiation-hazardous facilities on the environment and humans, considerable attention is currently paid to the problem of tritium and its compounds intake. It is important to note that to date there are no effective industrial technologies for efficient capture of this radionuclide. As a result, all the tritium produced during the operation of nuclear power plants with emissions and discharges is released into the environment. This leads to increased tritium concentrations in the environment, including vegetation. The aim of this work is to develop and adapt a set of methods for sample preparation and determination of tritium in vegetation samples. Methodology: A special Carbolite Gero MTT tube furnace was used to improve sample preparation methods and maximise the recovery of organically bound tritium from vegetation. Tritium was measured by liquid scintillation beta spectrometry. Results and Discussion: This research paper presents the results of the study and implementation of the method of tritium determination in vegetation near the VVR-K reactor located in the city of Almaty, Kazakhstan. Conclusions: The developed method of tritium determination in vegetation can be applied for radiation monitoring of tritium content and its compounds in the vicinity of nuclear industrial facilities. The presented data emphasise the need for systematic studies of tritium accumulation in environmental components. It is expected that in the future, using the implemented method, the studied area will be studied in detail, taking into account an extended set of factors: meteorological conditions, reactor operation mode and others. Thus, for a more complete and reliable assessment of tritium radionuclide activity determination, it is necessary to carry out works to determine the type of vegetation accumulating this isotope.

Preliminary study of the sub-medium São Francisco region overlooking the installation of future Brazilian nuclear power plants

Preliminary studies of site selection for the installation of nuclear plants in the northeast of Brazil have shown that the São Francisco river basin is a possible region for the implementation of these plants. For their operation, however, nuclear power plants require a reliable source of water for the cooling of heat rejected from the condenser that is sufficient for normal operation, shutdown, postulated accident conditions, and fire protection. The objective of this paper is to discuss safety issues and environmental impacts arising from the placement of nuclear power plants at the São Francisco river basin. The approach taken considered water availability throughout the year, the maintenance of thermal balance and climate changes. The present discussion indicates the necessity of a long-term management plan for the various uses of the São Francisco basin. An economic and social approach to the impacts of nuclear power plant operation and other agricultural and industrial activities in the region is also necessary. Finally, the study suggests the adoption of a variable-cycle cooling system, which will enable operation in all types of hydrological conditions expected in the São Francisco basin.

Influence of Cooling Water Parameters on the Thermal Performance of the Secondary Circuit System of a Modular High-Temperature Gas-Cooled Reactor Nuclear Power Plant

This study quantitatively analysed the influence of cooling water parameters on the performance of a modular high-temperature gas-cooled reactor (MHTGR) nuclear power plant (NPP). The secondary circuit system and cold-end system were modelled using EBSILON software, version 16.0. The influence of cooling water inlet temperature and mass flow rate on the thermal performance of the secondary circuit system was analysed over the full power range with the goal of optimising net power. Under 100% rated condition, for each 1 °C increase in cooling water inlet temperature between 10 and 33 °C, the net power and cycle efficiency decreased by 0.67 MW and 0.14%, respectively, whereas the heat consumption rate increased by 28.72 kJ/(kW·h). The optimal cooling water mass flow rates corresponding to cooling water inlet temperatures of 16 °C and 33 °C were obtained. The optimal cooling water mass flow rate decreased nonlinearly with decreasing power levels. At a cooling water inlet temperature of 33 °C, an increase in cooling water mass flow rate from the designed value (7697.61 kg/s) to the optimal value (10,922.14 kg/s) resulted in a 1.03 MW increase in net power. These findings provide guidelines for MHTGR NPP operation optimisation and economic improvement, especially under high-temperature weather conditions.

A fault diagnosis method for nuclear power plant rotating machinery based on adaptive deep feature extraction and multiple support vector machines

Rotating machinery is the essential component in nuclear power plants (NPPs). Effective fault detection and diagnosis is a main challenge in the operation and maintenance of NPPs rotating machinery. The performance of traditional fault diagnosis methods mainly depends on complex manual feature extraction and sufficient expert prior knowledge. This study proposes a fault diagnosis method based on adaptive feature extraction and multiple support vector machines (ResNet-SVMs) to overcome the limitations of the traditional intelligent fault diagnostics. First, the vibration information from different locations of the rotating machinery is collected and used as input data for the algorithm model. Then, the deep residual neural network adaptively extracts fault features from input data to obtain feature data of different depths. Finally, multiple support vector machines identify the feature data to realize the fault diagnosis. The effectiveness verification is carried out based on the experimental cases of induction motor and rolling bearing fault diagnosis. Compared with other advanced intelligent fault diagnosis methods, ResNet-SVMs model provides better diagnostic performance, which demonstrates its potential value for NPPs rotating machinery fault diagnosis.

