Experimental investigation on effective aerosol scavenging using different spray configurations with pre-injection of water mist for Fukushima Daiichi decommissioning

During the decommissioning of the Fukushima Daiichi nuclear power plant,it is important to consider the retrieval of resolidified debris both in air and underwater configurations.For the subsequent retrieval of debris from the reactor building,the resolidified debris must be cut into smaller pieces using various cutting methods.During the cutting process,aerosol particles are expected to be generated at the submicron scale.It has been noted that such aerosols sizing within the Greenfield gap(0.1-1μm)are difficult to remove effectively using traditional spraying methods.Therefore,to improve the aerosol removal efficiency of the spray system,a new aerosol agglomeration method was recently proposed,which involves injecting water mist to enlarge the sizes of the aerosol particles before removing them using water sprays.In this study,a series of experiments were performed to clarify the proper spray configurations for effective aerosol scavenging and to improve the performance of the water mist.The experimental results showed that the spray flow rate and droplet characteristics are important factors for the aerosol-scavenging efficiency and performance of the water mist.The results obtained from this study will be helpful for the optimization of the spray system design for effective aerosol scavenging during the decommissioning of the Fukushima Daiichi plant.

Investigation on Cutting Stability of Jacket in Decommissioning Process

Jacket cutting operation is one of the most complicated and highest risk operations in the process of decommissioning offshore piled platform, the security and stability of which must be assured. In this paper, the current research on offshore structure removal and jacket cutting is introduced, on the basis of which the types of load along with the load calculation method are determined. The main influences on the stability of a jacket in cutting are analyzed. The experiment test plan is drawn by using orthogonal testing method, and the formula of critical load during the cutting procedure is deduced by differential evolution algorithm. To verify the method and results of this paper, an offshore piled platform to be decommissioned in the South China Sea is taken for an example, and the detailed schedule for jacket cutting is made with the three-dimensional finite element model of the jacket established. The natural frequency, stress, strain and stability of the jacket during cutting process are calculated, which indicates that the results of finite element analysis agree well with that of the deduced formula. The result provides the scientific reference for guaranteeing the safety of jacket in cutting operation.

Cutting Techniques for Facilities Dismantling in Decommissioning Projects

Fuel cycle related activities were accomplished in IPEN-CNEN/SP in laboratory and pilot plant scale and most facilities were built in the 70-80 years. Nevertheless, radical changes of the Brazilian nuclear policy in the beginning of 90＇s determined the interruption of several fuel cycle activities and facilities shutdown. Some laboratory and pilot plant decommissioning activities have been performed in IPEN in the last years. During the operational activities in the decommissioning of old nuclear fuel cycle facilities, the personnel involved in the task had to face several problems. In old facilities, the need of large components dismantling and material removal use to present some difficulties, such as lack of available and near electricity supply. Besides this, the spread out of the superficial contamination in the form of dust or aerosols and the exposure of workers should be as much as possible avoided. Then, the selection and availability of suitable tools for the task, mainly those employed for cutting and segmentation of different materials is of significant importance. Slight hand tools, mainly those powered by rechargeable batteries, facilitate the work, especially in areas where the access is difficult. Based on the experience in the dismantling of some old nuclear facilities of IPEN-CNEN/SP, some tools that would have facilitated the operations were identified and their availability could have improved the quality and efficiency of different individual tasks. In this paper, different cutting problems and techniques, as well as some available commercial hand tools, are presented as suggestion for future activities.

Estimation of exposure dose for decontamination workers from contaminated soil at a nuclear decommissioning site in Korea

Assessment of the exposure dose for workers is crucial to protecting workers from the radiological risk.This preliminary study estimates the potential radiological exposure for a soil remediation worker at a nuclear decommissioning site contaminated with Cs-137 in Korea,and then calculates the maximum workable soil concentration to comply with the occupational dose constraint of 20 mSv per year.The Korean characteristic data,detailed exposure scenarios for workers by the type of work,and relevant exposure pathways were used in the dose estimation.As a result,the most severe exposure-induced work type was identified as the excavator operation with an annual individual dose of 5.92×10^-5 mSv for a unit concentration of soil,from which the derived maximum workable soil concentration was 3.38×105 Bq/kg.Furthermore,dose contribution by each exposure pathway was found to be decreased in the following order:external radiation exposure,soil ingestion,dust inhalation,and skin contamination.The results of this study are expected to be used effectively to optimize radiation protection for workers and establish appropriate work procedures for future site remediation.

