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At least 1,711 records · Page 95

Nuclear Safety [Vol. 35, No. 1, January-June 1994]

Nuclear Safety is a review journal that covers significant developments in the field of nuclear safety. Its scope includes the analysis and control of hazards associated with nuclear energy, operations involving fissionable materials, and the products of nuclear fission and their effects on the environment. Primary emphasis is on safety in reactor design, construction, and operation; however, the safety aspects of the entire fuel cycle, including fuel fabrication, spent-fuel processing, nuclear waste disposal, handling of radioisotopes, and environmental effects of these operations, are also treated. Table of Contents for this issue follows. THE CHERNOBYL ACCIDENT: 1 Chernobyl Accident Management Actions, A. R Sich; GENERAL SAFETY CONSIDERATIONS: 25 The IAEA-ASSET Approach to Avoiding Accidents is to Recognize the Precursors to Prevent Incidents, F. Reisch; ACCIDENT ANALYSIS: 36 A Review of the Available Information on the Triggering Stage of a Steam Explosion, D. F. Fletcher; 58 Analysis and Modeling of Flow-Blockage-Induced Steam Explosion Events in the High-Flux Isotope Reactor, R. P. Taleyarkhan, V. Georgevich, C. W. Nestor, U. Gat, B. L. Lepard, D. H. Cook, J. Freels, S. J. Chang, C. Luttrell, R. C. Gwaltney, and J. Kirkpatrick; 74 An Analysis of Disassembling the Radial Reflector of a Thermionic Space Nuclear Reactor Power System, M. S. El-Genk and D. V. Paramonov; CONTROL AND INSTRUMENTATION: 86 Standards for High-Integrity Software, D. R. Wallace, D. R. Kuhn, L M. Ippolito, and L. Beltracchi; DESIGN FEATURES: 98 Adoption of New Design Features for the Next Generation Nuclear Power Reactors, L. S. Tong; 114 Review of Nuclear Piping Seismic Design Requirements, G. C. Slagis and S. E. Moore; ENVIRONMENTAL EFFECTS: 128 PC-Based Probabilistic Safety Assessment Study for a Geological Waste Repository Placed in a Bedded Salt Formation, S. A. Khan; OPERATING EXPERIENCES: 142 Managing Aging in Nuclear Power Plants: Insights from NRC’s Maintenance Team Inspection Reports, A. Fresco and M. Subudhi; 150 Reactor Shutdown Experience, Compiled by J. W. Cletcher; 153 Selected Safety-Related Events, Compiled by G. A. Murphy; RECENT DEVELOPMENTS: 158 Reports, Standards, and Safety Guides, D. S. Queener; 168 Proposed Rule Changes as of Dec. 31, 1993; ANNOUNCEMENTS: 177 Symposium on Radioactive and Mixed Waste—Risk as a Basis for Waste Classification; 177 1995 Incineration Conference 178 Ninth Power Plant Dynamics Control and Testing Symposium; 174 The Authors

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Nuclear Safety [Vol. 33, No. 1, January-March 1992]

