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

Kori 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.


| INTRODUCTION
Various radionuclides are generated in nuclear power plants (NPPs) during nuclear fission. NPP workers are likely to be exposed to external radiation from the nuclides generated during operation. Radioactive materials floating in the air in work areas can also be ingested by the body, causing internal exposures. The radiation safety in NPPs is generally managed by establishing radiation-controlled areas (RCAs) to prevent workers from excessive exposure. The regulations on technical standards for radiation safety control provide the criteria for establishing RCAs in operating Korean NPPs. RCAs are areas where the external radiation dose rate is greater than 400 μSv per week, the concentration of radioactive material in the air is higher than the derived air concentration (DAC), or the level of contamination of the surface of an object contaminated with radioactive materials exceeds the acceptable surface contamination levels. These criteria are prescribed by the Nuclear Safety and Security Commission (NSSC). 1 The acceptable levels of surface contamination are less than 0.4 Bq cm −2 for radioactive materials emitting alpha particles and less than 4 Bq cm −2 for radioactive materials not emitting alpha particles. 2 High-radiation areas, such as the reactor core, are defined as areas where the external radiation dose rate may exceed 1 mSv h −1 at a distance of 30 cm from the radiation source surface or shield surface within the RCA. 3 In Korea, 24 NPPs are in operation, including 21 pressurized water reactors (PWRs) and three pressurized heavy water reactors (PHWRs). Two NPPs, Kori Unit 1 and Wolsong Unit 1, are currently being permanently shut down and will ultimately be decommissioned. 4,5 Table 1 shows the current status of Korean NPPs. 6 The RCAs in operating NPPs are designated according to regulations to protect workers from radiological hazards by maintaining occupational exposures as low as reasonably achievable (ALARA) during the normal operation and maintenance periods. Thus, in operating NPPs, radiation exposures are usually minimized by recognizing radiological hazard factors in advance and providing professional radiological protection techniques for workers depending on the classification of the RCAs. In contrast to operating NPPs, during the decommissioning of NPPs, dust and suspended materials containing radionuclides are likely to be observed in the air owing to decontamination, cutting, and demolishing operations. These substances are expected to remain and be adsorbed on structures and machinery and contribute to external or internal exposures to decommissioning workers, resulting in unexpected radiation exposures. Therefore, it is necessary to establish decommissioning RCAs (DRCAs) differing from the RCAs in operating NPPs, for example, considering the high likelihood of both external and internal radiation exposures in decommissioning fields. The DRCAs enable providing appropriate radiological protection techniques for workers depending on the classification of the DRCAs.
The ALARA characteristics used in operating NPPs can be applied to the decommissioning of NPPs. Thus, DRCAs can also be defined as workplaces where radioactive materials are present (similar to the RCAs in operating NPPs) or where workers are likely to be exposed to internal or external radiation during decommissioning. However, to achieve the ALARA goals dedicated to decommissioning workers, the design criteria for DRCAs should be selected differently from those for operating NPPs while considering the radiological characteristics of the decommissioning fields. Before decommissioning an NPP, radiological characterization is generally conducted to predict or identify radionuclides and residual radioactive contamination generated from structures, systems, and components (SSCs) activated by neutrons. For example, the Trojan NPP in the United States was decommissioned in 2005; before that, a radiological characterization of the SSCs and surrounding environments, such as RCAs and industrial areas, was conducted to estimate the level of radioactive contamination of the NPP. 7,8 Permanently shut-down reactors in Korea have also initiated the designation of DRCAs using radiological characterizations. Correspondingly, this study proposes an appropriate methodology for designating DRCAs based on an investigation of RCAs in operating Korean NPPs and overseas decommissioned NPPs.