Decommissioning of Uranium Pilot Plants at IPEN-CNEN/SP： Facilities Dismantling, Decontamination and Reuse as New Laboratories for Strategic Programs

From beginning of 90＇s, the Brazilian nuclear policy has been changed radically. This determined the interruption of most R＆D fuel cycle activities and the facilities shutdown at Nuclear and Energetic Research Institute （IPEN）. The existence of those facilities also implicated in the need of constant surveillance, representing additional obligations, costs and problems. The reasons to promote the dismantling of the IPEN＇s Nuclear Fuel Cycle Pilot Plants elapsed mainly from the need of physical space for new activities, since the R＆D in the nuclear fuel cycle area were interrupted. In the last decade, IPEN has changed its ＂nuclear profile＂ to a ＂comprehensive and multidisciplinary profile＂. With the end of most nuclear fuel cycle activities, the former facilities were distributed in four different centers. Each center has adopted a different strategy and priority to face the D＆D problem. The available resources depend on the specific program in each area＇s development （resources available from other sources, not only from Brazilian National Nuclear Energy Commission （CNEN）. One of those new activities is the IPEN＇s Environmental Program. This paper describes the procedures, problems faced and results related to the reintegration of the former pilot plant areas as new laboratories of the Chemical and Environmental Technology Center-CQMA of the IPEN.

Decommissioning of Mature Oil Fields and Artisanal Fisheries： The Case of Todosos Santos Bay, Brazil

Consequences of decommissioning oil fields on artisanal fishing activities are still little known in the literature. This paper is intended to shed some light on a process of dismantling and sinking of oil and gas structures in shallow waters, with severe disturbing impacts on low income artisanal fishing activities. From a socio-economic perspective, the relationship of oil industry with local communities is described, with the main perceived problems pointed out in local fishermen leadership perspective. The notions of ＂damages＂ and ＂mitigation＂ used by the oil industry are discussed in connection to the expansion and dismantling of oil installations during the past 20 yrs. A comparative view of oil fields decommissioning in Europe and Brazil during the late 1990s suggests the need to review transparency and social commitment standards which have been far less prominent in this Brazilian case. The authors believe that the Brazilian oil industry has acquired a social and environmental debt towards the whole society, as far as it has been unable to establish a clear and effective process for decommissioning their oil installations within the artisanal fishing areas of the Todosos Santos Bay. Furthermore, the discussion of fair and specific compensations has been avoided, which otherwise would be instrumental to regain local economic conditions found among fishermen just few decades ago.

Prototype of an Echo-PIV Method for Use in Underwater Nuclear Decommissioning Inspections

The ongoing decommissioning of the Fukushima Daiichi (1F) nuclear power plant requires the inspection of the inside of containment vessels that have been submerged in water. These inspections must locate leaks and map the distribution of fuel debris in water with very low visibility. This paper reports the design and testing of an echo-PIV system that uses a single divergent signal wave and delay-and-sum processing to efficiently map the interior and fluid flow within a submerged vessel. The diverging wave and delay-and-sum processing improve upon the performance of conventional ultrasound PIV methods specifically to meet the demands of containment vessel inspections. The imaging method uses an ultrasonic linear sensor array that emits a diverging wave that covers a wide angle with a single transmission. The delay-and-sum algorithm combines echo signals recorded by each element of the sensor array. We optimized the design of an echo-PIV system in laboratory-scale tests, and then tested the prototype with a mockup of a containment vessel in a water tank. The small-scale prototype successfully located a mock leak and mapped the surface of a piece of mock debris. This prototype can be scaled up readily for inspections at the Fukushima Daiichi plant.

