1. Introduction

Kori Unit 1, Korea’s first Nuclear Power Plant (NPP), was permanently shut down in June 2017. This is the first commercial NPP to be shut down after 30 years of operation and 10 years of extended operation. In addition, for other NPPs whose design life will be expired, if there is no extended operation, there will be an additional 12 more NPPs to be decommissioned by 2030. Major nuclear power nations such as the U.S., United Kingdom, and Germany have various nuclear decommissioning experience and have built a technology base. At the same time, they are continuously upgrading the technology to strengthen the safety, efficiency, and environmental friendliness of the technology.

Starting with Kori Unit 1, Korea will become a country that will start decommissioning in earnest. In order to decommission the NPP, it is necessary to prepare a draft of Decommissioning Plan (DP). The DP includes safety assessment, environmental impact assessment, radiation protection, fire protection, decontamination activities, and radioactive waste management. The environmental impact assessment, which will evaluate the impact of decommissioning on the environment and the exposures of nearby residents, will be a very important part to carry out decommissioning safely. However, in Korea, there are decommissioning experiences for small-scale low-radiation facilities through research reactor unit 1 and 2, but the experience for decommissioning large-scale radioactive facilities such as NPPs is still insufficient.

Radiological environmental impact assessment aims to confirm that off-site radiological dose from the radioactive material released from the facility does not exceed the regulatory criteria in order to promote the health and safety of residents around the nuclear power plant. The Nuclear Safety and Security Commission (NSSC) Notice No. 2015-8 requires the evaluation and description of environmental impact assessment in decommissioning. However, it is a guideline that an environmental impact assessment should be carried out.

Therefore, the purpose of this study is to review the overseas NPP decommissioning experience focusing on the radiological environmental impact assessment and to draw up a draft of radiological environmental impact assessment that reflects domestic situation.

2. Literature Review: IAEA and U.S.

In the United States (U.S.), the GEIS (General Environmental Impact Statement on Decommissioning of Nuclear Facilities, NUREG-0586) provides the guideline on environmental impact assessment in decommissioning nuclear power plants. The GEIS describes an analysis of environmental impacts from decommissioning activities that can be treated generically so that decommissioning activities for commercial nuclear power reactors conducted at specific sites will be bounded, to the extent practicable, by this and appropriate previously issued environmental impact statements. In this study, we examined the documents related to the environmental impact assessment in decommissioning of nuclear power plants in the IAEA and the U.S., and reviewed the assessment items.

2.1 IAEA

The International Atomic Energy Agency (IAEA) provides a measure of safety standards for member states the safety of all countries using nuclear energy. The WS-R-5 “Decommissioning of Facilities Using Radioactive Material” published by the IAEA [1], establishes safety requirements related to the decommissioning of nuclear facilities. This document contains decommissioning procedures, plans and other requirements. The IAEA defines operators which establish decommissioning strategies must make a plan for decommissioning in accordance with waste management. The Decommissioning Plan (DP) should be established during the design, operation, and shut down phases, and the operator must update the DP periodically at least every five years, especially during the operational phase. The IAEA Safety Reports Series No.45,”Standard Format and Safety Related Decommissioning Documents” defines guidelines for the creation of a minimum DP to ensure protection of the public, workers and environment. Most countries who have nuclear power plant are based on these guidelines when establishing guidelines for their DP. Table 1 shows the contents for the IAEA DP. The environmental assessment are listed in contents 10.

2.2 United States (U.S.)

The U.S. has the largest number of nuclear decommissioning experiences in the world. Until now, the U.S. has decommissioned 15 nuclear power plants and has various decommissioning cases. The U.S. NPPs decommissioning process is as follows. The regulations of the United States are related to the Atomic Energy Act and the Environmental Protection Act, Federal Regulations 10CFR, Nuclear Regulatory Commission (NRC) Regulatory Guides and NRC's reports (NUREG etc.). Decommissioning related regulatory procedures, submission documents, and end-oflicense criteria are specified in the U.S. federal regulations. The document review and environmental survey guideline follow in accordance with the NRC regulatory guide. In 1997, the U.S. enforced its regulatory system and License Termination Rule (LTR) procedures for decommissioning. The relevant regulations are specified in Subpart E of Federal Regulations 10CFR20 and in Federal Regulations 10CFR50.82. The U.S. regulatory process related to nuclear decommissioning is shown in Table 2 and process of decommissioning phase is shown in Fig. 1.