In-reactor behaviour and economic assessment of enriched gadolinia burnable absorbers

The increasing demand for energy and rising energy prices have increased the importance of the efficiency and economic viability of operating nuclear power plants. One approach to improving the reactivity control in such cases is the use of burnable absorbers such as gadolinium oxide (Gd2O3). While Gd2O3 has proven effective in regulating reactivity in light water reactors, it has certain drawbacks, including the displacement of fissile isotopes from the fuel composition and residual reactivity penalties caused by isotopes other than the main neutron absorbers. In this study, the potential impacts of 157Gd-enriched Gd2O3 on the operation, safety, and economy of nuclear power plants were assessed. Fuel cycle analyses were conducted using the advanced nuclear design code system Studsvik CASMO4/SIMULATE3. Several aspects were analysed, including peaking factors, reactivity feedback parameters, power distribution, and shutdown margin. The results of the analysis revealed that by removing the isotopes responsible for residual reactivity from Gd2O3, it was possible to achieve the same fuel cycle length with lower uranium enrichment levels, enabling a higher concentration of fissile isotopes and yielding economic benefits without compromising safety.

Method for solving atmospheric dispersion parameters of radioactive aerosols based on wind-tunnel laser measurement experiments

Certain fraction of radionuclides was inevitably discharged into the atmosphere during the normal operation of nuclear power plants. Therefore, the atmospheric dispersion of these airborne radioactive aerosols is an essential part of radiation environmental assessment during the siting, construction, and operation of nuclear power plants. Gaussian plume model is the most widely used method for this assessment. Evaluation uncertainty of this method mainly depends on the selection of atmospheric dispersion parameters. In this paper, the laser measurement method was carried out in the atmospheric wind-tunnel dispersion experiments of aerosols, and a method for solving atmospheric dispersion parameters based on high-resolution laser scattering images of plumes was proposed. Firstly, a full-frame statistical image of aerosol atmospheric plume trajectories was obtained through high-resolution laser measurement. Secondly, image processing was performed to remove noise, then to acquire light intensity of image pixels, and to make 95.45% (2σ) of the total light intensity fall within the plume trajectory to determine the plume boundary line at last. Finally, the atmospheric dispersion parameters were determined by optimal fitting, using the Gaussian plume model as a benchmark. Compared with the commonly used method for solving atmospheric dispersion parameters based on single-point densitometer detection experiments, the method based on laser measurement proposed in this work has advantages in reflecting directly realistic plume trajectory of both aerosols and particles with large sizes. This study can provide technical support for the accurate evaluation of aerosols or particles atmospheric dispersion.

State and federal nuclear support schemes in dynamic electricity market conditions: Insights from NYISO and PJM

Since 2017, several U.S. states have put in place out-of-market financial support schemes for nuclear power plants operating in deregulated electricity markets. In late 2021, the federal government announced the introduction of two new support schemes to secure the continued operation of nuclear power plants. This policy perspective evaluates the profitability of state subsidized nuclear power plants in the NYISO and PJM markets over a five-year period between 2017 and 2021. Results indicate that apart from 2019, nuclear power plants were financially robust, relying solely on market revenues without the need for state support schemes. More importantly, the recent upswing in competitive electricity market prices suggests that additional federal support schemes are not economically justified in current market conditions. I provide several suggestions to reconfigure the support schemes to reflect dynamic market conditions and ensure only vulnerable plants are granted out-of-market support.

Effects of video display terminal fatigue on situational awareness ability of operators and modeling study

In order to study the changing pattern of the posture perception ability of video display terminal operators in the main control room of energy power plants such as nuclear power plants in a state of fatigue, subjective and objective data of 19 energy system operators were collected through experiments. The effect of video display terminal fatigue on the operator's level of situational awareness was analyzed, and the subjective and objective data were selected to construct an XGboost model to predict the identified operator's situational awareness capability. The study results showed that the subjective and objective data showed significant differences, and it could be inferred that the subjects had developed video display terminal fatigue. The combination of data showed that fatigue affected the manipulator's ability to perceive and understand, decreasing the manipulator's situational awareness. The XGboost model, based on subjective and objective data, achieved a validation rate of 88.90%, indicating that the model can identify and predict the situational awareness of video display terminal manipulators. The study's results can be used to assess the situational awareness of video display terminal operators in nuclear power plants and provide a scientific basis for safety training in nuclear power plants and other energy power plants.

