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EPRI Report: Review of Geostatistical Approaches to Characterization of Subsurface Contamination - 17442

The key metric in the final release of a nuclear facility from radiological controls following plant decommissioning is the potential long-term radiation exposure to future users of the site. This is estimated from modeling of the exposure that could conceivably result from residual contamination remaining on the site in buildings, soil and groundwater after the completion of decontamination, dismantlement and remediation activities. A key input to such modelling is characterization data obtained from surveys and sampling. To date, the regulatory guidance for conducting the final status survey required to show compliance with regulator approved site release limits (i.e., radionuclide concentrations or contamination levels) has been limited to surface contamination. EPRI has completed a project that provides guidance for use of geo-statistics in the development of a site final status survey that will address the impact of dose to a future user of the site from subsurface contamination. (authors)

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Characterization and D and D of PET Cyclotron and Radioisotope Production Facility - 17536

The State University of New York at Buffalo is in the process of the decontamination and decommissioning (D and D) of a cyclotron and radioisotope production facility located in Parker Hall on the South Campus. Many unique characterization activities are needed for compliant waste packaging, transportation, and disposal. In addition to the cyclotron used for successful production of radioisotopes, the facility features hot cells and glove boxes used for the purification and conditioning of the final product. Many challenges exist for the decommissioning of the cyclotron and the radioisotope production facility. These challenges include the proper characterization and management of the cyclotron, its associated equipment, and the remaining facility. Slightly activated concrete constitutes the majority of the remaining radioactive materials to be disposed of during the decommissioning. Challenges for this project include; - Regulatory interface between the New York Department of Health (NYDOH) and the New York Department of Environmental Conservation (DEC) for license closure; - Characterization of the cyclotron, its support equipment and the activated vault areas; - The most cost effective disposal options and the Data Quality Objectives needed for the various disposal options. The paper primarily focuses on challenges for characterization of the cyclotron and the remaining radioisotope production facility at the University at Buffalo. (authors)

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The february 2014 accidents at WIPP - 15024 (What Happened and What We Know About Why)

With almost 15 years of successful and safe operations, the WIPP facility was suddenly shutdown in February 2014 due to two unrelated accidents underground. A fire burned the front tires and engine of a salt haul truck, creating significant soot and forced evacuation of the mine. A second unrelated incident occurred 9 days later when at least one drum of non-compliant waste from Los Alamos National Laboratory burst, introducing airborne radioactivity into the underground ventilation air. Some radioactivity was released to the atmosphere at the surface. Bioassay showed that 22 workers received low internal doses, with no long-term adverse health effects expected for these employees. Independent environmental monitoring indicated very low levels off-site and dose reconstruction modeling indicated no members of the public were exposed. Comprehensive accident investigations resulted in significant planned changes to enhance safety management programs at WIPP, and a recovery plan was developed. In addition to safety management program augmentation, recovery involves new and enhanced underground ventilation systems and decontamination of affected areas underground. Resumption of initial waste disposal operations is scheduled for early in FY16, with a return to normal operations (17 shipments per week) within about three years. (authors)

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Benefits from R. and D. for D. and D. projects - 15089

CEA (French Alternative Energies and Atomic Energy Commission) is both the operator of important nuclear facilities all over the nuclear cycle, in charge of major new built or D and D projects and a R and D group with dynamic policy of technology transfer: second in France for patents deposit, active partnership agreements with industries, and support for Start-ups. The position of CEA in D and D is unique because of the number and the wide diversity of facilities under decommissioning, with some high level of contamination. Innovative solutions are being developed in 6 main axes to protect the operators, to minimize the overall costs and the volumes of waste: - Investigations in the facilities - Radiological measurement of waste - Robotics, laser cutting devices, virtual reality to simulate and choose the best way to operate, - Decontamination of soils and structures - Waste treatment and conditioning - Methods and Information Technology (IT)Tools for project and waste management The last developments are shown and examples of industrial applications given: encapsulation of Magnesium or vitrification of high level waste for UP1 retreatment plant, treatment of sodium for Phenix fast breeder, treatment of organic liquids, etc. CEA is willing to share actions in partnership with other operators or with industrials so they can use the results for other contracting authorities. (authors)

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Robotic D and D: Smart robots - 15093