| RCAS IN OPERATING KOREAN NPPS
The RCAs in operating Korean NPPs are classified into several RCA zones based on radiation dose rates, working hours, and the need to take protective measures. All RCAs should maintain the occupational exposure ALARA and meet the occupational dose limit, that is, 100 mSv over 5 years with no more than 50 mSv in a single year. 9,10 To meet regulatory requirements, RCA zones are established based on the maximum radiation dose rates and working hours at a point 30 cm away from a radiation source or surface contaminated by radioactive materials. For instance, the RCAs in Kori Unit 1 are designated as any areas where an external radiation dose rate of 0.4 mSv (400 μSv) or more per week is expected to reach the main part of the body. 11 The individual radiation dose is controlled by limiting the working hours in the RCAs. The design criteria for RCA zones are different for each NPPs, depending on the radiological conditions of the individual NPP. [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26] High-radiation areas are also defined as any areas with external radiation dose rates greater than 1 mSv h −1 to the main part of the body in RCAs. Door locks should be installed at the entrance to high-radiation areas, and access to the areas is allowed only for workers who have work permits.
To determine the classifications of RCA zones in operating NPPs, this study investigated the final safety analysis reports of all Korean NPPs. As a result, the RCA zones in PWRs are divided into four, five, six, or eight zones depending on the design characteristics of the individual NPP and radiation dose rates. [11][12][13][14][15][16][17][18][19][20][21][22][23] For example, the RCA zones of Hanul Units 1 and 2 are classified into four zones: green, yellow, orange, and red, as shown in Table 2. 17 The green zone is the area with a radiation dose rate of less than 0.025 mSv h −1 and is always accessible. The yellow zone has a radiation dose rate of 0.025-2 mSv h −1 and is a limited-access area. The orange zone has a radiation dose rate of 2-100 mSv h −1 and is an access-controlled area. Finally, the red zone has the highest radiation dose rate (greater than 100 mSv h −1 ) and is an exceptional access area. The RCA zones of Kori Unit 2 are divided into five areas, as shown in Table 3. 12 The radiation dose rate for Zone 1 is 0.0025 mSv h −1 , with unlimited access. Zone 5 allows working hours of less than 1 h, with the highest radiation dose rate of 1 mSv h −1 or higher. NPPs with six RCA zones include Kori Unit 1, which is scheduled to be decommissioned; Kori Units 3 and 4; Hanbit Units 1, 2, 3, and 4; and Hanul Units 3 and 4, which are currently in operation. The radiation dose rates for the unlimited and restricted access areas are less than 0.005 mSv h −1 and greater than 1 mSv h −1 , respectively, as shown in Table 4. 11,[13][14][15]18 Shin-Kori Units 1, 2, 3, and 4, Hanbit Units 5 and 6, Hanul Units 5 and 6, Shin-Wolsong Units 1 and 2, and Shin-Kori Units 5 and 6 currently under construction have eight RCA zones, as shown in Table 5. 16,[19][20][21]23 The radiation dose rates for Zones 1-5 for unlimited and controlled access are set from a minimum of 0.001 mSv h −1 to a maximum of 1 mSv h −1 . Zone 1 is a general access area and its radiation dose rate is periodically measured to determine whether access control is necessary. Zones 6-8 are accessible to radiation workers only as authorized by the radiation safety department; they are classified as high-radiation areas with radiation dose rates from 1 to 5000 mSv h −1 or higher. 16,[19][20][21]23 The Wolsong NPP Units 1, 2, 3, and 4, that is, the PHWRs, have different criteria for the RCA zones, as listed in Table 6. [24][25][26] A conservation area is defined as an area where there is no system or facility with radioactive contamination and is always controlled to avoid radioactive contamination. The conservation areas include the turbine room, turbine auxiliary room, water treatment building, material warehouse, emergency generator room, main control room, second control area, auxiliary building corridor, mechanical maintenance room, electrical maintenance room, and instrument maintenance room. In addition, the RCAs are classified as areas requiring measures to control radiation exposures to workers, including the reactor building, decontamination room, laundry room, fuel machine maintenance room, spent fuel storage room, auxiliary building basement, heavy water upgrade building, air purification room, selfcalibration room, drum compression room, radioactive waste storage, pressure tube maintenance center, spent fuel dry storage facility, pressure tube storage facility, crane hall, part of tritium removal facility, part of maintenance warehouse, and contaminated equipment maintenance rooms. Access to the conservation areas is managed through security procedures. Access to the auxiliary building and part of the RCAs is classified as "R" for the access control level managed by the security and radiation protection procedures. Access to RCAs requires approval by the radiation safety staff. These limited-access areas are classified as "C," "B," "A," and "A + B," depending on radiological conditions. [24][25][26] As a result of investigating RCA zones in operating and permanently shut down NPPs in Korea, it is found that PHWRs designate RCA zones in more detail than PWRs and control the level of the DAC considering the internal exposure to tritium. Most RCA zones in PWRs have similar criteria for RCA zoning depending on the maximum radiation dose rates. The radiation work conducted in operating NPPs focuses on the maintenance of the system and components, not on demolition. According to the annual report concerning radiation management in Korean NPPs, most occupational exposures are mainly external radiation exposure (greater than 90%); thus, the criteria for RCA zones depend mainly on external radiation dose rates. 