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FY16 1st Quarter Transportation Report

Transportation report for the first quarter of FY16 for waste shipments at the Area 5 Radioactive Waste Management Complex. Presented by NNSA Nevada Field Office at Stakeholders public meeting on 02/03/16.

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Annual Summary Report for the Remote-Handled Low-Level Waste Disposal Facility—FY 2022

This Fiscal Year (FY) 2022 annual summary report (ASR) documents the continued adequacy of the performance assessment (PA), the composite analysis (CA) and associated operating disposal-authorization statement (ODAS) technical-basis documents for the Remote-Handled (RH) Low-Level Waste (LLW) Disposal Facility at Idaho National Laboratory. Annual review of the adequacy of the PA and CA for the RHLLW Disposal Facility ensures that conclusions of the analyses remain valid in accordance with requirements of Department of Energy (DOE) Order 435.1, “Radioactive Waste Management.” In FY 2022, no significant operational changes or other activities occurred that would cause deviation from the assumptions in the PA and CA pertaining to disposal geometry, verification of waste characteristics, tracking disposal inventories against total limits, facility-closure design, or institutional controls. Fifteen waste canister shipments were received at the RHLLW Disposal Facility, and 15 waste canisters were emplaced in disposal vaults.

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A Database for Radwaste Management in Germany-30 Years of Experience by TUV NORD - 20461

From the very beginning in the late 1980's TUV NORD EnSys is involved as an independent expert in quality assurance processes concerning interim storage facilities and the disposal for radioactive waste with negligible heat generation in Germany. A database has been developed since these times by TUV NORD EnSys. The development of this database over a long time will be discussed as well as the lessons learned within this process. (authors)

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Development of a Technical Standard for Radiological Characterization of DAW - 18062

Throughout its 70+-year history, the U.S. Department of Energy (DOE) and its predecessor agencies have performed a wide mission involving nuclear materials and weapons development, production, testing, and modernization. While the initial mission components relied heavily upon reactor physics and chemistry, the environmental programs have increasingly relied upon development of more accurate and effective measurement methodologies to determine the radiological and chemical properties of the unique waste streams that were generated during the weapons production and testing mission. Over time, the DOE laboratories and former production sites have developed a wide range of site-specific processes and procedures for conducting radiological characterization of dry active waste (DAW) that is managed as low-level radioactive waste. This has resulted in a Complex-wide variability among sites with respect to the methodologies and instrumentation used to characterize individual waste streams. The DAW-type waste was selected for development of a characterization standard since it is a simple, voluminous, and repetitive waste stream with a substantial knowledge base, established experience history at multiple site locations, and the potential for realization of programmatic benefits though standardization. The Energy Facility Contractors Group (EFCOG) Waste Management Working Group (WMWG) has proposed the development of a new DOE Technical Standard for radiological characterization of DAW. The purpose of the proposed new standard is to provide a technical resource that integrates and enhances the utilization of current site-specific methodologies and processes. A Technical Basis Document (TBD) has been prepared to support the development and utilization of the new standard by providing detailed information for use by site personnel when implementing the guidance provided in the standard. It also provides the rationale for and details concerning the recommended technical approaches for radiological characterization of representative DAW-type waste streams. The TBD will be included as an appendix to the proposed standard. Adoption of a standardized approach to DAW characterization will take advantage of multiple applications for a technology that is both mature and stable. The DAW characterization process is repetitive and lends itself to implementation at a wide range of operating locations - resulting in economies of scale, compliance with regulatory requirements, and consistent implementation of procedures which support design, operations, maintenance, and management of facilities, activities and programs. The purpose of the proposed new Technical Standard for DAW Radiological Characterization is to integrate and improve the utilization of current site-specific methodologies and processes and will include a comprehensive evaluation and comparison of current radiological characterization methodologies to determine which ones are most reliable and effective in producing relevant and valid data. In view of the long history and participation by several agencies in the regulation of nuclear programs, existing Voluntary Consensus Standards have also been reviewed for relevancy and applicability to the new proposed standard. The proposed new Standard will be developed in concert with existing scientific and regulatory guidance to produce a document that incorporates the state of current knowledge and site practices with a graded approach to applying those methodologies that are applicable and effective for characterizing a wide range of DAW-type wastes - including, but not limited to, debris, low specific activity (LSA) material, and surface contaminated objects (SCO). Under the leadership of the National Laboratory Subgroup of the EFCOG/WMWG), an EFCOG team will develop the proposed technical standard. This process will incorporate the information gathered during preparation of the TBD, which will serve as a technical resource to support the technical approach for selection of DAW characterization methodologies. Preparation of the TBD included a detailed survey of historical site practices and examination of the characterization approaches and measurement methodologies currently being applied to DAW-type wastes. Future activities include the development and submittal of a Project Justification Statement that will be submitted to the DOE Technical Standards Program for review and comment. The EFCOG/WMWG Team will respond to reviewer comments, as required. Following final concurrence by affected organizations through the DOE Technical Standards Coordination process, the EFCOG/WMWG Team will prepare the draft technical standard and respond to comments generated during RevCom review and final format review by the DOE Technical Standards Management Program. (authors)