Project' managers continually seek an ever-greater optimization of time between remote handling operations and those carried out manually; therefore, new technological solutions must be deployed. Robotics offers a great opportunity in this new field of technology to carry out, for example, samplings or remediation in hostile, cluttered surroundings. Teams in charge of dismantling at the CEA have therefore first defined robotizable functions. These functions have been assembled from existing technological blocks to arrive at robots which are operating today [RICAIII, patent: FR 2925702]. Lessons learned, particularly from experience with the RICA robot, have enabled the operating technical specifications to be fine-tuned. A new study phase has been launched applying the same principle of adapting existing, proven means. The growing role of robotics today is unquestioned. Led by research and the academic world; robots such as those equipped with wheels, tracks, feet or even helicopter rotors, are today accessible to the general public, particularly via broadening of the 'open source' concept. Added to these we need tools able to manage large component deconstruction systems, like MAESTRO. Industrialization of such high-potential technological solutions has been aided by: - Easy use, - Increasing reliability, - Flexibility of 'open source' solutions, - Widening skill networks, and therefore greater technical support - Lower costs. Decontamination and dismantling (D and D) projects must be able to meet a number of special demands, increasing the number of unit designs, their costs and delivery times. The complexity of dismantling works sites mean that each is a special case to be dealt with almost independently. Such a way of approaching these projects is not on the same wavelength as industry, with tool and method standardization. The answer to the challenge of operations in difficult environments is an eco-system of functions, performed by a set of inter-connected robots. The first step towards the construction of such robot teams is devoted to functions where strength is not necessary: investigating and clean-up in hostile environments. With this in mind, the CEA Marcoule teams have been given the objective of merging the strengthening commercial robotic world with the needs of D and D, and thus to improve the transversal use of the systems. (authors)

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Robotic systems for remote characterization and decommissioning - 15102

This paper provides an updated summary of the research being conducted at the University of Manchester, UK, in the area of remote characterisation through the use of robotic systems, in support of the decommissioning plan for the Sellafield nuclear site in Cumbria, UK. The research is being conducted in collaboration with a number of companies including Sellafield Ltd, the National Nuclear Laboratory and Forth Engineering Ltd. The progress of a number of novel mobile robotic platforms being developed at the University of Manchester is presented including the AVEXIS underwater vehicles, ground and sub-surface vehicles and alpha glove box decontamination robots. Also presented is the ongoing work on the remote sensing technologies and techniques which will be deployed on the robotic platforms. (authors)

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Experience with decommissioning of the underground reservoirs of object No.41 at NPP A1 site -Bohunice, Slovakia - 15110

A new concept of measurement procedures for clearance of building have been developed and implemented at NPP A1 (Bohunice). They are based on measurements of total RN activity per unit of surface area at the erected building according to EU Recommendation RP-113 (pure Cs-137 limit - 10 Bq/cm{sup 2}). However, as a priority the requirements of national legislation had to be complied, which, in the case of concrete structures, limits the massic activity of the concrete bulk material to be rose from the building demolition (300 Bq/kg for pure Cs-137) and surface activity of (0,3 Bq/cm{sup 2} for pure Cs-137). Advantage of the new concept is that it avoids costly whole volume measurement of building rubble (e.g. 200 L drum monitor) and potentially decreases amount of produced radioactive waste. Whole volume measurement has been replaced by whole surface monitoring of surface contamination of the walls by portable devices in 1 x 1 m grid. The methodology was implemented on underground tanks as well, whose clearance is one of the primary goals of 2. stage of the NPP A1 decommissioning project. The measurements proved that contamination on the outer side is rarely present and it is caused by overflowing or leak of contaminated water from reservoir. The most expensive clearance activities were: soil excavation around the reservoir, dry decontamination of concrete, as well as whole volume measurement of crushed concrete ruble from the top of reservoir by drum monitor. A lot of obstacles had to be overcome because of lack of experience with methodology (procedures were implemented as a pilot project), measurement and sampling techniques. During the pilot project rose other difficulties which had to be overcome. (authors)

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Hanford site asbestos management lessons learned - 15183