Efficient processing of tritiated water by using a two-stage Pd membrane reactor with Pt/TiO2 catalyst

Large amounts of tritiated water (HTO) will be produced during the operation of nuclear power plants and fusion devices, which is harmful to the environment and human due to its radioactivity and toxicity. So, the tritium concentration of tritiated water must be reduced to a very low value before discharge. Hydrogen-water isotope exchange reaction (H2 + HTO→H2O + HT) based on palladium membrane reactor has been proposed to process tritiated water. However, a comprehensive study about the influence of operation parameters on the membrane reactor performance is insufficient, which is not conducive to the design of reactor in practical application. Moreover, the commonly used Pt/Al2O3 or Ni/SiO2 catalysts are not active for tritiated water dissociation, so the catalytic activity of these catalysts is not high. In order to process tritiated water more effectively, a two-stage membrane reactor has been designed and established in this work, and Pt/TiO2 catalyst with rich oxygen vacancies is used to catalyze the hydrogen-water isotope exchange reaction for the first time. The membrane reactor performance shows an approximate linear relationship with a new combined parameter S0.5P1.5R/F2 (S is membrane area, F is water flow rate, P is vapor partial pressure, R is swamping ratio), which can be used predict the membrane performance. The isotope exchange reaction activity of Pt/TiO2 is better than that of Pt/Al2O3 due to its good ability for water dissociation and the hydrogen spillover effect. At last, a tritiated water processing experiment by using two-stage membrane reactor with Pt/TiO2 catalyst with rich oxygen vacancies has been carried out. The tritium decontamination factor reaches 40588, which is the highest experimental value so far. The results indicate that the two-stage Pd membrane reactor based on hydrogen-water isotope exchange reaction is an efficient technology for tritiated water processing.

Development of metal radioactive liquid reference material for proficiency test

This study developed liquid reference materials containing various metals, to be used for quality assurance of radiation measurements of the most common metallic wastes generated during the operation or decommissioning of nuclear power plants. The liquid reference materials were prepared by assuming the dissolution of stainless-steel using acid and melting of the major metals present in the stainless steel, namely Fe, Ni, Cr, and Mn, along with the standard sources (134Cs, 137Cs, 60Co, 90Sr). The theoretical massic activity of the standard sources added to the samples and the measured reference values of the gamma and beta emitters in the samples were compared, and they showed good agreement within a one-sigma confidence interval (k = 1). Using the developed reference materials, a proficiency test was conducted on three domestic labs, and the results were evaluated using Z-score. While the evaluation results showed good agreement between the reference values and the reported values for 137Cs and 60Co, all participating labs reported lower values than the reference value for 134Cs. For 90Sr, two out of the three labs reported significantly higher values than the reference value. Based on the results of this study, the developed metal radioactive liquid reference material is expected to be registered as certified reference material (CRM) in the future. They will be used as the CRM for measuring and ensuring the quality of radioactive metal waste.

Development of nuclear power in Belarus: a sociological analysis of the elasticity of public opinion

The article discusses the results of sociological monitoring of public opinion on the use of nuclear energy in Belarus. The main part presents an analysis of the data obtained from the results of a sociological study conducted by the Institute of Sociology of the National Academy of Sciences of Belarus in 2022 on the assignment “Conduct sociological monitoring of public opinion of the population of the Republic of Belarus in order to form a positive attitude towards nuclear energy” of event 8 “Information and analytical support for the development of nuclear Energy in the Republic of Belarus” of subprogram 3 “Scientific support for the efficient and safe operation of the Belarusian nuclear power plant and promising areas for the development of nuclear energy” of the State Program “Science-intensive technologies and equipment” for 2021– 2025. The time intervals within which important events had a direct or indirect impact on public opinion about nuclear energy are characterized. A sociological method of calculation has been developed that makes it possible to trace the vector of public opinion’s response to nuclear energy (increase or decrease in the level of loyalty) to various internal or external factors. An assessment of the elasticity of public opinion about nuclear power is carried out with the construction of a typology of this elasticity. Also, self-assessments of the respondents’ formation and stability of their position regarding the implementation of the project “Belarusian NPP” were revealed. The need for systematic information and explanatory work among the population on all the main aspects of the practical use of nuclear energy is shown.