Systematic Approach to Training for Design of Nuclear Power Plant Decommissioning Training in South Korea

In 1979, unavailability of MFWS （Main Feedwater System） in TMI （Three Mile Island） Unit-2 happened in the United States. To make it worse, due to malfunction of Isolation Control Valves in AFWS （Auxiliary Feedwater System）, the supply of cooling water to SGs （Steam Generators） was delayed approximately 8 minutes compared to AOP （Abnormal Operating Procedure）. In the long run, on account of deferred heat sink provision to SGs, the reactor core was melted partially. It was the first critical accident in the US commercial NPP （Nuclear Power Plant） history. Hence, after TMI Accident, US NRC （Nuclear Regulatory Committee） suggested more than one hundred alternatives to improve safety and reliability of NPP. Among these countermeasures, one proposal was related to training area. It was SAT （Systematic Approach to Training） methodology. Therefore, the goal of SAT is the enhancement of NPP stability through training point of view. Since the appearance of SAT in the nuclear industry, it has acquired the unwavering position in the US NPP training field. Meanwhile, significance of NPP decommissioning has been soared up in South Korea since the announcement of Kori Unit-1 decommissioning decision. According to the proclaimed plan from Korean government, Kori Unit-1 is scheduled to be decommissioned from June, 2017. Under this circumstance, nurturing sufficient number of NPP decommissioning engineers is one of the most urgent issues in South Korean nuclear industry. Hence, to elevate efficiency and consistency of training quality, SAT methodology can be a reliable solution for the training of decommissioning engineers. For this reason, the present study aims to design SAT based NPP decommissioning engineer training in South Korea.

The Optimization of Decontamination Methods Selected for Contaminated Areas Used in Decommissioning of CANDU-6 NPP

The objective of this paper is to provide information for nuclear field specialists and decision makers on opportunities for minimizing radioactive wastes arising from the decontamination ＆ decommissioning of a CANDU-6 NPP. The paper proposes a method for selection of appropriate decontamination techniques which may be used at Cernavoda NPP decommissioning, equipped with CANDU heavy water reactors, based on the simulation with ProVision software. The paper has a singular focus on physical decontamination techniques and does not address other aspects of decommissioning. The physical decontamination techniques which are the best for certain areas of the CANDU-6 NPP from point of view of effectiveness and cost were determined. A unit cost for each decontamination technique was determined by relating the total cost to the average surface to be decontaminated. In conclusion, physical techniques will apply more efficiently to concrete surfaces. The chemical decontamination methods, in comparison with physical decontamination methods are. more suitable for non-porous surfaces respectively metal and are less recommended for concrete surfaces.

The Implementation of Radiological Characterization for Reactor Decommissioning

The radiological characterization is to determine the type, the distribution and the radioactivity of the radionuclide in the reactor by investigation of the information, instrumentation detection, sampling analyses and theoretical calculation. It is used for determination of the decommissioning implementation option and radiological protection measure of the workers. After completion of the decommissioning it is used for determination of the site release. The radiological characterization should go through whole decommissioning process, which includes： the collection and review of historical file, the performing calculation of radionuclide inventory in the reactor, in situ measurement, sampling analyses, the review and evaluation of the data obtained and the comparison of calculated result with measured date etc.. The special attention should be paid to the radiological characterization information from the key part of reactor in decommissioning end state. The sampling from the ＂hot spot＂ should not be lost; the number of the sampling should be reasonable based on reliable statistics. The radioactivity density for site release should comply with the guide, standard and regulation of International Atomic Energy Agency and China.

A review of multi-attributes decision-making models for offshore oil and gas facilities decommissioning

With the development of the offshore fossil energy industry,the designing life of many offshore oil and gas facilities will end.The decommissioning of these facilities has become an urgent task due to unpre-dictable costs,high risks,and environmental protection issues of public concern.Decision-making,as the core in the pre-decommissioning stage,plays a decisive role in the cost,risk,and impact of the entire de-commissioning.Therefore,the multi-attribute decision-making model has attracted much attention from industry and academia.An efficient,accurate,and simply using multi-attribute decision-making model can enable governments,energy companies,other marine users,and environmental protection organi-zations to reasonably fulfill their concerns.It is of great significance to all parties.This review mainly studies the multi-attribute decision-making models that have been used in the decommissioning of off-shore oil and gas facilities,and conducts a more detailed interpretation of them,including the relevant regulations,frameworks,methodology,preferences and advantages and disadvantages of different mod-els.In addition,a more comprehensive review of the cost assessment model,an important part of the decision-making model,is carried out,including the general framework and methodology of the cost as-sessment model,and the accuracy of the models is explored.And then the current evaluation method of accuracy of the cost assessment model raises the author’s personal doubts.At the end of the article,this paper names two core problems of the current decision-making model,that is,the lack of basic data and the incomplete MCDA(Multi-criteria Decision Analysis)method.This review can provide a comprehen-sive reference and feasible research directions for future scholars who aims to study the decommissioning of offshore oil and gas facilities especially in the North Sea in the UK and point out the direction for the industry to improve its current multi-attribute decision-making models.