The U.S. Department of Energy (DOE) is responsible for the environmental cleanup of the Hanford Site central plateau. As part of this responsibility, DOE contractors conduct deactivation, decommissioning, decontamination, and demolition (D4) of retired/inactive facilities, including very large chemical processing facilities. To date, DOE contractors have demolished hundreds of facilities, reducing baseline site maintenance costs and reducing the environmental threats and hazards that the degrading buildings present. Many of these Hanford facilities include asbestos-containing materials (as well as other hazardous components), which must be managed in compliance with applicable regulations and standards. In most cases, the facilities are demolished as Comprehensive Environmental Response, Compensation and Liability Act (CERCLA) removal or remedial actions. In an effort to streamline cleanup operations and to utilize site cleanup funding more efficiently, while still being protective of personnel and the environment, agreements were reached between the US Environmental Protection Agency (EPA) Hanford Project Office, the Washington Department of Ecology (Ecology), the Benton Clean Air Agency (BCAA) and the US Department of Energy Richland Operations Office (DOE-RL) on approaches to be utilized for demolition. One of these approaches would involve leaving cement asbestos board siding (e.g. transite), an EPA National Emissions Standards for Hazardous Air Pollutants (NESHAP) Category II non-friable asbestos-containing material, in place during demolition using heavy equipment, employing a set of controls that would maintain protection of personnel and the environment. This agreement was documented in a number of formal communications, including Notices of Intent issued as required by the asbestos NESHAP regulation, letters between the various agencies, CERCLA work plans, and the approved contractor baselines. A large number of buildings were demolished with transite siding in place, using the agreed upon controls and approaches. Personnel breathing zone and work area perimeter monitoring verified that the controls employed were protective in that there were no exceedances of permissible exposure limits during or after the demolition operations. EPA later reconsidered their previous concurrence with demolishing transite materials in place and issued a joint letter with Ecology revoking concurrence on any of the aforementioned CERCLA decision documents and associated work plans. DOE and their contractors took action to comply with the approach to demolition preferred by EPA for future demolitions, and initiated a series of actions to modify asbestos management practices in their operations accordingly. This paper will discuss both the actions taken to address EPA concerns with sites where transite materials were left in place for demolition and actions taken to ensure that the central plateau D4 program complies with the 40 CFR 61 Subpart M, National Emission Standard for Asbestos, (Asbestos NESHAP) methods for asbestos management. (authors)

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Study of treatment as an alternative WM pathway: examples of I-graphite and metallic components such as steam generators - 15212

EDF is working continuously to optimize and secure its waste management pathways, leading in some case to develop appropriate treatment solutions that could be implemented parallel to reference solutions, complementary or as alternative solutions to already existing paths. This approach is illustrated by the examples of steam generators replaced during the operation of French PWR power plants, and of irradiated graphite (stacks and sleeves), coming from the decommissioning of UNGG reactors, which have been shut down. Concerning graphite wastes, the near surface disposal facility intended for this waste does not exist yet, and is currently giving rise to the research of a suitable site, and an evaluation of its performances. While accompanying ANDRA (French national agency for nuclear waste management), in charge of the development of the facility, and while waiting for more data to be available, EDF is continuing the consolidation of graphite wastes radiological inventory, and is working on the development of an alternative management solution, based on a thermal treatment process. Depending on the nature of the treatment, and on the choice of operating parameters, this treatment may contribute to reduce graphite wastes volume and/or promote its acceptance in a disposal facility. Reducing the radiological inventory by decontamination is one of the means to achieve these objectives. Concerning replaced steam generators, nearly 200 of them will have been removed by 2030, and stored on site waiting for their treatment, which represents about 65 000 tons of metal. Initially intended to be cut and packed on NPPs' sites during their dismantling, EDF is studying the economic value of having the steam generators treated in a centralized facility, which allows reducing the volume of final wastes by optimizing cutting operations, while considering recycling after melting. However, this studied pathway implies a number of difficulties to be overcome. In particular, the shipment of such large components to a centralized facility may be complex. Moreover, French regulatory framework does not allow recycling outside nuclear industry, therefore limiting recycling opportunities to storage containers for radioactive wastes. (authors)

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SORTIE DB - Source term integrated environmental management disposal facility database - 15249