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FY2017 Savannah River Site composite analysis annual review

The FY2017 Department of Energy (DOE) Order 435.1, Radioactive Waste Management (DOE 1999c), Annual Review for the Savannah River Site (SRS) Composite Analysis (CA) is documented, herein.

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Annual Summary Report for the Remote-Handled Low-Level Waste Disposal Facility—FY 2023

This Fiscal Year (FY) 2023 annual summary report (ASR) documents the continued adequacy of the performance assessment (PA), the composite analysis (CA) and associated operating disposal-authorization statement (ODAS) technical-basis documents for the Remote-Handled (RH) Low-Level Waste (LLW) Disposal Facility at Idaho National Laboratory. Annual review of the adequacy of the PA and CA for the RHLLW Disposal Facility ensures that conclusions of the analyses remain valid in accordance with requirements of Department of Energy (DOE) Order 435.1, “Radioactive Waste Management.” In FY 2023, no significant operational changes or other activities occurred that would cause deviation from the assumptions in the PA and CA pertaining to disposal geometry, verification of waste characteristics, tracking disposal inventories against total limits, facility-closure design, or institutional controls. Eleven waste canister shipments were received at the RHLLW Disposal Facility, and ten waste canisters were emplaced in disposal vaults.

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Integration of performance assessments and 3116 basis documents within the Savannah River Site liquid waste facilities - 15375

The end of the Cold War has left a legacy of over 136 million liters (36 million gallons) of radioactive waste in the aging waste tanks at the Department of Energy's Savannah River Site (SRS). A robust program is in place to remove waste from these tanks, treat the waste to separate it into a relatively small volume of high-level waste and a large volume of low-level waste, and to actively dispose of the low-level waste on-site. This process allows the US Department of Energy (DOE) to move forward with closure of the cleaned waste tanks and associated ancillary structures. To support performance-based, risk decision making for closure and disposal activities, three individual performance assessments (PAs) have been developed - salt-stone Disposal Facility, F-Tank Farm and H-Tank Farm. In addition, three Waste Determinations (WDs) have been made by the Secretary of Energy, in consultation with the Nuclear Regulatory Commission (NRC), under the authority of Section 3116 of the Ronald W. Reagan National Defense Authorization Act for Fiscal Year 2005 (NDAA Section 3116). To support these waste determination decisions, individual '3116 Basis Documents' were developed that describe the assumptions and conditions under which the criteria outlined in NDAA Section 3116 are met. The development of each of the PAs represented a long and arduous effort that involved the development of both deterministic and probabilistic conceptual models of the facilities, the development of assumptions and associated ranges, uncertainty and sensitivity analyses, model data collection and analyses, writing of the actual performance assessment, internal and external peer reviews, and ultimately approval by DOE. Similarly, the development of the 3116 Basis Documents represents similar time and financial commitments. At the end of these efforts, after years of preparation and millions of dollars in investment, we have thousands of pages of highly technical text, tables of data and hundreds of graphs and charts all contained in a series of thick binders that fit neatly on the shelf of a bookcase. We were done - right? Actually, we were just getting started. Performance Assessments and 3116 Basis Documents are living documents that shape day-to-day and long-term decision making in the operation of a low-level waste disposal facility (e.g., salt-stone Disposal Facility) or in area closure activities (e.g., F-Tank Farm or H-Tank Farm). Although these documents do not contain specifically described requirements per se, they do utilize specific assumptions that, if changed significantly, could result in no longer being able to demonstrate that there is reasonable assurance that the required performance objectives or the criteria from NDAA Section 3116 can be met. Savannah River Remediation LLC (SRR), the contractor responsible for Liquid Waste operations at SRS, has not only developed the PAs and 3116 Basis Documents to support this work and shepherded these documents through the DOE approval process, but has also developed the processes and procedures to ensure the successful implementation and integration of these documents into day-to-day decision making within the associated facilities. This paper describes these processes, including the Un-reviewed Waste Management Question process and the PA Maintenance process, and provides specific examples of their successful implementation. (authors)