Resource and waste quantification scenarios for wind turbine decommissioning in the United Kingdom

Wind power produces more electricity than any other form of renewable energy in the United Kingdom(UK)and plays a key role in decarbonisation of the grid.Although wind energy is seen as a sustainable alternative to fossil fuels,there are still several environmental impacts associated with all stages of the lifecycle of a wind farm.This study determined the material composition for wind turbines for various sizes and designs and the prevalence of such turbines over time,to accurately quantify waste generation following wind turbine decommissioning in the UK.The end of life stage is becoming increasingly important as a rapid rise in installation rates suggests an equally rapid rise in decommissioning rates can be expected as wind turbines reach the end of their 20-25-year operational lifetime.Waste data analytics were applied in this study for the UK in 5-year intervals,stemming from 2000 to 2039.Current practices for end of life waste management procedures have been analysed to create baseline scenarios.These scenarios have been used to explore potential waste management mitigation options for various materials and components such as reuse,remanufacture,recycling,and heat recovery from incineration.Six scenarios were then developed based on these waste management options,which have demonstrated the significant environmental benefits of such practices through quantification of waste reduction and greenhouse gas(GHG)emissions savings.For the 2015-2019 time period,over 35 kilotonnes of waste are expected to be generated annually.Overall waste is expected to increase over time to more than 1200 kilotonnes annually by 2039.Concrete is expected to account for the majority of waste associated with wind turbine decommissioning initially due to foundations for onshore turbines accounting for approximately 80%of their total weight.By 2035-2039,steel waste is expected to account for almost 50%of overall waste due to the emergence of offshore turbines,the foundations of which are predominantly made of steel.

Development of Measurement System for Flow and Shape Using Array Ultrasonic Sensors

In Fukushima Daiichi Nuclear Power Plant (FDNPP) accident, the fuel debris formed in the Reactor Pressure Vessel (RPV) and Primary Containment Vessel (PCV) at Unit 1 - 3. To accelerate and decide further decommissioning steps of the FDNPP, it is crucial to obtain realistic information of the debris and localize contaminated water leakage from PCV. Due to high radiation and dark environment inside the PCV, investigating instruments and techniques should necessarily to meet specification of radiation resistance, waterproofness, dust resistance and so on. This study focuses on development of ultrasonic measurement system using a couple of sectorial array sensors to localize contaminated water leakage and visualize shape of object that repre- senting fuel debris, simultaneously. In this study, Total Focusing Method (TFM) and Ultrasonic Velocity Profiler (UVP) methods are considered to visualize object shape and flow pattern around it, respectively. To demonstrate applicability and reliability of developed measurement system with sectorial array sensors, a mock-up experiment result of simulated water leakage and fuel debris shape were discussed in this paper.

Nondestructive high-sensitivity measurement method for activation estimation in accelerator room concrete

This study established a method for easily and quickly estimating the specific activity produced in the concrete walls and floors of accelerator rooms during long-term operation of accelerator,for advanced zoning of activated/nonactivated areas in planning the decommissioning of an accelerator.We propose a new,highly sensitive method for nondestructively estimating the specific activity in concrete that can be applied to activation zoning.In this method,instead of direct determination of the specific activities of important long-half-life radionuclides for decommissioning,such as 152 Eu and 60 Co,we determine the specific activities of short-half-life radionuclides,24 Na and 56 Mn,in situ to obtain neutron flux.The obtained neutron flux and accelerator operation history yield the specific activities of 152 Eu and 60 Co for the advance zoning of activated/non-activated concrete.This method is a powerful long-term prediction tool for concrete activation.

Evaluation of activated area in the electrostatic accelerator facilities

In order to clear the activated area in electrostatic accelerator facilities,four accelerator facilities were selected and typical neutron emission experiments were performed.Neutron flux during operation and induced activity caused by charged particles on the accelerator and its surrounding area after irradiation were measured.Also the monitored neutron flux and calculated value by Monte Carlo calculation using PHITS code were compared.It was confirmed that the results between calculated data and measured data showed the good agreement with each other.Finally,it was concluded that we have to take care the activation of beam line and target.But,it is not necessary to treat accelerator tank,surrounding materials,and building concrete as radioactive materials in case of decommissioning.