The Environmental Management Disposal Facility (EMDF) in Oak Ridge, Tennessee, is a proposed U.S. Department of Energy low-level Comprehensive Environmental Response Compensation and Liability Act (CERCLA) waste disposal facility with an operational start in the early 2020's. As a DOE low-level waste disposal facility, it is subject to DOE Order 435.1, requiring a composite analysis and possibly a performance assessment. The Source Term Integrated EMDF Data Base - SORTIE DB - provides source term estimates used in these assessments. An Oak Ridge Office of Environmental Management (OREM) Federal and Contractor team developed this state-of-the-art descriptive analytics and visualization schema. DOE OREM senior management has recognized complementary beneficial uses of SORTIE DB in decisions for accelerating clean-up progress, dealing with conflicting sequencing and budget priorities, and enhancing stakeholder and regulatory interfaces. SORTIE DB is designated as an OREM planning tool. SORTIE DB contains estimated forecast waste volumes and masses for over 800 Decontamination and Decommissioning (D and D) and Remedial Action (RA) sequenced baseline packages over the next 25+ years. Available characterization data, radionuclide identification and concentrations, and data from safety basis and emergency management documents are incorporated into SORTIE DB. (authors)

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Investigation robot on cables - 15250

The Decontamination and Decommissioning (D and D) Operations take place in hostile environments to the human intervention. In this context, robotic systems are a solution to achieve these operations while minimizing human intervention. Among these operations, the monitoring of lengthwise plant has to be performed in places where the radioactive contaminations make hostile environments. These monitoring operations need to measure several physics parameters in several locations in a precise and safe manner. These repetitive tasks can be made by robots that are simple, small sized and easily adaptable. In this scope, a robotic system on cables has been designed to control and monitor the inside of lengthwise nuclear facilities. In lengthwise installations, the using of cables allows to increase the covered zone of the robots which is an essential quality in such places. Unlike cable-driven parallel robots used in workspaces of 2D or 3D controlled by redundant tensioning motors, the current robot moves in a 1D workspace. Thus a tractors cable controlled by one tensioning motor is used to drive the robot on carrier cables. In this paper, we will describe the first results of this work by bringing out the innovation of our system. Then, we will discuss the perspective to upgrade the actual system whose applications could be perfectly imagined outside the nuclear D and D industry. (authors)

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The Cires facility in Morvilliers: from a VLL waste disposal facility to the development of industrial activities - 15252

The disposal facility of CIRES for very low level wastes was designed to provide safe and cost effective services to waste generators, in particular for decommissioning works. The facility could significantly increase waste annual deliveries to meet waste generators' needs and accommodate large disused components as PWR steam generators after decontamination. However an anticipated saturation of its capacity is foreseen as needs for disposal has doubled since its start-up. The geometry of the cells was optimized and the technical capacity of the repository is presently by 40% above its licensed capacity. Saturation has been delayed; however a new facility will be necessary by 2030 and other waste management options are to be considered as recycling of metallic wastes or crushed concrete rubble. CIRES facility also became Andra's industrial platform for the management of institutional wastes. A grouping and a storage facility have been built and a new processing facility should start up in 2016. (authors)

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Guidance for decommissioning plants entering safe storage - 15280

Although a number of plants worldwide have been placed into safe storage after permanent shutdown, there is no generic guidance for establishment of safe storage conditions. To address this need, EPRI is conducting a project to document the best practices to reduce risk, maintenance and monitoring requirements during safe storage, as well as practices that optimize decommissioning following the safe storage period. This project additionally evaluates potential options for establishment of safe storage conditions, such as performance of chemical decontamination, completion of environmental remediation activities, early removal of highly activated components, dismantlement of non-power block structures and partial site release in advance of completion of decommissioning of the nuclear island. (authors)

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Installation and operation of GeoMelt{sup R} in container vitrification in NNL Central Lab active rig hall at Sellafield - 15328