27,28 Unlike operating NPPs, decommissioning NPPs are likely to undergo more diverse work, such as direct cutting, decontamination, and demolition, resulting in various radioactive dust in the workplace. Therefore, it is the DRCA. Protective equipment and dosimeters should be provided to prevent radioactive contamination and monitor individual radiation doses, respectively. In highradiation areas, door locks should also be installed at the entrances to prevent unauthorized access. DRCAs can be changed under decontamination and demolition; if necessary, a temporary DRCA can be established depending on the radiological conditions. As decontamination, cutting, and demolition of decommissioning facilities progress, the shape of a decommissioning NPP continuously changes; thus, RCA zones classified previously by the radiological characterization may no longer be effective as radioactive contamination is removed after the dismantling work is completed. In particular, a graded approach can be applied to the radiological characterization of facilities and data acquisition. The graded approach applied in radiological characterization and data acquisition determines the list of radionuclides through historical literature review, sampling, and analysis, and uses the list to rate the level of risk during decommissioning. This can save effort and time in decommissioning and aid a decommissioning licensee in focusing on the most dangerous tasks. According to the public hearing material of the FDP for Kori Unit 1, the DRCAs are classified into five zones as shown in Table 7. 29 The DRCA zones are very similar to the RCA zones in Kori Unit 1, as shown in Table 4. This indicates that both the DRCA zones in decommissioning NPPs and RCA zones in operating NPPs classify zones depending on radiation dose rates only. The DRCAs should be established taking into account radiation dose rates, the concentration of radioactive material in the air, and the surface contamination according to the public hearing material of the FDP for Kori Unit 1; however, the current FDP for Kori Unit 1 uses radiation dose rates only to design the DRCA zones. If the DRCA zones are set in the same manner as the RCA zones in operating NPPs, adequate radiation protection may not be provided for decommissioning workers. This is because the radiological conditions in the field change constantly depending on the decommissioning work (such as cutting and demolition). Thus, the criteria for DRCA zones should include the results concerning the radiological characterization, such as the levels of DAC and surface contamination. In general, the radiation dose rates in operating NPPs are high owing to activation from neutron irradiation. By contrast, the radiation dose rates in decommissioning NPPs decrease over time from permanent shutdown until the end of decommissioning; thus, the radiation dose rates in decommissioning NPPs are expected to be relatively lower than those in operating NPPs. However, in the actual decommissioning process, workers are likely to be exposed to both high external exposures owing to short working distances and internal exposures owing to the inhalation of radioactive dust in the air during cutting and demolition. 4,30 For instance, the US Nuclear Regulatory Commission (NRC) postponed all radiation work at the Connecticut Yankee NPP for 14 months owing to internal exposures to alpha particulates during decommissioning, resulting in an internal radiation dose of 10 mSv for two individuals. 4,31

| PROPOSAL OF METHODOLOGY FOR DESIGNATING DRCAS IN DECOMMISSIONING NPPS
DRCAs should be designated based on a radiological characterization of the decommissioning facility to maintain ALARA for external and internal exposures to decommissioning workers. First, the results regarding the radiation source terms using computer calculations in the transition stage of the NPP life cycle, that is, the phase between the final shutdown and dismantling, should be verified through actual radiation measurements in the fields for designating DRCAs. A more indepth radiological characterization should also be conducted, including external radiation dose rates, concentrations of radioactive materials in the air, surface contamination levels, and radiological hazards potentially occurring during decommissioning work. For example, the Trojan NPP in the United States conducted all radiological characterizations (structure, system, activated components, and environment) to identify the radiological status of each system and structure. External exposure rates were measured, removable beta-gamma and alpha contamination levels were measured, and direct measurements of beta-gamma contamination were made. The Trojan NPP provided survey maps and tables showing the radiological conditions (exposure rates and surface contamination) in workplaces within the RCAs to prevent unexpected radiation exposure during decommissioning. 