Nuclear Safety is a review journal that covers significant developments in the field of nuclear safety. Its scope includes the analysis and control of hazards associated with nuclear energy, operations involving fissionable materials, and the products of nuclear fission and their effects on the environment. Primary emphasis is on safety in reactor design, construction, and operation; however, the safety aspects of the entire fuel cycle, including fuel fabrication, spent-fuel processing, nuclear waste disposal, handling of radioisotopes, and environmental effects of these operations, are also treated. Table of Contents for this issue follows. GENERAL SAFETY CONSIDERATIONS: 1 Technical Note: A New Approach to Fission Reactor Safety, Yu. V. Petrov; 5 Erratum; ACCIDENT ANALYSIS: 6 Analysis and Modeling of Fission Product Release from Various Uranium-Aluminum Plate-Type Reactor Fuels, R. P. Taleyarkhan; CONTROL AND INSTRUMENTATION: 23 Applications of a Surveillance and Diagnostics Methodology Using Neutron Noise From a Pressurized-Water Reactor, R. T. Wood, L. F. Miller, and R. B. Perez; DESIGN FEATURES: 36 Westinghouse Advanced Passive 600 Plant, B. A. McIntyre and R. K. Beck; 47 System 80+™ PWR Safety Design, C. W. Bagnal, R. A. Matzie, and R. S. Turk; ENVIRONMENTAL EFFECTS: 58 The MATS Experiments—Mesoscale Atmospheric Transport Studies at the Savannah River Site, A. H. Weber, S. Berman, R. J. Kurzeja, and R. P. Addis; 75 Book Review: Environmental Radioactivity in the European Community 1984-1985-1986, C. A. Little; WASTE AND SPENT FUEL MANAGEMENT: 76 Activities Related to Waste and Spent Fuel Management, M. D. Muhlheim and E. G. Silver; OPERATING EXPERIENCES: 87 Aging Assessment of BWR Control Rod Drive Systems, R. H. Greene; 100 Reactor Shutdown Experience, Compiled by J. W. Cletcher; 103 Selected Safety-Related Events, Compiled by G. A. Murphy; 110 Operating U.S. Power Reactors, Compiled by M. D. Muhlheim and E. G. Silver; RECENT DEVELOPMENTS: 129 General Administrative Activities, Compiled by M. D. Muhlheim and E. G. Silver; 139 Reports, Standards, and Safety Guides, D. S. Queener; 143 Proposed Rule Changes as of Sept. 30 1991; ANNOUNCEMENTS: 128 Harvard School of Public Health Announces Short Courses; 128 16th Biennial ANS Topical Meeting on Reactor Operating Experience: Present and Future Technologies—Applying Lessons Learned (Call for Papers); 147 The Authors; 150 Indexes to Nuclear Safety, Volume 32; 154 Errata.

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THERMAL ANALYSIS OF WASTE GLASS MELTER FEEDS

Melter feeds for high-level nuclear waste (HLW) typically contain a large number of constituents that evolve gas on heating, Multiple gas-evolving reactions are both successive and simultaneous, and include the release of chemically bonded water, reactions of nitrates with organics, and reactions of molten salts with solid silica. Consequently, when a sample of a HLW feed is subjected to thermogravimetric analysis (TGA), the rate of change of the sample mass reveals multiple overlapping peaks. In this study, a melter feed, formulated for a simulated high-alumina HLW to be vitrified in the Waste Treatment and Immobilization Plant, currently under construction at the Hanford Site in Washington State, USA, was subjected to TGA. In addition, a modified melter feed was prepared as an all-nitrate version of the baseline feed to test the effect of sucrose addition on the gas-evolving reactions. Activation energies for major reactions were determined using the Kissinger method. The ultimate aim of TGA studies is to obtain a kinetic model of the gas-evolving reactions for use in mathematical modeling of the cold cap as an element of the overall model of the waste-glass melter. In this study, we focused on computing the kinetic parameters of individual reactions without identifying their actual chemistry, The rough provisional model presented is based on the first-order kinetics.

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Qualitative and Quantitative Assessment of Nuclear Materials Contained in High-Activity Waste Arising from the Operations at the 'SHELTER' Facility