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Development of an Experimental Approach for Thermal Testing in Bedded Salt - 19431

Safe and permanent isolation of used nuclear fuel (UNF) and high-level nuclear waste (HLW) is an integral component of the cradle-to-grave philosophy of radioactive waste management. Out of the multitude of rock types considered for the permanent deep disposal of nuclear waste (tuff, shale, granite, clay, and salt), salt has received significant interest particularly because of the advantage offered by salt as an impermeable and dry medium with self-sealing properties. The concept of HLW disposal in salt has been investigated through several testing campaigns in the U.S. and in Germany. Serval knowledge gaps still exist in our understanding of how brine is generated and how it transports under heat generating conditions. These knowledge gaps limit our ability to build a robust safety case for the disposal of heat generating waste in salt. The current manuscript reports on efforts performed to develop a field-testing campaign to study brine and water vapor migration in heated salt. The paper summarizes initial work done in a phased thermal testing program in bedded salt at the Waste Isolation Pilot Plant (WIPP), Carlsbad, New Mexico. The testing to date has been focused on existing boreholes and is being used to 'shakedown' the process for implementation of a more refined testing program that will be implemented in freshly drilled boreholes planned for FY2019. We designed and deployed a heater assembly that consisted of a packer, borehole deformation gauge, heater block, a network of thermocouples, and a pressure transducer setup to measure in situ temperature and pressure. The assembly was deployed in an existing borehole and several heating and cooling experiments were performed to test the performance of the different instruments fielded. We report on the results obtained for brine generation as a function of time and heating and cooling cycles and temperature evolution in the rock salt. (authors)

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Experimental Technetium Release from Simulated Salt-stone Cementitious Waste Form - 18419

Experiments are being conducted to evaluate the early release of technetium (Tc) from fresh salt-stone waste forms using dynamic flow-through tests. Salt-stone is a chemically reducing, grout-based waste form used by the U.S. Department of Energy (DOE) to dispose of low-activity salt solutions arising from high-level radioactive waste tank closure activities at the Savannah River Site (SRS). A key safety function of salt-stone is maintaining a low-flow, chemically reducing environment that will attenuate the release of redox-sensitive radioelements such as Tc. Salt-stone also provides a physical barrier due to its low intrinsic permeability, which limits both water and oxygen ingress. These release experiments, conducted to support the U.S. Nuclear Regulatory Commission's monitoring role during tank closure, are designed to provide independent information on how well salt-stone will perform its safety function. The dynamic leach tests were conducted in a Hassler-type core-holder permeameter system that allows an accelerated flow rate of simulated SRS groundwater through an intact cylinder of salt-stone spiked with Tc-99 at a concentration of approximately 2,100 Bq/g (3 ppm). The first salt-stone specimen to be tested (Specimen 2) was prepared with Grade 100 ground granulated blast-furnace slag and aged for 119 days in a temperature-controlled, low-oxygen, high-humidity environment. Before test completion, 9.5 pore volumes (PV) of simulated SRS groundwater were passed through the salt-stone cylinder. After a few PV, apparent saturated hydraulic conductivity (K{sub sat}) values calculated from flow data reached a steady-state value of approximately 1.0 x 10{sup -9} cm/s, which is within the range of previously reported data. Tc-99 concentrations in leachate peaked early during the leach test at 2.0 x 10{sup -7} M and then declined to approximately 4 x 10{sup -8} M after 9.5 PV. The leachate Tc-99 concentration after elution of 9.5 PV is broadly consistent with a Tc solution concentration controlled by the solubility of reduced Tc solids. The range of Tc-99 concentrations is similar to the range reported for a column test that was sponsored by DOE, but the time pattern of release differs. The second salt-stone specimen tested (Specimen 3) was aged for 372 days and it further differed from the first specimen in that its Grade 100 slag component had been finely ground using a mortar and pestle in an attempt to make it more reactive. This second test yielded Tc release behavior broadly similar to that observed during the first test, except that the early Tc peak (at 1.2 x 10{sup -6} M) was six times higher and the concentration after 6.7 PV (8.8 x 10{sup -8} M) was approximately two times higher than in the first test. In addition, the steady-state K{sub sat} was an order of magnitude lower than that of the first specimen. During the second test, the injection pump was intentionally turned off for a period of 11 days (i.e., approximate residence time for 1 PV) and a Tc spike was observed when pumping resumed, suggesting that longer residence times may promote higher Tc effluent concentrations. During a second intentional shut-down of the pump for 25 days (approximate residence time for 2 PV), another Tc spike was observed. An unplanned excursion to higher confining pressure physically affected the specimen, temporarily lowering the apparent K{sub sat} followed by a subsequent increase in both K{sub sat} and Tc effluent concentration. One hypothesis is that the transient spike in confining pressure and resulting salt-stone compression and later decompression may have induced Tc release from otherwise inactive pores. (authors)