2.2.1 GEIS (General Environmental Impact Statement on Decommissioning of Nuclear Facilities, NUREG-0586)

The U.S. National Environmental Policy Act (NEPA) requires the NRC to assess the potential impact on the environment before issuing permits or operation permit. Accordingly, the NRC requires the applicant to submit an Environmental Report to license the facility. Procedures and requirements for environmental impact assessment are set out in 10CFR Part 51 (Environmental Protection Regulations for Domestic Licensing and Related Regulatory Functions). Also, the U.S. conducts an assessment of radiological environmental impacts based on the description in the General Environmental Impact Statement (GEIS) when decommissioning. The GEIS is to provide the results of environmental assessment that can be treated generically so that decommissioning activities for commercial nuclear power reactors conducted at specific sites will be bounded, to the extent practicable, by this and appropriate previously issued environmental impact statements [3].

The U.S. decommissioning documents based on GEIS are PSDAR and LTP. These documents contain information on radiological environmental impact assessment of nuclear decommissioning. The evaluation items of GEIS are shown in Table 3.

Notably, in the U.S., permission also to operate a nuclear facility is maintained at the decommissioning stage. And there is no PSDAR review and approval procedure for decommissioning (The NRC does not approve the PSDAR). The U.S. has experienced the decommissioning of many nuclear power plants. Based on this, they have only a procedure for receiving PSDAR similar to the decommissioning plan and explaining it to the residents. Instead, at the end of the license, which is the completion phase of the decommissioning process, they have a system that reviews and approves the LTP and Final Status Survey Report (FSSR) to terminate the license upon completion of decommissioning.

2.2.2 PSDAR (Post-Shutdown Decommissioning Activities Report)

The licensee must submit a permanent shut down certification to the NRC within 30 days since announcing that reactor will be permanently shut down. They also must submit the PSDAR to the NRC within 2 years from the date of the permanent shut down decision. The PSDAR is not required to be approved by the NRC, but it may require supplementation if the content of the PSDAR violates the law. The NRC shall notify the PSDAR to Federal Register and hold a public hearing. Before preparing the PSDAR, the licensee should assess the site-specific potential environmental impact of decommissioning activities. Potential environmental impacts from decommissioning activities should be compared to similar impacts from the Final Environmental Statement (FES), GEIS for decommissioning, and the site-specific environmental impact assessment. The PSDAR must include:

The licensee cannot perform any major decommissioning activities until 90 days after the NRC has received the PSDAR. The PSDAR is not required to be approved by the NRC, but it may be required the regulator as a supplement if there is something that violates the laws and regulations of the PSDAR.

2.2.3 LTP (License Termination Plan) [4]

The licensee shall submit the License Termination Plan (LTP) to the NRC for approval by the NRC prior to at 2 years the planned license termination date in the PSDAR. Finally, the licensee submits the FSSR to the NRC after the decommissioning is completed. The LTP contains supplemental environmental reports that describe new or important environmental changes related to the termination activity proposed by the license. The NRC concludes its confirmatory surveys after review and approval, and terminates the license. The LTP must include:

The NRC releases the LTP to the public and holds a public hearing. And the NRC authorizes LTP if it proves that it is not harmful to the health and safety of the general public. When the licensee conducts as planned and the NRC confirmed the following, the license is terminated.

2.2.4 Comparison of Environmental Impact Assessment among the U.S. NPPs

Table 4 shows the comparison of environmental impact assessment items in the PSDAR [5, 6, 7]. In particular, Kewaunee is the same type of reactor as Kori Unit 1, so it can be a reference.

In the U.S., the environmental impact assessment is compared with the GEIS when decommissioning a nuclear power plant, and decides whether an environmental impact assessment that requires site characteristics should be made. As a result of the review of the U.S. nuclear decommissioning environmental impact assessment, there was no environmental impact assessment, and all nuclear power plants were bounded by GEIS.

3. Literature Review: Korea

Considering overseas cases through the literature review and domestic situation, it is necessary to review the preparation of Radiological Environmental Report (RER) in NPP decommissioning. First of all, it need to review the guidelines and assessment items for radiological environmental impact assessment through domestic laws and regulations, and to confirm at which stage is carried out the environmental impact assessment in NPP decommissioning.