A method for searching the best static program for nuclear power unit control in the event of perturbations of different nature

Considering the current state of Ukraine's energy sector in a dangerous and unstable environment, the operation of nuclear power plants is one of the most important sources of electricity supply for the state. The development of the theory of optimal control and the technical level of automated process control systems in the current state of affairs make it possible not to reduce the efficiency of controlling a nuclear power unit, not only by changing the parameters at any load, but also by changing the structure of automation equipment capable of implementing a certain static control program of power, which currently eliminates the influence of internal and external disturbances, without reducing safety indicators. The article considers the situation when the linear programming method is not applicable for solving the control problem. In this case, the decision at each stage does not depend on the decision at the previous one. This is where target programming comes in handy –this is one of the methods of multi-criteria optimization, in the theory of which decision-making problems are solved simultaneously according to several criteria. The purpose of the work is to ensure the safe and efficient operation of a nuclear power unit in an energy system that is not constant in operational states. Using a mathematical model of a nuclear power unit, experiments were carried out to simulate the switching of controlprograms. The simulation model of the automated power control system, based on the bumpless switching of static programs according to the technological methods of operating power equipment, made it possible to form a change in the current model of the control program, as well as eliminate the static control error and get the response of process dependent parameters to program switching. Also, based on the results of the research, an objective function was proposed, which includes three normalized criteria with different objectives. In particular, the problem of optimizing the switching of static power control programs was solved by minimizing the objective function, which combines such characteristics as the efficiency and safety of the operation of a nuclear power unit.

Plutonium in sediments of the Eastern Guangdong coast-its sources and their contribution

The 239+240Pu activities and 240Pu/239Pu atom ratios of surface sediments from the Eastern Guangdong coast (EGDC) were determined by sector field ICP-MS in order to examine the sources of plutonium (Pu) and quantify their contributions. The 239+240Pu activities in the EGDC ranged from 0.113 to 0.451 Bq kg−1, with an average of 0.225 ± 0.090 Bq kg−1 (n = 17). Consistently high 240Pu/239Pu atom ratios, ranging from 0.218 to 0.274 (average = 0.254 ± 0.014, n = 17), indicate a non-global fallout Pu source in the EGDC. The horizontal distribution of the 240Pu/239Pu atom ratios in the EGDC sediment suggests the non-global fallout Pu is sourced from close-in fallout from the Pacific Proving Grounds (PPG). Using a simple two end-member mixing model, we calculated the relative proportions of Pu from the PPG and global fallout in the EGDC to be 57 ± 9 % and 43 ± 9 %, respectively. Moreover, from the well-defined relationship between 239+240Pu activity and total organic carbon content in sediments and a two end-member mixing model using δ13C, we further calculated the Terr-global fallout (riverine input) and Mar-global fallout (direct atmospheric deposition) to be 11 ± 2 % and 32 ± 6 %, respectively. Finally, from the activity levels and atom ratios of Pu isotopes in the EGDC, we established a baseline for future use in environmental risk assessment related to nuclear power plant operations.

A methodology to designate radiation‐controlled areas in decommissioning nuclear power plants

AbstractKori Unit 1, which was permanently shut down in 2017, is expected to be the first decommissioned commercial nuclear power plant (NPP) in Korea. Operating NPPs designate radiation‐controlled areas (RCAs) to protect workers from radiological hazards and provide appropriate measures. Decommissioning RCAs (DRCAs) in NPPs being decommissioned should also be designated by considering the radiological characteristics of workplaces and exposure routes of decommissioning workers, such as external and internal exposure. However, the criteria for the DRCAs in decommissioning Kori Unit 1 are presently the same as those during normal operation, according to the public‐hearing material of the final decommissioning plan for Kori Unit 1. This study analyzed criteria for RCAs in all Korean NPPs to propose criteria for DRCAs in decommissioning NPPs. Analysis results show that RCAs are classified into four, five, six, and eight zones in Korean pressurized water reactors with respective external radiation dose rates. The RCAs in Korean pressurized heavy water reactors are classified into six zones with external dose rates and derived air concentrations of tritium. This study proposes three classifications of DRCAs to keep occupational exposure as low as reasonably achievable while considering potential exposure routes, that is, external exposure, airborne contamination, and surface contamination areas. First, the external exposure areas are classified into several zones according to the levels of external radiation dose rates. Second, the airborne contamination areas are designated to prevent internal exposure to workers from the inhalation of radioactive material in the air during cutting and demolition. Last, the surface contamination areas are designated to minimize the skin contamination of workers as radioactive dust in the air is deposited on the surface of facilities and equipment over time.