As a result of the nuclear accident at the Chernobyl NPP in 1986, the explosion dispeesed nuclear materials contained in the nuclear fuel of the reactor core over the destroyed facilities at Unit No. 4 and over the territory immediately adjacent to the destroyed unit. The debris was buried under the Cascade Wall. Nuclear materials at the SHELTER can be characterized as spent nuclear fuel, fresh fuel assemblies (including fuel assemblies with damaged geometry and integrity, and individual fuel elements), core fragments of the Chernobyl NPP Unit No. 4, finely-dispersed fuel (powder/dust), uranium and plutonium compounds in water solutions, and lava-like nuclear fuel-containing masses. The new safe confinement (NSC) is a facility designed to enclose the Chernobyl NPP Unit No. 4 destroyed by the accident. Construction of the NSC involves excavating operations, which are continuously monitored including for the level of radiation. The findings of such monitoring at the SHELTER site will allow us to characterize the recovered radioactive waste. When a process material categorized as high activity waste (HAW) is detected the following HLW management operations should be involved: HLW collection; HLW fragmentation (if appropriate); loading HAW into the primary package KT-0.2; loading the primary package filled with HAW into the transportation cask KTZV-0.2; and storing the cask in temporary storage facilities for high-level solid waste. The CDAS system is a system of 3He tubes for neutron coincidence counting, and is designed to measure the percentage ratio of specific nuclear materials in a 200-liter drum containing nuclear material intermixed with a matrix. The CDAS consists of panels with helium counter tubes and a polyethylene moderator. The panels are configured to allow one to position a waste-containing drum and a drum manipulator. The system operates on the ‘add a source’ basis using a small Cf-252 source to identify irregularities in the matrix during an assay. The platform with the source is placed under the measurement chamber. The platform with the source material is moved under the measurement chamber. The design allows one to move the platform with the source in and out, thus moving the drum. The CDAS system and radioactive waste containers have been built. For each drum filled with waste two individual measurements (passive/active) will be made. This paper briefly describes the work carried out to assess qualitatively and quantitatively the nuclear materials contained in high-level waste at the SHELTER facility. These efforts substantially increased nuclear safety and security at the facility.

Cherkas, Dmytro↗

The Cementitious Barriers Partnership Experimental Programs and Software Advancing DOE’s Waste Disposal/Tank Closure Efforts – 15436

The U.S. Department of Energy Environmental Management (DOE-EM) Office of Tank Waste Management-sponsored Cementitious Barriers Partnership (CBP) is chartered with providing the technical basis for implementing cement-based waste forms and radioactive waste containment structures for long-term disposal. DOE needs in this area include the following to support progress in final treatment and disposal of legacy waste and closure of High-Level Waste (HLW) tanks in the DOE complex: long-term performance predictions, flow sheet development and flow sheet enhancements, and conceptual designs for new disposal facilities. The DOE-EM Cementitious Barriers Partnership is producing software and experimental programs resulting in new methods and data needed for end-users involved with environmental cleanup and waste disposal. Both the modeling tools and the experimental data have already benefited the DOE sites in the areas of performance assessments by increasing confidence backed up with modeling support, leaching methods, and transport properties developed for actual DOE materials. In 2014, the CBP Partnership released the CBP Software Toolbox –“Version 2.0” which provides concrete degradation models for 1) sulfate attack, 2) carbonation, and 3) chloride initiated rebar corrosion, and includes constituent leaching. These models are applicable and can be used by both DOE and the Nuclear Regulatory Commission (NRC) for service life and long-term performance evaluations and predictions of nuclear and radioactive waste containment structures across the DOE complex, including future SRS Saltstone and HLW tank performance assessments and special analyses, Hanford site HLW tank closure projects and other projects in which cementitious barriers are required, the Advanced Simulation Capability for Environmental Management (ASCEM) project which requires source terms from cementitious containment structures as input to their flow simulations, regulatory reviews of DOE performance assessments, and Nuclear Regulatory Commission reviews of commercial nuclear power plant (NPP) structures which are part of the overall US Energy Security program to extend the service life of NPPs. In addition, the CBP experimental programs have had a significant impact on the DOE complex by providing specific data unique to DOE sodium salt wastes at Hanford and SRS which are not readily available in the literature. Two recent experimental programs on cementitious phase characterization and on technetium (Tc) mobility have provided significant conclusions as follows: recent mineralogy characterization discussed in this paper illustrates that sodium salt waste form matrices are somewhat similar to but not the same as those found in blended cement matrices which to date have been used in long-term thermodynamic modeling and contaminant sequestration as a first approximation. Utilizing the CBP generated data in long-term performance predictions provides for a more defensible technical basis in performance evaluations. In addition, recent experimental studies related to technetium mobility indicate that conventional leaching protocols may not be conservative for direct disposal of Tc-containing waste forms in vadose zone environments. These results have the potential to influence the current Hanford supplemental waste treatment flow sheet and disposal conceptual design.