Cleanup and subsequent immobilization of wastes on the UK's NDA estate brings major challenges. With the exception of HLW where vitrification is utilized for immobilization, cement is typically used in the management and immobilization of non-heat generating wastes. However some legacy feeds such as those containing reactive metals can be incompatible with cementation technologies, and the application of engineered cement encapsulating product to raw wastes increases wasteform volume. Cementation has also been developed to be compatible with the repository concept, which provides it with a level of protection from the environment. Potential delays in repository implementation and as yet to be determined repository waste form acceptance criteria for some wastes may require the duration of above ground storage of immobilized wastes to be extended with potential effect on the integrity of the wasteform. Vitrification is a treatment option which destroys organics and hazardous inorganics such as asbestos, reduces wasteform volume, and produces a robust leach resistant wasteform. Kurion's GeoMelt{sup R} In-container Vitrification (ICV){sup TM} is a vitrification process wherein the treatment vessel can serve as an interim-storage, transport, and final long-term storage vessel - thus negating the need to pour glass into a separate container, effectively leading to a much simpler system than traditional waste melters. The inherent volume reduction from vitrification results in a dense product with self-shielding properties, and the GeoMelt treatment process has been demonstrated to homogenize elemental metals and radionuclide contaminants of concern, eliminating hot spots and mitigating criticality concerns. All of which opens up alternatives strategies for storage and disposal. GeoMelt has been proven in the commercial and US DOE waste treatment environment with over 26,000 tonnes of hazardous waste treated to date (half of this radioactive). Kurion and the UK's National Nuclear Laboratory (NNL) plan to demonstrate its application to Sellafield radioactive wastes. A small (engineering) scale demonstrator is being installed in the active rig hall at NNL's Central Laboratory at Sellafield UK with a twofold mission; 1) demonstration of the vitrification of ILW/LLW, and 2) processing of smaller volume orphan wastes that currently have no treatment path. The NNL facility will allow the handling of uranium containing materials which form a substantial component of ILW currently stored on the Sellafield site. Accurate DFs across the melter and off gas system are often difficult to obtain using inactive materials at the low concentrations present in radioactive wastes. Installation in the NNL facility will allow trace quantities of active species such as Cs-137 and Tc-99 to be processed as part of a simulant ILW stream and monitoring will allow accurate decontamination factors (DFs) to be established to support future vitrification facility design. In addition to underpinning melter operation and obtaining DFs across the system, the facility will allow the processing of radioactive waste arisings of low activity which may either be typical of larger waste volumes or may present as orphans without a disposition route. In either case the melter facility will be able to vitrify these wastes into a form that will be suitable for interim storage and disposal. Among the feeds envisaged for processing will be asbestos from power stations, contaminated soils, feeds containing uranium metals, ponds solids, sludge, and miscellaneous active laboratory wastes. The NNL Central Lab capability will be used to analyze the active product to support disposal requirements whether through letters of compliance for the Geological Disposal Facility (GDF) or waste acceptance criteria for the Low Level Waste Repository (LLWR). (authors)

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Radiometric characterization process for locating radioactivity hold-up and measuring non-uniformly distributed sources - 15342

A novel approach to facility radiometric characterization for non-uniformly distributed radiation sources has been developed by ANTECH and is currently being employed at the Argonne National Laboratory. It is being applied to the measurement of a wide range of objects and the interiors and contents of laboratories and buildings. The integrated non destructive assay measurement process involves the use of a scanning spectroscopic gamma ray camera as well as high purity Germanium detectors with different collimators and hence differing detector fields of view to measure and quantify non-uniformly distributed sources of radioactivity in laboratory equipment, glove boxes, storage tanks, pipework and general laboratory objects and process components. The purpose of the radiometric characterization is to quantify radiation sources and radioactive contamination levels in facilities containing nuclear material and to ensure compliance with facility characterization requirements and for decontamination and decommissioning planning and execution. The integrated measurement process also involves automated data capture and processing software and a database with which both measurement instrument operators and subject matter expert analysts can interact. An appropriate measuring instrument (gamma camera, scintillation detector, high purity Germanium detector system, neutron detector or alpha-beta counter) records the measurement data and the measurement site is recorded in a photograph. All of the data relevant to the measurement (or set of measurements for a particular object) are recorded in the database including measured gamma ray spectra, equipment description and relevant calibration, measurement site photograph and measurement descriptive data. Once data analysis protocols are established for specific geometries and measurement situations they can be applied to the measured data in a partially automated manner, reducing analysis and transcription errors. In addition to measurements and data analysis the process also utilises radiometric modelling computer codes including MicroShield and Monte Carlo Neutrons Photons in order to perform model calculations where appropriate. In a typical measurement, the ANTECH RadSearch spectroscopic gamma camera is utilized to find areas of concentrated activity so that these areas can be measured and calculated separately from areas with diffuse contamination. The use of the gamma camera in scanning mode helps to ensure that the assay does not overestimate the detected radiation source, which is a frequent consequence of using standard far field geometry and attenuation analysis codes that assume uniformity of both density and radioactive source distribution. Once the hot spots are identified, high purity Germanium detector measurements are made using various collimators with wide or narrow fields of view as required. These measurements are then processed through a semi-automatic calculation process assuming an appropriate source configuration as identified by RadSearch. These source configurations include point sources, line sources or surface sources. The Generalized Geometry Hold-up algorithms are employed to determine an estimate of the activity of the various sources that are identified in a measurement. The ANTECH integrated measurement process provides an automated calculation procedure where the analyst can select the source type, geometry and appropriate input data, and then the software calculates the activity by radionuclide for all sources identified in the measurement. The measurement and analysis process is controlled under the ANTECH ISO9001: 2008 Quality Assurance System and managed by a site specific Quality Assurance Plan. Both Argonne National Laboratory and Department of Energy technical reviewers have vetted the Integrated Measurement and Analysis Process. The application of the measurement and analysis process is described and measurement examples are provided. (authors)

