Interlaboratory comparison for ensuring validity of radiochemical analysis results of NPP decommissioning radioactive wastes.

Development of metal radioactive liquid reference material for proficiency test

Impurity sensitivity analysis for activated structure materials of OPR-1000

Magnesium potassium phosphate cements to immobilize radioactive concrete wastes generated by decommissioning of nuclear power plants

Models of the fuel and energy system and the unified electric power system are used to predict the economic consequences of the premature decommissioning of nuclear power plants in Russia. The components of the expenditures considered were capital investments for converting heat and power plants, additional capital investments for development of a fuel base and transportation of fuel and electricity, expenditures for improving the safety of nuclear power plants, and additional expenditures on fossil fuel. After model calculations were completed, results were compared for accelerated decommissioning and base variants and the difference of the indicators and additional expenditures were found. Conclusions drawn from the modeling results were: (1) premature decommissioning of BBER-440 and RBMK-1000 reactors will require capital investments and fuel expenditures which exceed estimates made by the European and World Banks; and (2) program implementation may be economically unfeasible; it may be more realistic to decommission separate nuclear power plants with the least reliable reactors and upgrade safety of the remaining plants. 9 refs., 5 tabs.

Before the decommissioning of a nuclear power plant, the core infrastructure and decommissioning equipment must be developed to complete the disassembly technology development. However, research and analysis of the detailed process and full application of technology for domestic decommissioning of nuclear power plants remain lacking. Therefore, a domestic nuclear power company needs to generate an initial market that can participate in the core competency of nuclear decommissioning and create a nuclear decommissioning ecosystem-based deployment. Further, training needs must be provided that are designed for professional staff, and measures need to be put in place, such as building partnerships that include overseas-based consolidation, establishing a nuclear-power plants decommissioning system, and decommissioning by relevant institutions, to prevent fire, ensure public safety, and give confidence to people. The author has written through a field trip on decommissioning of nuclear power plants in Spain to protect the safety of nuclear power plants from radiation prior to the decommissioning of Kori 1 nuclear power plants. Keywords: Decommissioning, Fire Protection, Radiation, Life Safety

The major factors influencing the choice of a national concept for the decommissioning of nuclear power plants are examined. The operating lifetimes of power generating units with nuclear reactors of various types (VVER-1000, VVER-440, RBMK-1000, EGP-6, and BN-600) are analyzed. The basic approaches to decommissioning Russian nuclear power plants and the treatment of radioactive waste and spent nuclear fuel are discussed. Major aspects of the ecological and radiation safety of personnel, surrounding populations, and the environment during decommissioning of nuclear installations are identified.

We are having 23 units of nuclear power plants in operation and 5 units of nuclear power plants under construction in Korea as of September 2012. However, we don’t have any experience on shutdown permanently and decommissioning of nuclear power plants. There are only two research reactors being decommissioned since 1997. It is realized that improvement of the regulatory framework for decommissioning of nuclear facilities has been emphasized constantly from the point of view of IAEA’s safety standards. It is also known that IAEA will prepare the safety requirement on decommissioning of facilities; its title is the Safe Decommissioning of Facilities, General Safety Requirement Part 6. According to the result of IAEA’s Integrated Regulatory Review Service (IRRS) mission to Korea in 2011, it was recommended that the regulatory framework should require decommissioning plans for nuclear installations to be constructed and operated and these plans should be updated periodically. In addition, after the Fukushima nuclear disaster in Japan in March of 2011, preparedness for early decommissioning caused by an unexpected severe accident became important issues and concerns. In this respect, it is acknowledged that the regulatory framework for decommissioning of nuclear facilities in Korea need to be improved. First of all, we focus on identifying the current status and relevant issues of regulatory framework for decommissioning of nuclear power plants compared to the IAEA’s safety standards in order to achieve our goal. And then the plan is established for improvement of regulatory framework for decommissioning of nuclear power plants in Korea. It is expected that if the things will go forward as planned, the revised regulatory framework for decommissioning could enhance the safety regime on the decommissioning of nuclear power plants in Korea in light of international standards.

The decommissioning of Nuclear power plant involves many activities different from the normal operation stage of Nuclear power plant. In the process of decommissioning, there are many new safety problems, which usually require new safety evaluation. The safety management of decommissioning runs through the whole decommissioning stage until the decommissioning of the plant site is completed. The management level depends on the risk level of each stage of decommissioning, especially the decommissioning process of high radioactivity in nuclear power plant, so it is necessary to pay attention to the risk of different stages of decommissioning and improve the decommissioning safety management. At present, probabilistic safety assessment method has become an effective tool to support and supplement deterministic safety assessment, and is used in regulatory activities. The safety risk analysis of nuclear power plant in the decommissioning stage in China is in the initial stage, with little experience. Therefore, it is necessary to study the corresponding technical methods and risk management applications. This paper study on the probabilistic safety assessment in the decommissioning of nuclear power plant, including its scope of application, risk-informed assessment method and safety management application. The probabilistic safety assessment of decommissioning of nuclear power plant is an effective means to evaluate the potential risks related to decommissioning activities and their possible consequences. This method can be used for safety review and safety management in the decommissioning stage of nuclear power plant.