The Palmanova Cantonments： Conservation, Value-Enhancement and Transformation for an Integrated and Overall Regeneration

Italian military real-estate is highly varied as regards its location, intended uses, its typological, stylistic, and constructive features and its state of conservation. What historical and documental value can we attribute to the typological and technical aspects of military buildings？ What problems and strategies have to be studied before such buildings can be repurposed for inclusion into a circuit of social and civil uses？ Some attempts were made to answer these questions by analysing the military real estate of Palmanova, the fortress city founded by the Serenissima Republic of Venice in 1593, a city designed by engineers, military analysts, and expert military architects all answerable to the Fortifications Office of Venice. There are a number of barracks situated inside the city＇s fortified walls, within a somewhat confined area： Montezemolo, Isonzo, Ederle, Filzi, Montesanto and others in outlying villages. Barracks built in different periods （some during the Renaissance, others in the eighteenth century and some even after the Second World War） have been gradually phased out of service. Their restoration and functional leverage, in the early years of this century, were discussed in terms of an economic and cultural strategy that would not upset the city. New regeneration strategies are called for if these abandoned military structures are not to undergo further deterioration. These strategies should be based upon a knowledge of these structures＇ features--their layout, architecture, technologies--and should also embrace local policies, but first and foremost they require real, contextualized and economically sustainable projects.

Molten Salts as Stripping Media for Radioactive Superficial Decontamination

The main practical difficulty associated to the task of the dismantling and decommissioning of the IPEN＇s old nuclear fuel cycle facilities has been the big amount of radioactive waste generated in the dismantling operations. The waste is mainly in the form of contaminated carbon steel structures. In the IPEN, the presence of contamination in the equipments, structures and buildings, although restricted to low and medium activity levels, constituted an important concern due, on one hand, to the great volume of radioactive wastes generated during the operations. On the other hand, it should be outstanding that the capacity of radioactive wastes stockpiling in IPEN found been exhausted. In function of the large waste volume generated in the dismantling operations, the main concems and focuses of research and technological development in the IPEN＇s Chemical and Environmental Center--CQMA have been the effluent and waste treatment subjects, besides the development of some special decontamination techniques, since most old nuclear fuel cycle facilities are installed in the CQMA＇s area. The reduction of the radioactive waste volume has a significant impact in the decommissioning costs and in the amount of material to be stored. The mentioned steel structures, during the operations and after ten or twelve years after the facilities shut down, have presented severe corrosion. In the past, to protect them, several layers of paint were applied. Traditional decontamination methods were tried, such as acid pickling, alkaline washing and ultrasonic baths. Nevertheless, these methods have failed to reach effective decontamination. In this paper, we described some aspects and problems in decommissioning of IPEN＇s nuclear fuel cycle facilities and it is presented an innovative method for radioactive superficial decontamination of steel structures using different molten salt compositions and temperatures as stripping media.

Analysis of molten metal spreading and solidification behaviors utilizing moving particle full-implicit method

To retrieve the fuel debris in Fukushima Daiichi Nuclear Power Plants(1F),it is essential to infer the fuel debris distribution.In particular,the molten metal spreading behavior is one of the vital phenomena in nuclear severe accidents because it determines the initial condition for further accident scenarios such as molten core concrete interaction(MCCI).In this study,the fundamental molten metal spreading experiments were performed with different outlet diameters and sample amounts to investigate the effect of the outlet for spreading-solidification behavior.In the numerical analysis,the moving particle full-implicit method(MPFI),which is one of the particle methods,was applied to simulate the spreading experiments.In the MPFI framework,the melting-solidification model including heat transfer,radiation heat loss,phase change,and solid fraction-dependent viscosity was developed and implemented.In addition,the difference in the spreading and solidification behavior due to the outlet diameters was reproduced in the calculation.The simulation results reveal the detailed solidification procedure during the molten metal spreading.It is found that the viscosity change and the solid fraction change during the spreading are key factors for the free surface condition and solidified materials.Overall,it is suggested that the MPFI method has the potential to simulate the actual nuclear melt-down phenomena in the future.