7 However, data on the concentration of radioactive dust in the air within the RCAs were not provided in the radiological characterizations of the Trojan NPP. The Connecticut Yankee NPP also conducted an initial radiological characterization to determine the levels of radioactive contamination in the system, structure, and area. Due to an internal contamination incident involving two workers, the Connecticut Yankee NPP counted smears of areas for alpha particles as well as beta and gamma radionuclides and updated beta-to-alpha ratios for areas based on the smear survey results. These ratios were used to establish trigger levels for continuous air monitor alarms and the posting of areas as airborne contamination areas. 31 One of the radiological hazards that must be considered when designing DRCAs is the inhalation of radioactive materials (particularly alpha particles) in the air by decommissioning workers during decontamination and cutting. Alpha particles have a radiation weighting factor of 20, so their radiological impact on internal exposure is much greater than that of beta and gamma particles with a radiation weighting factor of 1. Thus, it is necessary to check the conditions of radioactive contamination on the SSCs, evaluate the potential contamination owing to leakages, and apply the radiological results in the DRCA zones. Furthermore, radiation monitoring, including monitoring of the external dose rates, DAC levels, and surface contamination, should be continuously conducted, because the radiological conditions in the decommissioning field change constantly depending on decontamination, cutting, and demolition. 32 This study proposes that DRCAs should comprise three types of areas to achieve ALARA for external and internal exposures to decommissioning workers in NPPs: external exposure, airborne contamination, and surface contamination areas. First, similar to the RCA zones in operating NPPs, the external exposure area should be classified into several zones according to the levels of external radiation dose rates. Measurements should be performed in places where workers frequently enter and exit. Additional measurements should also be conducted by selecting a point where the change in the radiation dose rate is expected to be relatively large. The zones of the external exposure areas ensure that all workers receive appropriate radiation protection measures and external exposure control depending on the zone. Second, the airborne contamination area should be designated to prevent internal exposure to workers from the inhalation of radioactive dust during cutting and demolition. In decommissioning workplaces, the concentrations of radioactive materials in the air as well as the types and sizes of the radionuclides change continuously during work; thus, it is necessary to ensure that workers wear respiratory protective equipment when working. For instance, when dismantling a research reactor in Korea, the decommissioning areas were divided into daily or weekly measurement points to determine the concentrations of radioactive materials in the air. 32 Similar to zones in the external exposure area, the airborne contamination area should be classified into several zones depending on the level of DAC.
Furthermore, a ventilation system should be designed to flow air from an area with a low potential for contamination to one with a high potential for contamination to minimize the concentration of radioactive dust in the air. For areas with a potential for airborne radioactive contamination, the system should be designed to exhaust a larger amount of air than the supplied air volume to minimize leakages in the area. Last, the surface contamination areas should be 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. It is also necessary to classify the zones of surface contamination areas to prevent the spread of radioactive contamination from removing contaminated objects from DRCAs. According to the NSSC Rule No. 29 (Regulations on Technical Standards for Radiation Safety Control), when objects are removed from RCAs, the level of radioactive contamination on the surfaces of the objects taken out should not exceed one-tenth of the acceptable levels of surface contamination. 1 Thus, the surface contamination areas should ensure that the levels of surface contamination are less than 0.04 Bq cm −2 for objects emitting alpha particles and less than 0.4 Bq cm −2 for objects not emitting alpha particles. The numerical criteria for DRCA zoning can be different depending on the results of radiological characterization. If the external exposure rates and the levels of DAC and surface contamination in a workplace are measured, the numerical criteria for classifying DRCA zones are established not to exceed the occupational dose limits taking into account maximum working hours in the workplace.