Concrete waste accounts for approximately 70~80% of the total waste generated during the decommissioning of nuclear power plants (NPPs). Based upon the concentration of each radionuclide, the concrete waste from the decommissioning can be used in the determination of the clearance threshold used to classify waste as radioactive. To reduce the cost of radioactive concrete waste disposal, it is important to perform decontamination before self-disposal or limited recycling. Therefore, it is necessary to estimate the internal radioactivity distribution of radioactive concrete waste to ensure effective decontamination. In this study, the performance metrics of various Compton reconstruction algorithms were compared in order to identify the best strategy to estimate the internal radioactivity distribution in concrete waste during the decommissioning of NPPs. Four reconstruction algorithms, namely, simple back-projection, filtered back-projection, maximum likelihood expectation maximization (MLEM), and energy-deconvolution MLEM (E-MLEM) were used as Compton reconstruction algorithms. Subsequently, the results obtained by using these various reconstruction algorithms were compared with one another and evaluated, using quantitative evaluation methods. The MLEM and E-MLEM reconstruction algorithms exhibited the best performance in maintaining a high image resolution and signal-to-noise ratio (SNR), respectively. The results of this study demonstrate the feasibility of using Compton images in the estimation of the internal radioactive distribution of concrete during the decommissioning of NPPs.

Development of concrete reference material for quality assurance/quality control of gamma radioactivity measurement for nuclear power plant decommissioning waste

The decommissioning of a Nuclear Power Plant leads to the generation of a high volume of metallic waste, of which a large quantity can be recycled, after separating it from radioactive metal. The methodology that allows to separate radioactive metal from non-radioactive metal is an essential part of Decommissioning, and it requires complex equipment, procedures and controls, both inside Enresa and external (Regulatory Body). After undergoing these controls, most of the metallic material is sent to recycling facilities, where it is mixed with a much larger proportion of metal coming from conventional scrap yards, both here in Spain and abroad. In recent years, there have been a few incidents in melting plants, due to the presence of undetected radioactive material among certain batches of scrap metal. In order to tackle the public concern associated with potential risk, a series of measures have been designed to prevent these incidents or minimise their effects, should they occur. The following presentation will first describe the Spanish protocol established by different national institutions to prevent the presence of radioactive waste among the raw material for recycling, should this occur detect and control it, and secondly the methodology that guarantees that Enresa does not erroneously send radioactive material arising from the decommissioning of nuclear power plants to any smelting facility.

The most used materials in civil engineering is concrete and steel. Their unique properties made them candidate materials for components of engineered barrier system for high- and intermediate-level radioactive waste (ILW and HLW) deposition including material from decommissioning of nuclear power plants. Activated materials include mainly stainless steel of nuclear reactor structural elements or carbon steel and shielding concrete of the reactor shaft construction materials. This study is focused on standard and alternative cementitious matrices for deposition of such activated materials mainly in terms of its long-term sustainability in the presence of microorganisms.Four different matrices including cement paste based on Ordinary Portland Cement (OPC), cement paste enriched with bentonite or nano-iron, and finally geopolymer, are exposed to conditions that simulate real repository (anaerobic groundwater). One of the objectives is to describe the growth of microorganisms on/in these matrices as a potential risk for the long-term sustainability of such disposal. After a defined time, changes in microbial activity of the matrices, water leachate and interface between matrix and metal coupons simulating activated waste are monitored using cultivation-dependent and independent approach. Here we will demonstrate results of first samplings after 6, 12 and 24 months of incubation in anaerobic conditions. The results will shed more light on evolution of microbial activity in such extreme conditions in time and bring more information on processing and detection of microbial activity in alkaline materials.

The complete life of a nuclear power plant consists of three stages: construction, operation and decommissioning. In the last stage of the operation life of nuclear power plants, they have to face the problem of decommissioning. The safe decommissioning of nuclear power plants is the guarantee for the sustainable development of nuclear power. After the termination of the operation of nuclear power plants, in order to ensure the safety of the public and the environment, the plant site should be purified, demolished and cleaned to reach the restricted utilization level or unrestricted opening. This paper studies the operation and decommissioning status of nuclear power plants from both international and domestic levels, and analyzes the real time cycle and development trend of decommissioning projects. The research shows that in the international nuclear power plant decommissioning market, the nuclear power pioneer countries have successively established national laboratories or research centers to carry out research on the decommissioning technology of nuclear power plants, developed a large number of advanced technologies and tooling equipment, and formed their own technical characteristics and technical advantages; the nuclear power plant decommissioning is increasingly researched in China, but the decommissioning practice has not been started yet in this country. The industry and relevant parties should carry out systematic construction for the decommissioning of nuclear power plants from the aspects of capital sources, regulations, standards, technical reserves, organizational structure and talent reserves.

In recent years, concern about the decommissioning of nuclear power plants has been growing according to the nuclear power plants aging. Although site reuse is one of the most important issues in doing decommissioning of nuclear power plants in view of the internal affairs, there is currently no specific standard of the site release criteria for site reuse in the Republic of Korea. In this study, we analyzed the international safety standards for the site release(IAEA`s Safety Guide No. WS-G-5.1) and the present domestic condition. Also, we studied the site release criteria and real life examples about advanced countries such as United states and Europe, which already have experience of decommissioning or site release. As a results of the study, we suggested proper standards and future consideration to establish site release criteria. This will be used for preliminary data for establishing the domestic site release criteria after the decommissioning of nuclear power plants.

During the decommissioning of nuclear power plants, a significant amount of cement based composites should be disposed as radioactive waste. The use of material with low-activation constituents could effectively reduce radioactivity of concrete. The subject of the paper is the content of trace elements with large activation cross section in concrete constituents due to their ability to be activated in radiation shielding structures. Various Portland cement specimens were subjected to elemental analysis by neutron activation analysis and prompt gamma activation analysis to assess the dominant long-lived residual radioisotopes. Concentrations of the radionuclides, such as Europium-152, Cobalt-60 and Caesium-134 were assessed. Their half-life time is 13.5, 5.27, and 2.07 years, respectively. On the basis of the obtained results, recommendations for cement selection for low-activation concrete are proposed in order to economize decommissioning cost by reducing a radioactive concrete waste.