3.1 Domestic Regulation

The framework for domestic nuclear safety regulations is shown in Fig. 2. The Nuclear Safety Act is the highest law and this is a law that stipulates matters concerning the prevention of disasters caused by nuclear research, development, production, use and radiation, and public safety. Next, there is the Enforcement Decree of the Nuclear Safety Act that specifies requirements for the management and operation. And then The Enforcement Regulations of the Nuclear Safety Act prescribe the matters delegated by the Enforcement Decree of the Nuclear Safety Act and the Nuclear Safety Act and the matters necessary for its enforcement.

The Nuclear Safety Act and Enforcement Decree of the Nuclear Safety Act related to radiological environmental impact assessment is shown in Table 5.

According to the current Nuclear Safety Act, the applicant for the construction and operation permission of the nuclear reactor for power generation should carry out the radiological environmental impact assessment. In accordance with the provisions of the Nuclear Safety and Security Commission (NSSC) Notice No. 2015-8 “Regulation for the Preparation of Nuclear Decommissioning Plans” [9], it is stipulated that a decommissioning safety assessment and radiological environmental impact assessment should take place together with the plan.

3.2 Radiological Environmental Impact Assessment

The contents of the preparation of radiological environmental impact assessment report are specified in the NSSC Notice No. 2016-4 Article 5 “Regulations for the Preparation of Radiological Environmental Impact Assessment Report for Nuclear Facilities at the Nuclear Energy Safety Commission” (Table 6). Applicants for nuclear power construction permit must submit a RER to the NSSC after conducting radiological environmental impact assessment under the Nuclear Safety Act. When preparing the RER, draft of a RER should be prepared, and public hearings should be held to collect opinions of residents and considers them in the contents of the RER (Nuclear Safety Act Article 103-1). The NSSC Notice No. 2016-16 specifies the requirements to be satisfied by the radiological impacts of radioactive effluents discharged to the environment due to the operation of nuclear power plants.

The assessment items of RER can be classified into normal and accident. Radiological dose at Exclusion Area Boundary (EAB) by radioactive effluents released into the environment during normal operation of the reactor facility shall be maintained below the levels specified in Table 7 (NSSC Notice No. 2016-16 “Standards on Radiation Protection”) [10]. Also, the dose of radioactive material released to the environment in the event of a nuclear reactor accident shall not exceed the value specified in the NSSC Notice No. 2014-10 “Technical Standards for Location of Reactor Facilities”.

3.3 Nuclear Power Plant Decommissioning Procedure

There are three major strategies to decommission a nuclear power plant: DECON, SAFSTOR, and ENTOMB [3]. DECON is defined as the immediate dismantling soon after the nuclear facility closes with equipment, structures, and parts of the facility containing radioactive contaminants being removed or decommissioned. SAFSTOR is known as “deferred dismantling” where the facility is maintained and monitored, which allows for radioactive decay prior to the plant being dismantled and the property decontaminated. ENTOMB is defined as the permanent encasement of radioactive contaminants on the site in structurally sound materials such as concrete. The facility is maintained and monitored until the radioactivity levels reach to a set point.

Kori Unit 1 will be decommissioned by DECON. The DECON type can reduce decommissioning costs compared to SAFSTOR and can be reused the site quickly. It also has a great advantage in that it can quickly acquire decommissioning techniques. The Kori Unit 1 decommissioning roadmap is shown in Fig. 3.

The decommissioning procedure is divided into 4 stages:

The Final Decommissioning Plan (FDP) must be submitted to the NSSC for approval of decommissioning within 5 years after the permanent shut down of the NPP. In the first half of 2019, Korea Hydro & Nuclear Power (KHNP), the licensee, plans to prepare a decommissioning plan that includes decommissioning plans, methods, safety assessment, environmental impact assessment, radioactive waste management, and collects opinions from residents and after that they must submit to the NSSC. The NSSC will evaluate the appropriateness of the decommissioning plan through the IAEA's peer review until June 2022 and decide whether to approve it. The environmental impact assessment of the FDP describes the environmental impacts caused by decommissioning of nuclear power plants in a quantitative manner. In order to confirm the extent of this, it shall establish and describe an environmental monitoring plan before and during decommissioning of nuclear facilities.