RCAs in operating NPPs are classified by zones based on individual compartments with unit areas. By contrast, in decommissioning NPPs, certain dismantling tasks, such as system decontamination, device cutting, and structure demolition, are conducted across several areas. Thus, it may be reasonable to integrate several areas where the same work is being conducted across several areas and to designate the same DRCA zone using a radiological characterization. To designate appropriate DRCAs, it is necessary to evaluate the decommissioning radiation source terms, including the radionuclides, residual activity, and distribution, in the workplace at the time of the permanent shutdown of the NPP. This study proposes the process for designating DRCAs in decommissioning NPPs with five steps, as shown in Figure 1. In the first step, the design data of the decommissioning NPP is obtained for identifying the buildings and structures and their corresponding heights, including the NPP site drawings, SSC layout drawings, and RCA layout drawings. In the second step, both the design characteristics and radioactive contamination factors are reviewed to classify workplaces by similar radiological conditions based on the design data of the NPP and existing criteria for RCAs during normal operation. In the third step, a draft of the DRCAs can be made by investigating records (such as those concerning spills and device leaks) from the NPP operation history that may indicate previous radioactive contamination in the workplace. In the fourth step, the draft can be modified and further developed based on actual radiological data from direct measurement, sampling, and analysis in the workplace. In the last step, the DRCAs are designated as one of three types of areas: external exposure areas, airborne contamination areas, and surface contamination areas, depending on the external dose rates, concentrations of radioactive materials in the air, and levels of surface contamination. For example, some workplaces can be designated as having two or more DRCAs because not only external radiation exposure to workers but also the inhalation of radioactive materials in the air can occur simultaneously during cutting or demolition. Additional information on radiological hazards is also provided to the workers depending on the DRCA.

| DIFFERENCES BETWEEN RCAS AND DRCAS
In operating Korean NPPs, RCA zones are determined based only on external radiation dose rates. In general, the workplaces in operating NPPs have relatively high radiation dose rates compared to those in decommissioning NPPs owing to the reactor operation. According to the annual report of radiation management at Korean NPPs, occupational exposures during the maintenance period account for approximately 88% of the total radiation exposures to workers. 27,28 Furthermore, most radiation works during the maintenance period focus on the maintenance of systems and components, not demolition; thus, external exposures are the main contributor to occupational exposures in operating Korean NPPs, accounting for approximately 98%. 27,33 Particularly, external exposures contribute to 99.9% of the total occupational exposures in Korean PWRs, indicating that internal exposures are not likely to occur during normal radiation works. 27,34 By contrast, internal exposures account for approximately 16% of total occupational exposures in Korean PHWRs from the inhalation and skin absorption of tritium (used as a moderator and coolant in Canada Deuterium Uranium reactors). 27,35 Thus, although the current RCA zones in operating Korean NPPs do not cover the risks of internal exposures in workplaces, there are no significant radiological issues in the field, as the contribution of internal exposures to the total occupational exposure is much lower than that of external exposures.
Unlike operating NPPs, most radiation works in decommissioning NPPs focus on cutting and demolition of SSCs, not maintenance; thus, the radiological conditions in decommissioning fields are very different from those in the workplaces during the maintenance periods in operating NPPs. For example, leakages of radioactive materials may occur in pipes and other components owing to long-term reactor operation. During the normal operation of NPPs, workers' access to these potential areas of radioactive contamination from leakages is restricted, but access to these contaminated areas during decommissioning is essential for conducting decontamination and demolition and may cause direct exposure to these radiological hazards. In addition, there is a likelihood of airborne contamination in the workplaces from radioactive dust owing to the decontamination, cutting, and demolition conducted during decommissioning. In particular, when alpha particles are scattered into the air owing to cutting or demolition, special attention is required because relatively high internal exposures can occur to decommissioning workers relative to those of gamma nuclides in spite of the same radioactivity concentration; this is owing to the high radiation weighting factor for alpha particles.