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Hanford Site Composite Analysis Technical Approach Description: Integrated Computational Framework.

The U.S. Department of Energy (DOE) in DOE O 435.1 Chg. 1, Radioactive Waste Management, requires the preparation and maintenance of a composite analysis (CA). The primary purpose of the CA is to provide a reasonable expectation that the primary public dose limit is not likely to be exceeded by multiple source terms that may significantly interact with plumes originating at a low-level waste disposal facility. The CA is used to facilitate planning and land use decisions that help assure disposal facility authorization will not result in long-term compliance problems; or, to determine management alternatives, corrective actions, or assessment needs if potential problems are identified.

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RoboCount{sup TM} 2020 - A Robotic Non-Destructive Waste Assay System - 19331

A robotic system for non-destructive assay of radioactive waste - RoboCount{sup TM} 2020ab - has been designed, manufactured, and a prototype delivered to a customer. RoboCount{sup TM} 2020 is based on an industrial 6-axis articulating robot platform, combined with a dedicated waste package platform and a high-resolution HPGe gamma spectrometer. The system enables measurement of waste packages including drums (100-l, 200-l, 400-l), crates (up to 1200 x 800 x 800 mm), 1 m{sup 3} flexible intermediate bulk containers (FIBC), and others. Assay type can be freely defined, ranging from currently accepted protocols such as segmented gamma scan (SGS) or integral gamma scan (IGS) to new protocols developed for specific non-cylindrical waste packages, e.g., measurement of FIBCs from all four sides and the top. As a result of the robotic hardware flexibility, reconfiguration of the system for a new task is a matter of software changes only. In addition, while primarily geared towards waste characterization, the system can be configured for free release (clearance) by installing a second detector and field-of-view shielding. The prototype is currently in operation at a NPP site in Europe where it is used for D and D waste characterization in crates and FIBCs. Additional features beyond the basic functionality have been implemented such as an automatic lead collimator change based on measured HPGe detector dead time and an automatic liquid nitrogen refill, performed by the robot via a docking station at predefined time intervals. (Use of electrically cooled HPGe detectors is also possible). (authors)

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Hanford Site Composite Analysis Technical Approach Description: Atmospheric Transport Modeling.

The U.S. Department of Energy (DOE) in DOE O 435.1 Chg. 1, Radioactive Waste Management, requires the preparation and maintenance of a composite analysis (CA). The primary purpose of the CA is to provide a reasonable expectation that the primary public dose limit is not likely to be exceeded by multiple source terms that may significantly interact with plumes originating at a low-level waste disposal facility. The CA is used to facilitate planning and land use decisions that help assure disposal facility authorization will not result in long-term compliance problems; or, to determine management alternatives, corrective actions or assessment needs, if potential problems are identified.