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Ensuring Longevity: Ancient Glasses Help Predict Durability of Vitrified Nuclear Waste

How does glass alter with time? For the last hundred years this has been an important question to the fields of object conservation and archeology to ensure the preservation of glass artifacts. This same question is part of the development and assessment of durable glass waste forms for the immobilization of nuclear wastes. Researchers have developed experiments ranging from simple to highly sophisticated to answer this question, and, as a result, have gained significant insight into the mechanisms that drive glass alteration. However, the gathered data have been predominately applicable to only short-term alteration times, i.e. over the course of decades. What has remained elusive is the long-term mechanisms of glass alteration[1]. These mechanisms are of particular interest to the international nuclear waste glass community as they strive to ensure that vitrified products will be durable for thousands to tens of thousands of years. For the last thirty years this community has been working to fill this research gap by partnering with archeologists, museum curators, and geologists to identify hundred to million-year old glass analogues that have altered in environments representative of those expected at potential nuclear waste disposal sites. The process of identifying a waste glass relevant analogue is challenging as it requires scientists to relate data collected from short-term laboratory experiments to observations made from long-term analogues and extensive geochemical modeling.

Ancient Glass↗

Waste Treatment and Immobilization Plant U. S. Department of Energy Office of River Protection Submerged Bed Scrubber Condensate Disposition Project - 13460

The Hanford Waste Treatment and Immobilization Plant (WTP) will generate an off-gas treatment system secondary liquid waste stream [submerged bed scrubber (SBS) condensate], which is currently planned for recycle back to the WTP Low Activity Waste (LAW) melter. This SBS condensate waste stream is high in Tc-99, which is not efficiently captured in the vitrified glass matrix [1]. A pre-conceptual engineering study was prepared in fiscal year 2012 to evaluate alternate flow paths for melter off-gas secondary liquid waste generated by the WTP LAW facility [2]. This study evaluated alternatives for direct off-site disposal of this SBS without pre-treatment, which mitigates potential issues associated with recycling. This study [2] concluded that SBS direct disposal is a viable option to the WTP baseline. The results show: - Off-site transportation and disposal of the SBS condensate is achievable and cost effective. - Reduction of approximately 4,325 vitrified WTP Low Activity Waste canisters could be realized. - Positive WTP operational impacts; minimal WTP construction impacts are realized. - Reduction of mass flow from the LAW Facility to the Pretreatment Facility by 66%. - Improved Double Shell Tank (DST) space management is a benefit. (authors)

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The Role of the Sellafield Ltd Centres of Expertise in Engaging with the Science, Environment and Technology Supply Chain and University Sector to Support Site Operations and Decommissioning in the UK Nuclear Industry - 13018

The development and maintenance of the broad range of the highly technical skills required for safe and successful management of nuclear sites is of vital importance during routine operations, decommissioning and waste treatment activities.. In order to maintain a core team of technical experts, across all of the disciplines required for these tasks, the approach which has been taken by the Sellafield Ltd has been the formation of twenty five Centres of Expertise (CoE), each covering key aspects of the technical skills required for nuclear site operations. Links with the Specialist University Departments: The CoE leads are also responsible for establishing formal links with university departments with specialist skills and facilities relevant to their CoE areas. The objective of these links is to allow these very specialist capabilities within the university sector to be more effectively utilized by the nuclear industry, which benefits both sectors. In addition to the utilization of specialist skills, the university links are providing an important introduction to the nuclear industry for students and researchers. This is designed to develop the pipeline of potential staff, who will be required in the future by both the academic and industrial sectors. (authors)