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Development of ion specific media to treat Sr-contaminated water at Fukushima Daiichi Nuclear Power Plant - 15486

Since April of 2011, Kurion, Inc. contracted with the Tokyo Electric Power Company (TEPCO) to remediate cooling water using Ion Specific Media targeting cesium (Cs). The effluent of the Cs-sorption systems routed into a reverse osmosis (RO) system. While the RO permeate was recirculated into the cooling loop, the RO reject was captured in carbon-steel tanks. However, the cesium-extracted tank water at Fukushima Daiichi also has a high strontium (Sr) activity (∼4 x 10{sup 5} Bq/mL) and needs to be reduced to lower the onsite and boundary doses. To treat this highly contaminated water, Kurion developed the Kurion Mobile Processing System (KMPS). The KMPS uses a powder batch-contact addition step in concert with a series of ion exchange vessels to decontaminate the high Sr-activity water. Kurion tested and developed several ion specific media to treat the water. Several inorganic media were evaluated in the down-select for the system. Equilibrium batch tests, shortened contact time batch tests and column tests were performed to assess the media depending on water conditions. Two media were selected for KMPS: FAS-P (a powdered zeolite) to reduce Ca{sup 2+} and Sr{sup 2+} concentrations and TS-G (a synthetic titanosilicate) to polish the Sr{sup 2+} downstream. The results of these laboratory tests and their performance in the field will be discussed. The operation of the system has led to the continued reduction of dose at the Fukushima Daiichi nuclear power plant. This system and these media can be applied to other difficult wastewater solutions involving high levels of contaminants and salinity. (authors)

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Process systematic research initiatives on decommissioning of nuclear power plants - 15493

This paper considers how process systems engineering (PSE) principles can be employed in the process of decommissioning and decontamination of nuclear power plants. PSE has been associated with design, operation, control, and optimization of chemical and physical processes. It has been shown to be very powerful in the context of analysis, synthesis, and evaluation of chemical and petrochemical industries. This paper aims to identify the research opportunity in employing the PSE principles in the decommissioning of nuclear power plants in order to minimize their cost and time. (authors)

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Overcoming challenges in delivering 5 Avantech water treatment systems at Fukushima - 15544

The Great East Japan Earthquake has left the Fukushima Daiichi Nuclear Station with many challenges related to water treatment. This paper will provide information on three systems provided for the treatment of [1] accumulated water associated with the Circulated Water Cooling System, [2] sub-drain water removed from wells adjacent to the Unit 1-4 Reactor and Turbine Buildings, and [3] wash water from decontamination of vehicles and equipment. Specific information will be presented on work that was completed to overcome process, installation and logistical challenges associated with these water streams including the following: - Selection of technology and equipment for removal of specific radionuclides - Performance results of highly selective adsorbents used for removing radionuclides in the presence of varying concentrations of chlorides and other natural constituents - Description of process flowsheets and equipment configuration - Discussion of the post-accident work environment and the related work site restrictions Results show that the customized solutions will enable the utility to clean-up the wastewater for cooling, reuse and potential discharge. The technologies used for the three water treatment systems are directly applicable to the treatment of similarly challenging water streams at commercial nuclear power plants, fuel reprocessing plants and governmental nuclear facilities worldwide. The use of these technologies will aid in the lowering of radioactivity released to the environment, worker radiation exposure and the amount of secondary waste requiring long term storage and/ or disposal. (authors)

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