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Design, Construction, and Commissioning of the RH LLW Disposal Facility at INL - 19445

The newly-commissioned Remote-Handled Low-Level Waste (RH LLW) Disposal Facility at Idaho National Laboratory (INL) provides permanent disposal capability critical for continuing INL nuclear research and Naval Reactors missions at the Idaho site. The facility mission need [critical decision (CD)- 0] was approved in 2009. Alternative selection (CD-1) was finalized in 2011. The project performance baseline (CD-2/3) was approved and design was initiated in 2014 and construction began in 2015. Construction was completed and transitioned to Materials and Fuels Complex (MFC) Operations in 2017. The facility successfully achieved readiness with authorization to begin operations (CD-4) in 2018. The $77 M line-item capital-acquisition project was completed six months ahead of the congressional commitment date and significantly under budget. This paper presents highlights of the RH LLW Disposal Facility project delivery and a summary of facility features and critical characteristics. Highlights include: - As a hazard category II nuclear facility, the project complied with United States Department of Energy (DOE) requirements for incorporation of nuclear safety into facility design and construction as identified in DOE-STD-1189 as well as 10 CFR 835 Subpart K requirements for incorporation of ALARA principles in facility design. - From an environmental compliance perspective, the facility was subject to National Environmental Policy Act requirements resulting in a Finding of No Significant Impact as determined by an Environmental Assessment. An operating disposal authorization statement from the Low-Level Waste Disposal Facility Federal Review Group (LFRG) authorizing waste disposal operations in accordance with DOE Order 435.1 was obtained. - The project was delivered using a design-build delivery method with a firm-fixed price with incentive fee contracting mechanism. The project was executed as a line-item capital-acquisition project, in full compliance with DOE Order 413.3B under INL's certified Earned Value Management System (EVMS) program. - The facility supports twenty years of waste disposal operations with five disposal vault configurations in four vault arrays supporting six different cask/canister system configurations. Three of the six cask/canister systems currently exist and three will be developed to support future operations. There are a total of 446 waste disposal vaults that will accommodate disposal of a total of 939 stainless steel radioactive waste canisters. The facility is designed to accommodate canisters with contact radiation dose rates as high as 600 Sievert/hour (60,000 Rem/hour). - The facility underwent a rigorous readiness review process in accordance with DOE Order 425.1D. Readiness activities included rigorous facility testing and shakedown activities, a management-self assessment, a contractor operational readiness review, and a DOE operational readiness review. Readiness was demonstrated for an existing cask/canister system (the MFC HFEF-5 cask). Separate readiness activities will be conducted for each cask/canister system as they are brought online for facility operations. INL's successful delivery of the project has provided waste disposal capability to ensure long-term viability of planned and current facilities and missions associated with both INL and the Naval Reactors Facility. Successful execution of the project has proven to be strategically important to future capital investments in capabilities necessary to advance INL's mission. (authors)

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Combined Assay Systems for the Characterisation of Historical ILW at of the Dounreay Shaft and Silo-18140

In 1955 the Dounreay nuclear power development establishment was created on the northern coast of Scotland primarily to pursue the UK Government policy of developing Fast Breeder Reactor (FBR) technology. The site operated then by the United Kingdom Atomic Energy Authority (UKAEA) saw the development, test and operation of 3 nuclear reactors, two of them FBRs, alongside fabrication and reprocessing facilities for the FBR fuel elements. From the late 1950's until 1977 Intermediate Level radioactive Waste (ILW) generated on site was disposed of into a 65 m deep, 4.6 m diameter shaft. In January 1977, an explosion thought to be caused by hydrogen generated from sodium and potassium wastes reacting with water occurred in the upper part of the shaft, thus stopping any further waste disposal. A second ILW storage facility, the ILW-Silo, started operation in 1971 to deal with the increasing volume of intermediate level waste generated on site in the mid-1960's and continued receiving waste until 1998. The decommissioning of the Shaft and Silo facilities is a challenging engineering task due to the complexity and potential hazards linked with the retrieval and handling of historical waste. Following recovery it is intended to shred the majority of the waste and load it into 200-l assay drums. Sludges would be separated and solidified within a special annulus drum to make them suitable for assay. To support the decommissioning strategies put forward by Dounreay Site Restoration Limited (DSRL), Mirion Technologies Canberra UK Ltd have designed and completed the manufacture of a pair of combined non-destructive waste assay (NDA) systems. The two identical automated ILW counters are intended to provide a means to characterise the waste materials by performing active and passive neutron measurement as well as segmented high resolution gamma spectrometry (HRGS) of 200-l sacrificial waste drums. The active neutron technique is based on the Differential Die Away (DDA) technique using a pulsed Deuterium-Tritium neutron generator to interrogate fissile material present in the waste. The active neutron measurements support, as well as the passive neutron coincidence measurements, a matrix correction capability by use of an Add-a-Source mechanism. The publication will describe in broad lines the approach proposed by DSRL in the processing of the waste retrieved from both the Shaft and Silo facilities. It will also present a description of the overall design of the NDA counters, illustrating how the measurements to be performed will allow DSRL to safely characterise the retrieved waste materials. (authors)