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A History of the Environmental Management Advisory Board: 20 Years of Service and Partnership - 13219

The Environmental Management Advisory Board (EMAB or Board) was chartered under the Federal Advisory Committee Act (FACA) in 1992 to provide the Assistant Secretary for Environmental Management (EM) with independent and external advice, information, and recommendations on corporate issues relating to accelerated site clean-up and risk reduction throughout the EM complex. Over the course of the past 20 years, the composition and focus of the Board have varied widely to address the changing needs of the program. EMAB began as the Environmental Restoration and Waste Management Advisory Committee, formed to provide advice on an EM Programmatic Environmental Impact Statement. In 1994, the Board was restructured to function more as an executive-level, limited member advisory board whose membership provides insight of leading industry experts and the viewpoints of representatives from critical stakeholder constituencies. Throughout the 20 years of its existence, EMAB has covered a wide variety of topics and produced nearly 200 recommendations. These recommendations have resulted in several policy changes and improvements within EM. Most recently, EMAB has been credited for its contribution to the EM Energy Park Initiative, forerunner of the DOE Asset Revitalization Initiative; creation of the EM Offices of Communications and External Affairs; improvement of acquisition and project management strategies and culture; and several recommendations related to the Waste Treatment Plant and the tank waste programs at Hanford and the Savannah River Site. The wealth of experience and knowledge the Assistant Secretary can leverage through utilization of the Board continues to support fulfillment of EM's mission. In commemoration of EMAB's 20. anniversary, this paper will provide further context for the evolution of the Board, the role FACA plays in its administration, and a look at the members' current objectives and EM's expectations for the future. (authors)

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One System Integrated Project Team: Retrieval and Delivery of Hanford Tank Wastes for Vitrification in the Waste Treatment Plant - 13234

The One System Integrated Project Team (IPT) was formed in late 2011 as a way for improving the efficiency of delivery and treatment of highly radioactive waste stored in underground tanks at the U.S. Department of Energy's (DOE's) 586-square-mile Hanford Site in southeastern Washington State. The purpose of the One System IPT is to improve coordination and integration between the Hanford's Waste Treatment Plant (WTP) contractor and the Tank Operations Contractor (TOC). The vision statement is: One System is a WTP and TOC safety-conscious team that, through integrated management and implementation of risk-informed decision and mission-based solutions, will enable the earliest start of safe and efficient treatment of Hanford's tank waste, to protect the Columbia River, environment and public. The IPT is a formal collaboration between Bechtel National, Inc. (BNI), which manages design and construction of the WTP for the U.S. Department of Energy's Office of River Protection (DOEORP), and Washington River Protection Solutions (WRPS), which manages the TOC for ORP. More than fifty-six (56) million gallons of highly radioactive liquid waste are stored in one hundred seventy-seven (177) aging, underground tanks. Most of Hanford's waste tanks - one hundred forty-nine (149) of them - are of an old single-shell tank (SST) design built between 1944 and 1964. More than sixty (60) of these tanks have leaked in the past, releasing an estimated one million gallons of waste into the soil and threatening the nearby Columbia River. There are another twenty-eight (28) new double-shelled tanks (DSTs), built from 1968 to 1986, that provide greater protection to the environment. In 1989, DOE, the U.S. Environmental Protection Agency (EPA), and the Washington State Department of Ecology (Ecology) signed a landmark agreement that required Hanford to comply with federal and state environmental standards. It also paved the way for agreements that set deadlines for retrieving the tank wastes and for building and operating the WTP. The tank wastes are the result of Hanford's nearly fifty (50) years of plutonium production. In the intervening years, waste characteristics have been increasingly better understood. However, waste characteristics that are uncertain and will remain as such represent a significant technical challenge in terms of retrieval, transport, and treatment, as well as for design and construction of WTP. What also is clear is that the longer the waste remains in the tanks, the greater the risk to the environment and the people of the Pacific Northwest. The goal of both projects - tank operations and waste treatment - is to diminish the risks posed by the waste in the tanks at the earliest possible date. About two hundred (200) WTP and TOC employees comprise the IPT. Individual work groups within One System include Technical, Project Integration and Controls, Front-End Design and Project Definition, Commissioning, Nuclear Safety and Engineering Systems Integration, and Environmental Safety and Health and Quality Assurance (ESH and QA). Additional functions and team members will be added as the WTP approaches the operational phase. The team has undertaken several initiatives since its formation to collaborate on issues: (1) alternate scenarios for delivery of wastes from the tank farms to WTP; (2) improvements in managing Interface Control Documents; (3) coordination on various technical issues, including the Defense Nuclear Facilities Nuclear Safety Board's Recommendation 2010-2; (4) deployment of the SmartPlant{sup R} Foundation-Configuration Management System; and (5) preparation of the joint contract deliverable of the Operational Readiness Support Plan. (authors)