4. Review Results

4.1 Review of the Need to Prepare Separate Radiological Environmental Impact Assessment in Decommissioning

In the overseas case (United States, Canada, United Kingdom, and France), the environmental impact assessment and the radiological environmental impact assessment are operating in an integrated. In other words, the environmental impact assessment includes a radiological environmental impact assessment. In Table 8, the decommissioning plan of the IAEA is compared with the domestic decommissioning plan.

Environmental impact assessment is included in Chapter 10 of the IAEA's Decommissioning Plan (DP). The environmental assessment of the IAEA is normally a separate document that is referenced and summarized in the DP. The conclusions of the assessment are provided in the DP. Since the environmental assessment is normally a separate document, some information is repeated, which would not be required if it is directly incorporated in the DP [2]. The domestic DP also includes the Environmental Impact Assessment in Chapter 10. The comparison of the IAEA and domestic DP shows that both documents are very similar.

In this study, it is considered appropriate to compose the environmental impact assessment in the DP without applying separate radiological environmental impact assessment.Table 9

4.2 Consideration for Decommissioning Radiological Environmental Impact Assessment

The environmental impact assessment for decommissioning Kori unit 1 should be followed by the NSSC Notice No. 2014-12 “Regulation on the Radiation Environment Survey and Radiological Environmental Impact Assessment around Nuclear Facilities” [11], and can be prepared by referring to the environmental impact assessment report for operation permit of nuclear facilities. The contents can be represented for three steps as shown in Table 10, and Table 11 is the result of the draft of domestic decommissioning radiological environmental impact assessment.

4.3 Consideration of Exposure Pathways

The exposure pathways of residents due to decommissioning of nuclear facilities are divided into gaseous effluents, liquid effluents and direct exposure from the NPP. Gaseous effluents are floated in the air or deposited on crops, surfaces, and water, depending on their physical and chemical characteristics. The main gaseous exposure pathways are contaminated air, external exposure from the soil, ingestion of contaminated agricultural and animal products, and internal exposure by inhalation of contaminated air. In addition, the process of ingesting contaminated groundwater that is permeated by radioactive material may be an important exposure pathway. Exposure pathways for liquid effluents include external exposures from contaminated seawater and beaches, internal exposures due to ingestion of contaminated aquatic products. Computer program codes such as ENDOS, TED II, Visual Shield and MCNP can be used for dose assessment based on the operation of nuclear facilities. The impact of decommissioning on residents could also apply the same exposure pathways. However, it is necessary to evaluate the source term that is generated from the decommissioning activities. Fig. 4 and 5 show the exposure pathway through effluents.

4.3.1 Gaseous Pathways

Exposure by gas phase emissions is divided into individual dose and collective dose assessments. In each assessment, there are four exposure pathways such as external exposure due to polluted air, external exposure due to contaminated ground surface, internal exposure due to inhalation, and food intake should be evaluated.

4.3.2 Liquid Pathways

Exposure by liquid phase emissions is divided into individual dose and collective dose assessments. In each assessment, external exposure due to maritime activities (beach activities, swimming or aquatic activities), and internal exposure due to ingestion of aquatic products should be evaluated.

5. Conclusion

Starting with Kori Unit 1, the decommissioning of domestic nuclear power plants is expected to start in earnest. In Korea, Nuclear Safety Act article 103 stipulates that a draft radiological environmental impact assessment report or a decommissioning plan should be made when you making a decommissioning plan. However, domestic regulations only provide general items of DP and radiological environmental impact assessment. Because of this, there is a high possibility that the decommissioning operator will have difficulty in preparing the decommissioning radiological environmental impact assessment. Therefore, this study compares and analyzes of the U.S. related guidelines that have many experiences of decommissioning nuclear power plants, and developed a decommissioning radiological environmental impact assessment (draft) suitable for Korea. First of all, the documents related to the radiological environmental impact assessment during the decommissioning of the U.S. and the evaluation items were reviewed. In addition, the domestic nuclear laws, regulations and existing radiological environmental impact assessments have been reviewed to describe issues to be considered gaseous and liquid pathway in decommissioning. Considering all these factors, we have developed radiological environmental impact assessment (draft) for decommissioning. In this study, it is considered that radiological environmental impact assessment (draft) developed could serve as a stepping stone for the decommissioning of domestic nuclear power plants.