A previous decommissioning experience with a research reactor in Korea showed that the concentration F I G U R E 1 Five steps for designating decommissioning radiation-controlled areas (DRCAs) in decommissioning nuclear power plants (NPPs). of alpha particles in the air in decommissioning workplaces was 1.15-2.1 Bq m −3 . 32 In addition, unexpected internal exposures of alpha particles in the decommissioning workplaces at Connecticut Yankee NPPs caused the rescheduling of the radiation work plan and a corresponding increase in health and physical requirements. As a result, the suspension of all radiation work for 14 months at Connecticut Yankee NPPs was required by the US NRC. This meant that not only the decommissioning schedule was delayed, but also the cost of decommissioning was greatly increased. 4,8,31 According to the report on the decommissioning experience, the Connecticut Yankee NPPs established measures to avoid internal exposures to alpha particles again as follows. 31 First, the areas contaminated by alpha and beta-gamma radionuclides were monitored through smear techniques. Second, regular updates of the ratios of alpha radionuclides to beta and gamma radionuclides in the areas were conducted using the smear results. These ratios were used continuously to designate "airborne contamination areas" as well as to set air monitoring alarms. Third, an additional check for airborne contamination in high-alpha-contamination areas was conducted using a special "alpha cam," a continuous air monitoring equipment. In summary, one of the radiological hazards that must be carefully considered when designing DRCAs is the inhalation of radioactive dust in the air, especially alpha particles.

| CONCLUSION
This study investigated RCAs in 24 NPPs (including PWRs and PHWRs) in Korea currently in operation, aiming to propose a methodology to designate DRCAs for decommissioning NPPs. All of the RCAs in the PWRs are classified into five to eight zones, depending on the external radiation dose rates. The RCA zones in the Hanul NPPs are classified into four colors: green, yellow, orange, and red. By contrast, PHWRs have different criteria for RCA zones, including "R," "C," "B," "A," and "A + B," depending on both the external radiation dose rates and DAC levels owing to internal exposures to tritium. Currently, the DRCAs in Kori Unit 1, which was permanently shut down in 2017 and is expected to be the first decommissioned commercial reactor in Korea, have not yet been approved by the Korean nuclear regulatory body. According to the public hearing material of the FDP for Kori Unit 1, the DRCAs are classified into five zones, that is, very similar to the RCA zones in Kori Unit 1 during operation. Both the DRCA zones in decommissioning NPPs and RCA zones in operating NPPs are classified based only on the radiation dose rates.
However, the radiological conditions in the decommissioning field change constantly depending on the work, such as cutting, demolition, and decontamination; therefore, suitable radiation protection may not be provided for decommissioning workers if the DRCA zones are set to be the same as the RCA zones in operating NPPs.
In general, most radiation works in operating Korean NPPs focus on the maintenance of systems and components, not demolition; thus, controlling external exposures is important in radiation protection. Contrary to operating NPPs, most radiation works in decommissioning NPPs focus on the cutting, demolition, and decontamination of SSCs, not maintenance; thus, internal exposures and skin contamination can also be potential contributors to occupational exposures. These characteristics of radiation works indicate that the design criteria for DRCAs should be selected differently from those for operating NPPs to achieve the ALARA goals dedicated to decommissioning workers. This study proposes that DRCAs should include three types of areas: external exposure area, airborne contamination area, and surface contamination area, considering the radiological characterization of the decommissioning fields. To maintain ALARA external and internal exposures, this study also proposes five steps for designating DRCAs: collection of design data, review of the design characteristics and radioactive contamination factors, investigation of the NPP operation records, direct measurement or sampling and analysis, and designation of DRCAs. Because external radiation exposures, inhalation of radioactive dust in the air, and skin contamination can occur simultaneously during cutting, demolition, or decontamination, certain workplaces can be designated as having two or more DRCAs. Radiological characterization may need more time to obtain additional radiological information in the field if the methodology proposed in the study is implemented to designate DRCAs. It also increases decommissioning costs accordingly. However, the DRCAs enable providing appropriate radiological protection techniques for workers. Finally, this can save overall time and costs in decommissioning due to decreased incidents of external and internal exposure. The methodology for designating DRCAs proposed in this study is expected to contribute to achieving the ALARA goals in decommissioning NPPs.