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Identification of Mission Sensitivities with Mission Modeling from the One System Organization at Hanford - 13292

The Hanford site in southeast Washington contains approximately 207 million liters of radioactive and hazardous waste stored in 177 underground tanks. The U.S. Department of Energy's Office of River Protection is currently managing the Hanford waste treatment mission, which includes the storage, retrieval, treatment and disposal of the tank waste. Two recent studies, employing the modeling tools managed by the One System organization, have highlighted waste cleanup mission sensitivities. The Hanford Tank Waste Operations Simulator Sensitivity Study evaluated the impact that varying 21 different parameters had on the Hanford Tank Waste Operations Simulator model. It concluded that inaccuracies in the predicted phase partitioning of a few key components can result in significant changes in the waste treatment duration and in the amount of immobilized high-level waste that is produced. In addition, reducing the efficiency with which tank waste is retrieved and staged can increase mission duration. The 2012 WTP Tank Utilization Assessment concluded that flowsheet models need to include the latest low-activity waste glass algorithms or the waste treatment mission duration and the amount of low activity waste that is produced could be significantly underestimated. (authors)

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Experimental Methods to Estimate Accumulated Solids in Nuclear Waste Tanks - 13313

The Department of Energy has a large number of nuclear waste tanks. It is important to know if fissionable materials can concentrate when waste is transferred from staging tanks prior to feeding waste treatment plants. Specifically, there is a concern that large, dense particles, e.g., plutonium containing, could accumulate in poorly mixed regions of a blend tank heel for tanks that employ mixing jet pumps. At the request of the DOE Hanford Tank Operations Contractor, Washington River Protection Solutions, the Engineering Development Laboratory of the Savannah River National Laboratory performed a scouting study in a 1/22-scale model of a waste tank to investigate this concern and to develop measurement techniques that could be applied in a more extensive study at a larger scale. Simulated waste tank solids and supernatant were charged to the test tank and rotating liquid jets were used to remove most of the solids. Then the volume and shape of the residual solids and the spatial concentration profiles for the surrogate for plutonium were measured. This paper discusses the overall test results, which indicated heavy solids only accumulate during the first few transfer cycles, along with the techniques and equipment designed and employed in the test. Those techniques include: - Magnetic particle separator to remove stainless steel solids, the plutonium surrogate from a flowing stream. - Magnetic wand used to manually remove stainless steel solids from samples and the tank heel. - Photographs were used to determine the volume and shape of the solids mounds by developing a composite of topographical areas. - Laser range finders to determine the volume and shape of the solids mounds. - Core sampler to determine the stainless steel solids distribution within the solids mounds. - Computer driven positioner that placed the laser range finders and the core sampler over solids mounds that accumulated on the bottom of a scaled staging tank in locations where jet velocities were low. These devices and techniques were very effective to estimate the movement, location, and concentrations of the solids representing plutonium and are expected to perform well at a larger scale. The operation of the techniques and their measurement accuracies will be discussed as well as the overall results of the accumulated solids test. (authors)

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