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Impact of dilution-induced precipitates on the filtration of Hanford liquid tank wastes

To facilitate its vitrification, a portion of the radioactive wastes currently stored at the Hanford Site will be staged and treated using tank-side operations to render their chemistry compliant with the requirements of Hanford’s low-activity waste vitrification facility. Initial sampling of staged feeds indicates that process-water dilution, used to reduce waste feed sodium content to levels acceptable for vitrification (5–6 M Na), may cause precipitation of fine, difficult to settle solids that could affect downstream tank-side filtration and ion-exchange. However, dilution-induced precipitation has not been demonstrated under controlled, rigorous laboratory conditions. This paper presents a set of qualitative and quantitative assessments of dilution-induced precipitation using a nonradioactive, Hanford Tank AP-105 simulated waste. Further, these studies found that dilution of AP-farm waste simulants induced precipitation of up to 150 ppm solids, regardless of whether dilution was done with process water (which contains, among other analytes, naturally occurring Ca and Mg) or deionized water. Naturally occurring process-water analytes appeared to accelerate the rate (and possibly extent) of precipitation. Filtration of diluted waste simulants also found that the precipitated solids challenged prototypic tank-side filter operations; however, the impact to filtration performance was readily managed through waste staging settle/decant operations.

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Corrosion Behavior of Fe-7Cr-1Mo-12Zr Metal Waste Form Alloy in Simulated Repository Environment

Metal waste forms (MWF) are solid metallic waste categorized as high-level radioactive waste generated during pyro-reprocessing of spent metallic fuels and geologically disposed off. This waste form generated requires an excellent corrosion resistance in a geological repository environment. In the present work, Fe-7Cr-1Mo-12Zr MWF alloy was developed by casting in an arc melting furnace. The x-ray diffraction analysis revealed the formation of stable phases of α-Fe solid solution and the intermetallic phases of Fe{sub 2}Zr and Fe{sub 23}Zr{sub 6}. The corrosion behavior of Fe-7Cr-1Mo-12Zr alloy was investigated using electrochemical techniques in aggressive (highly acidic with Cl{sup −}) and nominal repository pH environment. Cyclic potentiodynamic polarization studies indicated the shift in corrosion potential toward cathodic potential in highly acidic solution with Cl{sup −}. The corrosion mechanism of pitting is associated with acidified pH medium with more Cl{sup −}, whereas uniform corrosion or transpassive dissolution is resultant of mild acidity or mild alkaline medium. The passive region is wider in pH 5 and 8 when compared to pH 1 and 3. Electrochemical impedance spectroscopic (EIS) analysis revealed the lowering of passive film stability in the highly acidic medium in the presence of Cl{sup −}. The role of passive oxide layers on the corrosion resistance of the Fe-7Cr-1Mo-12Zr MWF alloy is discussed.

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Improvement of Discharge Regulation System for Liquid and Gaseous Radioactive Materials in Korea - 18050

In this study, we analyzed radioactive waste management practices and discharge regulations for liquid and gaseous radioactive materials generated from the nuclear power plants. Liquid and gaseous radioactive materials are discharged into the environment in a controlled and monitored state after proper treatment. In order to prevent radiological hazards due to the release of radioactive materials, the standards for effluent control limits and off-site dose constraints at the boundary of exclusion area shall be met. In December 2015, the Nuclear Safety Act was partially amended to add the 'Discharge Plan for Liquid and Gaseous Radioactive Materials' to the application form for the power reactor operating licenses. The Discharge Plan shall include the total amount of liquid and gaseous radioactive materials per site, period (annual, quarterly, etc.), and radionuclide group. Therefore, nuclear power plant operators are required to set in advance the total amount of liquid and gaseous radioactive materials for each radionuclide group per site, and keep them below the control limits during the operation of the facilities. Accordingly, it is expected that public trust regarding regulations on effluent discharge as well as effluent control itself can be further improved. (authors)

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